Achieving cryogenic wear resistance in multi-principal element alloy via coherent precipitation and gradient nanostructuring

Developing cryogenic structural alloys with simultaneous high strength, damage tolerance, and wear resistance remains challenging because conventional incoherent second phases, although beneficial for hardening, often intensify interfacial strain localization and premature damage under low-temperature deformation. Here, a CoCrNi-based multi-principal element alloy strengthened by a high density of coherent L1₂ nanoprecipitates is developed to establish a microstructure design strategy for cryogenic load-bearing applications. The alloy exhibits pronounced cryogenic strengthening, with the yield strength and ultimate tensile strength increasing from 721 to 1057 MPa at 233 K to 856 and 1162 MPa at 113 K, respectively, while retaining an elongation of about 8.0 %. Under sliding conditions, the friction coefficient decreases from 0.48 to 0.35 and the wear rate declines from 17.3 × 10^–5 to 6.5 × 10^–5 mm³/Nm as the temperature decreases from 233 to 113 K, corresponding to a 2.7-fold improvement in wear resistance and clearly surpassing the single-phase CoCrNi counterpart. Multiscale characterization reveals a transition in subsurface deformation from localized plasticity at 233 K to a deeper gradient nanostructure at 113 K, accompanied by distributed dislocation activity, dynamic nanotwinning, and suppressed delamination. Molecular dynamics simulations further confirm deeper dislocation penetration and stronger local atomic rearrangements under cryogenic sliding, consistent with more spatially distributed plastic deformation. The present work demonstrates that coherent precipitation engineering, together with deformation-induced gradient nanostructuring, provides an effective route to simultaneously enhance cryogenic strength and wear resistance in advanced structural alloys.