The Influence of Direct Laser Deposition on the Structure and Properties of Ni–Cr–W–Mo Heat-Resistant Nickel Alloy

Abstract

The quality of metal powder composition (MPC) made of heat resistant alloy EP648 (Ni–Cr–W–Mo) used for fabrication of parts by direct metal deposition (DMD technology) has been analyzed. It has been established that, regarding the main requirements (chemical composition, particle size distribution, purity, bulk density, yield, moisture content), the MPC meets the requirements of Technical Specifications TU 136-225-2019. The influence of the parameters of direct laser deposition (power of laser radiation, cladding speed) on the structure and microhardness of experimental specimens has been analyzed. The highest number of defects (multiple shrinkage cavities and incomplete fusion) is formed in the specimen fabricated at the power of laser radiation P = 1000 W and the cladding speed v = 40 mm/s. At the same time, the defects have the maximum dimensions. The minimum number of defects is observed in the specimens fabricated at P = 1400 and 1600 W and v = 45 and 38 mm/s. In this case, the most homogeneous structure of laser cladding is formed owing to complete fusion of powder particles and melt spreading. Nevertheless, the structure of the specimen deposited at P = 1600 W and v = 38 mm/s contains cracks located at the subgrain boundaries in the center of cladding tracks. Their formation is caused by overheating of the metal due to higher power of laser radiation and accumulation of high internal stresses after previously deposited layers. The microhardness of the specimens fabricated by all modes of direct laser deposition changes insignificantly in the range of 270–310 HV. On the basis of the obtained experimental results, it has been determined that the most optimum structure is formed in the specimen at the laser power of 1400 W and the cladding speed of 45 mm/s.