Study On Microstructure And Mechanical Properties Of （Ti₅Si₃,TiC,TiB） Multi-Element And Multi-Scale Hybrid Reinforced Titanium Matrix Composites

In this paper,micro-nano scale binary（Ti₅Si₃+TiC）and ternary（Ti₅Si₃+Ti C+Ti B）reinforced titanium matrix composites were synthesized with Ti powder,Si powder,Si C powder,Ti B₂ powder and C powder as raw materials by in-situ autogenic reaction using powder metallurgy technology.Ti C and Ti B are micron scale,and Ti₅Si₃ is nano scale.The microstructure and mechanical properties of binary and ternary reinforced titanium matrix composites were analyzed by XRD,OM,SEM,EDX,hardness,compression test and other characterization methods.The main research contents and results are as follows:Firstly,the effects of sintering temperature and sintering time on TMSC55 were studied.In the sintering temperature range,with the increase of temperature,the density and mechanical properties of TMSC55 showed a trend of increasing first and then decreasing,and the density and mechanical properties of TMSC55 were the highest at 1350℃.The Rockwell hardness value is 48.7 HRC,the yield strength is 1624 MPa and the compressive strength is 2401 MPa.It can be seen from the microstructure that the number of holes in TMSC55 decreases,the matrix grain boundaries are gradually formed,the number of reinforcement phases increases,the grain size increases,and the matrix and reinforcement grow abnormally when the temperature is too high.In the range of sintering time,with the increase of sintering time,the mechanical properties showed a trend of increasing first and then decreasing,and the mechanical properties reached the best at 90 min,resulting in the highest density.It can be seen from the microstructure that the matrix will grow abnormally when the sintering time is too long.In conclusion,1350℃/90 min is the best sintering condition.Four kinds of binary reinforced titanium matrix composites were prepared under these conditions,and the mechanical properties were ranked as TMSC55>TMSC64>TMSC46>TMSC37 from high to low.It can be seen that as the ratio of（Ti₅Si₃:Ti C）volume fraction increases,the mechanical property presents a trend of first increase and then decrease.When the ratio of Ti₅Si₃/Ti C volume fraction is 1,the mechanical property of the composite material is the best.Secondly,the effects of sintering temperature and sintering time on TMSCB433 were studied.In the sintering temperature range,the mechanical properties of TMSCB433 showed a trend of first increase and then decrease with the increase of temperature,and the mechanical properties were the best at 1300℃.The Rockwell hardness value is 49.1 HRC,the yield strength is 1649 MPa and the compressive strength is 2435 MPa.It can be seen from the microstructure that the number of holes in TMSCB433 is reduced,the grain boundary is gradually clear,the number of reinforcement phase is increased,the grain size is increased,and the matrix will grow abnormally when the temperature is too high.In the range of sintering time,with the increase of sintering time,the mechanical properties showed a trend of first rising and then decreasing.At 90 min,the mechanical properties were the best and the density was the highest.There is no significant difference in morphology and distribution between matrix structure and reinforcement phase.In conclusion,1300℃/90 min is the best sintering condition.Under these conditions,four kinds of ternary reinforced titanium matrix composites were prepared.Mechanicalpropertiesfromhightolowrank:TMSCB433>TMSCB424>TMSCB415>TMSCB442.It can be seen that when the volume fraction of Ti₅Si₃ remains unchanged at 4%,the mechanical properties of the composite materials show a trend of first increasing and then decreasing with the increase of the ratio of（Ti C:Ti B）volume fraction.When the ratio of Ti C/Ti B is 1,the mechanical properties of the composite materials are the best.Finally,the heat treatment process of TMSC55 and TMSCB433 was explored.The results showed that the optimal heat treatment process for TMSC55 and TMSCB433 was solution at1250℃and aging at 800℃.The mechanical properties of composites can be improved by heat treatment because:（1）.The morphology and size of the matrix are changed.By heat treatment,the near-equiaxialα-Ti is transformed into lamellarα-Ti,and the grain size of the matrix is refined.（2）.The size and distribution of Ti₅Si₃ particles were regulated.After heat treatment,the Ti₅Si₃ particles in the network agglomeration were precipitated into finer particles and distributed uniformly on the matrix.Under these conditions,four kinds of binary and ternary reinforced titanium matrix composites with different proportions were heat treated.After heat treatment,the Rockwell hardness values of four kinds of titanium matrix composites with different proportions were as follows:TMSC55>TMSC64≥TMSC46>TMSC37;After heat treatment,the Rockwell hardness values of four titanium matrix composites with different proportions were ranked as TMSCB433>TMSCB415>TMSCB442>TMSCB424 from high to low.After heat treatment,the strengthening methods of binary and ternary reinforced titanium matrix composites are the same,including fine crystal strengthening,dispersion strengthening and particle bearing strengthening.