Novel concepts in weld science: Role of gradients and composite structure

Abstract

The effects of compositional and microstructural gradients on weld metal properties were investigated. The effects of compositional gradients were analyzed using thermodynamic and composite models. Brittle and ductile cracking behavior were investigated using both binary alloy single crystals and large grain castings. In both cases, the crack propagated along regions where the compositional gradients were the steepest. High temperature deformation of large wavelength compositonally modulated structures vas investigated to understand creep behavior in veld metal. At moderate temperatures, the creep behavior of cored materials was found to follow predictions based on the rule of mixtures composite analysis. At higher temperatures with the advent of dynamic mass transport the creep process is influenced by diffusion-promoted vacancy flow and time-dependent compositional gradient. The investigation found the critical gradient which will promote Kirkendall voids and has reported a creep rate behavior that suggests strong structural dependence, localized stress and vacancy transport influence. Weld metal, based on metal matrix composite, was also demonstrated.