Zavertannyu M. Pressure butt welding technologies of high temperature alloys in dissimilar combination.

The temperature conditions for the formation of welded joints of dissimilar nickel superalloys EP741NP, VZhL12U and EI698VD during friction welding were investigated. Achieving the solidus temperature of EP741NP and VZhL12U alloys along the joint line was established. The influence of the thermal cycle of friction welding and post-welding heat treatment on the distribution of residual stresses in welded joints was determined. The process of billets deformation during the formation of welded joints of EP741NP alloy with VZhL12U and EI698VD alloys was investigated. The minimum friction pressures were determined, which provide upsetting of billets during friction welding of dissimilar nickel alloys. Namely, they amount to 80 MPa for the combination of EP741NP with EI698VD alloys and 300 MPa for the combination of EP741NP with VZhL12U alloys. The step character of upsetting during friction welding of VZhL12U with EP741NP alloys at exceeding a certain critical value of friction pressure was revealed. In particular, for a circumferential speed of 1 m/s, the critical value of friction pressure is 550 MPa. The microstructure of welded joints of EP741NP and VZhL12U alloys was studied. The formation of an intermediate layer along the joint line, in which welding defects are concentrated, is shown. It is shown that intensification of plastic deformation of the near-contact volumes of metal at the final stage of friction welding process provides the formation of defect-free joints. The change in the morphology of strengthening γ'-phase in the zone of welded joint of EP741NP, VZhL12U and EI698VD alloys was investigated. It was established that in the dynamic recrystallization zone, γ'-phase of the base metal is completely soluble. During cooling of welded joints of VZhL12U and EP741NP alloys, dispersion of strengthening phase particles with a size of 20-25 nm occurs. In the dynamiс recrystallization zone of EI698VD alloy, γ'-phase is not precipitated during cooling of the joints. The distribution of microhardness of welded joints of EP741NP and VZhL12U alloys was investigated. The absence of areas with reduced values of hardness was established. For the joints produced through the intermediate element of EI698VD alloy, a decrease in microhardness in the joint area after welding was established, which can be eliminated applying heat treatment on the mode of a deformed alloy. The formation of welded joints during resistance butt welding of titanium aluminide (γ-TiAl) and γ-TiAl with titanium VT5 alloy through intermediate nanolayer foils was investigated. It was established that the use of nanolayer foils of eutectic composition allows producing welded joints at a heating temperature, which is lower than the liquidus temperature in the system Ti-Al. The width of the diffusion zone in welded joints γ-TiAl with titanium VT5 alloy amounts to about 50 μm. The intervals of changing technological parameters of friction welding and resistance butt welding processes were determined, which provide the formation of defect- free joints of high temperature alloys. The technology of friction welding of dissimilar joints of nickel In713C alloy with steel 40Kh was developed. Metallographic examinations of welded joints showed that the width of the diffusion zone does not exceed 5 μm.