Synergistic effects of multi-strengthening mechanisms in exceptionally high-strength W-Ni-Fe composites

Abstract

Tungsten heavy alloys (WHAs) are typical tungsten-based composites and are considered as important materials in kinetic energy penetrators that currently use depleted uranium munitions. However, the incongruity between strength and plasticity is the “Achilles’ heel”, which restricts further application in national defense and military industries. Herein, a novel fine-grained La2O3 strengthened W-Mo-Ni-Fe composites were fabricated successfully via using nanoscale solid-solution composite powder and the optimized two-stage sintering as well as vacuum heat-treatment techniques. In the model W-xMo-4.9Ni-2.1Fe-1La2O3 composites (x = 2.5, 5, 10 and 20 wt%), the heat-treated alloys had a highly homogeneous microstructure, consisting of equiaxed W grains, matrix phase and dispersed La2O3 reinforced particles. Increasing Mo content promoted microstructure refinement and caused the formation of MoNi3 intermetallic compound (IMC). As a result, benefiting from the multiple strengthening mechanisms containing fine-grained, solid-solution and oxide dispersion strengthening effects, the 88 W-5Mo-4.9Ni-2.1Fe-1La2O3 composite exhibited a superb synergy of tensile strength and ductility (1116 MPa and ∼ 15%). Moreover, the analysis of the lattice strain fluctuations and dislocation behaviors of WHAs were conducted by means of the geometric phase analysis (GPA) approach for the first time. The plastic deformation mechanism was studied to elucidate the fracture characteristics and slip systems with Schmid factor (SF) and Kernel Average Misorientation (KAM) analysis. Our findings not only shed light on the understanding of the deformation mechanisms of WHAs, but also provide a new avenue for the design of WHAs with outstanding mechanical properties.