能量约束的单晶高温合金激光外延修复试验研究

针对单晶高温合金激光外延修复层中常常出现"杂晶"的问题,提出能量约束的单晶高温合金激光外延修复工艺,并研究了激光功率和单晶母材宽度对修复层形貌与组织结构的影响。结果表明,能量约束的单晶高温合金激光外延修复层内几乎保持完全的定向外延生长枝晶,"杂晶"出现的概率大大降低。在优化参数下,修复层内获得连续的定向外延枝晶,单层厚度达到1220μm。随着激光功率升高,修复层厚度有所增加;在光斑直径和激光功率相同的条件下,随着单晶母材宽度的增加,修复层厚度先增加后减小,并呈现"扁平化"特征。当母材宽度为3mm时,修复层内呈现明显的流线特征,结合高速摄像照片,观察发现激光熔覆时熔池内金属从中心底部向表面流动,随后向四周扩散,最终沿着熔池底部回流至中心底部,如此反复。

Experimental Analysis on Energy-retrained Laser Epitaxial Restoration of Single Crystal Superalloy

In order to reduce the"stray grain"presented in laser restoration layer on single crystal superalloy,an energy-retrained laser epitaxial restoration(ERLER)process was put forward.The effects of laser power and the width of single crystal superalloy base metal on the morphology and microstructure of restoration layer were investigated.The results reveal that,the restoration layer produced by ERLER process possesses directionally epitaxial grains in almost entire layer,and the formation probability of"stray grains"is decreased greatly.Under the optimized parameters,continuous epitaxial grains can be obtained in restoration layer with a thickness of 1220μm.With the increase of laser power,the layer thickness is increased to some extent.At the same laser power and laser spot diameter,the layer thickness is increased and then decreased with flattening morphology when the base metal width is increased.For the case of 3 mm width,obvious flow paths are presented in the restoration layer.Combined with the photos taken by high-speed camera,the flow behavior in the laser molten pool can be revealed as follows:the metal firstly rised up from bottom of molten pool center to surface and spreaded to around,then flowed back to the center bottom along with the molten pool bottom.