# Patent

## Title
Al2O3 dispersion-strengthened Ti2AlN composites and a method for producing the same

## Abstract

The invention provides Al2O3 dispersion-strengthened Ti2AlN composites, wherein Ti2AlN matrix and Al2O3 strengthening phase both are reactively formed in situ. The volume fraction of Al2O3 is 5% to 50%; the particle size of Al2O3 ranges from 500 nm to 2 μm, with the mean size of Al2O3 particles about 0.8 μm to 1.2 μm; the shape of Ti2AlN grain is plate-like about 80 nm to 120 nm thick and 0.5 μm to 2 μm long. The composites exhibit excellent deformability at high temperature under compression and flexure stresses, and possess excellent oxidation resistance at 1100° C. to 1350° C. for long time (100 h). The composites show typical metallic conductor behavior and the electrical resistivity at room temperature is 0.3 to 0.8 μΩ·m. The invention also provides a method for preparing the same: First, nanoparticles in Ti—Al binary system were prepared in continuous way by hydrogen plasma-metal reaction (HPMR) using Ti—Al alloy rods with Al content 20% to 60% by atom, or pure Al rods and pure Ti rods. The atmosphere used in HPMR is the mixture atmosphere of nitrogen-containing gas, H2 and Ar, with total pressure of 0.8 to 1.2 atm, wherein volume ratio of H2 and Ar is 1:0.8-1.2, and volume fraction of nitrogen-containing gas is 0 to about 20%. Second, the nanoparticles were compacted by vacuum hot pressing at temperature of 800° C. to 1200° C., pressure of 40 MPa to 60 MPa, time of 4 h to 6 h, and vacuum of 2×10−2 Pa to 5×10−3 Pa.

## Background
This Application is a US National Phase of the International Application No. PCT/CN2005/001048 filed Jul. 15, 2005 designating the US and published in China on Jan. 19, 2006 as WO 2006/005267, which claims priority of Chinese Patent Application No. 200410020970.4, filed Jul. 15, 2004.
FIELD OF THE INVENTION
The invention relates to ceramic composites and a method for preparing the same, and specifically, the invention relates to Al2O3 dispersion-strengthened Ti2AlN composites and preparation methods thereof. The ceramic composites possess high hardness, high strength and excellent oxidation resistance of Al2O3, and have metal-like characteristics such as electrical conductivity, machinability etc. of Ti2AlN.
BACKGROUND OF THE INVENTION
In the 1960s, Nowotny and his co-authors have prepared many ternary carbides or nitrides and studied their structural characteristics (H. Nowotny, Prog. Solid State Chem., 2, 27 (1970)). These ternary carbides and nitrides are expressed by a general formula of Mn+1AXn, where M is a transition metal, A is a main group (mostly IIIA and IVA) element, X is either C or N element, and n is 1, 2, or 3. The ternary layered compounds, Mn+1AXn, are abbreviated to MAX phases (M. W. Barsoum, Prog. Solid State Chem., 28, 201 (2000)). The ternary layered compounds all have hexagonal structures which can be described as octahedron being interleaved with atoms layers, and their physical and mechanical properties are closely related to the corresponding carbides and nitrides.
The common characteristic of MAX phases is that they are comprised of covalent bonding, metallic bonding and ionic bonding. So, MAX phases possess combination properties of both ceramics and metals, such as good electrical and thermal conductivity, machinability, excellent thermal shock resistance, high modulus, and high specific strength and so on. In MAX phases, TiAX phases, including Ti3SiC2, Ti2AlC, Ti2AlN, and Ti4AlN3, have been extensively investigated.
In the early 1960s, Jeitschko et al. (W. Jeitschko, H. Nowotny, F. Benesovsky, Monatsh. Chem., 95, 1198(1963)) discovered and deciphered the cell structure of Ti2AlN. In the mid 1970s, Ivchenko et al. (V. I. Ivchenko, M. I. Lesnaya, V. F. Nemchenko, T. Y. Kosolapova, Porosh. Metall., 160, 60 (1976); V. I. Ivchenko, T. Y. Kosolapova, Porosh. Metall., 150, 1 (1975); V. I. Ivchenko, M. I. Lesnaya, V. F. Nemchenko, T. Y. Kosolapova, Porosh. Metall., 161, 45 (1976); V. I. Ivchenko, T. Y. Kosolapova, Porosh. Metall., 164, 56 (1976)) fabricated Ti2AlN bulk sample with a density of 90% to 92% and measured some of their properties. Ivchenko et al. reported that microhardness values were higher than 20 GPa, comparable to the hardness of binary nitride. This is much higher than the hardness (4 GPa) of Ti2AlN subsequently reported by Barsoum et al. (M. W. Barsoum, M. Ali, T. El-Raghy, Met. Mater. Trans., 31A, 1857 (2000)). With reference to the other properties of TiAX phases, it can be deduced that the properties of Ti2AlN reported by Barsoum et al. are very close to the truth. Although Ti2AlN is the first ternary nitride discovered and extensively researched, it is relatively difficult to produce pure Ti2AlN. The Ti2AlN sample made by Barsoum et al. also includes three other phases (11% to 20% by volume), in addition to the Ti2AlN matrix, which are Al2O3, Ti3P, and a phase with a Ti:Al:N ratio of 4:1:3. Despite their best efforts, the sample of this “413” phase cannot be eliminated. The best samples contained 10% to 15% “413” phase. This “413” phase is not Ti4AlN3 (A. T. Procopio, T. El-Raghy, M. W. Barsoum, Met. Mater. Trans., 31A, 373 (2000)) that was reported as Ti3Al2N2 phase in 1984 by Schuster and Bauer (J. C. Schuster, J. Bauer, J. Solid State Chem., 53, 260 (1984)).
Ti2AlN is a ternary nitride ceramic of hexagonal-close-packed structure, with Ti at 4f, Al at 2c positions, and N filling the interspaces of Ti octahedron. The methods of synthesizing Ti2AlN reported so far include solid reaction method (M. W. Barsoum, M. Ali, T. El-Raghy, Metall. Mater. Trans., 31A, 1857 (2000)) and magnetron sputtering method (T. Joelsson, A. Horling, J. Birch, L. Hultman, App. Phy. Lett. 86, 111913 (2005)). Ti2AlN bulk sample with 80% (by volume) Ti2AlN phase was obtained after reactive hot-isostatic pressing (HIP) at 1400° C. under a pressure of 40 MPa for 48 hours, with micron-scale pure Ti powder and AlN powder, in Barsoum's method. But Barsoum's preparation method had some shortcomings such as high reactive temperature, long time, large grain size of the bulk and the like. For the magnetron sputtering method, relatively pure Ti2AlN thin film can be obtained, but it is difficult to produce bulk materials and the yield is relatively low. Ti2AlN is a potential candidate of high-temperature structure materials for use in the temperature range of 1000° C. to 1300° C. However, the oxidation behavior follows the parabolic law in the range of 1000° C. to 1100° C. for time shorter than 20 h; for time longer than 20 h, the oxidation behavior deviates from the parabolic law and becomes linear law. Thus, the high-temperature oxidation properties are unsuitable for the use at a temperature range of 1000° C. to 1300° C. for a long time. So it is necessary to improve the high-temperature oxidation properties of Ti2AlN.
Al2O3 is an ionic oxide with slight distortion hexagonal-close-packed structure, with O2− at hexagonal-close-packed lattice position, and Al3+ filling the interspaces of O2− octahedron. This structure remains relatively stable up to the melting point, so the working temperature of Al2O3 can approach to 1800° C. There is almost no loss or gain in weight when Al2O3 is used in an air atmosphere. Moreover, Al2O3 and Ti2AlN are very close in density and thermal expansion coefficient, are compensated each other in hardness and compressive strength. Al2O3 is chosen to strengthen Ti2AlN matrix, which can improve the high-temperature oxidation properties at the same time. Table 1 shows the main properties of Al2O3 and Ti2AlN.







