Study On Microstructure And Properties Of SLM Processed TC4 Alloy Reinforced By Nanoceramic Particles

Titanium alloys have a promising future in aerospace,automotive and military applications due to their high-temperature resistance,high specific strength,high specific stiffness and good creep resistance.The mechanical properties of titanium alloys are an important reference indicator for their service and life,so it is important to continuously improve the mechanical properties of titanium alloys in order toimprove their performance and expand their applications.In this paper,a composite powder of TC4 alloy and TiC nano-particles was prepared by powder mechanical mixing method.TC4 alloys containing trace amounts of TiC particles were prepared by selective laser melting(SLM)technology.The effects of the addition of TiC particles and solid solution treatment on the microstructure and mechanical properties of the TC4 alloy were investigated at different energy density forming parameters.The changes in grain size,martensite morphology and dimensions were analysed in depth to elucidate the relationship between SLM forming parameters,heat treatment process,microstructural properties and performance.The main findings are as follows:At low energy density(50 J/mm~3)parameters,the addition of trace TiC nano-particles acted as grain refinement,while the number of twins,martensite morphology,size andβ-phase number also changed.When 0.1 wt.%TiC was added,the microstructure in the alloy mainly showed a basket wave shape,the martensite was mainly composed of lamellar martensite,thin-lamellar martensite and butterfly martensite,and the dislocation density decreased.The number of secondary,tertiary and quaternary martensite increased,the martensite long axis became shorter and the short axis became wider.The number of near-nanometer twins in secondary,tertiary and quaternary martensite also increased.When the TiC content is increased to 0.5 wt.%,lath martensite forms in the alloy,the number of tertiary martensite,quaternary martensite andβ-phase increases and macroscopic defects increases significantly.The TC4 alloy with the addition of 0.1 wt.%TiC nano-particles had the best comprehensive mechanical properties,reaching a tensile strength of 1394 MPa and an elongation of 13.2%,an increase of 25.36%and 60%respectively.With increasing solid solution temperature,below theβ-phase transformation temperature,the acicular martensite gradually transforms into the lathα-phase.As the TiC content increased,the average grain size of equiaxedβgrains tended to decrease,the width of lath martensite decreased and theβ-phase content increased.The TC4 alloy with 0.5wt.%TiC has the best comprehensive mechanical properties after solid solution at 850°C,with a tensile strength of 1300 MPa and elongation of 19.6%.At high energy density(89.3 J/mm~3),the grain size of TC4 alloy tends to decrease and then increase as the content of TiC nano-particles increases,the martensite long axis size decreases and the short axis size increases.The TC4 alloy with 0.1 wt.%TiC nano-particles has a tensile strength of 1300 MPa and an elongation of 10.3%.As the TiC content increased,the number of defects in the alloy increased,but the size of the defects decreased.After solid solution treatment at 750°C,the equiaxedβgrain size and martensite width did not change significantly.While after solid solution treatment at850°C,the equiaxedβgrain size and martensite size decreased and the TC4 alloy with 0.5wt.%TiC nano-particles added had better properties with a tensile strength of 1150 MPa and an elongation of 12.5%.