Study On In-situ Synthesized Dense TiC_x/SiC Composites

In this paper,dense TiC_x/Si C composites with different content of Si C were in situ synthesized by vacuum hot-pressing sintering method and hot isostatic pressing sintering method.Raw materials were nano-powders of?-SiC and graphite,and micron-sized TiH₂powders.To investigate the underlying relations between the structure,synthesis parameters and properties of TiC_x/SiC composites,their texture and microstructure were observed,and then their mechanical properties were tested.And conclusions are as follows:The x value of TiC_x phase is changing with the change of molar ratios of raw materials.When the raw materials ratio of TiH₂:C:?-SiC was y:0.8y:1?y=0.3,1,2.5,5,and10?,the nonstoichiometric ratio of vacuum hot-pressing sintered TiC_x/SiC composites were TiC_0.80?Ti C_0.86?TiC_0.87?TiC_0.89?and Ti C_0.90.With the decreasing of Si C in composites,the content of Ti₃Si C₂ was increasing,from 0 vol%to 7 vol%?11 vol%?16 vol%and 19vol%.When the content of Si C was below 49 vol%,the relative density of vacuum hot-pressing sintered composites?1900?+60MPa+30min?was above 97%and kept increasing with the decrease of SiC.Voids inside tend to gatherer around SiC grains,so excessive content of SiC will decrease the density of composites.In the composites,nano sized SiC particles coexisted with micro sized TiC_x grains and inhibited the growth of TiC_x grains.With decreasing content of SiC,the Vickers hardness and fracture toughness of composites were decreased,but flexural strength increased.The TiC_x/Si C composites which contain 63 vol%TiC_x,26 vol%SiC and 11 vol%Ti₃Si C₂ presents super properties:corresponding to the flexural strength of 669.6 MPa,Vickers hardness of 20.8 GPa,and fracture toughness of 5.2 MPa·m^1/2.The TiC_x and Ti₃Si C₂ grains exhibited the transgranular fracture and the SiC particles presented the intergranular mode.The raw materials ratio of TiH₂:C:?-Si C for hot isostatic pressing sintering was y:0.8y:1?y=0.5,1,3?,and when this ratio was y:0.95y:1,y was 5.The content of SiC in synthesized TiC_x/Si C composites was 67 vol%?49 vol%?22 vol%and 17 vol%respectively.The content of Ti₃SiC₂ was growing from 0 vol%to 7 vol%and 12 vol%respectively,with the decreasing of SiC.When the ratio of raw materials was y:0.95y:1,no Ti₃SiC₂ was found in the XRD of composite.When the content of Si C in TiC_x/SiC composites which synthesized by hot isostatic pressing sintering method?1600?+100MPa+4h?was below 49 vol%,the relative density could approach 99%.Compared with the hot pressing sintering method,the density become more high.It is prove that high pressure?HIP?is beneficial to the density of composites.With the decrease of SiC,TiC_x/SiC composites presented lower Vickers hardness and fracture toughness,but higher flexural strength,which was similar to vacuum hot-pressing sintered TiC_x/Si C composites.Besides,composites which contain 83 vol%of TiC_x and 17vol%of SiC shown optimum combination property,and its flexural strength,Vickers hardness and fracture toughness was 537.7 MPa?24.8 GPa and 5.31 MPa·m^1/2 respectively.Either TiC_x/Si C composites were synthesized by HP or HIP,the formation of Ti₃SiC₂phase was restrained effectively with the ratio of graphite in raw materials.When the ratio of raw materials was y:0.95y:1,no Ti₃Si C₂ was found in composite.