| This thesis reports the results of an investigation of the effects of bonding temperature and joint gap size on isothermal solidification rate, and on the nature of interfacial/grain boundary particles formed during the transient liquid phase (TLP) bonding of IN 738LC superalloy using a ternary Ni-Cr-B filler alloy, Nicrobraz 150.; In contrast to the solidification behavior predicted by the current TLP models, isothermal solidification occurred under two separate regimes, depending on the bonding temperature and joint gap size. The rate of isothermal solidification in the first regime was faster than in the second regime. This led to a deviation in isothermal solidification completion time from that predicted by a conventional TLP model. The change in solidification rate was attributed to the substantial enrichment of the liquid interlayer with the base alloy solute elements and its continuous modification during isothermal solidification. These factors also influenced the nature of the phases formed in the centerline eutectic constituents subsequent to the incomplete isothermal solidification.; Also, in addition to eutectic constituents, which were observed at the centerline of a 100 mum joint that was bonded for 1 hr at 1067°C, nickel-rich and chromium-rich boride particles were observed at the original substrate/insert interface. The formation of these particles was however prevented by brazing at a suitable temperature and/or gap size. (Abstract shortened by UMI.)... |
