In the gas turbine industry, nickel-base superalloys are used widely for components that are designed to withstand particularly harsh operating conditions, particularly with regard to temperature and stress. Welding remains one of the most important manufacturing processes in this industry, particularly for combustor and compressor assemblies. However, the alloys used can be difficult to weld; this situation arises as a consequence of the excellent elevated temperature properties that are displayed. Solidification cracking is a common form of weld defect which can arise during manufacturing. Traditionally, welding procedures for these alloys have been designed empirically, with little recourse to numerical modelling. It is possible that this situation will change, as models for weldability become more sophisticated. In the present paper, the factors that influence the susceptibility of a superalloy to solidification cracking will be identified. A short review of existing models for the prediction of hot tearing will be given, some of which have been presented in the casting community. In the case of welding, it is shown that it is necessary to treat the phenomena of stress/strain and microstructure evolution in a coupled way. A model is proposed which incorporates a thermo-mechanical analysis and a treatment of microsegregation. Simple calculations are developed for the determination of the temperature field, the strain evolution and the prediction of microsegregation. Validation of these models is attempted by comparison with experimental data for the residual stress field, as determined by the neutron diffraction technique. Comparison is also made with a more sophisticated model based upon the finite-element technique. The solidification cracking criterion is applied to the tungsten inert gas (TIG) welding ofIN718 superalloy sheet.
