表面纳米化对镍基高温合金焊接液化裂纹的影响

Effect of surface nanocrystallization on welding liquation cracking of nickel-base superalloy

采用搅拌摩擦处理对Waspaloy高温合金进行表面纳米化,并用激光对搅拌区域进行重熔,研究表面纳米化对液化裂纹的影响.利用扫描电镜和电子背散射衍射,研究了搅拌区域和重熔区域的显微组织.结果表明,搅拌摩擦处理在Waspaloy合金表面制备出200～700 nm的等轴纳米晶粒,细化机制为不连续动态再结晶;从搅拌区表层至底部,晶粒尺寸整体上逐渐增大;经激光重熔后,发现纳米晶层有效抑制了热影响区液化裂纹.纳米化过程改变了碳化物的分布,避免液化相富集于晶界,晶粒尺寸减小则使晶界面积大大增加,从而减小了液膜厚度,抑制了裂纹的形成.

Friction stir processing(FSP)of Waspaloy superalloy was carried out to prepare surface nanocrystallite layers as a pre-treatment of laser remelting to explore the effect of FSP on liquation cracking.The microstructures of FSP and laser remelted regions were analyzed through scanning electron microscope and electron backscatter diffraction.The results showed that the equiaxed grains with size of 200~700 nm were successfully prepared in Waspaloy superalloy by FSP.The refinement mechanism was discontinuous recrystallization.From the topmost surface to the bottom of FSP region grains size increased gradually.The ultrafine grains were found to be effective to suppress liquation cracking in laser remelting of Waspaloy superalloy.Surface nanocrystallization changed the carbide redistribution and avoided more liquid phase in grain boundaries.The grain refinement made grain boundary area increase and reduced the thickness of liquid film,thus the liquation crackings were effectively suppressed.