ZGH451镍基高温合金SLM成形开裂机制分析

Analysis of SLM Forming Cracking Mechanism of ZGH451 Nickel-Based Superalloy

摘要:

以SLM成形ZGH451镍基高温合金为研究对象，揭示凝固液膜导致裂纹萌生的机制，澄清合金元素、织构对裂纹缺陷产生的作用。结果表明：ZGH451镍基高温合金SLM成形过程中产生的裂纹主要分为内部凝固裂纹和边缘冷裂纹2类。在凝固末期枝晶间存在低熔点相液膜，凝固前沿高熔点Cr元素颗粒会阻碍熔体补缩，枝晶间液膜在补缩不足和枝晶热应力的双重作用下发生破裂导致材料心部凝固裂纹的形成。合金轮廓区域冷却速率高、热应力大，累积的残余应力超过材料强度极限或晶界结合强度导致冷裂纹形成。输入激光能量密度低于45 J/mm³时合金中未熔合缺陷沿建造方向密集分布，超过 140 J/mm³时锁孔与气孔形成概率陡增，这些缺陷会在应力作用下诱发裂纹。枝晶间析出的WC等颗粒越多、晶粒取向差越大合金裂纹敏感性越高。沉积态ZGH451镍基高温合金以γ、γ ′相为主，样品在(100)晶面具有择优取向，晶粒平均纵横比达到11.25，组织织构显著加剧了晶粒边缘与尖端应力集中，促进裂纹的萌生、改变裂纹延伸方向。

Abstract:

This study focuses on the selective laser melting (SLM)-formed ZGH451 nickel-based superalloy, revealing the mechanism that solidification liquid films lead to crack initiation and clarifying the roles of alloy elements and texture in forming crack defects. Experimental results indicate that cracks of ZGH451 nickel-based superalloy in the SLM process can be mainly categorized into internal solidification cracks and edge cold cracks. During the late solidification stage, low-melting-point phase liquid films exist between dendrites, and high-melting-point Cr element particles at the solidification front hinder melt feeding. The insufficient feeding and thermal stress between dendrites cause the liquid film's rupture, leading to solidification cracks in the core of the material. In the alloy's contour region, high cooling rates and significant thermal stress lead to residual stress accumulation, which exceeds the material's strength limit or grain boundary cohesion strength, resulting in the formation of cold cracks. When the input laser energy density is below 45 J/mm3, the unfused defects in the alloy are densely distributed along the building direction. Once exceeding 140 J/mm³, the probability of keyhole and pore formation sharply increases. These defects can induce cracks under stress. The more the WC and other carbide particles precipitated between dendrites, the greater the grain misorientation, and the higher the alloy's crack sensitivity. The deposited ZGH451 nickel-based superalloy is mainly composed of γ and γ' phases, with a preferred orientation on the (100) plane. The average aspect ratio of the grains reaches 11.25, and the significant texture exacerbates stress concentration at the grain edges and tips, promoting crack initiation and altering crack propagation direction.