News Academy of Engineering Sciences A.M. Prokhorov Annotation << Back Research of the mechanism of cracks emergence in workpieces from alloys during welding of designs of liquid rocket engines V.N. SEMENOV The article considers the nature of the cracks in large workpieces made of precipitation-hardening alloys based on nickel-chromium when welding in the manufacture of liquid rocket engines (LRE). A characteristic feature of the alloys is their tendency to change the mechanical properties during the heating process. This is especially true change is observed in the range of 700–850 0С. The elongation alloys drops sharply and is no more than 4 %. The cause of the fall of plasticity are the structural changes associated with the precipitation of a solid solution hardening phases mainly in finely divided form and appearance here segregated inclusions. Similar changes also occur when welding alloys in the area bordering the weld (heat-affected zone, HAZ). Studies have shown changes in the structure affects not only the reduction of ductility of alloys in the area of the HAZ. It is also a cause of stress concentration here. Sudden loss of plasticity and the emergence of stress concentrator cause cracking in the HAZ alloys which sometimes in the weld. Conducted research in the study of the complex nature of the cracks allowed the development of a number of technological methods to prevent cracking when welding alloys. Keywords: precipitation-hardening alloys, dislocation clusters, stress concentrator, welding, hardening. Contacts: Е-mail: vnsemenov77@gmail.com Pp. 28-31.