Effect of Pulsed Plasma Beams on the Structure and Mechanical Properties of the Surface Layer in an Inconel 718 Alloy

The influence of pulsed helium ion (HI) and helium plasma (HP) fluxes on an Inconel 718 alloy fabricated by an additive technology via selective laser melting and subsequent heat treatment is studied. The structural changes in the surface layer (SL) after irradiation are analyzed for two different modes: soft (at radiation power density q = 2 x 10(8) W/cm(2) and pulse duration tau = 50 ns) and hard (at q = 1.5 x 10(9) W/cm(2), tau = 25 ns). The number of pulses in each mode is N = 10 and 20. Both before and after irradiation, the structure of the alloy is found to be a single-phase solid solution based on nickel with an fcc lattice. The action of pulsed HI and HP fluxes on the alloy changes its texture from initial < 220 > to the < 111 > direction. This texture change promotes plastic deformation in the irradiated SL. During this process, slip occurs primarily along the {111} planes in fcc metals subjected to thermal stresses. The irradiation conditions affect the lattice parameters of the alloy. Soft HI and HP irradiation reduces lattice parameter a as compared to the initial value, which can be caused by residual macrostresses and the evaporation of impurity atoms located in interstitial lattice sites from SL. Hard mode irradiation increases parameter a mainly due to the influence of helium ion implantation, which promotes its growth. The observed structural changes in the SL of the alloy are shown to decrease the microhardness and to soften the remelted layer. A numerical simulation is used to estimate the role of thermal and shock-wave effects in the plastic deformation and the structural changes in SL under the applied irradiation conditions.