Laser Direct Metal Deposition Technology and Microstructure and Composition Segregation of Inconel 718 Superalloy

Abstract

Multilayer of laser direct metal deposition (DMD) was prepared by depositing a gas atomized pre-alloyed powder with a composition close to Inconel 718 alloy on Inconel 718 high temperature alloy substrate. The effects of the DMD parameters on the build-up rate and the structure of the deposited layer were studied. The laser DMD sample was further processed by a solution treatment. The microstructure and property of the laser DMD zone before and after heat treatment were investigated as well. The results show that the laser parameters of actual laser power of 650 W, scanning speed of 5. 8 mm/s, beam diameter of 1 mm, powder feed rate of 6. 45 g/min, with a corresponding specific energy of 90–130 J/mm², can be recommended as optimum parameters for high build-up rate of Inconel 718 alloy. Under the condition of optimized parameters, a directional solidification microstructure was obtained and the average distance between the columnar crystals was 5–10 μm. The microcomposition segregation was found between the columnar crystal trunk and columnar crystal. The elements of Nb, Mo, Ti concentrated in the columnar crystal trunk. After the heat treatment, the segregation was greatly minimized, and the segregation ratios were close to 1. The hardness of the laser deposited layer did not show obvious difference along the height of the layer either for the as-deposited layer or for the heat treated layer. However, the microhardness of the laser DMD zone after heat treatment was obviously higher than that after the as-deposited treatment. During the heat treatment process, some Nb- and Mo-rich phases precipitated and strengthened DMD layer.