Ni_3Al基合金堆焊层开裂的研究

INVESTIGATION ON CARACKING IN SURFACING WELDING LAYER OF NI_3AL BASED ALLOY

本文结合Ｎｉ＿３Ａｌ基合金堆焊熔池凝固过程中的相变分析和堆焊层中的热应力分析，研究了电弧堆焊条件下Ｎｉ＿３Ａｌ基合金堆焊层中热裂纹产生的原因。分析表明，当电弧堆焊速度比较高时，由于堆焊熔池中液相快速冷却而发生非平衡相变，使所析出的富Ｎｉ枝晶γ相间的富Ａｌ液相最后发生共晶反应，而生成γ相和β′相片层组织。另外，高的堆焊速度使堆焊层中产生高的热应力。当堆焊层中局部热应力超过γ′相和β′相的内聚强度时，产生枝晶间开裂。若将电弧难焊工艺从沿直线堆焊变为沿‘Ｚ’形堆焊时，由于熔池中液相的冷却速度降低，使γ相枝晶间片层组织的生成受到抑制，同时使堆焊层中的热应力降低。

The causes of cracking in the electric arc surfacing welding layer of Ni3Al based aIloy were investigated by analysing both the liquid-to-solid transfor Ination in the fusion pool and the distrbution of thermal stress within the surfacing welding layer.The resuIts were found that higher surfacing welding rate(higher cool ing rate of liquid metal in fusion pool)resuIted in the occurrence of eutectic reaction between dendritic y phase and high thermal stress in surfacing welding layer; when the locaI thermal stress in the surfacing welding layer is higher than the cohesive strength of y phase and the interdendritic eutectic phase β,interdendritic cracking occurs.As the direction of welding changed from straight to Z-shape pattern,the in terdendritic eutectic reaction was suppressed and the thermal stress in surfacing welding layer decreased duo to the reduced cooling rate of liquid in fusion pool,so that the interdendritic cracking in the surfacing welding layer of Ni3Al based alloy was Drevented.