Most nickel based superalloys are found to be non-weldable. Only with using extreme precautions and advanced welding processes are some nickel based superalloys weldable with fusion processes. Fusion welds may experience hot cracking (cracking during solidification), intergranular cracking (cracking during cooling) or post weld heat treat cracking (cracking initiated by phase transformation stresses and thermal stresses during heat treating).
Laser machining is currently being used in advanced automated balancing systems. The laser ablates metal from the balance land in precise target locations and amounts at surface speeds as high as 30,000 in/min. Laser machining is a fusion process where the metal is heated through the liquid state to the vapor/plasma state. Metal that is not vaporized or removed during the liquid state resolidifies and becomes a recast layer. The solidification process of this recast layer is similar to that of the fusion welding process except that the amount of liquid metal is much smaller, normally 10 to 100 microns thick. The cooling rates are very fast because of the heat sink provided by the much greater size of the parent metal compared to the amount of recast layer.
This paper presents the results of an investigation into the metallurgical reactions found in the laser machined residual surface. The effects on alloys Inconel 718, Waspaloy, and IN713 will be discussed. The role of carbides will be examined in the laser machining process. Appropriate microstructures and elemental maps of cross sections through the recast layer will be presented.