Study Of Hollow Cathode Plasma Sintering Process

Development of new sintering techniques, which main characteristics is rapid heating, achieving high-density and high-performance, has became a very important field of powder metallurgy. Hollow cathode plasma sintering is one of the new PM techniques. High temperature and rapid heating is its characters.In this work, Ti-5Al-2.5Fe alloy and the TiC particle reinforced titanium matrix composites were sintered in a hollow cathode glow discharge furnace. Through the study of normal hollow cathode effect, a special hollow assistant cathode structure was designed and adopted by taken into account in the process of sintering temperature changes.The effects of different sintering parameters on the properties of Ti-5Al-2.5Fe alloy were investigated. The results show that temperature and the holding time are the more important factors, whereas pressure and the distance between assistant cathode and specimen are secondary. Based on experiments,the optimum process parameters were concluded as below:Sintering temperature is 1300℃, holding 6 hours, the distance between assistant cathode and specimen is 10mm, and the working pressure is 20~30Pa. The sintered density reached 4.3g/cm3. The bending strength was above 400 MPa. The bending fracture exhibited brittle features. The existence of pores was the main cause for lower toughness.The effects of sintering parameters as well as the particle fractions on the properties of TiC reinforced titanium matrix composites were also investigated. The results show that 5%TiC/Ti-6Al has high performance under the optimum process parameter of 1300℃, 6hr, 20Pa, and a distance between assistant cathode and specimen of 10mm. SEM observation indicated a well interfacial bonding between the particulates and Ti matrix. The bending fracture is also a brittle mechanism.At last, the oxidation experiment of specimens of pure titanium and Ti-6Al matrix composites reinforced with TiC particle was investigated at 800℃. The results show that the specimen of 15%TiC/Ti-6Al exhibited the best oxidation resistance. Its weight gain is just a half of that of the Ti-6Al alloy.