Beliaiev G. Influence of sulfur impurities on cracks formation in welded joints of heat-resistant nickel alloys.

The dissertation work is devoted to the study of the influence of sulfur impurities on the cohesion energy of grain boundaries in alloys as a criterion formation of ductility-dip cracks in welded joints in Inconel alloys when multi-ball welds are applied and the effect of thermoplastic deformation as a precondition for anomalously rapid movement of sulfur atoms from the grain to grain boundary. It has been established that the segregation of sulfur on high-angle grain boundaries of alloys reduces the cohesion energy from 3.1 ... 3.3 J/m2 to 0.916 ... 0.97 J/m2 in the temperature range of the ductility dip T = 650 – 1050°C at which the dislocation mechanism is realized anomalously fast transfer S atoms during the application of a subsequent weld with FM52 wire. It has been established by experimental and computational methods that an increase the velocity of dislocations by preventing increase their density and uniform distribution reduces the sensitivity to the formation of ductility-dip cracks in high-resistance nickel alloys type as Inconel.