Study On Laser Additive Manufacturing And Heat Treatment Of Titanium Alloy

Titanium alloy refers to a variety of alloy metals made from titanium and other met-als（Ti,Ti6Al4V,Ti6Al7Nb,etc.）.It is an ideal material for aerospace and other industries because of its high specific strength,corrosion resistance and good biocompatibility.Ti-tanium alloys have become a research hotspot at home and abroad,but the current re-search mainly focuses on process optimization and microstructure,but there are few re-ports on the heat treatment system and electrochemical corrosion.In this paper,process optimization and heat treatment optimization experiments were carried out based on La-ser Metal Deposition（LMD）forming Ti6Al4V（TC4）alloy,and multi-layer TC4 alloy cladding specimens were prepared.Na Cl solution for the study of electrochemical corro-sion behavior.The main findings obtained are as follows.The organization of the deposited TC4 alloy is mainly（α+β）two-phase orga nization,with a dense row of hexagonal structure of theα-phase dominating,and the presence of a small amount of body-centered cubic structure of theβ-phase.Some of the specimens also underwent phase transformation within the originalβ-phase,forming a Weiss organization consisting of disordered needle-like marten site（α-phase）and residualβ-phase.The Vickers hardness of TC4 alloy reached408.9 HV at a laser power of 550 W,a scanning rate of 600 mm/min,and a la p step of 0.6 mm,when the microhardness was optimal.TC4 alloy specimens annealed at 850～950°C（not exceeding T_β,which is about995±5°C）after the primaryβ-phase transformation into a basket weave structure,the mi-crostructure of the specimens mainly consists of a fine（α+β）basket weave structure,a small amount of slate-likeα-phase and secondaryα-phase precipitated along the grain boundaries.And when heat treated at 1020°C above T_β,the slate-likeαphase grows larger and occurs aggregation,results in coarser grains.For the annealing treatment,the highest microhardness can be obtained by heating to 980°C for 3h.At this time,the average Vick-ers hardness can reach 469.76 HV,while for the solution aging treatment,the heat treat-ment scheme for the specimen with the highest Vickers hardness is 950°C/1h,AC+650°C/4h,AC,which can reach 434.45 HV.The corrosion resistance is best when the annealing temperature is 900°C.At this time,the self-corrosion potential is-0.379 V,the corrosion current density is 7.700×10^-7A/cm²,and the fitted n_f and R_f are 0.857 and 1320Ω/cm²,respectively.For solid solution aging,the best heat treatment parameters for the corrosion resistance of TC4 alloy are:solid solution temperature of 980°C,air cooling,aging temperature of 550°C,and aging time of 6 h.Among all the solid solution-aged specimens,the specimen with a solid so-lution temperature of 950°C for 1h air cooling followed by 6h aging at 550°C has the highest self-corrosion potential of-0.284V,and the lowest corrosion current density of9.053×10^-8A/cm².At this time the fitted n_f and R_f are 0.914 and 40457Ω/cm²,respectively.