Metallurgy and Metallography of Braze Joints

摘要

Metallographic examination of braze joints involves standard metallographic procedures with a need for special attention to some unique characteristics of braze joints. These unique characteristics include very thin joints and dissimilar metal combinations. The thin joint geometry sometimes requires special sectioning techniques. The dissimilar metal combinations, usually involving soft and hard metals, can result in problems during polishing and etching. Imperfections that one should be on the lookout for in the metallographic examination of braze joints include cracks, entrapped flux, porosity, intermetallics phases, incomplete joining, corrosion, and erosion. In investigating possible origins of failure of braze joints, nonmetallurgical factors should not be overlooked. Improper design, particularly those that result in poor distribution of stress or improper clearances are often responsible for failures of braze joints. Inadequate cleaning or protection of parts and incorrect choices of heating process, filler metal and flux may all lead to a poor braze joint. (ERA citation 10:037102)