WEAR RESISTANT CERAMIC MATERIALS

Abstract: Tough and wear-resistant ceramic materials based on reactive metal bonded alumina-titanium nitride. The ceramic composite body contains a metal phase with reactive metal components such as Zr, Ti, Hf, or Y to obtain the characteristic of toughness. The compositions were extremely useful for applications such as metal cutting operations where improved toughness is required in addition to the exceptional wear resistance which ceramics usually possess.

Description: EAR RESISTANT CERAMIC MATERIALS Technical Field The present invention relates to ceramic compo¬ sitions which, in addition to the characteristic wear resistance of ceramic, are characterized by their toughness as evidenced by their superior impact resistance. The ceramic compositions of the present invention comprise from 1 to 30 weight percent of a metal phase containing at least one weight percent reactive metal component such as zirconium, hafnium, titanium and yttrium. Background Art Although it is known that ceramics have excellent wear resistance properties compared to metals and carbides, they lack substantially in toughness. This fact is probably the single most important reason why ceramics have not been as widely used as carbides in the metal removal industry. Albeit, in some metal removal operations, pure aluminum oxides have been used but only with extreme precautions due to their poor impact resistance. Recent developments in machine tool technology coupled with the need for increased productivity has prompted industry to more readily accept ceramics as cutting tool materials. Still, the aforementioned lack of toughness continues to limit the use of ceramic materials to carefully controlled operations and has all but excluded their use in cutting operations involving interrupted cuts in order not to impart severe impact blows to the ceramic cutting inserts. In an attempt to meet the abovenoted deficiencies of ceramic materials, prior workers attempted to modify the properties of ceramic compositions to make them more impact resistant. Yates U.S. Patent 3,409,419 represents one such attempt. Yates generally discloses OMPI ceramic compositions consisting of essential nitrides bonded with a binder metal selected from iron, cobalt, nickel and their alloys and also including a wear resistant component selected from aluminum nitride, titanium nitride, alumina and their mixtures. Yates does not utilize a reactive metal component in his ceramic compositions. Disclosure of Invention The present invention relates to ceramic compo¬ sitions which contain 1 to 10 weight percent of a metal phase containing at least one weight percent metal component such as zirconium, hafnium, titanium and yttriu and wherein the ceramic phase comprises 20 to 80 weight percent alumina and 80 to 20 weight percent nitride of group IVB and VB elements. The ceramic compositions are extremely useful for applications such as metal cutting operations where toughness (impact resistance) is require in addition to exceptional wear resistance. Detailed Description Ceramics have long been known to have excellent wear resistance properties but have suffered from a lack of toughness thus severely limiting their use in the meta removal industry. Oxides and nitrides are chemically more stable than carbides and should be superior materials for use in mechanical applications where wear resistance is a prime requisite if their bond strengths could be enhanced to improve the toughness (impact resistance) of the material It has now been found that by incorporating a reactive metal component in the ceramic composition, the reactive metal component can bond the ceramic grains such as oxide grains by the following chemical reaction: aMb0 c + dR eRfOg + hM where M = metal species forming the ceramic oxides; R = a metal component more reactive than M; a, b, c, d, e, f, g, h = numbers satisfying the reaction. The overall result of these chemical reactions is to improve the bonding strength between individual ceramic grains and thus the toughness (impact resistance) of the material. Among the useful ceramic materials are aluminum oxide and nitrides of group IVB and group VB elements. These materials all have excellent wear resistance properties in comparison to carbides and metals. The reactive metal phase can be either Zr, Hf, Ti or Y which, according to the equation, form thermodynam- ically more