Microstructure investigation of bronze/steel brazed joints proposed for HHF components of ITER manufacturing

Abstract

Brazing is considered as one of the perspective option of high heat flux components of ITER manufacturing. CuCrZr bronze, austenitic steel AISI 321-type and PM-17-type (Ni–Mn–Fe–Si–Sn–B alloy) brazed material were used for the development of brazing technology. Two type of brazing have been studied within the framework of recent investigation: • Hot isostatic pressing (HIP)-assisted brazing. • Furnace-assisted brazing (with uniaxial compression loading). For the hydrostatic pressing (HIP) the brazed components were pressed out for about 175 MPa during 2.5 h at the temperature 1035–1040 °C. For the furnace-assisted brazing all components were inserted into the sealed can, vacuumed and heated up to brazing temperature ∼950 °C. Fast cooling and ageing heat treatment (500 °C and 4 h) were applied to provide high strength of CuCrZr bronze. Microsections of specimens cut from the joints were studied by optical microscopy and by scanning electron microscopy (SEM). The microstructure, distribution of alloying elements of base metals and of brazed material components were studied in the joints. Results of these studies are discussed in this paper. The data shows that there is a potential for using more simple and cheap (in comparison with common HIP) technologies of bronze to steel joining with satisfactory quality.