激光成形TC4钛合金亚临界退火组织及形成机制

Microstructure and forming mechanism of a laser melting deposited TC4 titanium alloy after sub-critical annealing

研究激光熔化沉积TC4钛合金亚临界点退火显微组织特征及显微组织演变规律,研究退火温度及退火后冷却方式(水冷、空冷)对组织形态的影响规律。结果表明,激光熔化沉积TC4钛合金在Tβ温度以下15～25℃范围内等温退火后,获得由蟹状初生α及细小层片状β转变组织组成的"特种双态组织"。随退火温度升高,蟹状形态特征愈加明显,但体积分数降低,宽度增加,长径比减小。亚临界退火后冷却过程中β→α+β转变的充分进行及一定固溶温度以产生足够的β相是蟹状初生α及特种双态组织形成的必要条件。

Characteristics and evolution of microstructure in a laser melting deposited TC4 fifanium alloy after annealing treatments were investigated.Effects of annealing temperature and cooling ways on the microstructure were examined.A unusual bi-model microstructure consisting of coarse crab-like primary α and fine lamellar transformed β is obtained by sub-critical annealing in the temperature range of 15-25 ℃ below β-transus temperature in the laser melting deposited TC4 alloy.The crab-like morphology becomes more manifest with increasing annealing temperature.The volume fraction and aspect ratio of coarse primary α decreases,while the width of coarse primary α increases with increasing annealing temperature.Decomposition of β phase during air cooling after sub-critical annealing and plenty volume faction of β phase by annealing above a certain temperature is necessary for the formation of crab-like primary α and the bi-model microstructure.