Effects of friction stir processing on strength and ductility of laser directed energy deposited AerMet100 steel

Due to thick columnar crystals and obvious pores as typical defects, the mechanical properties of AerMet100 steel fabricated by laser directed energy deposition (LDED) are adversely affected, limiting its applicability in aerospace industry. Aiming at both defects, we developed friction stir processing as a post treatment to strengthen the LDEDed specimens, with two following advantages: (i) it significantly reduced the porosity and homogenized the microstructure, and the average grain size was decreased from 4.75 μm to 1.24 μm; and (ii) it significantly enhanced room temperature tensile properties by eliminating the pores, leading to the fact that the elongation increased from 3.51% to 7.38%, and the ultimate tensile strength increased from 1458 MPa to 1561 MPa. Therefore, FSP generated a simultaneous improvement in both the strength and elongation of the LDEDed AerMet100 steel. •FSP was an effective way to improve mechanical properties of LDEDed specimen.•FSP generated an improvement in strength and ductility by 7.08% and 110.26%.•FSP caused a remarkably decrease from 0.92% to 0.13% in the porosity rate.•Schematic diagram of FSP-induced crack propagation path for LDEDed steel was proposed.