The effects of brazing parameters on microstructure and properties of diffusion-brazed joint of IN-738 superalloy.

摘要

This thesis reports an investigation of the effects of gap width and brazing parameters (temperature and time) on the microstructure and properties of diffusion-brazed joints in IN-738 superalloy, using two commercial filler alloys, Amdry “DF3” and Nicrobraz 150.; Residual liquid present at brazing temperatures, transformed on cooling into centreline ternary eutectic phase in “NB 150” brazement. It consisted of Nickel rich boride, Chromium rich boride and γ austenitic solid solution phase. In “DF3” brazement, MC carbide, Ni ₃Ti based intermetallic and Chromium rich boride formed from the residual liquid along the centre of the joint. Precipitation of these second phases was found to increase with increase in gap size at a given brazing temperature and time. In addition to the centreline eutectic in “NB 150” brazement, Chromium rich borides and Nickel rich borides were observed at the substrate—braze interface of samples brazed below quoted eutectic temperature range of Ni-B system (1080°C—1140°C). Above this temperature range only Chromium rich borides were observed at the interface. (Abstract shortened by UMI.)