Mechanical Properties Of Ta-Ti-TiC Composites Fabricated By Plasma Activated Sintering

The Ta-based composites have been widely used in the aerospace,nuclear,electronics,biomedical industry due to its high melting point,excellent chemical stability,low coefficient of linear expansion,enthalpy retention and good biocompatibility.Due to the high density and ductility of Ta-based composite materials,its applications of weapons and defense heavy industry develop rapidly.However,Ta has a high melting point and low thermal conductivity and has a high affinity to oxycarbon impurities,making it difficult to prepare.In addition,the room temperature strength of Ta is low and the tensile strength is only about 380 MPa,which limits its application.Aimed at the key problems such as the difficulty in preparation of bismuth-based composite materials and low mechanical strength,this paper designs plasma-activated sintering?PAS?to fabricate Ta-based composites and explores the relationship between sintering process and microstructure.In this paper,Ti is added to the Ta matrix to reduce the sintering temperature by alloying and the relative density and mechanical properties of the composites are improved.On the basis of this,nano-ceramic phase TiC is added to further strengthen it.The effects of sintering process parameters?sintering temperature,sintering pressure,holding time?and the content of second phase on the microstructure and mechanical properties of Ta-based composites were discussed.The results show that the density of Ta-Ti composites increases with the increasement of sintering temperature within the experimental conditions of this paper.The density reaches 99.2%at 1500°C and then does not change remarkablely with temperature.The density increases with the increase of pressure.After the sintering pressure reaches 50 MPa,the density does not increase substantially.After the holding time exceeds 3 min,the density does not change much.When the Ti content exceeds 2%,the density does not change significantly with increasing of Ti content.Therefore,the optimum sintering process is 1500 ^oC-50 MPa-3 min and the optimum content of Ti is 2 wt%.The sintering kinetics and densification mechanism are analyzed.Grain boundary diffusion and dislocations creep are the main densification mechanisms.The addition of Ti reduces the activation energy of the interface and promotes the sintering densification process.The microhardness of Ta-Ti composites increases and then decreases when increasing the sintering temperature.The microhardness decreases with the increasement of Ti content.When the sintering temperature is 1500 ^oC and the Ti content is 2%,the hardness is 222.9 HV.The yield strength and bending ultimate strength of increase first and then decrease with the increasement of temperature.At1500 ^oC,the bending yield strength of Ta-2Ti composite is 917.6 MPa,the ultimate bending strength is 1345.5 MPa and the bending strain is 15.5%.The compressive yield strength increases first and then decreases with increasing temperature.At 1500^oC,the Ta-2Ti compressive yield strength is 564.6 MPa,the compressive strain exceeds 50%,indicating that this composite has high ductility.The addition of Ti plays a significant role in the improvement of the strength of Ta-Ti composites.The main strengthening mechanism is solid solution strengthening and second phase dispersion strengthening.The main toughness is attributed to the purification of Ti by matrix.The addition of nano-ceramic phase TiC significantly improves the hardness of the composites.When the TiC content is 4 wt%,the hardness of the Ta-Ti-4TiC composite is 385 HV,which is 73.4%higher than that of the Ta-2Ti composite,because of the in-situ formation of high hardness ceramic phase Ta₂C during sintering.The flexural strength and compressive strength of Ta-Ti-TiC composites increase with increasing TiC content,but the strain gradually decreases.The ultimate flexural strength of Ta-Ti-4TiC composites is 1595.9 MPa,the ultimate compressive strength is 1850.2 MPa and the compressive strain is 32.8%,which is still at a high level.The addition of TiC further enhances the strength of the Ta-2Ti matrix.The main strengthening mechanisms are solid solution strengthening,fine grain strengthening and second phase strengthening.The second phase strengthening contributes up to about 50% of the strength.