JOINT FORMATION PROCESSES DURING DIFFUSION WELDING ON THE COVERED SURFACES OF TITANIUM-STEEL ADAPTER
Abstract
The article presents the results of experimental studies of joints diffusion welding on the covered surfaces of titanium alloy Ti-6Al-4V and stainless steel AISI 321. Microstructural analysis of AISI 321- Ti-6Al-4V joints and concentration curves of titanium and aluminum showed that with a decrease in welding time, the width of the transition zone of the joint decreases due to the reduction of the diffusion area on the side of the titanium alloy. On the side of steel, the concentration of titanium does not change and leads to the formation of intermetallic layers, the width of which decreases slightly. This is explained by the high rate of formation of intermetallics in welding conditions. Changing additional factors that affect the rate of formation of intermetallics, such as reducing the welding temperature and pressure, will not allow to obtain the necessary contact area and ensure sufficient activation of the surfaces to be welded for the formation of a diffusion connection between the parts. The calculated values of the diffusion coefficients are higher than the tabular volume diffusion coefficients by several orders of magnitude (103...104), which confirms the dislocation mechanism of elements diffusion in the AISI 321-Ti-6Al-4V joint, obtained by the method of diffusion welding on the covered surfaces. The strength of the joints increases with a decrease in the exposure time to a certain limit, and then increases slightly, which confirms the assumption of a high rate of intermetallics formation. The strength of welded joints is significantly lower than the strength of the base metal - stainless steel (the strength of steel AISI 321 per cut is 330-380 MPa). In order to obtain connections on the covered surfaces of titanium alloy Ti-6Al-4V and stainless steel AISI 321 with the required strength, it is advisable to investigate the process of diffusion welding through an intermediate copper layer.
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