PSI - Issue 14

V. Srikanth et al. / Procedia Structural Integrity 14 (2019) 952–956 V. Srikanth/ Structural Integrity Procedia 00 (2018) 000–000

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Key words : residual stress, elasto-plastic, tensile.

1. Introduction Joining of dissimilar materials is more prevalent in modern industries for effective, efficient and economical functioning of modern processing equipments. There are many applications for joints between stainless steel (SS) and Zr-based alloys in nuclear industry. These applications include joining calendria tube to calendria side tube sheet joints, pressure tube to end fitting joints in PHWRs and in mounting temperature and pressure monitoring assemblies with different components of reactor for continuous in-pile monitoring [1]. The main problem encountered with these joints was, generation of residual stresses at the joint interface owing to the difference in thermo-physical properties of both the joining materials. The thermal expansion coefficient of Zr-based alloys is much lower than SS; for instance the thermal expansion coefficient of zircaloy is 60% that of SS 410 which has lowest expansion coefficient of all the steels [2]. These residual stresses generated can have deteriorating effect on the bond integrity and mechanical properties of the joint and can cause catastrophic failure of the components that are employed in above mentioned applications. So, there is a need for understanding of severity of the residual stresses developed at the interface. To minimize these stresses, many researchers have employed different interlayer materials between the base materials in their joining experiments [3, 4]. Three important criteria’s considered for interlayer selection are 1) metallurgical compatibility of interlayer material with base materials, 2) interlayer material should be soft and have accommodate the stresses that are developed and 3) thermal expansion coefficient of the interlayer material should be in between that of the base materials. Shu Xu et al. [5] calculated the thermal stresses generated at the interface of joints between 45/1Cr9Mo and 45/0Cr18Ni9 while heating the joints from ambient temperature to 723 K using finite element method (FEM). Hattali et al. [6] also performed FEM simulations to measure the residual stress distribution in a solid state diffusion bonded joint, made between alumina and nickel alloy (HAYNES 214) using Ni interlayer. The main objective of the present work was to calculate the residual stresses developed in SS304L/Zr-2.5%Nb dissimilar joints using finite element method. To study the effect of interlayers on residual stresses, simulations were performed with and without using interlayers. Simulations were carried out using Ni and Ti interlayers of thickness 200 µm each and the corresponding results were compared with that of the joints bonded without using interlayers.

Figure 1: Schematic showing the different parts for diffusion bonded joints (a) without and (b) with using