National University of Science and Technology MISiS, Moscow, Russia:

M. G. Khomutov, Leading Engineer of Laboratory of Hybrid Additive Technologies, e-mail: khomutov@misis.ru
A. Ya. Travyanov, Director of EkoTekh Institute, e-mail: trav@misis.ru
P. V. Petrovskiy, Deputy Director of EkoTekh Institute, e-mail: petrovskiy@misis.ru
V. V. Cheverikin, Senior Researcher of a Chair of Physical Metallurgy of Non-Ferrous Metals, e-mail: cheverikin80@rambler.ru

Our paper studies the structure and mechanical properties of the EP708 (ЭП708) alloy samples, obtained by selective laser melting and subject to heat treatment and hot isostatic pressing (HIP). We made a comparison of mechanical properties of grown samples with hot rolled ones. According to the results of microstructure analysis of the grown samples, the microstructure of the heat-treated sample slightly differs from the sample after growing. As opposed to the grown and heat-treated sample, the appearance of equiaxed grains is observed in the microstructure, which indicates that the polygonization process has passed. In the places where the concentration of particles on the boundary is small or non-existent, the grains become large, which results in an increased average grain size — (22 ± 5) μm and plasticity. The presence of tungsten carbide particles is also shown where chromium and molybdenum are partially dissolved. It can be seen that the size and concentration of these particles at the grain boundaries of grown samples and with HIP treatment are higher than those of grown heat-treated samples. According to the results of tensile tests, it was revealed that the sample from the EP708 alloy after growing has a low level of strength characteristics and high plasticity indexes (0.2 = 621 MPa, max = 831 MPa,  = 21%). After heat treatment, the grown sample, due to incomplete stress relaxation, and also because of the appearance of carbide particles, showed an increase in strength, but with a sharp decrease of ductility (0.2 = 801 MPa, max = 897 MPa, 3.4%). However, when using the HIP process, it was possible to obtain the best level of strength properties in comparison with other samples obtained by the SLP method, close to the level of the hot-rolled and heat-treated sample (0.2 = 838 MPa, max = 1143 MPa,  = 26%).
Our research was carried out with the support of the Ministry of Education and Science within the agreement No. 14.581.21.0017 (02.11.2015; unique ID: RFMEFI58115X0017).

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