TABLE 1







Physical and mechanical properties of Ti2AlN and Al2O3











Properties
Ti2AlN
Al2O3















Density (g/cm3)
4.31
   3.9



Vickers Hardness (GPa)
4
 26



Compressive Strength (MPa)
450
2945 



Electrical Resistivity (μΩ · m)
0.25, 0.312
   >1018



Thermal Expansion Coefficient (K−1)
8.2 × 10−6
8.3 × 10−6



Young's Modulus (GPa)
—
380





386



Shear Modulus (GPa)
—
175



Melting Point (° C.)
—
2054 










Generally, Al2O3 dispersion-strengthened Ti2AlN composites are compacted by hot pressing or hot isostatic pressing via powder metallurgy method. There are the following several methods to proportion powders:
1. The use of Al2O3 powders and Ti2AlN powders, which belongs to the type of no in situ reaction;
2. The use of Al2O3 powders and raw powders to form Ti2AlN, which belongs to the type of in situ reaction to form Ti2AlN;
3. The use of raw powders, which belongs to the type of in situ reactions to form Al2O3 and Ti2AlN.
For the first and second method, there are problems such as non-homogenous distribution, easy agglomeration and significant particle growth of Al2O3. These problems become more severe with increasing volume fraction of Al2O3. For the third method, the in situ formed Al2O3 particles are fine and uniformly dispersed and the volume fraction of Al2O3 can be controlled up to 50%.
In order to obtain in situ formed Al2O3 particles dispersion-distributed in the Ti2AlN grains formed by an in situ reaction, powders are produced by a hydrogen plasma-metal reaction method (HPMR). HPMR is suitable for industrial production for use of the preparation of nanoparticles of various metals and alloys. The fundamental principle of HPMR is a process in which atoms are changed from a liquid state to a gas state by using a plasma heat source In the gas state, atom clusters collide with inert gas to transfer energy and make gas clusters cool quickly, producing nanoparticles. During the development of HPMR, Wada (N. Wada, Jpn. J. Appl. Phys., 6, 553 (1967); N. Wada, Jpn. J. AppI. Phys., 7, 1287 (1968); N. Wada, Jpn. J. Appl. Phys., 8, 551 (1969)) first investigated the effects of pressure and kinds of gases on the particle size of as-prepared powder and found that the addition of hydrogen to atmosphere can accelerate the evaporation of metals. Uda et al. (M. Uda, Bull. Japan Inst. Metals., 22, 412 (1983); S. Ohno, M. Uda, J. Japan Inst. Metals., 48, 640 (1984); S. Ohno, M. Uda, J. Japan Inst. Metals., 53, 946 (1989)) extended Wada's method by using a mixture of hydrogen and argon gas with a total pressure of 1 atm, and by substituting the plasma jet gun with an general tungsten electrode. These measures improved the yield of nanopowders from laboratory scale to industrial production. Uda et al. (S. Ohno, M. Uda, J. Japan Inst. Metals., 48, 640 (1984)) found in their study that the driving force for generation of nanoparticles from metals is closely related to these factors such as the heat of evaporation of metals, the heat of formation for recombination from atoms (dissolved in metal) to molecules (evolved into gas phase) of hydrogen and melting points of metals. Ohno and Uda (S. Ohno, M. Uda, J. Japan Inst. Metals., 53, 946 (1989)) studied the evaporation rules of a series of pure metals, and investigated the preparation and characteristics of nanoparticles of Fe—Ni, Fe—Cu and Fe—Si binary alloys. The Chinese Patent Application No. 03133805.4 investigated the synthesis of nanoparticles of Ti-Al binary system. The research disclosed that the concentration of Al of the nanoparticles deviate positively from that of the master alloys. Components of nanoparticles to be used for the preparation of the composites have been designed according to research results of the patent.
From the above, we know that it is relatively difficult to synthesize Ti2AlN. The available technologies are mainly solid reaction methods, and the recently reported magnetron sputtering method was used to synthesize Ti2AlN thin film but not bulk material. Little research has been performed on Ti2AlN due to the difficulty in synthesis. Up to now, there has been no report on the Ti2AlN composites strengthened by Al2O3.
SUMMARY OF THE INVENTION
An objective of the invention is to provide Al2O3 dispersion-strengthened Ti2AlN composites with high hardness, high strength, good oxidation resistance, and good electrical conductivity and easy workability.
The inventors have carried out extensive research in order to overcome the existing problem in the prior art.
The invention provides Al2O3 dispersion-strengthened Ti2AlN composites. The ceramic composites comprise Ti2AlN matrix and Al2O3 strengthening phase, with Al2O3 particles dispersed homogenously in the Ti2AlN matrix. The characteristics of the composites include high hardness, high strength, excellent oxidation resistance due to Al2O3, and at the same time metal-like properties such as good electrical conductivity and easy machinability due to Ti2AlN.
In the as-provided Al2O3 dispersion-strengthened Ti2AlN composites of the invention, Ti2AlN matrix and Al2O3 strengthening phase are both reactively formed in situ. Al2O3 particles are equiaxed, and the particle size of Al2O3 distributes in the range of 500 nm and 2 μm with an average of about 0.8 μm to 1.2 μm; the grains of Ti2AlN are plate-shaped with a thickness of about 80 nm to 120 nm and a length of 0.5 μm to 2 μm, and an average geometric size of about 0.2 μm to 0.5 μm. The average geometric size means a value obtained by extracting a square root of a product of the length and width.
In the as-provided Al2O3 dispersion-strengthened Ti2AlN composites of the invention, the volume fraction of Al2O3 is 5% to 50%, preferably 15% to 45%, further preferably 20% to 40%.
In the as-provided Al2O3 dispersion-strengthened Ti2AlN composites of the invention, the Vickers hardness is 7 GPa to 12 GPa.
In the as-provided Al2O3 dispersion-strengthened Ti2AlN composites of the invention, the compressive strength at room temperature is 1000 MPa to 1900 MPa.
In the as-provided Al2O3 dispersion-strengthened Ti2AlN composites of the invention, the mass gain per unit area in a temperature range of 1100° C. to 1350° C. is 0.5 mg/cm2 to 15 mg/cm2.
In the as-provided Al2O3 dispersion-strengthened Ti2AlN composites of the invention, the electrical resistivity at room temperature is 0.3 μΩ·m to 0.8 μΩ·m.
The invention also provides a method for preparing Al2O3 dispersion-strengthened Ti2AlN composites. The composites comprise Ti2AlN matrix and Al2O3 strengthening phase, with Al2O3 particles dispersed homogenously in the Ti2AlN matrix. The Ti2AlN matrix and Al2O3 strengthening phase are both reactively formed in situ. The characteristics are summarized as follows.
The method includes: preparing nanoparticles of Ti—Al binary system by the hydrogen plasma-metal reaction; and then compacting the nanoparticles by vacuum hot pressing or hot isostatic pressing.
In the as-provided preparation method of Al2O3 dispersion-strengthened Ti2AlN composites, the atmosphere is a mixture atmosphere of a nitrogen-containing gas, H2, and Ar with a pressure of 0.8 atm to 1.2 atm.
In the as-provided preparation method of Al2O3 dispersion-strengthened Ti2AlN composites, the nitrogen-containing gas is N2 or NH3 gas, with a volume fraction of 0 to 20%.
In the as-provided preparation method of Al2O3 dispersion-strengthened Ti2AlN composites, the nanopowders of Ti—Al system are prepared with Ti—Al master alloys, wherein the Ti—Al master alloys are Ti—Al alloy rods with Al content of 20% to 60% by atom, pure Al rods and pure Ti rods, in a manner of continual feeding.
In the as-provided preparation method of Al2O3 dispersion-strengthened Ti2AlN composites, the nanopowders of Ti—Al system are nanopowders with Ti or Al pure element, or alloy nanopowders.
In the as-provided preparation method of Al2O3 dispersion-strengthened Ti2AlN composites, the nanoparticles of Ti—Al system include Ti, TiN, intermetallic compounds of Ti—Al system, Al, and AlN.
In the as-provided preparation method of Al2O3 dispersion-strengthened Ti2AlN composites, the oxygen content of the nanopowders of Ti—Al system is 0 to 20% by weight.
In the as-provided preparation method of Al2O3 dispersion-strengthened Ti2AlN composites, the parameters of the vacuum hot pressing are: temperature of 800° C. to 1200° C.; pressure of 40 MPa to 60 MPa; time of 4 h to 6 h; and vacuum of 2×10−2 Pa to 5×10−3 Pa.
The invention also provides a preparation method of Ti2AlN bulk material. The method includes: preparing nanoparticles of Ti—Al binary system by HPMR; and then compacting the nanoparticles by vacuum hot pressing or hot isostatic pressing.



