Effect of direct metal deposition technology on the structure and properties of Ni–Cr–W–Mo heat-resistant nickel alloy

The study covers the quality of a metal powder composition (MPC) made of a heat-resistant EP648 alloy (Ni–Cr–W–Mo system) used to produce parts by direct metal deposition (DMD). It was established that the MPC meets the TU 136-225-2019 specification in terms of basic requirements (chemical composition and grain size distribution, purity, bulk density, fluidity, moisture content). The effect of direct metal deposition parameters (laser radiation power, surfacing speed) on the structure and microhardness of test samples was studied. The largest number of defects (looseness, pores and lack of fusion) is formed in the sample obtained at a laser radiation power (RP) of 1000 W and a surfacing speed of 40 mm/s. At the same time, the defects have maximum dimensions. The smallest number of such defects is observed in samples obtained at a RP power of 1400 and 1600 W and a surfacing speed of 45 and 38 mm/s. In this case, the most homogeneous structure of laser surfacing zones is formed due to the complete melting of powder particles and the melt spreading. Nevertheless, the sample obtained at a RP of 1600 W and a surfacing speed of 38 mm/s has a structure with cracks located along the faces of subgrains in the center of surfacing tracks. Crack formation is caused by material overheating due to the increased laser radiation power and accumulated high internal stresses from the previous deposited layers. The microhardness of samples obtained at all direct metal deposition modes varies slightly and amounts to 270– 310 HV. According to the research results, it was found that the most optimal structure is formed in the sample obtained at a RP of 1400 W and a surfacing speed of 45 mm/s.