Elements diffusion law of DD407/FGH95 diffusion bonding under hot isostatic pressing I. building diffusion bonding model

Abstract

Turbine platform and blade are two main parts of aero engines and gas turbines. Due to different requirements in practice, platforms are always fabricated by single crystal superalloys, which have high temperature strength and resistance to hot corrosion and oxidation. The platforms employed at relatively lower temperatures can be made of powder superalloys. Therefore there is a great demand for bonding single crystal superalloys to powder superalloys. Because of high content of γ' forming elements, traditional fusion welding methods employed in bonding the two materials are high susceptibility to cracking. Hot isostatic pressure (HIP) bonding is a preferable technique now to join nickel base superalloys. However, using experimental methods to explore appropriate HIP bonding parameters is time consuming and costly. This work puts forward a calculated method to simulate diffusion process and phase distribution of diffusion couples obtained by HIP diffusion bonding. In this work, the numerical model of HIP diffusion bonding was built, and distribution of elements and phases of DD407/FGH95 diffusion couples under different HIP temperature and bonding time were calculated with DICTRA and Thermal-Calc software. The simulated results indicated that the appropriate HIP temperature should be chosen between 1120°C and 1210°C. γ' in DD407 and FGH95 kept initial concentration under 1120°C HIP bonding. γ' in FGH95 began to entirely solute and γ' in DD407 partly solute under 1170 HIP bonding, and under 1210°C HIP bonding, γ' in DD407 could solute completely near the interface and partly solute away from the interface. The simulated results also implied that appropriate time for 1120°C HIP bonding is 3-5 h, 1-3 h for 1170 and 1210°C HIP bonding. © Copyright.