The enhanced performance of high-temperature nickel base superalloys depend on the underlying microstructure that is achieved during fabrication and its stability during service. With the recent focus on repairing of these alloys after service, there is an increased need to understand the microstructure evolution during welding. This microstructure evolution during weld solidification and cooling controls the weld cracking tendency. Since the weld microstructure evolution is controlled by composition of the alloy and also cooling conditions, the development of repair welding procedure is complicated for each and every geometry and alloy specification. In fact, the development of crack-free welds becomes an expensive and time-consuming development process. To address this critical need an integrated weld modeling framework has been developed.

In this integrated model, a finite-element model predicts the spatial variation of temperature and strain as a function of process parameters and restraint conditions. This model also captures weld solidification conditions, as well as, the repeated heating and cooling during multiple passes. The spatial variations of thermal cycles are then given as an input to the microstructure model. The microstructure model, based on computational thermodynamic and kinetic theories, allows for the prediction of various phases including gamma-prime precipitation. This microstructure information is then qualitatively related to metallurgical susceptibility for weld cracking. By coupling these results, weld-cracking tendency can be evaluated as a function of process, process parameters, filler metal composition, base metal composition and welding geometry. Some example calculations for repair welding of polycrystalline nickel base superalloys will be discussed.

The talk also will highlight some of the innovative approaches to deliver these modeling tools to industry by using automated calculation techniques and web-based interfaces. The enhanced performance of high-temperature nickel base superalloys depend on the underlying microstructure that is achieved during fabrication and its stability during service.  With the recent focus on repairing of these alloys after service, there is an increased need to understand the microstructure evolution during welding.  This microstructure evolution during weld solidification and cooling controls the weld cracking tendency.  Since the weld microstructure evolution is controlled by composition of the alloy and also cooling conditions, the development of repair welding procedure is complicated for each and every geometry and alloy specification.  In fact, the development of crack-free welds becomes an expensive and time-consuming development process.  To address this critical need an integrated weld modeling framework has been developed. 

In this integrated model, a finite-element model predicts the spatial variation of temperature and strain as a function of process parameters and restraint conditions.  This model also captures weld solidification conditions, as well as, the repeated heating and cooling during multiple passes.  The spatial variations of thermal cycles are then given as an input to the microstructure model.  The microstructure model, based on computational thermodynamic and kinetic theories, allows for the prediction of various phases including γ’ precipitation.  This microstructure information is then qualitatively related to metallurgical susceptibility for weld cracking.  By coupling these results, weld-cracking tendency can be evaluated as a function of process, process parameters, filler metal composition, base metal composition and welding geometry.  Some example calculations for repair welding of polycrystalline nickel base superalloys will be discussed. 

The talk also will highlight some of the innovative approaches to deliver these modeling tools to industry by using automated calculation techniques and web-based interfaces.