Impact of scratch depth on vacuum tightness of diffusion bonded parts

Abstract

AbstractThe surface roughness or solitary grooves decides about success or failure of diffusion bonding and vacuum tightness of the parts to be welded. Since surfaces have to be mated at atomic level to enable diffusion of atoms across bonding planes, also single deep scratches must be avoided to achieve vacuum tightness. Up to now there are no criteria which grooves can be tolerated. In fact, personal experience of the operator is essential to evaluate the surface before diffusion bonding. In this paper different load on top of a spike made of hard metal and sliding across the surface of austenitic stainless steel sheets of 1.4301 are employed to prepare grooves of different depth. A scanning electron microscope is used to visualize the dimension of the grooves. By white light interferometry, the depths according the load of the spice is evaluated. Diffusion bonding is performed at T = 1075 °C, t = 4 h, p = 12 MPa as well as with additional short peak loads. It turns out that the depth of grooves corresponds very well with the degree of leakage rate. Hence, by measuring the depth of grooves, prediction of leak rate can be predicted.