DESCRIPTION OF THE DRAWINGS
FIG. 1 is a typical bright-field TEM micrograph of alloy nanoparticles produced by HPMR, with nearly spherical shape;
FIG. 2 is a typical bright-field TEM micrograph of alloy nanoparticles produced by HPMR, with nearly cubic shape (Inset is the selected-area electron diffraction (SAED) pattern of cubic particle);
FIG. 3 shows particle size distribution of alloy nanoparticles produced by HPMR;
FIG. 4 is an appearance view of the Al2O3 dispersion-strengthened Ti2AlN composite;
FIG. 5 shows an x-ray diffraction pattern of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5;
FIG. 6 is an optical image of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5;
FIG. 7 is a high-magnification SEM image of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5;
FIG. 8 shows (a) TEM bright-field image, (b) and (c) EDS x-ray spectra from A and B in (a), (d) and (e) the SAED patterns from zone A and zone B, respectively, for as-HPed sample of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5;
FIG. 9 shows a graph of the relation between the microhardness and indentation load of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5;
FIG. 10 shows compression stress-strain curves of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5 at different temperature, with initial strain rate of 3×10−3/s;
FIG. 11 shows flexure stress-strain curves of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5 at different temperature, using a constant cross-head speed of 0.5 mm/min;
FIG. 12 shows the variation relation of the maximum compressive stress with annealing temperature of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5 tested at 1100° C., wherein the values of Ti2AlN and Al2O3 as indicated in the figure are taken from literatures respectively, (M. W. Barsoum, M. Ali, T. El-Raghy, Metall. Mater. Trans., 31A, 1857 (2000)) and (W. Alexander, J. Shackelford, CRC Materials Science and Engineering Handbook (CRC, 5th Edition, 2001));
FIG. 13 shows a graph of variation of the mass gain per unit area at 1100° C. to 1350° C. with time for the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5, wherein the dashed lines represent fits of the corresponding experimental data of 1100° C. to 1300° C. to the cubic root law, the dotted line is a fit of the experimental data of 1350° C. to the parabolic law, and inset plots the oxidation properties of Ti3SiC2-based material; and
FIG. 14 shows a graph of variation of the electrical resistivity with temperature for the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5.



