Microstructural models for the creep strength and ductility of diffusion-bonded 316H steel

Diffusion bonded compact heat exchangers have exceptionally high heat transfer efficiency, might significantly improve the performance and reduce the cost of supercritical carbon-dioxide Brayton cycle power plants using high temperature heat sources, like high temperature nuclear reactors and concentrating solar plants. Diffusion bonded compact heat exchangers have an excellent service history for lower temperature applications, but considerable uncertainty remains on the performance of diffusion bonded material operating in the creep regime. This presentation describes a microstructural modeling framework connecting the diffusion bonding processing parameters to the expected creep life and ductility of the resulting bonded material. The framework applies the phase field method to simulate grain growth and recrystallization at a bond line and a crystal plasticity finite element framework to predict the resulting material performance. Key conclusions of the study include plausible mechanisms to explain the reduced creep ductility and strength of diffusion bonded material, compared to wrought, and potential means to improve the structural reliability of the material and the resulting components by optimizing the material processing parameters.