Investigation of structure and crack formation in welded joints of single crystal NI-base alloys

Conditions of initiation of hot cracks in welding of single crystal heat-resistant alloys with a 56 % content of the γ'-phase were studied. Conditions for providing a polycrystalline structure in HAZ and part of the weld metal were artificially created in one region of a welded joint with the single crystal structure. Welding of the single crystal alloy was performed by the electron beam method in vacuum. Cracks in a low-temperature ductility dip range (ductility dip cracking) were found to form in HAZ and weld of a welded joint with the polycrystalline structure. The nature of cracking of the single crystal weld is related to formation of low-melting point eutectoid interlayers, as well as to exhausting of the safety factor for ductility. Cracks in the single crystal weld along the strain grain boundaries are formed by a similar mechanism.