Microstructure and tribological properties for additive manufactured Inconel 718

The present work was performed to improve the knowledge and understanding about the microstructure and tribological properties of additive manufactured Inconel 718 made with the technique Electron beam melting (EBM). The objective is to see if the microstructure and the properties have some anisotropy and if different processing routes differ. Additive manufacturing (AM) or 3D printing in metal has in recent time attracted considerable interest to produce fully functional parts with complex geometries. To get there requires a better knowledge of the materials microstructure and how the materials behave, for example in tribology, which is important in all mechanical contacts. Inconel 718 is a widely used superalloy in aerospace, an early adopter of additive manufacturing, and also known hard to machine and unwanted phases easily forms during casting. The study was performed on AM material with four different post treatments and one as built from the machine. The post treatments include hot isostatic pressing and two different for Inconel 718 standard heat treatments, AMS 5662 and AMS 5664. The wear tests were performed with a bearing steel ball sliding in a reciprocating motion against the samples, primarily in dry contact but also in lubricated. The microstructure and wear tracks were analyzed using optical microscope, SEM with EDS and optical profilometry. Hardness measurements and scratch tests were also performed. The AM material turned out to have a microstructure consisting of long crystalline columns or grains directed in the build direction, in contrast to the equiaxed grains in the conventional material. The build direction is perpendicular to the metal powder layers which build up the material. No major differences in microstructure were seen between the different heat treated samples. Neither the hardness nor the friction differs between the cuts perpendicular and parallel with the build direction. The hardness for the heat treated samples was ~485 HV and for the as built lower at ~410 HV. The friction was also slightly lower for the as built. The wear is equal at the perpendicular cut and in the direction over the columns on the parallel cut, but is for most of the samples smaller in the direction parallel with the columns on the parallel cut. The wear was hard to estimate due to wear debris which gets stuck in the wear tracks.Additive Manufacturing - Development of Process and Material