stable ceramics than the parent ceramics. (Oxides of these elements are thermodynamically more stable than most other engineering oxides.) They can be in elemental form or in alloyed forms with other elements such as Ni, Co or Fe. The advantage of using an alloyed form is that the melting point of the metallic phase is lowered significantly compared to the pure substances. The reactive metal phase used in the present invention includes Ni-Zr alloy powders from Ventron Corp. , NiTi powders from Ventron Corp. and a complex Ni-base superalloy available from the International Nickel Co. as IN100, containing Ti and Zr. The ceramic components of the composition of the present invention include aluminum oxide, titanium nitride and zirconium nitride. The following procedures were employed to produce comparative ceramic compositions. The individual components were carefully weighed, blended and wet-milled in a ball mill for 48 hours. After milling, the powder slurries were vacuum dried at 260°C. and hot pressed at 1600-1800°C. for 4 to 10 minutes. Hot pressing pressure was 280 kg/cm 2 for all compositions. The hot pressed cylinders were ground on both sides with a diamond grinding wheel before measuring hardness. Test samples of a dimension of 2.54 mm x 2.54 m x 19.05 mm were made out of the hot pressed cylinders to measure the transverse rupture strength of the materials by 3-point bending tests. The bars were ground with a 15 micron diamond grinding wheel before the test to remove any machining defects. For selected compositions, cutting inserts having a geometry 12.7 mm square and 4.75 mm thick were fabricated. In the machining test, a metal slab (work material) was machined by turning on a Lodge and Shipley lathe. The slab was cut with a depth of cut (D.O.C.) of 15.24 mm and a feed rate of .254 mm per revolution. The work material was 4340 steel with a Rockwell hardness of Rc 30 in the form of a 25.4 mm thick slab so that in actual cutting, the inserts encountered two interrupted cuts, or impacts, during each complete revolution of the work piece. The number of these interrupted cuts (impacts) made before the corner of the tool was broken were recorded. Table 1 below shows the results of physical testing for the different compositions of each of the Examples described below. Table 2 shows the results of machining tests for selected compositions. EXAMPLE 1 195 grams of alumina powder of average particle size less than one micron, 90 grams of titanium nitride of average particle size of 1.5 micron and 15 grams of Ni-30 Zr alloy powders of particle size less than 44 microns were blended and wet ball milled for 48 hours. The powde slurry was then dried and hot pressed into 25.4 mm diameter and approximately 6.35 mm thick cylinders at 1775°C. for 4 minutes at 280 kg/cm 2 . The product had a Rockwell hardness of 94.5, and a transverse rupture strength of 10,150 kg/cm 2 . U O. . W EXAMPLE 2 207 grams of alumina, 90 grams of titanium nitride and 3 grams of Ni-30 Zr powders were processed exactly the same as in Example 1. The product had a Rockwell hardness of R^ 94.0 and a transverse rupture strength of 9660 kg/cm 2 . EXAMPLE 3 195 grams of alumina, 90 grams of titanium nitride and 15 grams of a complex nickel-based superalloy (IN100) powders were processed exactly the same as in Example 1. The product had a Rockwell hardness of R^ 93 and a transverse rupture strength of 9800 kg/cm 2 . EXAMPLE 4 90 grams of alumina, 195 grams of titanium nitride and 15 grams of Ni-30 Zr powders were processed exactly the same as in Example 1. The product had a Rockwell hardness of R^ 93, and a transverse rupture strength of 10,150 kg/cm 2 . EXAMPLE 5 240 grams of alumina, 45 grams of titanium nitride, and 15 grams of Ni-30 Zr were processed exactly the same as in Example 1. The product had a Rockwell hardness of R^ 94 and a transverse rupture strength of 9800 kg/cm 2 . EXAMPLE 6 182 grams of alumina and 78 grams of titanium nitride were processed exactly the same as in Example 1. The product had a hardness of R^ 94.5, and a transverse rupture strength of 6020 kg/cm 2 . EXAMPLE 7 207 grams of alumina, 90 grams of titanium nitride and 2.25 grams of MgO were processed exactly the same as in Example 1. The product had a Rockwell hardnes of R A 94.5, and a transverse rupture strength of 5390 kg/cm 2 . EXAMPLE 8 195 grams of alumina, 90 grams of titanium nitride and 15 grams of nickel powders