bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoelectric Material Design in Pseudo Binary Systems of Mg2Si – Mg2Ge – Mg2Sn on the Powder Metallurgy Route
Authors: Aizawa Tatsuhiko , Song Ren Bo , Yamamoto Atsushi
Published: March 2009

Fundamental studies on the thermoelectricity have been mainly done in the pseudo binary systems of Mg2Si – Mg2Ge – Mg2Sn. In recent years, their thermoelectricity is revisited because of light-weight, low initial const and short turning back time in addition to high potential in figureof- merit for ZT approaching to unity or more. Conventional melting and solidification, or, normal PM routes fail in precise, wide-range control of chemical composition and microstructure control. New PM route via bulk mechanical alloying is developed to fabricate the solid solution semiconductive materials with Mg2Si1-xGex and Mg2Si1-ySny for 0 < x, y < 1 and to investigate their thermoelectric materials. Since Mg2Si is n-type and both Mg2Ge and Mg2Sn are p-type, pntransition takes place at the specified range of germanium content, x, and tin content, y. Through optimization of chemical composition, solid-solution type thermoelectric semi-conductive materials are designed both for n- and p-type materials. In addition, appropriate doping condition can be searched in the specified range of x and y.
The Effect of Deformation Stress-Strain and Temperature on The Ic Degradation of Bi-2223/Ag Tapes
Authors: Ha Hong Soo , Kim Sang Cheol , Ha Dong Woo , Oh Sang Soo , Joo Jin Ho
Published: March 2009

Bi-2223/Ag tapes are usually used for superconducting power cables and magnets. Bi-
2223 ceramic superconducting core can be damaged under complicated stress and strain conditions
such as winding tension, bending and twisting. In this study, we have presented the effect of axial
stress and bending strain on the superconducting properties of Bi-2223/Ag tapes. In order to
establish the value for 95% retained Ic of the Bi-2223/Ag tapes under various stress-strain
conditions, the tension apparatus with bending former was used to apply the tension and bending
stress-strain. Tension and bending stress-strain simultaneously applied to the tapes could reduce the
critical current even though each applied stress and strain values were not higher than that of 95%
retained Ic of the tapes. Complex stress-strain conditions including the thermal stress-strain have
accelerated the degradation of the Bi-223/Ag tapes. The deformation temperature was important to
maintain the 95% retained Ic of the Bi-2223/Ag tapes after bending or tension deformation because
mechanical strength of the tapes can be changed drastically between room temperature and 77 K.
Characteristics of Porous YAG Powders Fabricated by PVA Polymer Solution Technique
Authors: Lee Sang Jin , Shin P.W. , Kim J.W. , Chun S.Y.
Published: March 2009

Pure and stable YAG (Y3Al5O12) powders were synthesized by a PVA (polyvinyl alcohol) polymer solution technique. PVA was used as an organic carrier for the precursor ceramic gel. The PVA affected crystallization behavior, powder morphology, specific surface area and crystalline size of the synthesized powders. The precursor gels were crystallized to YAG at relatively a low temperature of 900 °C. The synthesized powders, which have nano-sized primary particles, were soft and porous, and the porous powders were ground to sub-micron size by a simple ball milling process. The ball-milled powders were densified to 94% relative density at 1500 °C for 1h. In this study, the characteristics of the synthesized YAG powders were examined by using X-ray diffractometer, simultaneous differential scanning calorimetry and electrophoretic light scattering spectrophotometer. And the morphologies of the powders and the densified samples were observed by scanning electron microscopy.
Carbon Nanotube Reinforced Metal Matrix Nanocomposites via Equal Channel Angular Pressing
Authors: Pham Quang , Jeong Young Gi , Yoon Seung Chae , Hong Sun Ig , Hong Soon Hyung , Kim Hyoung Seop
Published: March 2009

