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.
This paper presents the development of stable modes of additive technology of direct laser growing, using the starting material - a metal powder made of heat-resistant EP648 alloy of Russian production. The subsequent heat treatment of the manufactured samples was tested in order to avoid the formation of cracks in the structure of the material formed as a result of the presence of internal stresses after surfacing. Recommendations for further research are given.
The article reviews the results of experimental studies of microstructure and redistribution of alloying elements in heat-resistant alloy HN45VMTYUBR during laser beam welding (alloy produced according to GOST 5632-14). Impression of laser emission on redistribution of alloying elements throughout the depth of a welding seam is demonstrated. Analysis covers the microstructure of several welding and heat-affected zones and redistribution of the alloying elements in these zones. Increase in tungsten content in weld root is detected. Redistribution of alloying elements in welding zones is proven to impact strength characteristics of the seam.
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