MODE OF CARRYING OUT THE INVENTION
The Al2O3 dispersion-strengthened Ti2AlN composites of the invention comprise Ti2AlN matrix and Al2O3 strengthening phase, with Al2O3 particles dispersed homogenously in Ti2AlN matrix. The characteristics of the composites are high hardness, high strength, excellent oxidation resistance due to Al2O3, and at the same time metal-like properties such as good electrical conductivity and easy machinability etc. due to Ti2AlN.
In the Al2O3 dispersion-strengthened Ti2AlN composites of the invention, Ti2AlN matrix and Al2O3 strengthening phase are both reactively formed in situ. Al2O3 particles is equiaxed crystals, and the particle size of the Al2O3 distributes in the range of 500 nm and 2 μm, the mean size of the Al2O3 particles is about 0.8 μm to 1.2 μm; and The grains of Ti2AlN is plate-like, about 80 nm to 120 nm thick and 0.5 μm to 2 μm long, and with an average geometric size of about 0.2 μm to 0.5 μm.
In the Al2O3 dispersion-strengthened Ti2AlN composites of the invention, the volume fraction of Al2O3 is 5% to 50%.
The Al2O3 dispersion-strengthened Ti2AlN composites of the invention were prepared according to the method characterized in that:
First, nanoparticles of the composites were prepared by HPMR continuously supplied with the master alloys of Ti—Al alloy rods with Al content, in atom %, of 20% to 60%. The chamber atmosphere is the mixture gas of N2, H2 and Ar, with volume fraction of N2 from 0 to 20%, and volume ratio of H2 and Ar in the range of 0.8 to 1, with a total pressure of 0.8 to 1.2 atm. FIGS. 1 and 2 show the TEM bright field images of nanopowders prepared with N2 volume fraction of 10%. Inset in FIG. 2 is the micro-diffraction pattern of a cubic nanoparticle. There are two typical micrographs of the nanopowders produced in situ, a nearly spherical shape and cubic shape, wherein the cubic shape particles are ceramic powder of TiN phase. FIG. 3 displays the particle size distribution of nanopowders measured by TEM photographs. As shown in FIG. 3, nanopowders distribute in the range of 10 nm to 200 nm, mainly in the range of 20 nm to 60 nm, little in the range of 100 to 200 nm, with the average size of 42 nm.
Second, the nanopowders were compacted by vacuum hot pressing. The parameters of this process include: the temperature is 800° C. to 1200° C., the pressure is 40 MPa to 60 MPa, time is 4 h to 6 h, the vacuum is 2×10−2 Pa to 5×10−3 Pa. FIG. 4 shows macro-photograph of the Al2O3/Ti2AlN composite sample 50 mm in diameter and 5 mm in height. Metallographic observation, phase analysis by X-ray, electrical resistivity, and hardness test were carried out for the as-produced composites. The compression and flexure properties at different temperature and the oxidation behavior at high temperature of the composites were systematically studied.
An Al2O3/Ti2AlN composite with 40% (by volume) Al2O3 was made as example to demonstrate the structural characteristics, mechanical properties and high-temperature oxidation properties of Al2O3 dispersion-strengthened Ti2AlN composites. FIG. 5 shows the XRD pattern of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5. It is shown that the composite mainly comprises the as-formed phases of Al2O3 and Ti2AlN, additionally with a small amount of reaction phases: TiN and TiAl3. FIG. 6 is an optical image of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5. Black spots in the image represent Al2O3 particles, with size mostly in the range of 500 nm to 2 μm, and mean size of about 0.8 μm to 1.2 μm. Al2O3 particles disperse uniformly in Ti2AlN matrix. FIG. 7 shows a high-magnification SEM image of the etched sample of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5. As shown in FIG. 7, it is clearly observed that Ti2AlN matrix is fine and plate-like shape grains, different from the equiaxed grains of Al2O3. FIG. 8 shows (a) TEM bright-field image of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5, (b) and (c) are EDS x-ray spectra from A and B in (a), (d) and (e) are the SAED patterns from zone A and zone B, respectively. As shown in FIG. 8(a), it is known that Al2O3 particles were interleaved by Ti2AlN grains, and grain boundaries were not observed in Al2O3 particles, indicating that Al2O3 particles belong to single crystal. Ti2AlN phase is in the form of plate-shaped grains about 100 nm thick and 0.5 μm to 2 μm long. Quantitative measurements from EDS curves of FIG. 8 (b) and (c) show that, zone A comprises 44.45% by atom of Al and 55.55% by atom of O; zone B comprises, 29.33% by atom of Al, 14.28% by atom of N and 56.39% by atom of Ti. This indicates apparent difference in composition between the two phases. Combined analysis of EDS and electron diffraction suggests that the in situ formed Al2O3 is thermodynamically stable α-Al2O3, and complies with stoichiometric relation, while the matrix is Ti2AlN phase.
FIG. 9 shows a graph of the relation between the microhardness and indentation load of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5, the microhardness data of Ti2AlN are taken from literature (M. W. Barsoum, M. Ali, T. El-Raghy, Metall. Mater. Trans., 31A, 1857 (2000)). It is seen that hardness of the composite is 2.5 times that of Ti2AlN. In situ formed Al2O3 significantly improves the hardness of the composite which does not change much with indentation load. FIG. 10 shows compression stress-strain curves of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5 at different temperature, with initial strain rate of 3×10−3/s. It can be seen from the drawing that when the temperature is less than 1050° C., the stress-strain curve is close to a straight line, and the fracture is brittle fracture. The fracture strength decreases from 1870 MPa to 720 MPa with test temperature increasing from room temperature to 950° C. At 1050° C., the stress-strain curve deviates from a straight line, with so-called yield phenomenon appearing, and the permanent strain at failure is 5%. At 1100° C., the stress-strain curve exhibits the characteristics of metal deformation. Three typical regions exist: an elastic regime, a hardening regime and a softening regime. The composite exhibits excellent deformability and has engineering strain at least of 60%. At 1150° C., the stress-strain curve mainly exhibits the softening regime at very low stress, with a distinctly shortened elastic regime and hardly any hardening regime. It is noted that the ends of curves in FIG. 9 for the tests at 1100° C. and 1150° C. do not represent fracture; the tests were simply interrupted due to the measurement limit of test machine. The excellent compressive deformability of the composite has not been reported in TiAX phase. Meanwhile, the large deformation of the Al2O3/Ti2AlN composites was attained at relatively low temperature (<1200° C.) and relatively rapid strain rate (3×10−3/s), compared with that of other ceramics, which is important for the hot workability of the composites.
FIG. 11 displays flexure stress-strain curves of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5 at different temperature. The flexure stress-strain curve at room temperature is linear to failure, with the characteristics of brittle failure. The flexure strength is 580 MPa, close to that of Al2O3. At 1000° C., the stress-strain curve deviates from a straight line, and exhibits three stages: an elastic regime; a transient, apparent hardening regime and a softening regime. The flexure strength is 140 MPa and the flexure strain at failure is 1.8%. At 1100° C., the elastic regime and the transient, apparent hardening regime are shortened, while the softening regime significantly increases. The flexure strength is 40 MPa and the sample does not fracture. Microcracks were observed at the tensile stress side. At 1200° C., the elastic regime and hardening regime disappear, and only the softening regime exists. The curve nearly parallels to the axis of flexure strain. The flexure strength is 10 MPa, the sample does not fracture, and microcracks were not observed at the tensile stress side of the sample.
FIG. 12 shows the variation relation of the maximum compressive stress with annealing temperature of as-annealed samples of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5 tested at 1100° C., with initial strain rate of 3×10-3/s. HP, 1100S, 1200S, 1250S, 1300S, and 1350S in FIG. 12 represent respectively the as-HPed sample, the as-annealed samples at 1100° C./20 h, 1200° C./20 h, 1250° C./20 h, 1300° C./20 h, 1350° C./20 h, respectively. It is seen that the MCS of HP sample is lower than that of Ti2AlN, while MCS of the as-annealed samples are all higher than that of Ti2AlN, wherein the MCS of the samples annealed at 1200° C. and 1300° C. are very close to that of Al2O3. This demonstrates that the high-temperature strength of HP sample can be effectively improved by annealing treatment, and the high-temperature strengths of the samples annealed at 1200° C. and 1300° C. are close to that of Al2O3.
FIG. 13 shows a graph of the variation of the mass gain per unit area at 1100° C. to 1350° C. with time of as-HPed samples of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5. For oxidation at 1100° C., the mass gain per unit area (Δm/A) gradually increases before 5 h, and remains nearly stable with time increasing. For oxidation at 1200° C. and 1250° C., the mass gain per unit area still increases slowly with time. The mass gains per unit area at 1100° C./100 h, 1200° C./100 h, 1250° C./100 h are 0.72 mg/cm2, 1.2 mg/cm2 and 1.9 mg/cm2, respectively. For oxidation at 1300° C., the mass gain per unit area gradually increases before 5 h, and still increases slowly with time. For oxidation at 1350° C., the mass gain per unit area increases slowly before 5 h; after 5 h, the mass gain per unit area increases faster with time than that of samples oxidized at low temperatures. The mass gains per unit area at 1300° C./100 h, and 1350° C./100 h are 3.79 mg/cm2 and 11.6 mg/cm2, respectively. Compared with results of Sun et al. Z. M. Sun, Y. C. Zhou. M. S. Li, Acta Mater., 49, 4347(2001)), the mass gain per unit area of the as-HPed composite oxidized at 1100° C./20 h is only 3.7% that of Ti3SiC2-based material; and the mass gain per unit area of the as-HPed composite at 1200° C./20 h is only 1.8% that of Ti3SiC2-based material. Barsoum et al. ((M. W. Barsoum, N. Tzenov, A. Procopio, T. El-Raghy, M. Ali, J. Electrochem. Soc., 148, C551 (2001)) reported that the oxidation experimental results of the TiAlX phases are: oxidation follows the parabolic law in the range of 1000° C. to 1100° C., for time shorter than 20 h; while for time longer than 20 h, the oxidation follows the linear law, which indicates the materials do not resist the oxidation, and it is thought that the oxidation resistance of TiAlX phases was not as good as that of Ti3SiC2. The oxidation properties of Ti3SiC2 were improved by adding Al to form solid solution by Zhang et al. (H. B. Zhang, Y. C. Zhou, Y. W. Bao, M. S. Li, Acta Mater., 52, 3631 (2004)). The mass gains per unit area of the as-HPed composite oxidized at 1100° C. to 1300° C. for 20 h are comparable to that of Zhang'results. But the mass gain per unit area of the as-HPed composite oxidized at 1350° C. for 20 h is 3.8 mg/cm2, 5% that of Zhang's result (80 mg/cm2). Even, the mass gain per unit area of the as-HPed composite oxidized at 1350° C. for 100 h is 11.6 mg/cm2, significantly smaller than that of Zhang's sample oxidized at 1350° C. for 20 h. It can be seen that, compared with the oxidation resistance of the TiAlX phases, the as-HPed composites exhibit excellent oxidation resistance in the range of 1100° C. to 1350° C. for long time (100 h), which demonstrates the significant improvement of high temperature oxidation properties by the in situ formation of Al2O3.
FIG. 14 shows a graph of the variation of the electrical resistivity with temperature of the Al2O3 dispersion-strengthened Ti2AlN composite produced in Example 5. It can be seen that, the electrical resistivity of the Al2O3/Ti2AlN composite decreases linearly with temperature from 300 K to 100 K. By a linear fit of the experimental data, the expression of electrical resistivity (ρ) and temperature (T) can be obtained.