Carbon nanotubes (CNTs) have been the subject of intensive study for applications in the
fields of nanotechnologies in recent years due to their superior mechanical, electric, optical and
electronic properties. Because of their exceptionally small diameters (≈ several nm) as well as their
high Young’s modulus (≈ 1 TPa), tensile strength (≈ 200 GPa) and high elongation (10-30%) in
addition to a high chemical stability, CNTs are attractive reinforcement materials for light weight
and high strength metal matrix composites. In this study, bottom-up type powder processing and
top-down type SPD (severe plastic deformation) approaches were combined in order to achieve full
density of CNT/metal matrix composites with superior mechanical properties by improved particle
bonding and least grain growth, which were considered as a bottle neck of the bottom-up method
using the conventional powder metallurgy of compaction and sintering. ECAP (equal channel
angular pressing), the most promising method in SPD, was used for the CNT/Cu powder
consolidation. The powder ECAP processing with 1, 2, 4 and 8 route C passes was conducted at
room temperature. It was found by mechanical testing of the consolidated CNT/Cu that high
mechanical strength could be achieved effectively as a result of the Cu matrix strengthening and
improved particle bonding during ECAP. The ECAP processing of powders is a viable method to
achieve fully density CNT-Cu nanocomposites.
Densification Behavior of Iron Powder during Cold Stepped Compaction
Authors: Kang Choun Sung , Lee S.C. , Kim K.T. , Rozenberg Oleg
Published: March 2009

Densification behavior of iron powder under cold stepped compaction was studied. Experimental data were also obtained for iron powder under cold stepped compaction. The elastoplastic constitutive equation based on the yield function of Shima and Oyane was implemented into a finite element program (ABAQUS) to simulate compaction responses of iron powder during cold stepped compaction. Finite element results were compared with experimental data for densification, deformed geometry and density distribution. The agreement between finite element results and experimental data was very good for iron powder. The distributions of hydrostatic pressure and the Mises stress of iron powder under cold stepped compaction were also studied.
Fabrication of Rod type Cu54Ni6Zr22Ti18 Bulk Amorphous Alloy by Warm Extrusion Process
Authors: Lim Sung Chul , Kim Kyung Hoon , Lee Heung Bok , Lee Hyo Soo , Kwon Hyouk Chon
Published: March 2009

In this study, rod type Cu54Ni6Zr22Ti18 bulk amorphous alloy fabricated by warm
extrusion of amorphous powders was investigated. To get bulk type amorphous alloy, the
Cu54Ni6Zr22Ti18 amorphous powders which has a particle size below 63( and wide supercooled
liquid region of 53K were prepared by a high-pressure gas atomization method. The powders were
filled in a Cu can with an inner dimension 20×2×50mm in air, evacuated, sealed and then precompacted
in the press. Before extrusion, the billet was heated with heating rate of 50K/min and
the holding time was about 5min. The extrusion temperature was 723K and the extrusion ratio was
increased from 2 to 5. By warm extrusion of amorphous powders, a fully amorphous
Cu54Ni6Zr22Ti18 bulk type alloys were successfully synthesized. The conditions for extrusion were
decided based on the time-temperature-transformation curve and DSC analysis. Phase analysis was
performed by XRD. The result of the phase analysis indicated that Cu54Ni6Zr22Ti18 bulk rod type
samples having fully amorphous phase could be obtained until extrusion ratio of 4 at extrusion
temperature of 723K, but partial crystalline phase would be observed in the bulk rod type alloy
fabricated at extrusion ratio of 5.
Flow Patterns in Green Bodies Made by High-Speed Centrifugal Compaction Process
Authors: Suzuki Hiroyuki Y. , Urabe Katsuaki , Takano Tomoki , Kuroki Hidenori
Published: March 2009

High-Speed Centrifugal Compaction Process (HCP) is a wet compacting method, in
which powders are compacted under a huge centrifugal force. The HCP was well applied to small
alumina specimens, but the compact easily cracked when we applied the HCP to other materials. In
the present study we clarify the mechanism that introduces such cracks. Firstly, we observed HCP
alumina, dyeing with iron oxide powder or by the Immersion Liquid Technique, and found that
there was a kind of flow pattern generated during the HCP. A simple simulation also revealed that
the formation of such a flow pattern was related to the Colioli’s force in the centrifugal field, and
therefore was hard to suppress. Nonetheless, the actual introduction of inhomogeneity along the
flow was largely affected by another factor. Die releasing oil was dragged in the flows and formed
low density regions along the flow.
Green Body Behaviour of High Velocity Pressed Metal Powder
Authors: Jonsén Par , Häggblad Hans Åke , Troive Lars , Furuberg Joachim , Allroth Sven , Skoglund Paul
Published: March 2009