were processed exactly the same as in Example 1. The product had a Rockwell hardness of R^ 93.5, and a transverse rupture strength of 8680 kg/cm 2 . EXAMPLE 9 207 grams of alumina, 90 grams of titanium nitride and 3 grams of Ni powders were processed exactly the same as in Example 1. The product had a Rockwell hardness of R^ 94.5, and a transverse rupture strength of 6650 kg/cm 2 . EXAMPLE 10 57 grams of alumina, 199.5 grams of titanium nitride and 15 grams of Ni-30 Zr powders were processed exactly the same as in Example 1. The dried powders were processed at 1650°C for 7 minutes. The product had a Rockwell hardness of R^ 94.0, and a transverse rupture strength of 9450 kg/cm 2 . EXAMPLE 11 228 grams of alumina, 57 grams of titanium nitride and 15 grams of Ni-30 Zr powders were processed exactly the same as in Example 10. The product had a Rockwell hardness of R^ 94.0, and a transverse rupture strength of 9940 kg/cm 2 . EXAMPLE 12 195 grams of alumina, 90 grams of zirconium nitride and 15 grams of Ni-30 Zr powders were processed exactly the same as in Example 10. The product had a Rockwell hardness of R & 94.0 and a transverse rupture strength of 9800 kg/cm 2 . EXAMPLE 13 195 grams of alumina, 90 grams of zirconium nitride and 15 grams of Ni-30 Ti powders were processed exactly the same as in Example 10. The product had a Rockwell hardness of ^ 93.5, and a transverse rupture strength of 9100 kg/cm 2 . OMPI TABLE 1 Summary of Transverse Rupture Tests for Comparative Compositions Example Composition (wt. percent) Hardness Transverse Rupture No. Alumina TiN ZrN Ni -30Zr Ni-30Ti IN100 Ni Strength (kg/cm 2 ) 1 65 30 0 5 0 0 0 94.5 10,150 2 69 30 0 1 0 0 0 94.0 9,660 3 65 30 0 0 0 5 0 93.0 9,800 I 4 30 65 0 5 0 0 0 94.5 10,150 00 I 5 80 15 0 5 0 0 0 94.5 9,800 6 70 30 0 0 0 0 0 93.5 6,020 7 69 30 0 0 0 0 1-MgO 94.5 5,390 8 65 30 0 0 0 0 5 93.0 8,680 9 69 30 0 0 0 0 1 94.0 6,650 10 21 73 0 5 0 0 0 94.0 9,940 11 76 19 0 5 0 0 0 94.0 9,940 12 65 0 30 5 0 0 0 94.0 9,800 13 65 0 30 0 5 0 0 93.5 9,100 TABLE 2 Summary of Machine Testing* for Selected Compositions Example Composition (wt. percent) No. of Interrupted Cuts** No. Aim TIN ZrN Ni-30ZR Ni-30-Ti IN100 Ni Made before Breakage 1 65 30 0 5 0 0 I 2 69 30 0 1 0 0 0 6000+ VO I 4 30 65 0 5 0 0 0 1163 6 70 30 0 0 0 0 0 584 9 69 30 0 0 0 0 1 Broke on impact 10 21 73 0 6 0 0 0 1025 11 76 19 0 5 0 0 0 6000+ Work Material: 4340 steel slab of 25.4 mm thickness Hardness: Re 30 DOC: 1.5 mm Feed Rate: 0.25 mm per revolution ** The tool makes one interrupted cut every time it hits the slab Examination of both Tables 1 and 2 will reveal that the reactive metal component is essential in obtaining the required impact properties in the resultin ceramic materials. Thus, direct comparison of Example 1 with Example 8 and Example 2 with Example 9 clearly show that exceptional impact resistance is achieved when a reactive metal is present while its absence results in a ceramic material of minimal value in applications where toughness is required. Similar results will be observed for ceramic compositions containing only alumina and TiN (Examples 6 and 7).

Claims: HAT IS CLAIMED IS: 1. A ceramic composition having increased impact resistance comprising a ceramic phase and a metal phase, said ceramic phase comprising about 90 to 99 weight percent of the ceramic composition and being comprised of about 20 to 80 weight percent aluminum oxide and about 80 to about 20 weight percent nitrides of group IVB and group VB elements, said metal phase comprising about 10 to 1 weight percent of the ceramic composition and contains at least one weight percent of a reactive metal selected from the group consisting of zirconium, hafnium, titanium, yttrium or combinations thereof. 2. A ceramic composition according to claim 1 wherein the nitride is titanium nitride. 3 A ceramic composition according to claim 1 wherein the nitride is zirconium nitride. 4. A ceramic composition according to claim 1 wherein the metal phase is an alloy powder of nickel and zirconium. 5. A ceramic composition according to claim 1 wherein the metal phase is an alloy powder of nickel and titanium. 6. A ceramic composition according to claim 1 wherein the metal phase is an alloy powder of nickel, titanium and zirconium.

Inventors: LEE S
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING & MFG CO
Application year: 1980
Main classification: C04B35
IPC codes: C04B35, C22C29