The positive influences of shell printing on the sintering densification, microstructure, and mechanical properties of binder jetting 316 L stainless steel

Binder jetting (BJ) is a versatile additive manufacturing (AM) process for various metallic materials. Unfortunately, the residual pores after debinding and sintering deteriorate the performance of BJ materials. In this study, the influences of shell printing on the sintering densification, microstructure, and mechanical properties of BJ 316 L stainless steel were investigated to develop an effective means of enhancing the performance of BJ 316 L. Moreover, the effects of the position of the tensile specimens in the powder bed in relation to the building direction Z (0°XY, 45°, and 90°YZ) on BJ 316 L were also studied.

The results indicated that whether or not shell printing was used, the building direction did not obviously affect the sintered density, microstructure, or mechanical properties of BJ 316 L. In the 90°-built samples, shell printing slightly increased the sintered density from 7.83 g/cm³ to 7.91 g/cm³, decreased the porosity from 0.68 % to 0.20 %, increased the amount of δ-ferrite from 0.6 % to 3.0 %, and increased the grain size from 55.8 μm to 58.4 μm. Moreover, the ultimate tensile strengths and elongations of BJ 316 L ranged from 524 MPa to 563 MPa and from 78 % to 87 %, respectively. Shell printing did not improve the tensile properties. However, shell printing significantly improved the impact energy by 43 % because impact energy is extremely sensitive to porosity. BJ 316 L with superior tensile properties and impact toughness can be successfully obtained with shell printing.