High velocity compaction (HVC) is a production technique with capacity to significantly
improve the mechanical properties of powder metallurgy (PM) parts. Several investigations indicate
that high-density components can by obtained using HVC. Other characteristics are low ejection
force and uniform density. Investigated here are green body data such as density, tensile strength,
radial springback, ejection force and surface flatness. Comparisons are performed with conventional
compaction using the same pressing conditions. Cylindrical samples of a pre-alloyed water atomized
iron powder are used in this experimental investigation. The different behaviour of HVC-pressed
green bodies compared to conventional pressed green bodies are analysed and discussed. The HVC
process in this study resulted in a better compressibility curve and lower ejection force compared to
conventional quasi static pressing. Vertical scanning interferometry (VSI) measurements show that
the HVC process gives flatter sample surfaces.
Investigation of Mechanical Properties of Powder Metallurgy Parts with Control of Microstructure
Authors: Khorsand H. , Habibi S.M.
Published: March 2009

In the present work, two kinds of steel powder were (Distaloy HP-1 & Ultrapac-LA)
selected and subjected to powder metallurgy processing. For Ultrapac-LA, a heterogeneous
microstructure consisting of tempered martensite, nickel-rich ferrite, divorced pearlite and nickelrich
regions surrounding pores was observed. For Distaloy HP-1 in slow cooling rates (0.4 °C.s-1),
the amounts of martensite and bainite varied between 50-60% and 30-40%. However, for fast
cooling rates (1.2 °C.s-1), the variation was between 70-80% and 10-20%. The mechanical
properties of the prepared samples were studied with controlled production conditions such as
cooling rate and heat treatment. The increasing porosity was found to play an important role in the
tensile stress and fatigue strength. The ultimate tensile strength and fatigue strength were more than
1000 MPa and 400 MPa in this research (for Distaloy HP-1, 7.2 g.cm-3, 0.5% carbon content and
fast cooling rates). Macroscopic examination of the fracture surfaces for all specimens revealed that
fatigue crack growth and final fracture regions were brittle and without noticeable permanent
deformation. The final fracture regions for all tests were very similar, and the final fracture in these
two material conditions revealed brittle macrobehavior and ductile microbehavior.
Development of High Performance Stainless Steel Powders
Authors: Schade Christopher , Schaberl John
Published: March 2009

Advanced melting technology is now being employed in the manufacture of stainless
steel powders. The new process currently includes electric arc furnace (EAF) technology in
concert with Argon Oxygen Decarburization (AOD), High Performance Atomizing (HPA) and
hydrogen annealing. The new high performance processing route has allowed the more consistent
production of existing products, and has allowed enhanced properties, such as improved green
strength and green density. This paper will review these processing changes along with the potential
new products that are being developed utilizing this technology. These include high strength
stainless steels such as duplex and dual phase as well as stainless steel powders used in high
temperature applications such as diesel filters and fuel cells.
Warm Compression of Al Alloy PM Blends
Authors: Jiang Z. , Falticeanu C. Lucien , Chang I.T.H.
Published: March 2009

With the onging trend of reducing the weight of automotive parts, there is also an
increasing trend in the use of light alloys. Recently, aluminum powder metallurgy has been the
subject of great attention due to the combination of the lightweight characteristics of aluminium and
the efficient material utilisation of the powder metallurgical process, which offer attractive benefits
to potential end-users.
Conventional press and sinter route of non-ferrous P/M products are based compaction at room
temperature prior to the sintering cycle. However, warm compaction process has successfully
provided increased density in ferrous powder metallurgy parts, which contributes to better
mechanical properties and consequently overall performance of those parts. This study is aimed at
exploring the use of warm compaction process to aluminium powder metallurgy. This paper
presents a detailed study of the effect of warm compression and sintering conditions on the resultant
microstructures and mechanical properties of Al-Cu-Mg-Si PM blend.
Computer Aided Engineering Design of Powder Injection Molding Process for a Dental Scaler Tip Mold Design
Authors: Hwang Chul Jin , Ko Y.B. , Park Hyung Pil , Chung S.T. , Rhee Byung Ohk
Published: March 2009

