Effect of Aging Heat Treatment on Microstructure and Properties of Laser Deposition Repaired GH738 Alloy

The effects of bipolar aging heat treatment on the microstructure and mechanical properties of GH738 alloy repaired by laser deposition were studied. The results show that the microstructure of repair area presents typical characteristics of the epitaxial growth of columnar crystals and the dendrite spacing is about 10 gm. After the aging treatment, the repair area begins to grow and merge. The results of SEM analysis show that there is no gamma' at the as-deposited sample, and the cubic MC type carbide is formed at the interdendritic, and the M23C6 type carbide at the dendrite arm. After the aging treatment, gamma' phase precipitates at the repair area whose average size is 37 nm, and the carbide precipitates in the grain boundary with the discontinued character when the temperature of the stabilization step is 820 degrees C. With the increase of the stabilization temperature, the size of the gamma' and carbide increases. When the temperature is 840 degrees C, the average size of the gamma' is about 76 nm, and the carbide is precipitated in the form of necklace. With increasing the temperature of the stabilization step to 860 degrees C, the average size of the gamma' does not increase obviously, and part of the gamma' is obviously coarsened and the size reaches to 150 nm; meanwhile the carbides at the grain boundaries begin to be closed. The results of mechanical property show that the tensile strength of the sample increases obviously after aging treatment, and with the increase of the temperature, the tensile strength increases first and then decreases, and the elongation decreases continuously.