Understanding the microstructural evolution and mechanical behavior induced by Al/Ti co-doping in CoCrNi alloys fabricated by laser directed energy deposition

In this work, a series of (CoCrNi)_100–2x(AlTi)_2x (x = 0, 3, 6 at%) alloys were successfully fabricated using the laser directed energy deposition technique. All the as-built alloys exhibited a good combination of strength and ductility. The effects of Al/Ti content on the phase constitution, microstructure, mechanical properties, deformation and strengthening mechanisms were systematically investigated. With Al/Ti content increasing, the average grain size decreased from 73.65 ± 75.27 μm (x = 0) to 65.10 ± 69.73 μm (x = 3) and 51.83 ± 53.74 μm (x = 6), while the dislocation density increased from 4.3*10¹⁴ to 8.2*10¹⁴ and 1.4*10¹⁵ m⁻², and the texture was weakened. The presence of nanoscale L1₂ and submicron L2₁ precipitates were observed in the as-built alloy with a total 12 at% Al/Ti co-doping content. The combination of solid solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation strengthening led to a significant enhancement in yield strength (YS). The YS improved from 581.9 ± 1.8 MPa for CoCrNi to 688.2 ± 5.0 MPa for (CoCrNi)₉₄Al₃Ti₃ and 882.3 ± 4.9 MPa for (CoCrNi)₈₈Al₆Ti₆, while a favorable ductility of over 20 % was maintained. © 2026 Elsevier B.V.