Preparation Of Ultra-fine Cu/Ti₃AlC₂ Composite Powders And Its Bulk Materials

Previous research work has shown that Ti₃AlC₂ powders with finer grain size and higher surface energy in the Cu/Ti₃AlC₂ and Ni/Ti₃AlC₂ as well as composites plays important role in the enhancement of the mechanical and electrical properties of the composites. However, because of the generation of the heating, oxidation and passivation etc. during the milling process, it was difficult to fabricate ultra-fine Ti₃AlC₂ particles with higher surface activities. Hence, this thesis focuses on fabrication of Cu/Ti₃AlC₂ composite powders to obtain ultra-fine fine Ti₃AlC₂ with higher surface activities using Cu as milling media. Consequently, dense bulk Cu/Ti₃AlC₂ composites can be fabricated at lower temperature.The results show that:1. For a given ball mill equipment and ball to material ratio, milling time has a significant effect on the refinement of Ti₃AlC₂ particles and Cu particles. In the case of ball to material ratio 20:1, the particle size of milled powders did not changed after ball milling 2 h and 6 h. After milling up to 10h, the particle size of milled powder decreased greatly. The particle size of Ti₃AlC₂ particles reduced from the initial 22.62 μm reduce to 8.51 μm.2. The volume ratio of Cu and Ti₃AlC₂ also has a significant influence on the morphologies and particle size of the milled powders after ball milling. Because of the increased surface activities of the milled particles and the viscosity of Cu, the size of the secondary aggregated powders increased significantly with the increased Cu content.3. Addition of a small amount of stearic acid in the starting materials can prevent the secondary aggregation formation of milled Cu/Ti₃AIC₂ composite powders after milling process resulted in a further size reduction of Cu and Ti₃AlC₂ particles.4. The sinterability of Cu/Ti₃AlC₂ composite powders are improved due to the milling process. Cu/Ti₃AlC₂ composites with higher volume fraction of ceramic reinforced can be obtained by hot pressing at 950℃ for 1 h under a pressure of 30 MPa. During the sintering process, a mild reaction between Cu and Ti₃AlC₂ occurred by formation of Cu19Al4 and TiCx phases.5. With the prolonged milling time, the density of as prepared composites are enhanced. The density of 20 vol.% Cu/Ti₃AlC₂ composite increased from 4.71 g/cm3 to 5.43 g/cm3 when the milling time increased from 2 h up to 10 h while the density of 30 vol.% Cu/Ti₃AlC₂ composite increased from 5.01 g/cm3 to 5.68 g/cm3.6. Extending the milling time the increasing the Cu content in the starting materials can significantly improve the physical and mechanical properties of Cu/Ti₃AlC₂ composites. The 30 vol.% Cu/Ti₃AlC₂ composites made from the composite powder with a milling time of 10 h, the electrical conductivity、 hardness and flexural strength could reach 3.35%IACS,4.66 GPa and 507.72 MPa, respectively which is better than the ones of 20 vol.% Cu/Ti₃AlC₂ composites prepared at same conditions （3.08% IACS、4.66 GPa and 470 MPa, respectively）.