铸造缺陷对一种高温合金可焊性的影响

Influence of Casting Defects on Weldability of a Nickel-Based Superalloy

摘要:

使用钨极氩弧焊（TIG）方法对预制不同深度与宽度的“U”形槽的K4951高温合金进行焊接，探讨了铸造缺陷对合金可焊性的影响。采用光学显微镜、扫描电子显微镜、透射电子显微镜和能谱仪对焊后接头进行观察，并对接头微观结构、裂纹形态以及析出相进行分析。结果表明，铸造缺陷的尺寸对K4951合金的可焊性有很大影响，缺陷深度大于2 mm会导致裂纹快速扩展，而较宽的缺陷则会缓和裂纹的扩展进程。接头焊缝中观察到元素偏析和析出相（如MC碳化物）的形成，这与焊接裂纹的萌生相关。另外，凹槽深宽比在0.2至0.5之间时，裂纹形成倾向最小，接头抗拉伸强度高，接头高温拉伸后呈脆性与韧性混合断裂模式。

Abstract:

The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas (TIG) welding. The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and widths were TIG welded, and the microstructures, cracks morphology, and precipitated phases were analyzed using optical microscope, scanning electron microscope, transmission electron microscope, and energy dispersive X-ray spectrometer. The results reveal that the dimensions of casting defects significantly affect the weldability of K4951. Deep defects (greater than 2 mm) lead to rapid crack propagation, while wider defects can moderate the propagation process of cracks. Elemental segregation and the formation of precipitated phases, such as MC carbides, are observed in the fusion zone, contributing to welding cracks. An optimal groove aspect ratio (depth-to-width) between 0.2 and 0.5 minimizes crack formation tendency and enhances tensile strength, resulting in a mixed brittle-ductile fracture mode of joint after high-temperature tensile testing.