| Particulate reinforced titanium matrix composites(PTMCs)are widely used in military and civilian fields owing to their isotropic mechanical properties,excellent high temperature oxidation and wear resistance.Due to their poor processing properties,near-net shaping methods such as powder metallurgy and high-energy beam(arc,laser,electron beam,etc.)deposition are favored in recent years,and PTMCs with uniform distribution of reinforced particles have received much attention.Based on this,starting with the raw material powder required by the above processing methods,in-situ synthesis of Ti-based composite powders with uniformly distributed reinforcing particles was carried out by mechanical alloying(MA)method in this paper.The microstructure and properties of the composite coating formed by electron beam melting are investigated.In this paper,based on extensive relevant literatures and preliminary experimental exploration,the research program consisting of process parameters and formation mechanism of composite powder,analysis in anti-"collapse" property of composite powder transition layer,formation of composite coating by electron beam cladding was confirmed.The main work was carried out in the following aspects:(1)Using Ti powder and graphite powder as raw materials,TiC/Ti composite powder was processed by MA method.Process parameters including MA equipment,milling speed,ball-to-powder weight ratio and milling time as well as the formation mechanism of the composite powder was analyzed;The MA device was determined to be a German Pulverisette-6 planetary ball mill,and the optimum process parameters were ball milling speed of 300 rpm,ball-to-powder weight ratio of 20: 1 and ball milling time of 15 h.During the process of MA,repeatedly occurred cold welding and fracture produced a large number of defects and decreased the diffusion distance between atoms,which made the synthesis of nano-TiC carried out at room temperature.The nano-TiC particles have been obviously formed when the ball milling time reaches 10h(TiC/Ti composite powder was formed).The particle size of the composite powder tends to be stably about 2?m after 15 h milling time,and the nano-TiC particles are uniformly distributed in the composite powder.(2)TiC/Ti composite powder transition layer was prepared on the pure Ti matrix by using the ideal technology explored above.The formation mechanism and anti-“collapse”property of the composite powder transition layer prepared in different milling time were studied.It is found that the thickness of the composite powder transition layer tends to be a maximum value of about 40?m when the milling time reaches 15 h.The transition layer contains a large amount of TiC/Ti composite powder and was combined with the Ti matrix tightly.The rate of "powder blowing" is only about 13.2%.(3)Electron beam cladding of TiC/Ti composite powder transition layer was carried out under different scanning speed.The phase structure,hardness,elastic modulus and wear properties of TiC/Ti composite coating were studied.When the scanning speed is 5 mm / s,TiC mainly exists as coarse dendrites.When the scanning speed increases to 10 mm / s and 15 mm / s,TiC disperses in the matrix with short rod and equiaxed shape;When the scanning speed is 15 mm / s,the TiC/Ti composite coating has the best performance,which has hardness of 8.29 GPa,elastic modulus of 135.2GPa and friction coefficient of about 0.48;the smaller particle size and the more uniform distribution of TiC is,the higher performance of hardness,elastic modulus,wear resistance is.Theoretical and applied foundation for manufacturing TiC/Ti composites by electron beam was formed based on the above results. |
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