ABSTRACT
Defects reduce the yield and increase the cost of castings. As a result, understanding the mechanism of why defects form, developing tools to predict when defects occur, and establishing a processing strategy to prevent the formation of defects are crucial to casting process engineers. However, it should be understood that the definition of defects is both alloy and application dependent. Defects such as shrinkage, porosity, distortion, and cracking are considered as "universal" defects to all types of castings. On the other hand, microstructure related defects are relevant in castings of superalloys, titanium alloys, and aluminum alloys [I, 2]. Currently, a number ofpostcasting repairing techniques are used to improve the casting integrity. These include welding repair for shrinkage defects, HIP (hot isostatic press) for internal pores (Fig. I) [3], and mechanical straightening for geometrical distortions. By using these repairing procedures, the requirements for the casting as-cast quality can sometimes be relaxed to a certain extent.
