For the purpose of obtaining basic information on the development of lead-free materials, a high density composites (a) W-Cu, (b) W-Sn (c)W-Cu-Sn and (d) W-Cu-Ni were fabricated by the P/M method. The particle size of used metal powders were under 325 mesh, inner size of compaction mould was mm, and compaction pressure was 400 MPa. A High density composite samples were sintered at a temperature between and for 1 hour under Ar atmosphere. The microstructure, phase transformation and physical properties of the sintered samples were investigated. As the results, the highest relative density of 95.86% (10.87 g/) was obtained particularly in the sintered W-Cu-Sn ternary system sample sintered at 450 for 1hr. And, Rockwell hardness (HRB) of 70.0 was obtained in this system.

The effect of extrusion temperature on the microstructure and mechanical properties were studied in He-gas atomized alloy powders and their extruded bars using SEM, tensile testing and thermal expansion testing. The extruded bar of alloy consists of a mixed structure in which fine Si particles with a particle size below 20∼500nm and very fine compounds with a particle size below 200nm are homogeneously dispersed in Al martix with a grain size below 500nm. With increasing extrusion temperature, the microstructural scale was decreased. The ultimate tensile strength of the alloy bars has incresed with decreasing extrusion temperature from 500 to 35 and alloy extreded at 35 shows a highest tensile strength of 810 MPa due to the fine namostructure. The addition of Ni and Ce decreased the coefficients of thermal expansion and the effects of extression temperature on the thermal expansion were not significant.

In order to produce good wear resistance powder metallurgy Al-Si alloys with high strength, addition of glass forming elements of Ni and Ce in Si alloy was examined using SEM, TEM, tensile strength and wear testing. The solubility of Si in aluminum increased with increasing Ni and Ce contents for rapidly solidified powders. These bulk alloys consist of a mixed structure in which fine Si particles with a particle size below 500 nm and very fine A1Ni, A1Ce compounds with a particle size below 200 nm are homogeneously dispersed in aluminum matrix with a grain size below 600 nm. The tensile strength at room temperature for Si, SiNiCe, and SiNiCe bulk alloys extruded at 674 K and ratio of 10 : 1 is 281,521, and 668 ㎫ respectively. Especially, SiNiCe bulk alloy had a high tensile strength of 730 ㎫. These bulk alloys are good wear-resistance bel ter than commercial I/M 390-T6. Specially, attactability for counterpart is very little, about 15 times less than that of the I/M 390-T6. The structural refinement by adding glass forming elements such as Ni and Ce to hyper eutectic Si alloy is concluded to be effective as a structural modification method.d.tion method.d.

The effect of extrusion temperature on the microstructure and mechanical properties was studied in gas atomized TEX>Al81Si19 alloy powders and their extruded bars using SEM, tensile testing and wear testing. The Si particle size of He-gas atomized powder was about 200-800 nm. Each microstructure of the extruded bars with extrusion temperature (400, 450 and 50) showed a homogeneous distribution of primary Si and eutectic Si particles embedded in the Al matrix and the particle size varied from 0.1 to 5.5 . With increasing extrusion temperature from 40 to 50, the ultimate tensile strength (UTS) decreased from 282 to 236 ㎫ at 300 K and the specific wear increased at all sliding speeds due to the coarse microstructure. The fracture behavior of failure in tension testing and wear testing was also studied. The UTS of extrudate at 40 higher than that of 50 because more fine Si particles in Al matrix of extrudate at 40 prevented crack to propagate.