Preparation Technology And Application Of In-situ （TiC+Ti₅Si₃）/TC4 Composites

Titanium matrix composites are widely used in aerospace,military equipment and other fields due to their high specific strength,high elastic modulus and high wear resistance.In-situ autogenesis is one of the most common methods for preparing titanium matrix composites.The reinforced phase prepared by in-situ autogenesis method has the characteristics of high stability,good interfacial bonding and easy uniform distribution.In this study,the（Ti C+Ti₅Si₃）/TC4 composites were prepared by adding 0.5wt%Si C（TMC1）,1wt%Si C（TMC2）,1.5wt%Si C（TMC3）,2wt%Si C（TMC4）,4wt%Si C（TMC5）and 6wt%Si C（TMC6）by induction melting casting method combined with in-situ autogenesis Firstly,the as-cast microstructure and mechanical properties of the composites were studied,and then the influence of heat treatment process on the microstructure and mechanical properties of the composites was studied to reveal the microstructure evolution rule and the strengthening and toughening effect.Finally,the tribological and wear characteristics of（Ti C+Ti₅Si₃）/TC4 titanium matrix composites were studied.The main research results obtained in this paper are as follows:（1）The effects of different Si C additions on the microstructure and properties of as-cast composites were studied.With the increase of Si C addition amount,Ti C+Ti₅Si₃ phase was formed by chemical reaction with TC4 titanium alloy.The morphology of enhanced Ti C phase changed from granular to short rod,long strip and coarse equiaaxial,and the morphology of Ti5Si3 phase changed from granular to net-like.Theαandβlamellae spacing of the composite matrix was refined from 37μm to 4μm,and the tensile strength of the composite first increased and then decreased with the increase of the content of reinforcing phase,while the hardness gradually increased.At TMC4,the tensile strength,elongation and Rockwell hardness are 952.8MPa,4.3%and 43.1HRC,respectively.The Rockwell hardness is 51.7%higher than that of TC4 titanium alloy.（2）The effect of heat treatment on microstructure evolution and mechanical properties of TMC4 composites was studied.Firstly,after solution treatment,granular dissolution occurred in Ti C strips,Ti₅Si₃ was dissolved in small amount,andβ-transformed tissues were formed in matrix tissues.When the solution treatment is 1050℃/2h/WC,the tensile strength,elongation and Rockwell hardness are 985.8MPa,5.1%and 48.5HRC,respectively.Subsequently,After solution treatment at 1050℃,the sample was aged at different temperatures.With the increase of aging temperature,the enhanced Ti₅Si₃ phase was gradually precipitated,the Ti C particles had little change,and some metastable phases in theβtransition structure were decomposed.When the solution@aging treatmenst was performed at1050°C/2h/WC+600°C/8h/AC,the mechanical performance of titanium matrix composites is the best.Tensile strength and elongation reached 997.3MPa and 3.4%,respectively.Moreover,the TMC4 composites exhibited the largest Rockwell hardness about 48.2HRC.（3）The tribological and wear properties of（Ti C+Ti₅Si₃）/TC4 titanium matrix composites as cast and heat treated at room temperature were investigated.As the load increases,the overall wear rate increases,and the friction coefficient is always smaller than TC4.Under the same load,the minimum wear rate of TMC6 as-cast composites is 1.2×10^-3mg/m with the increase of Si C addition,and the shear force and depth are relatively shallow.There are a few particles and adhesion phenomena on the worn surface,and the three-dimensional roughness is relatively smooth.The wear mechanism is mainly adhesive wear and abrasive wear,and the wear resistance is the best.After heat treatment,the wear rate of TMC4 composites increases with the increase of load,and the friction coefficient increases first and then decreases with the solution temperature.Under the same load,the solution temperature is 1050°C,the wear rate is the minimum 1.1×10^-3mg/m,almost no furrow and plastic deformation,three-dimensional morphology is smooth,wear mechanism is abrasive wear,wear resistance is the best.