Influence of an aluminizing process on the microstructure and tensile strength of the nickel superalloy IN 718 produced by the Selective Laser Melting

Abstract

The paper presents the impact of a surface treatment (an aluminizing process) on the microstructure and tensile strength of the nickel superalloy IN 718 produced by Selective Laser Melting (SLM). The aluminizing process was carried out by means of chemical vapor deposition with the participation of AlCl3 vapors, in a hydrogen atmosphere as the carrier gas The microstructure of the nickel superalloy IN 718 after 3D printing and thermo-chemical treatment was observed through a optical microscope and an electron scanning microscope. X-ray diffraction made it possible to analyze the phase composition and to determine the residual stresses (sin2Ψ method). Moreover, it was found that the material had a crystalline texture. A static tensile test was carried out on a Zwick/Roell Z005 testing machine. On the basis of the tests, it was ascertained that, with SLM and an appropriate selection of technological parameters, it is possible to obtain a nickel superalloy IN 718 characterized by a fine column microstructure and crystal dendrites. The samples of the nickel superalloy IN 718 produced featured a high strength, similar to that of nickel superalloy IN 718 produced by conventional methods. It was also shown that an aluminizing process carried out by the CVD method makes it possible to attain an intermetallic layer mainly comprised of a AlNi phase characterized by compressive residual stresses. The tensile strength tests proved that the aluminizing process reduced the strength of the nickel alloy IN 718.