Powder Injection Molding (PIM) has recently been recognized as an advanced
manufacturing technology for low-cost mass production of metal or ceramic parts of complicated
geometry. With this regards, design technology of dental scaler tip PIM mold, which has complex
shape and a slim core pin of 0.6 mm diameter, with the help of computer-aided analysis for powder
injection molding process was developed. Computer-aided analysis for dental scaler tip mold was
implemented by finite element method with non-Newtonian fluid, modified Cross model viscosity,
PvT data of powder/binder mixture. The core deflection analysis of dental scaler tip PIM mold
during PIM filling process was also investigated. Compter-aided analysis results, such as filling
pattern, weldline formation, and air vent position prediction were investigated and eventually
showed good agreements with experimental results.
Gas Nitriding Mechanism in Titanium Powder Injection Molded Products
Authors: Osada Toshiko , Miura Hideshi , Yamagami Takanobu , Nishiyabu Kazuaki , Tanaka Shigeo
Published: March 2009

Gas surface treatment is considered to be especially effective for Titanium because of its
high reactivity. In this study, we investigated the gas nitriding mechanism in titanium sintered parts
produced by metal powder injection molding (MIM) process. In MIM process, gas nitriding can be
surface-treated subsequently after debinding and sintering process. Then, the microstructure and
nitrogen content of sintered MIM parts are considered to be greatly influenced by not only nitriding
conditions but also sintered conditions. In this study, the effects of sintering time on microstructure
such as nitrided layer thickness and hardness was investigated. Focus was given to the effects of
specimen size on nitriding process, because the size of micro metal injection molding (μ-MIM)
product is so small and the specific surface of that product is so large that the mechanical and
functional properties can be subject to change by nitriding.
Fabrication of Micro Spur Gear in Nano Grained Al Alloy
Authors: Lee Won Sik , Jang Jin Man , Ko Se Hyun
Published: March 2009

In present work, manufacturing technologies of micro parts by micro forging and
pressing were studied using strain softening phenomenon in nano grained Al-1.5mass%Mg alloy.
During compressive test at 300, the Al alloy showed stain softening phenomenon by grain
boundary sliding regardless of strain rate. Micro spur gear with ten teeth (height of 200 μm and
pitch of 250 μm) was fabricated with sound shape by micro forging. During micro forging, increase
of applied stress induced by friction between material and die surface was effectively compensated
by decrease of stress by strain softening behavior and as a result, flow stress increased only about
50 MPa more than that in compressive test. However, in micro pressing, flow of material did not
occurred sufficiently to fill die and the resultant shape of gear was very poor.
Establishment of Laser Sintering Technique for Titanium Powder
Authors: Miura Hideshi , Maeda Hiroyuki , Uemura Makoto , Takemasu Teruie , Otsu Masaaki
Published: March 2009

This paper investigates the characteristic of single-layered and multi-layered compacts
made by selective laser sintering using titanium powder. The surface texture and tensile strength
were investigated by using single-layered compacts. There were few defects in surface of specimen
laser sintered in vacuum, and the roughness was smoother than that of the specimen laser sintered in
argon. Maximum tensile strength of single-layered compact laser sintered in vacuum was about
200MPa. The shrinkage and mechanical strength were investigated by using multi-layered compacts.
There was a unique tendency in the shrinkage of multi-layered compacts, which the density was
around 75% and the adhesive bonding was not observed between layers, resulted in 70MPa of
maximum bending strength and 50MPa of maximum tensile strength.
Formation of Rod-Like Al2TiO5 Via Mechanical Activation Followed by Thermal Processing
Authors: Chen Xiao Hu , Chen Xiao Min , Zhao Huang , Wu Ji Huai
Published: March 2009

