Microstructure and Mechanical Properties of Laser Deposition Repair GH536/GH738 Alloy with Aging-Treatment; [激光沉积修复GH536/GH738合金时效热处理组织及力学性能]

GH738 alloy was widely used in aviation, aerospace and other fields because of its good performance, especially for the manufacture of engine turbine disks, sealing rings and other parts. However, under the working environment of high temperature and high pressure, GH738 alloy parts would inevitably appear fatigue cracks, wear damage and other failures. GH536 powder was used to repair them. Residual stresses would inevitably occur in the parts after repair, so it was necessary to take appropriate follow-up heat treatment and other processes to further optimize the organization of the repair area, so that the performance of the repaired parts could reach the best. GH536 powder was used to perform laser deposition repair test on the GH738 alloy matrix on the LDM-800 system, performed heat treatment experiments at different temperatures on the repaired specimens, and conducted tensile tests on the specimens at room temperature. Optical microscope (OM) and scanning electron microscope (SEM) were used to characterize different areas. The microstructure and tensile fracture were observed, tested and analyzed, and the effect of aging heat treatment at different temperatures on the microstructure and mechanical properties of GH536/GH738 alloy repaired by laser deposition was studied. The results showed that the microstructure of the repaired area in the as-deposited sample was epitaxially grown columnar crystal. After aging heat treatment, the columnar crystals began to merge and expand to equiaxed crystal transformation. As the aging temperature increased, the columnar crystal structure gradually weakened. The M6C carbides in the as-deposited samples were intermittently precipitated in the form of particles, and the size was small. After the aging heat treatment, the precipitation of carbides increased. As the aging temperature increased, the tendency of carbides to form a continuous state increased. When the stabilization temperature reached 860 ℃, the carbides were in the form of continuous strips. The tensile strength of the repaired samples with different aging heat treatments was higher than that of the sedimentary state. When the stabilizing temperature was 840 °C, the tensile strength and yield strength were the highest, reaching 72.3% and 72.4% of the GH738 forgings. The tensile fracture of the as-deposited specimen had deep equiaxed dimples and was ductile fracture. After double-stage aging heat treatment, the dimple size was reduced, white torn edges appeared, and there was a tendency to change to brittle fracture. The hardness of the repair zone of the two-stage aging heat treatment was higher than that of the sedimentary state. After the aging treatment heat, the microhardness of the repair zone and the matrix were closer. Therefore, GH738 matrix could be repaired by laser deposition with GH536 powder. After two-stage aging heat treatment, the columnar crystals began to merge and expand, and the columnar crystal structure gradually weakened and transformed into equiaxed crystals as the stabilization temperature increased. The carbides in the deposited sample were distributed intermittently, and the amount was small; as the temperature increased, the carbides gradually changed from intermittent to continuous film, and the amount of precipitation increased. Compared with the deposited state, the tensile strength was increased after aging heat treatment. When the stabilization temperature was 840 ℃, the tensile strength and yield strength were the highest of respectively 922.3 and 565 MPa, reaching 72.3% and 72.4% of the GH738 forgings. The elongation was lower than that of the deposited state. After aging heat treatment, the microhardness of the repaired area was about HV0.5 320, which was higher than that of the deposited state HV0.5 272. Compared with the deposited state, the microhardness of the repaired specimen after aging heat treatment was the same as that of the substrate and the hardness was closer. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.