激光立体成形TC17钛合金组织研究

Research on Microstructure of TC17 Titanium Alloy Fabricated by Laser Solid Forming

通过对激光立体成形（LSF）TC17钛合金沉积态、去应力退火后状态及时效热处理后状态下的微观组织分析,研究了不同热处理方式对激光立体成形组织的影响。结果表明,沉积态组织由贯穿多个熔覆层呈外延生长的粗大柱状晶组成,柱状晶主轴垂直于激光扫描方向或略向扫描方向倾斜;沉积态原始β晶内组织是编织极其细密的网篮组织,α板条长度为1~3μm,宽度仅0.1~0.2μm,为典型的α＋β两相组织特征。沉积态试样经600℃保温1 h,炉冷（FC）退火后,显微组织无明显变化,仍为典型的网篮组织,但α板条长度和宽度有所增加,长宽比减小;经550℃保温4 h,空冷（AC）退火后,显微组织中出现部分等轴α相。对沉积态试样进行时效热处理时,随着保温时间的增加,α相呈长大趋势,长宽比逐渐减小,当保温时间达到8 h时,α相发生明显的球化,仅残留有少量的α板条。

The influences of different heat treatments on the microstructure of TC17 alloy fabricated by laser solid forming（LSF） are investigated,while the alloy in three states of as-deposited,after relief annealing and aging treatment.The results indicate that the microstructure of as-deposited sample consists of coarse columnar grains which grow epitaxially from the substrate along the deposition direction z.The microstructure within the columnar grain shows typical α＋β structure.The original β grains are composed of extremely fine basketweave microstructure.And the α phase has lath morphology,its length and width are 1～3 μm and 0.1～0.2 μm,respectively.After furnace cooling（FC） annealing treatment following 1 h holding at 600 ℃,the length and width of the α lath both increased while the length/width ratio decreased,but no other changes can be observed.The equiaxed α phase will be observed on the β matrix after air cooling（AC） annealing treatment following 4 h holding at 550 ℃.During aging treatment,the α laths coarsen continuously as the aging time increases,whereas their length/width ratio gradually decreases.When the holding time reaches 8 h,most of the α laths are spheroidized,only a few left.