Ultrasonic Non-Destructive Evaluation of Solid State Welds

Abstract

In the simplest view solid state welding of metals occurs when intimate contact is achieved by clean metal surfaces. These two requirements, contact and cleanliness, are attained as a result of thermal diffusion and mechanical deformation. Not surprisingly, the bond plane defects of greatest concern are incomplete contact (porosity) and residual contamination. These are illustrated in Figure 1: (a) bondline pores in Ti-6V-4A1, with good bonding between the pores; and (b) intimate contact along the entire surface, but bonding impeded by contamination, in this example 304L stainless steel. For many diffusion bonds, both of these defects are found, and of course the amount and severity varies considerably. The work reported here is specifically directed towards characterizing the second type of defect, intimate contact achieved with a thin (less than one micron) contaminant layer impeding full metallurgical bonding.