ρ(T)=0.49945×[1+0.00356×(T−300)]T>100K 

The temperature coefficient of the resistivity of the composite is 0.00356 K−1. The electrical resistivity of the Al2O3/Ti2AlN composite at room temperature is 0.49945 μΩ·m. The electrical resistivity for Ti2AlN at room temperature is 0.312 μΩ·m, and for pure Ti is in the range of 0.40 μΩ·m to 0.492 μΩ·m. It is seen that the electrical resistivity of the Al2O3/Ti2AlN composite is a little higher than that of Ti2AlN, and comparable to that of pure Ti. This indicates the as-prepared composites with the excellent conductivity; meanwhile it effectively demonstrates the composites with good micro-structure.
The Al2O3 dispersion-strengthened Ti2AlN composites and the production method thereof provided by the invention possess the following merits:
The Al2O3/Ti2AlN composites were prepared with nanopowders (mean particle size of 42 nm) by HPMR. The Ti2AlN matrix and Al2O3 strengthening phase are both reactively formed in situ. Al2O3 particles are equiaxed crystals, and particle size of Al2O3 distributes in the range of 500 nm and 2 μm, the mean size of Al2O3 particles is about 0.8 μm to 1.2 μm. The grains of Ti2AlN are plate-shaped, about 80 nm to 120 nm thick and 0.5 μm to 2 μm long.
The microhardness of the Al2O3 dispersion-strengthened Ti2AlN composites is 7 GPa to 12 GPa, 1.8 to 3 times that of Ti2AlN. In situ formed Al2O3 significantly improves the hardness of the composite. The compressive strength of the composites at room temperature is comparable to that of Al2O3, while the high-temperature strength falls between that of the coarse-grained Al2O3 and Ti2AlN. The excellent high-temperature deformability of the composites under both compression and flexure stresses is achieved at relatively low temperature and relatively rapid strain rate, which is important for the hot workability of the composites.
Compared with the oxidation resistance of TiAlX phases, the as-HPed samples of the Al2O3 dispersion-strengthened Ti2AlN composites exhibit excellent oxidation resistance in the range of 1100° C. to 1350° C. for long time (100 h), which demonstrates that the high temperature oxidation resistance properties of the composites are greatly improved by in situ formation of Al2O3.
The electrical resistivity graph of the Al2O3 dispersion-strengthened Ti2AlN composites shows metallic characteristics. The electrical resistivity of the composites at room temperature is 0.3 μΩ·m to 0.8 μΩ·m, which is a little higher than that of Ti2AlN, and comparable to that of pure Ti.
The hot pressing temperature of the Al2O3/Ti2AlN composites bulk is lower by 200° C. to 500° C. than that of Ti2AlN by hot isostatic pressing using micron-scale powder, and synthesis time is shorter by 20 hours to 40 hours. Thus, a lot of energy can be saved.
EXAMPLE 1
First, TiN nanopowders were prepared by HPMR continuously supplied with Ti rods. The chamber atmosphere is the mixture gas with a total pressure of 1 atm of N2, H2 and Ar, with 10% (by volume) N2, and the H2 to Ar ratio of 1:1 by volume. Al nanopowders were prepared by HPMR continuously supplied with Al rods. The chamber atmosphere is the mixture gas with a total pressure of 1 atm of H2 and Ar, with H2 and Ar ratio of 1:1 by volume. When Al rods were changed to Ti rods, Ti nanopowders were obtained by using the same process as that for Al nanopowders. The procedures of HPMR are: Samples were taken as anode, and tungsten electrode as cathode; when vacuum of the chamber reached to 3×10−3 Pa, Ar, H2 and N2 were charged at a given ratio; after a stable arc was established between the cathode and anode, the electrical current was stabled at about 200 A, and voltage was stabled at about 30 V; after every 0.5 h, N2 was supplied to keep the total pressure at about 1 atm; and after working for 4 to 6 h, the arc power was turned off; once nanopowders deposited in the collecting chamber, the nanopowders were collected in a glove case with vacuum of 3×10−3 Pa. For an atmosphere of the mixture of H2 and Ar, the supply of N2 was omitted, while other operations were the same as those for the nitrogen atmosphere.
The powders were mixed according to the following expression:

Ti+Al+TiN→Ti2AlN

Second, TiN nanopowder 12.4 g in weight, Al nanopowders 5.4 g in weight and Ti nanopwders 9.6 g in weight were measured. After homogeneously mixing, the mixture powders were placed in a graphite mold of φ50×60. The mold was placed in a hot pressing furnace. After the hot pressing furnace was vacuumed, the mixture powders were heated to a predetermined temperature of 850° C. After temperature reached to 850° C., a pressure of 45 MPa was applied. The temperature and pressure were kept constant for 4.5 h. After hot pressing, a sample 3.5 mm thick was obtained.
The as-produced material was Ti2AlN bulk, with Vickers hardness of about 4.5 GPa. Compressive strength at room temperature is 450 MPa, and electrical resistivity at room temperature is 0.30 μΩ·m.
EXAMPLE 2
First, TiN nanopowders were prepared by HPMR continuously supplied with Ti rods. The chamber atmosphere is the mixture gas with a total pressure of 1 atm of N2, H2 and Ar, with 12% (by volume) N2, and the H2 to Ar ratio of 1:0.9 by volume. Al nanopowders were prepared by HPMR continuously supplied with Al rods. The chamber atmosphere is the mixture gas with a total pressure of 1 atm of H2 and Ar, with H2 and Ar ratio of 1:0.9 by volume. When Al rods were changed to Ti rods, Ti nanopowders were obtained by using the same process as that for Al nanopowders. After Ti and Al nanopowders were subjected to surface passivation treatments, oxygen content of Ti nanopowders and Al nanopowders is about 5% and about 8% by weight, respectively. The procedures of HPMR are: Samples were taken as anode, and tungsten electrode as cathode; when vacuum of the chamber reached to 3×10−3 Pa, Ar, H2 and N2 were charged at a given ratio; after a stable arc was established between the cathode and anode, the electrical current was stabled at about 200 A, and voltage was stabled at about 30 V; after every 0.5 h, N2 was supplied to keep the total pressure at about 1 atm; and after working for 4 to 6 h, the arc power was turned off, and Ar gas was charged to 0.8 atm; the nanopowders flowed rapidly under the work of gas-circulated pump; during this process, air was slowly charged and reached to 1 atm; then input valve was turned off, and gas-circulated pump continuously worked for 0.5 h and was turned off; once nanopowders deposited in the collecting chamber, the nanopowders were collected in a glove case with vacuum of 3×10−3 Pa. For an atmosphere of the mixture of H2 and Ar, the supply of N2 was omitted, while other operations were the same as those for the nitrogen atmosphere.
The powders were mixed according to the following expression:

4Ti+6Al+4TiN+3O→4Ti2AlN+Al2O3 

Second, TiN nanopowder 12.4 g in weight, Al nanopowders 8.1 g in weight and Ti nanopwders 9.6 g in weight were measured. After homogeneously mixing, the mixture powders were placed in the graphite mold of φ50×60. The mold was placed in the hot pressing furnace. After the hot pressing furnace was vacuumed, the mixture powders were heated to a predetermined temperature of 900° C. After temperature reached to 900° C., the pressure of 55 MPa was applied. The temperature and pressure were kept constant for 5.5 h. After hot pressing, sample 3.60 mm thick was obtained.
The as-produced material is Al2O3/Ti2AlN composite bulk, with about 20% (by volume) Al2O3. Vickers hardness of the composite is about 7 GPa. Compressive strength at room temperature is 1200 MPa, and electrical resistivity at room temperature is 0.35 μΩ·m. Microstructure of as-HPed sample is the same as that of the composite with 40% (by volume) Al2O3 described in MODE OF CARRYING OUT THE INVENTION section. Table 2 shows the compressive strength of as-HPed samples at different temperature, with initial strain rate of 3×10−3/s. Table 3 shows the compressive strength of as-annealed samples tested at 1100° C., with initial strain rate of 3×10−3/s. Table 4 displays the mass gain per unit area of as-HPed samples oxidized at different temperature for 100 h.







TABLE 2







The compressive strength of the as-HPed samples at different


temperature










Test temperature (° C.)
Compressive strength (MPa)














Room temperature
1200



 850
850



 950
600



1050
300



1100
160



1150
30

















TABLE 3







The compressive strength of the as-annealed samples tested at 1100° C.








