Study On Surface Modification Of TC4 Powder And Preparation And Properties Of Composite Materials

Titanium and titanium alloys are widely used in advanced engineering fields such as aerospace,military,and petroleum due to their low density,high specific strength and good corrosion resistance.And higher requirements are put forward for the mechanical properties of titanium and titanium alloys.Titanium matrix composites（TMCs）have the characteristics of light weight,high strength and heat resistance.However,although TMCs with a one-scale network distribution of reinforcements can obtain high strength by increasing the content of reinforcements,the elongation of TMCs will decrease sharply,which limits the further application of TMCs.Therefore,in this paper,copper modified TC4 composite powders with typical core-shell structure（denoted as Cu@TC4）was obtained by magnetron sputtering technology.The TiB₂-Cu@TC4 composite powders with two-scale core-shell structure was obtained by low-energy ball milling on the basis of Cu@TC4 powders.TMCs with strong plasticity matching were obtained by spark plasma sintering（SPS）technology.The effects of magnetron sputtering process on the structure of composite powder,the effects of copper content and heat treatment process parameters on the microstructure and mechanical properties of Ti₂Cu reinforced TC4 composites with micro-network structure were studied,and the effects of TiB₂ content on the microstructure and mechanical properties of Ti₂Cu+TiB_wreinforced TC4 composites with two-scale network structure were studied,and the strengthening and toughening mechanism of the composites was clarified.The following main conclusions can be drawn from the present work:（1）The Cu@TC4 composite powders with core-shell structure was prepared by magnetron sputtering method by adjusting sputtering power,sputtering time and bias voltage.The results shown that with the increase of sputtering power,the copper content in the composite powder increases gradually,while the bias voltage has little effect on the copper content in the composite powders.When the power is 200 W,the bias voltage is 0 V,and the sputtering time is 4 h,the Cu layer of Cu@TC4 composite powders are complete and evenly distributed,and which have a typical core-shell structure.（2）Ti₂Cu/TC4 composites were obtained by SPS technology.The effects of copper content on the microstructure and mechanical properties of sintered and heat treated Ti₂Cu/TC4 composites were studied by optical microscope（OM）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,Vickers hardness tester and universal electronic testing machine.The results show that the microstructure of the sintered Ti₂Cu/TC4 composites are mainly Widmanstatten structure,and the nano-scale intermetallic compound Ti₂Cu is distributed along theα/βphase boundary in a micro-network structure.In the heat-treated Ti₂Cu/TC4 composites,Widmanstatten structure and eutectoid structure are mixed and distributed,accompanied by a small amount of basketweave structure.The room temperature tensile strength of the sintered composites increases with the increase of copper content,while the elongation decreases gradually.The maximum tensile strength and yield strength are 1155.6 MPa and 1023.8 MPa,and the elongation is 5.5%.The tensile fracture surface is distributed with dimples,tearing edges and a small number of holes,showing obvious mixed fracture characteristics.After heat treatment,the tensile strength of the composites only decreased by 24.0 MPa,but the elongation increased by 41.8%.The main strengthening mechanism of Ti₂Cu/TC4 composites is the second phase strengthening,and the main reason for maintaining excellent elongation is the formation of a micro-network structure in which Ti₂Cu nanoparticles surround theαphase.（3）（Ti₂Cu+TiB_w）/TC4 composites were obtained on the basis of Ti₂Cu/TC4 composites by low energy ball milling and SPS technology.The effects of TiB₂ content on the microstructure and mechanical properties of two-scale network structure（Ti₂Cu+TiB_w）/TC4 composites were studied by OM,SEM,TEM,Vickers hardness tester and universal electronic testing machine.The results shown that TiB_w are distributed around the original TC4 particles to form a primary network structure,which significantly refines the originalβgrain size.Ti₂Cu nanoparticles are distributed on theα/βphase boundary and form a secondary network structure aroundα-Ti.The tensile strength and yield strength of（Ti₂Cu+TiB_w）/TC4 composites at room temperature are 1271.9 MPa and 1160.3 MPa,respectively.Compared with TC4 alloy,the tensile strength of（Ti₂Cu+TiB_w）/TC4 composite at 450,500 and 550℃ increased by 38.1%,37.2%and 40.4%,respectively,and the elongation did not decrease significantly.The strengthening mechanism of two-scale network structure（Ti₂Cu+TiB_w）/TC4 composites are fine grain strengthening,load transfer strengthening of TiB whiskers and Ti₂Cu nanoparticles.