The purpose of this paper is to investigate the possibility of rod-like Al2TiO5 formation via
a mechanical activation process. A QM-ISP-4 Planetary Mill was employed to activate mechanically
the mixtures of anatase and corundum in air at room temperature for different times. The milled
powder mixtures were then sintered in air at 1300°C for 1 h. The XRD results showed that the milled
powder mixtures were completely transformed into Al2TiO5 after sintering, except the mixtures
milled for 5 and 10 hours. The SEM observations showed the typical morphology of rod-like Al2TiO5
vary in the range: widths from 0.6 to 1.2 μm, and lengths from 3.0 to 6.0 μm. The rod-like Al2TiO5
formation was attributed to the positive effects caused by the mechanical activation.
Liquid Phase Sintering of a Boron Alloyed Austenitic Stainless Steel
Authors: Molinari Alberto , Menapace Cinzia , Kazior Jan , Pieczonka Tadeusz
Published: March 2009

It is well known that PM stainless steels have lower corrosion resistance than the
corresponding wrought steels, since they are affected by the presence of the open porosity.
A way to obtain a surface densification is the addition of a small quantity of boron (from 0,3 to
0,5%wt.) to the stainless steel. The presence of boron produces a liquid phase phenomenon that
results in a final microstructure consisting of a boron-rich phase network surrounding the stainless
steels grains. Close to the surface, a boron-free layer was observed in which pores are very few,
closed and round. This leads to an improvement in the steel corrosion resistance.
Oxygen Removal during Sintering of Steels Prepared from Cr-Mo and Mo Prealloyed Powders
Authors: Danninger Herbert , Xu Chen , Lindqvist Björn
Published: March 2009

The removal of oxygen during sintering by carbothermic reduction and the resulting
carbon loss were studied for steel compacts prepared with the compositions Fe-3%Cr-0.5%Mo-
0.5%C and Fe-1.5%Mo-0.5%C, respectively, prepared from prealloyed powders. The compacts
were prepared by pressing at 600 and 1000 MPa, and sintering was done at 1100 and 1300°C in
vacuum. It showed that for the Cr-Mo steel, deoxidation strongly depends on the sintering
temperature, in contrast to the plain Mo steel; at 1300°C very low oxygen levels were measured
with the standard density compact while after pressing at 1000 MPa, still significant oxygen is
contained, which is in agreement with the lower carbon loss measured. This indicates inhibition of
final deoxidation by pore closure; nevertheless, the impact energy was very high and exceeded that
of the Mo alloyed steels, indicating that finely dispersed oxides within the matrix are irrelevant if
only the surface oxides have been completely removed.
Pulsed Electric Current Sintering of Nano-Crystalline Iron-Base Powders
Authors: Li Yuan Yuan , Long Yan , Li Xiao Qiang , Liu Yun Zhong
Published: March 2009

A new process of pulsed electric current sintering was developed. It combines
compaction with activated sintering effectively and can manufacture bulky nano-crystalline
materials very quickly. Pulsed electric current sintering of high-energy ball-milled nano-crystalline
iron-based powders is investigated in this work. A nanostructured steel is obtained with high
relative density and hardness by this process. The average grain size of iron matrix is 58nm and the
carbide particulate size is less than 100nm. The densification temperature of ball-milled powders is
approximately 200°C lower than that of blended powders. When the sintering temperature increases,
the density of as-sintered specimen increases but the hardness of as-sintered specimen first
increases and then decreases. Microstructure analysis results show that the decrease of hardness is
caused by the dramatic grain growth of iron matrix.
Influence of Tempering Temperature and Microstructure on Wear Properties of Low Alloy PM Steel with 1-2 % Ni Addition
Authors: Tekeli Süleyman , Güral Ahmet , Gürü Metin
Published: March 2009

The effect of tempering temperature and microstructure on dry sliding wear behavior of quenched and tempered PM steels was investigated. For this purpose, atomized iron powder was mixed with 0.3 % graphite and 1-2 % Ni powders. The mixed powders were cold pressed and sintered at 1200°C. The sintered specimens were quenched from 890°C and then tempered at 200°C and 600°C for 1 hr. Wear tests were carried out on the quenched+tempered specimens under dry sliding wear conditions using a pin-on-disk type machine at constant load and speed. The experimental results showed that the wear coefficient effectively increased with increasing tempering temperature. With increasing Ni content, the wear coefficient slightly decreased at all tempering temperatures due to the high amount of Ni-rich austenitic areas.
Gigacycle Fatigue Endurance Strength of High Density Mo and Cr-Mo Prealloyed Sintered Steel
Authors: Xu Chen , Danninger Herbert , Khatibi Golta , Weiss Brigitte
Published: March 2009