Heat treatment parameters
Compressive strength at 1100° C. (MPa)





1100° C./20 h air cooling
350


1200° C./20 h air cooling
500


1250° C./20 h air cooling
450


1300° C./20 h air cooling
460


1350° C./20 h air cooling
400
















TABLE 4







The mass gain per unit area of the as-HPed samples oxidized at different


temperature for 100 h











Mass gain per



Oxidation temperature (° C.)
unit area for 100 h (mg/cm2)














1100
0.9



1200
1.4



1250
2.2



1300
4.1



1350
14.5










EXAMPLE 3
First, TiN nanopowders were prepared by HPMR continuously supplied with Ti rods. The chamber atmosphere is the mixture gas of N2, H2 and Ar, with a total pressure of 1 atm with 13% (by volume) N2, and H2 to Ar ratio of 1:0.8 by volume. Al nanopowders were prepared by HPMR continuously supplied with Al rods. The chamber atmosphere is the mixture gas of H2 and Ar with a total pressure of 1 atm, with H2 to Ar ratio of 1:0.8 by volume. When Al rods were changed to Ti rods, Ti nanopowders were obtained by using the same process as that for Al nanopowders. After Ti and Al nanopowders were subjected to surface passivation treatments, oxygen contents of Ti nanopowders and Al nanopowders are about 6% and about 10% by weight, respectively. The procedures of HPMR are: Samples were taken as anode, and tungsten electrode as cathode; when vacuum of the chamber reached to 3×10−3 Pa, Ar, H2 and N2 were charged at a given ratio; after a stable arc was established between the cathode and anode, the electrical current was stabled at about 200 A, and voltage was stabled at about 30 V; after every 0.5 h, N2 was supplied to keep the total pressure at about 1 atm; and after working for 4 to 6 h, the arc power was turned off, and Ar gas was charged to 0.75 atm; the nanopowders flowed rapidly under the work of gas-circulated pump; during this process, air was slowly charged and reached to 1 atm; then input valve was turned off, and gas-circulated pump continuously worked for 0.5 h and was turned off; once nanopowders deposited in the collecting chamber, the nanopowders were collected in a glove case with vacuum of 3×10−3 Pa. For an atmosphere of the mixture of H2 and Ar, the supply of N2 was omitted, while other operations were the same as those for the nitrogen atmosphere.
The powders were mixed according to the following expression:

7Ti+13Al+7TiN+9O→7Ti2AlN+3Al2O3 

Second, TiN nanopowder 13 g in weight, Al nanopowders 10.5 g in weight and Ti nanopwders 10 g in weight were measured. After homogeneously mixing, the mixture powders were placed in the graphite mold of φ50×60. The mold was placed in the hot pressing furnace. After the hot pressing furnace was vacuumed, the mixture powders were heated to a predetermined temperature of 950° C. After temperature reached to 950° C., the pressure of 60 MPa was applied. The temperature and pressure were kept constant for 4 h. After hot pressing, sample 4.00 mm thick was obtained.
The as-produced material is Al2O3/Ti2AlN composite bulk, with about 30% (by volume) Al2O3. Vickers hardness of the composite is about 8 GPa. Compressive strength at room temperature is 1400 MPa, and electrical resistivity at room temperature is 0.40 μΩ·m. Microstructure of as-HPed sample is the same as that of the composite with 40% (by volume) Al2O3 described in MODE OF CARRYING OUT THE INVENTION section. Table 5 shows the compressive strength of as-HPed sample at different temperature, with initial strain rate of 3×10−3/s. Table 6 shows the compressive strength of as-annealed samples tested at 1100° C., with initial strain rate of 3×10−3/s. Table 7 displays the mass gain per unit area of as-HPed samples oxidized at different temperature 100 h.







TABLE 5







Compressive strength of as-HPed samples at different temperature










Test temperature (° C.)
Compressive strength (MPa)














Room temperature
1400



 850
900



 950
650



1050
350



1100
240



1150
50

















TABLE 6







Compressive strength of as-annealed samples tested at 1100° C.








Heat treatment parameters
Compressive strength at 1100° C. (MPa)





1100° C./20 h air cooling
400


1200° C./20 h air cooling
530


1250° C./20 h air cooling
450


1300° C./20 h air cooling
480


1350° C./20 h air cooling
410
















TABLE 7







The mass gain per unit area of as-HPed samples oxidized at different


temperature for 100 h











Mass gain per unit area



Oxidation temperature (° C.)
for 100 h (mg/cm2)














1100
0.80



1200
1.30



1250
2.10



1300
3.92



1350
12.6










EXAMPLE 4
The single-phase nanopowders were used in the former Example 1 to 3, while in situ mixture nanopowders were obtained by using alloy master in Example 4 to 5. First, mixture nanopowers were prepared by HPMR continuously supplied with Ti—Al alloy rods with Al content 40% by atom. The chamber atmosphere is the mixture gas of N2, H2 and Ar with a total pressure of 1 atm, with 13% (by volume) N2, and the H2 to Ar ratio of 1:0.8 by volume. The mixture nanopowders consist of TiN, TiAl and Al phases, and oxygen content of mixture nanopowders is about 12% by weight. The procedures of HPMR include: Samples were taken as anode, and tungsten electrode as cathode; when vacuum of the chamber reached to 3×1031 3 Pa, Ar, H2 and N2 were charged at a given ratio; after a stable arc was established between the cathode and anode, the electrical current was stabled at about 200 A, and voltage was stabled at about 30 V; after every 0.5 h, N2 was supplied to keep the total pressure at about 1 atm; after working for 4 to 6 h, the arc power was turned off, and Ar gas was charged to 0.75 atm; the nanopowders flowed rapidly under the work of gas-circulated pump; during this process, air was slowly charged and reached to 1 atm; then input valve was turned off, and gas-circulated pump continuously worked for 0.5 h and was turned off; once nanopowders deposited in the collecting chamber, the nanopowders were collected in a glove case with vacuum of 3×10−3 Pa.
The powders were mixed according to the following expression:

