Influence of Pulsed Beam-Plasma Impacts on the Structural Characteristics and Mechanical Properties of the Surface Layer in Inconel 718 Alloy

Abstract

The results of studying the effects of pulsed flows of helium ions (HI) and helium plasmas (HP) on the Inconel 718 alloy prepared by additive technology by selective laser melting followed by heat treatment are presented. The main structural changes in the irradiated surface layer (SL) are determined for two modes of irradiation - soft (with radiation power density q = 2 ∙108 W/cm2 at pulse duration τ = 50 ns) and hard (at q = 1.5 ∙109 W/cm2, τ = 25 ns). The number of pulsed actions in each mode was N = 10 and 20. It has been found that in the initial state and after irradiation, the alloy under study is a single-phase nickel-based solid solution with an fcc lattice. The impact on the alloy of pulsed HI and HP flows leads to a change in the initial texture in the 220 direction to texture 111. This change in the texture favored the occurrence of the plastic deformation (PD) process observed in the irradiated SL, during which in metals with an fcc lattice, under the action of applied thermal stresses, slip occurs predominantly along the {111} planes. The influence of the irradiation mode of the investigated alloy on the parameter of its crystal lattice is noted. In the soft mode of exposure to HI and HP flows, the lattice parameter a decreases compared to the initial value, which may be due to the action of residual macrostresses, as well as to the evaporation of atoms of impurity elements located in lattice interstices from the SL. In the hard irradiation regime, the parameter a increases, which is due to the dominant influence of the mechanism of implantation of helium ions into the alloy, which contributes to the increase in the value of a. It have been shown that the observed structural changes in the SL of the alloy lead to a decrease in microhardness and softening of the remelted layer. The role of thermal and shock-wave effects in the processes of PD and structural changes in SL under the implemented irradiation conditions was estimated by numerical simulation.