For attaining optimum fatigue resistance of PM steels, high density levels are necessary.
In this work, sintered steels Fe-1.5%Mo-0.6%C and Fe-1.5%Cr-0.2%Mo-0.6%C were produced
with density levels of 7.1 to 7.6 g.cm-3. Ultrasonic fatigue testing with 20 kHz was performed in
push- pull mode up to 10E9 cycles. It was shown that the fatigue endurance strength is strongly
improved by higher density levels, but also higher sintering temperatures are beneficial. The Cr-Mo
steels proved to be superior to the plain Mo alloyed, due to a more favourable as-sintered matrix
microstructure.
Processing Routes for Obtaining Novel High Performance Mn-Containing PM Steels
Authors: Castro F. , Sarasola M. , Sainz S. , Gómez-Acebo T.
Published: March 2009

A Mn-containing master alloy (MA) has been specially designed, through
thermodynamic and metallurgical criteria, for obtaining high performance low alloy PM steels by
SPSS or DPDS. This MA exhibits improved characteristics with respect to ferromanganese and
other Mn carriers for alloying PM steels preventing oxidation, keeping a high compressibility of the
powder mixture and providing opportunities for low temperature processing. The improved
sinterability through the formation of a transient liquid phase leads to dimensional stability and high
reproducibility of mechanical properties after sintering at 1120°C. The microstructural development
of the PM steels was studied during the sintering cycles. The final microstructure of these PM
steels, after defined sintering cycles, was characterised by LOM while the mechanical properties of
the consolidated materials were determined by tensile testing.
Hydrogen Storage Properties of Nb-Zr-Fe Alloys Disintegrated by Hydrogen Gas
Authors: Okuyama Hideo , Uda Masahiro , Uchikoshi Tetsuo , Suzuki Tohru , Sakka Yoshio
Published: March 2009

The disintegration of 6 different Nb-Zr-Fe alloys and their hydrogen storage properties
due to hydrogenation have been investigated. The hydrogenation was performed in a 0.1MPa
hydrogen pressure held at room temperature in arc melting chamber without exposure to air
atmosphere. The thermal stability of hydrogen dissolved in disintegrated powder was measured in
the temperature range from room temperature to 600°C by using the thermal analysis equipment.
Hydrogen contents in alloys were evaluated from the mass difference of TG curve and chemical
determinations for hydrogen gas analysis. The values of hydrogen content are in accordance with
both chemical and mass difference methods. The hydrogen contents of disintegrated alloys
synthesized were in the range of 1.2-2.0 wt% which depend on the composition of alloys.
Blended Elemental P/M Synthesis of Titanium Alloys and Titanium Alloy-Based Particulate Composites
Authors: Hagiwara Masuo , Emura Satoshi
Published: March 2009

Titanium alloys and Titanium alloy-based particulate composites were synthesized using the blended elemental P/M route. First, processing conditions such as the fabrication of master alloy powder were investigated. Ti-6Al-4V, Ti-5Al-2.5Fe, Ti-6Al-2Sn-4Zr-2Mo, IMI685, IMI829, Timetal 1100 and Timetal 62S, and Ti-6Al-2Sn-4Zr-2Mo/10%TiB and Timetal 62S/10%TiB were then synthesized using the optimal processing conditions obtained. The microstructures and mechanical properties such as tensile strength and high cycle fatigue strength were evaluated.
Development of P/M Aluminum Alloy with Fine Microstructure
Authors: Tokuoka Terukazu , Kaji Toshihiko , Nishioka Takao
Published: March 2009

