工艺参数对激光快速成形TC4钛合金组织及成形质量的影响

Influence of Processing Parameter on the Microstructure and Forming Characterizations of Ti-6Al-4V Titanium Alloy after Laser Rapid Forming Processing

通过改变激光快速成形过程中激光功率、扫描速度、搭接率、Z轴增量ΔZ等工艺参数,研究了各工艺参数对Ti-6Al-4V合金组织及成形质量的影响规律。结果表明:随着激光功率P的提高,柱状晶的长度逐渐变短并转变为类似等轴晶的不规则晶粒;在相同的激光功率下,柱状晶的尺度随着激光扫描速度V的增加变得细且长;当P/V值大于933W·s/mm时,晶粒呈现等轴晶形态。存在一个临界搭接率,当搭接率为30%时,成形件内部组织基本质量良好,只是在靠近基材区域有少量的熔合不良;如搭接率小于30%,两相邻熔覆道之间的搭接区将出现形状不规则的熔合不良现象。另外,ΔZ过小会造成重熔深度变大,层与层的结合处组织粗大;ΔZ过大时会造成层间熔合不良。

Laser rapid forming （LRF） of Ti-6Al-4V （TC4） alloys was experimentally investigated systematically, the influence of the processing parameters, such as laser power, scanning velocity, powder feeding rate, overlaps and single-layer offset along Z axis, on microstructures and forming characterizations were analyzed. The results indicate that columnar prior β grains shorten and coarsen with the increase of laser power P and the decrease of scanning velocity V, finally change to irregular coarsen equiaxed grains. Under the same laser power, the columnar grains become fine and long with the increase of scan velocity. When P/V is larger than 933 W·s/mm, the grains characteristic is equiaxed. There exists a critical overlap for the forming quality. When overlap is 30%, the microstructures present good quality just with a little ill-bonding between the traces near the substrate. If overlap is less than 30%, irregular ill-bonding will occur in the region of adjacent cladding layer in whole LRF parts, otherwise, there is no defect in the whole cladding layers. In addition, when single-layer offset along Z axis is less than the height of single cladding layer, the coarse a laths will be obtained which result from the over reheating of the post deposition layers, and, much larger △Z will result in ill-bonding between the cladding layers.