7TiAl+7TiN+9O+6Al→7Ti2AlN+3Al2O3 

Second, mixture nanopowders 40 g in weight were measured. After homogeneous mixing, the mixture powders were placed in a graphite mold of φ50×60. The mold was placed in a hot pressing furnace. After the hot pressing furnace was vacuumed, the mixture powders were heated to the predetermined temperature of 950° C. After temperature reached to 950° C., the pressure of 60 MPa was applied. Temperature and pressure were kept constant for 5 h. After hot pressing, sample 4.9 mm thick was obtained.
The as-produced material is Al2O3/Ti2AlN composite bulk, with 30% (by volume) Al2O3. Vickers hardness of the composite is about 8.2 GPa. Compressive strength at room temperature is 1400 MPa, and electrical resistivity at room temperature is 0.41 μΩ·m. Microstructure of as-HPed sample is the same as that of the composite with 40% (by volume) Al2O3 described in MODE OF CARRYING OUT THE INVENTION section. Mechanical and oxidation properties at different temperature are nearly the same as those of Example 3.
EXAMPLE 5
First, mixture nanopowders were prepared by HPMR continuously supplied with Ti—Al alloy rods with Al content 50% by atom. The chamber atmosphere is the mixture gas of N2, H2 and Ar with a total pressure of 1 atm, with 14% (by volume) N2, and the H2 to Ar ratio of 1:0.9 by volume. The mixture nanopowders comprise TiN, and TiAl3 phases, with TiN and TiAl3 mol ratio of 1:0.9, and oxygen content of mixture nanopowders is about 15% by weight. The procedures of HPMR are: Samples were taken as anode, and tungsten electrode as cathode; when vacuum of the chamber reached to 3×10−3 Pa, Ar, H2 and N2 were charged at a given ratio; after a stable arc was established between the cathode and anode, the electrical current was stabled at about 200 A, and voltage was stabled at about 30 V; after every 0.5 h, N2 was supplied to keep the total pressure at about 1 atm; after working for 4 to 6 h, the arc power was turned off, and Ar gas was charged to 0.7 atm; the nanopowders flowed rapidly under the work of gas-circulated pump; during this process, air was slowly charged and reached to 1 atm; then input valve was turned off, and gas-circulated pump continuosly worked for 0.5 h and was turned off; once nanopowder deposited in the collecting chamber, the nanopowders were collected in a glove case with vaccume of 3×10−3 Pa.
The powders were mixed according to the following expression:

TiAl3+TiN+3O→Ti2AlN+Al2O3 

Second, mixture nanopowders 26 g in weight were measured. After homogeneous mixing, the mixture powders were placed in a graphite mold 50 mm in diameter and 60 mm in height. The graphite mold was placed in a hot pressing furnace. After the hot pressing furnace was vacuumed, the mixture powders were heated to the predetermined temperature of 1000° C. After temperature reached 1000° C., the pressure of 50 MPa was applied. Temperature and pressure were kept constant for 5 h. After hot pressing, sample 3.28 mm thick was obtained.
The as-produced material is bulk Al2O3/Ti2AlN composite, with 40% (by volume) Al2O3. Vickers hardness of the composite is about 10 GPa. Compressive strength at room temperature is 1800 MPa, and electrical resistivity at room temperature is 0.50 μΩ·m. Microstructural characteristics, mechanical and oxidation properties, were described in MODE OF CARRYING OUT THE INVENTION section. Table 8 shows the compressive strength of as-HPed samples at different temperature, with the initial strain rate of 3×10−3/s. Table 9 shows the compressive strength of as-annealed samples tested at 1100° C., with the initial strain rate of 3×10−3/s. Table 10 displays the mass gain per unit area of as-HPed samples oxidized at different temperature for 100 h.







TABLE 8







Compressive strength of as-HPed samples at different temperature










Test temperature (° C.)
Compressive strength (MPa)














Room temperature
1870



 850
1050



 950
720



1050
420



1100
260



1150
40

















TABLE 9







Compressive strength of as-annealed samples tested at 1100° C.








Heat treatment parameters
Compressive strength at 1100° C. (MPa)





1100° C./20 h air cooling
445


1200° C./20 h air cooling
586


1250° C./20 h air cooling
460


1300° C./20 h air cooling
573


1350° C./20 h air cooling
440
















TABLE 10







The mass gain per unit area of as-HPed samples after oxidized at


different temperature for 100 h











Mass gain per unit area



Oxidation temperature (° C.)
for 100 h (mg/cm2)














1100
0.72



1200
1.20



1250
1.90



1300
3.79



1350
11.60

## Claims

1. Al2O3 dispersion-strengthened Ti2AlN composites comprising Ti2AlN matrix and Al2O3 strengthening phase, with Al2O3 particles dispersed uniformly in the Ti2AlN matrix, characterized in that Ti2AlN matrix and Al2O3 strengthening phase both are produced by in situ reactive process.

2. The Al2O3 dispersion-strengthened Ti2AlN composites of claim 1 wherein the volume fraction of Al2O3 is 5% to 50%.

3. The Al2O3 dispersion-strengthened Ti2AlN composites of claim 1 wherein the shape of Al2O3 particles is equiaxed, and particle size of Al2O3 distributes in the range of 500 nm to 2 μm, with the mean size of 0.8 μm to 1.2 μm; the shape of Ti2AlN grain is plate-like, 80 nm to 120 nm thick and 0.5 μm to 2 μm long, and with an average geometric size of 0.2 μm to 0.5 μm, wherein the average geometric size means a value obtained by extracting a square root of a product of the length and width.

4. A method for preparing Al2O3 dispersion-strengthened Ti2AlN composites according to claim 1, comprising:
preparing nanopowders of Ti—Al system by a hydrogen plasma-metal reaction method, and compacting the nanopowders by vacuum hot pressing or hot isostatic pressing.

5. The method for preparing Al2O3 dispersion-strengthened Ti2AlN composites of claim 4 wherein the method is carried out in is a mixture atmosphere of nitrogen-containing gas, H2, and Ar with a pressure of 0.8 to 1.2 atm.

6. The method for preparing Al2O3 dispersion-strengthened Ti2AlN composites of claim 4 wherein the nanopowders of Ti—Al system are prepared with Ti—Al master alloys, wherein the Ti—Al master alloys selected from the group consisting of Ti—Al alloy rods with Al content of 20% to 60% by atom, and pure Al rods and pure Ti rods, in a manner of continual feeding.

7. The method for preparing Al2O3 dispersion-strengthened Ti2AlN composites of claim 4 wherein the nanopowders of Ti—Al system are selected from the group consisting of pure element nanopowders of Ti and Al, alloy nanopowders with Ti and Al elements, and ceramic nanopowders with Ti, Al, O, and N elements.

8. The method for preparing Al2O3 dispersion-strengthened Al2O3 composites of claim 4 wherein the oxygen content of the nanopowders of Ti—Al system is 0 to 20% by weight.

9. The method for preparing Al2O3 dispersion-strengthened Ti2AlN composites of claim 4 wherein the parameters of the vacuum hot pressing are: temperature of 800° C. to 1200° C.; pressure of 40 MPa to 60 MPa; time of 4 h to 6 h; and vacuum of 2×10−2 Pa to 5×10−3 Pa.

10. The method for preparing Al2O3 dispersion-strengthened Ti2AlN composites of claim 4 wherein the nitrogen-containing gas is N2 or NH3 gas, with a volume fraction of 0 to 20%.

11. The method for preparing Al2O3 dispersion-strengthened Ti2AlN composites of claim 4 wherein the nanoparticles of Ti—Al system are selected from the group consisting of Ti, TiN, intermetallic compounds of Ti—Al system, Al, and AlN.