Asymmetry in the tension and compression flow stress and the effect of sub-cell size on the hardness of a Selective Laser Melt 316L stainless steel

Abstract

An asymmetry between tension and compression tests was determined experimentally in the Selective Laser Melt (SLM) stainless steel 316L alloy in the building direction. The asymmetry was ascribed to the used biaxial scanning strategy which resulted in a strong alignment of 〈110〉 along the build direction (fiber texture) and a random distribution of 〈100〉, 〈110〉 and 〈111〉 directions normal to the building direction. The strong fiber texture in the building direction induced lower twinning stress in tension than in compression, while the tension and compression twining stresses were found similar in the normal to building direction. The favored twinning in the specimens tested in the building direction resulted in a higher tensile true fracture strain; hence, a higher ductility. Lastly, the hardness measurements made on the specimens having similar gain sizes, but different sub-cell sizes processed using higher and lower laser powers tended to support that the sub-cell boundaries in SLM-316L alloy acted as imperfect barriers to the dislocation motion.