元素混合法激光立体成形钛合金过程中缺陷形成研究

Investigation on Formation of Defects in Laser Solid Forming of Titanium Alloys From Blended Elemental Powders

研究了不同成形条件下,以元素粉末为送进原料时,激光立体成形Ti-xAl-yV合金熔覆层内的缺陷类型、形貌特征及形成原因。结果发现,成形件内部可能出现4种类型的缺陷:气孔、熔合不良、未熔颗粒及成分偏析。其中,非球形的Al、V颗粒所携带的气体进入激光熔池且被固液界面捕获是产生气孔的主要原因;熔合不良的产生往往是由于工艺参数选择不当;未熔粉末颗粒产生的原因是由于元素粉末熔点温度低于合金化后合金固相线温度,粉末颗粒进入不熔区且被固液界面捕获;成分偏析带主要存在于V含量较高的合金熔覆层内,导致成分偏析带产生的原因在于V含量较高的合金粘度大,固液界面附近熔体流动速度过低。

The type, morphology and the forming mechanism of the defects in laser solid forming （LSF） of Ti-xAl-yV from blended elemental powders under different processing parameters were discussed. It is found that there are four kinds of defects in the cladding layers, including the gas porosity, ill bonding, un-melted powder particle and the composition segregation. The porosity is caused by the gas adding into the molten pool by the irregular A1 powder and V powder. The improper selection of the processing parameters usually leads to the ill bonding defects in the cladding layers. When the melting point temperature of the elemental powder is lower than the solidus temperature of the titanium alloy obtained by LSF, the elemental powder particle may enter into the zone in which can not be melted completely in molten pool, and the un-melted powder particle may be captured by the solid-liquid interface and further retain in the cladding layer. The composition segregation can be found in LSF titanium alloy with high V content, and the formation of the composition segregation is caused by the high viscosity of the alloy and low flow velocity near the solid-liquid interface in molten pool.