Application of hot isostatic pressing (HIP) technology to diffusion bond refractory metals for proton beam targets and absorbers at CERN

Abstract

A target assembly, composed of several collinear molybdenum (Mo)-based and tungsten (W)-based cylindrical blocks, will reside in the core of the new beam dump facility (BDF) being designed at the European Laboratory for Particle Physics (CERN). The target blocks will be protected from the cooling water erosion-corrosion by a tantalum (Ta)-based cladding. In order to obtain intimate and reliable bonding between the several cylinders composing each target block and with the cladding, hot isostatic pressing (HIP) assisted diffusion bonding technique was explored. Several down-scaled target block prototypes were conceived to investigate the bondings. Starting from the previously gained experience in Ta cladding on W from neutron spallation targets, here, we present results on Ta cladding on TZM (Mo alloy), Ta2.5W (Ta alloy) cladding on TZM and W, and on TZM to TZM and W to W self-bondings. The resulting interfaces were systematically characterized with electron microscopy, tensile testing, and thermal conductivity measurements. Successful diffusion bonding was achieved for all the studied material combinations, resulting in homogeneous and defect-free interfaces, strong interfacial bondings, and limited interfacial thermal contact resistance. The HIP parameters and diffusion interfacial aids were of great importance to optimize the interface and bulk material properties.