Heat Treatment Of TC17 Titanium Alloy By Laser Deposition

TC17 titanium alloy is a kind ofα+βtitanium alloy,with excellent strength,fracture toughness and corrosion resistance,so it is widely used in the manufacture of various parts,such as integral blade disc,compressor disc,etc.Compared with the traditional manufacturing technology,the laser deposition manufacturing/repair technology using metal powder as raw material and laser as energy source has the advantages of large flexibility,high utilization rate,digital forming and free from material restrictions,which has become one of the hot directions in the field of additive manufacturing.However,since the microstructure of TC17 titanium alloy manufactured/repaired by laser deposition is obviously different from that prepared by traditional methods,it is necessary to use heat treatment to regulate the microstructure,and systematically study the influence of heat treatment process on the microstructure and properties of TC17titanium alloy.The main research contents and conclusions are as follows:（1）In view of the low surface hardness and poor wear resistance of TC17 titanium alloy manufactured by laser deposition,solid solution aging strengthening treatment was carried out.The results show that the microstructure is transformed into coarse basket microstructure after solution aging treatment.With the increase of solution temperature,the primaryαphase（α_p）coarses gradually and the volume fraction decreases.After aging,the volume fraction of secondaryαphase（α_s）precipitates from theβtransition microstructure.With the aging temperature increasing,the thickness of the secondaryαphotographic layer increases obviously.After solution aging treatment,the microhardness increased significantly.After solution aging treatment at 840℃×1h/AC+800℃×4h/WQ+630℃×8h/AC,the maximum microhardness was447.6HV_0.3,14%higher than that of deposition,and higher than the forging standard(400HV_0.3).The lowest average friction coefficient is 0.21,which is 34%lower than that of the deposition,and the wear amount is 3.4mg at least,which is about 1/3 of that of the deposition（9.7mg）,showing good anti-wear performance.（2）In the process of laser deposition repair,due to the characteristics of rapid melting and rapid condensation,the distribution of the repaired parts will be uneven,unbalanced metastable state,and the strength of the repaired parts is poor.The effects of annealing and double annealing on microstructure and properties of TC17 titanium alloy repaired by laser deposition were investigated.The results show that with the increase of annealing temperature,αphase coarsening occurs,and its aspect ratio and volume fraction decrease gradually.Compared with deposition,the microhardness of annealed repaired specimens in different regions has no obvious change.However,after annealing at 600℃×4h/AC,the tensile strength of TC17 repaired specimens（1138MPa）is 3.27%higher than that of deposited specimens（1102MPa）,and higher than the forging standard（1120MPa）.With the increase of double annealing temperature,theαphase size after the first stage annealing increases,while the secondaryαphase coarsened gradually and the volume fraction increased first and then decreased.After annealing at600℃×4h/AC+550℃×4h/AC,the average hardness of the repaired sample in the deposition area(404.6HV_0.3)is higher than that in the deposition area(391.5HV_0.3).And the wear resistance increases;in addition,compared with annealed state,the tensile strength is slightly reduced but plasticity is increased,showing better comprehensive properties.（3）For large thin-walled parts,the use of vacuum integral heat treatment will lead to the design and production of the fixture is extremely difficult.Therefore,local heat treatment of TC17 titanium alloy repaired by laser deposition is required.The results show that:with the increase of holding time,theαphase size decreases first and then increases and the volume fraction increases.Compared with the deposited state,the tensile strength of TC17 titanium alloy repaired after local annealing treatment increases to 1128MPa,but the plasticity decreases slightly but is higher than the forging standard,and the strong plasticity decreases slightly compared with the whole annealed state.