Optimum Temperature for HIP Bonding Invar Alloy and Stainless Steel

The structure of the target vessel for the spallation neutron source will be modified. The Invar alloy which has a low coefficient of thermal expansion has to be reinforced by enclosing it completely in stainless steel using hot isostatic pressing bonding to reduce the thermal deformation of the additional flange. We examined the optimum temperature conditions for HIP bonding the Invar alloy and 316L stainless steel. The metallographic observation and mechanical tests on specimens bonded at 700 degrees C, 900 degrees C, 1100 degrees C and 1200 degrees C were conducted. The experimental results showed that the bonding region increased when the bonding temperature increased, but the tensile strength reduced when the bonding temperatures increased. The tensile strength of a specimen bonded at 1200 degrees C was approximately 10% lower than that of the Invar bulk. From the residual stress analysis using the ABAQUS code, the tensile stress near the bonding region of the specimen bonded at 700 degrees C was found to be 84 MPa; this stress increased with the bonding temperature up to 90 MPa. From these results, it is concluded that the optimum temperature for bonding temperature was 900 degrees C.