Laser-driven in-situ synthesis of boride-reinforced Inconel 718 for overcoming high temperature deformation instabilities

Abstract

Additive manufacturing (AM) of Inconel 718 suffers from severe high-temperature ductility loss and dynamic strain aging (DSA) attributed to solute-dislocation interactions and microstructural heterogeneities. This study introduces a laser-driven in-situ boride-formation strategy using laser powder-directed energy deposition (LPDED) with SMART-processed powders containing up to 3 wt% TiB2. During deposition, TiB2 decomposes and reacts with Cr, Mo, and Nb to form thermally stable (Cr,Mo,Nb)3B2 borides, while increasing Al2O3 particle density and refining the microstructure. These in-situ phases reduce thermal conductivity, promote Zener pinning during heat treatment, and modify gamma '/gamma '' precipitation by enriching the matrix in Ti and depleting Nb. Mechanical testing demonstrates that TiB2 addition enhances both strength and strain-hardening at room and high temperatures. At 650 degrees C, the 1 wt% TiB2 composite achieved a yield strength of 1013 MPa with 12.6 % elongation, exceeding the AMS requirement. While the unreinforced alloy exhibited pronounced DSA-induced serrations, TiB2-reinforced samples exhibited smooth flow behavior. DSA suppression arises from the sequestration of Nb, Cr, and Mo into stable M3B2 borides, eliminating solute-dislocation pinning, while the borides provide barriers. Overall, in-situ boride formation effectively addresses deformation instabilities in AM Inconel 718, enabling simultaneous improvements in high-temperature strength, ductility, and thermal stability.