We successfully developed Al -Si -Transition Metal (TM) -Rare Earth (RE) Powder
Metallurgy (P/M) alloy with fine microstructure, which has high strength at high temperature. For
example, at 473K, the ultimate tensile strength was 290MPa and fatigue strength on 107 cycles was
130MPa, which is an 80% improvement compared with conventional Aluminum cast alloys. This
material was compacted rapidly solidified powder and directly consolidated by hot extruding or
forging. The microstructure consists of fine Al crystal grains (grain size; around 200-500nm), and
inter-metallic compounds. Before consolidating, rapid heating was performed on powder
compaction in order to keep the fine microstructure in powder state. The effect of plastic
deformation on consolidating was examined to stabilize properties of this material. The mechanical
properties of the present alloy are expected] to contribute to improve performance of various
automobile engine parts.
Effect of Hot-Forging on NiTi Shape Memory Alloy Fibers Reinforced Mg Alloy Composite
Authors: Guo Qi , Li Gang , Tang Jian Ren , Yan Biao
Published: March 2009

The composite used in this paper was prepared by hot-pressing ball-milled Mg alloy powders, in which NiTi shape memory alloy fibers in a row were sandwiched. The microstructure were examined by an optical microscope, scanning electron microscope, X-ray diffraction, and transmission electron microscope to measure its microhardness and density. It is shown that the composite consisted of a homogenous matrix with uniformly distributed NiTi shape memory alloy fibers, where recrystallization took place in the Mg alloy matrix that was subjected to plastic deformation. It is known that plastic deformation is beneficial to the refinement of the grains, that is an adequate bonding forms between the matrix and fibers, the density of the composite increases after the hot-forging; its tensile strength increases significantly because of the grain refinement; the hot-forging process improves the properties of the NiTi shape memory alloy fibers reinforced Mg matrix composite.
Effect of Post Deformation on the Structure and Properties of Sintered Al-Cu-SiC Composites
Authors: Chung Hyung Sik , Heo Ryun Min , Kim Moon Tae , Ahn Jae Hwan
Published: March 2009

Sintered composites of Al-8wt%Cu-10vol%SiCp were deformed by repressing or equal
channel angular pressing(ECAP) at room temperature, 500°C and 600°C. Their microstructures and
transverse rupture properties were compared. Repressing produced more densification than ECAP
but ECAP resulted in much higher strengths than repressing. In both cases, the transverse rupture
strengths, after deformation at room temperature and 500°C, are much lower than those deformed at
600°C, despite of only slight differences in density. Fractured SiC particles were observed after the
deformation, very frequently at room temperature, less frequently at 500°C and rarely at 600°C.
Some interfacial de-bonding between the matrix and SiC particles were also observed particularly
in the ECAPed specimens. The higher bend strengths and less SiC fracturing at 600°C are
attributable to the presence of an Al-Cu liquid phase during deformation. ECAP at 500°C and 600°C
caused recrystallization and produced very fine grain structures. Grain refinement, as well as
enhanced bonding between particles due to high shear deformation associated with ECAP, is
considered the major reason for the much higher strengths. The employment of copper coated SiC
instead of bare SiC particles for preparing the composites was found not beneficial neither for
minimizing the particle fracturing nor for improving the properties.
Preparation of Warm Compacted NbC Reinforced Iron-Based Composite and Its Tribological Behavior
Authors: Xiao Zhi Yu , Ngai Tungwai Leo , Wen Li Pin , Li Yuan Yuan
Published: March 2009

A 15 wt.% NbC particulate reinforced iron-based composite was prepared by using warm compaction PM technique. It possesses a high relative density of 98%, a tensile strength of 515 MPa, a hardness of HRC 58 and a remarkable tribological behavior. Warm compaction was used because it can provide compacts with high green density and also increase the formability of the mixed powder. Furthermore, it can provide green strength that is strong enough to handle compacts before sintering. Block on ring tribotester was employed to study the compact’s friction and wear behavior using GCr15 steel as counterpart. A load of 980 N was used. The friction coefficient was 0.085 when the number 20 engine oil as lubricant was used. The results showed that the sintered composite has excellent wear resistivity. This material was then applied in the valve-guide cup of a combustion engine and subject to 500 hour bench test. The cup showed good performance for this test and did not shown any severe wear on the working surface after the test was completed. Therefore, it is a suitable material for parts that are exposed to severe wear condition.