Ultrasonically determined elastic constants of additively manufactured 316L stainless steel

Abstract

We determined the effect of laser speed on the elastic constants of additively manufactured (AM) 316L stainless steel using resonant ultrasound spectroscopy (RUS). The alloy (316L) has biomechanical applications, such as medical implants. AM disks were manufactured at a constant power of 100 W and varying laser speeds of 800, 1000, and 1200 mm/s. RUS samples were extracted from the disks to determine the effects of fabrication parameters on elastic constants, as well as variations in properties across a single disk. As laser speed increases, the longitudinal (c11) moduli decreases from 284.74 GPa to 226.84 GPa, while the shear (c44) moduli exhibits minimal change. The measurement error in both moduli increases as laser speed decreases, which is attributed to the textured polycrystal nature of the samples built at lower speed. At lower speed, a greater amount of energy is deposited within the volume, allowing grains more time to grow. The grain structure determined by electron backscatter diffraction shows large crystallite formations in the 800 mm/s sample while the 1200 mm/s sample shows more homogenous small-grain distribution, which is expected of an ideal polycrystal. Variations of properties across the disk will also be presented.