Effect of bimodal powder on densification and mechanical properties of 316L stainless steel fabricated by binder jet 3D printing

Obtaining fully densified metal parts presents significant challenges for binder jet 3D printing (BJ3DP). Replacing the unimodal powder feedstocks with bimodal powders provided a promising approach to increasing the densities of the printed parts. While it was demonstrated that bimodal powders increase the packing density of the powder bed, research into their effects on the green parts and the capabilities of the final components remains limited. In this study, bimodal 316 L stainless steel (SS) powders with three different coarse-fine ratios, including fine fraction proportions of 10 wt% (#C90F10), 15 wt% (#C85F15), and 20 wt% (#C80F20), were printed with green relative densities of approximately 59.0 %, 59.9 %, and 60.9 %, respectively. The densities of the green samples exhibited a positive correlation with the fine fraction proportions. Subsequent sintering at 1400 degrees C for 3 h revealed that the densification effect did not increase linearly with increasing fine fraction due to agglomeration. The #C80F20 sintered samples exhibited optimal mechanical properties, relative densities of approximately 92.8 %, tensile yield strengths (YS) of -202 MPa, ultimate tensile strengths (UTS) of -477 MPa, and elongations of -54.7 %. The results of this study provide valuable insights into densification and strengthening with bimodal powder and open new avenues for the use of BJ3DP to produce fully densified metal parts.