Ultrafine-grained surface layer of tungsten via a simple two-step microstructure modulation

Surface nanocrystallization, which involves the generation of ultrafine or nanosized grains on the surface layer, presents attractive potential to improve the properties of metallic materials. Here, we report a simple two-step microstructure modulation strategy to achieve an ultrafine-grained surface layer on pure tungsten (W). Abundant deformation embryos of dislocations among the W surface layer are firstly created by mechanical grinding and then evolve into ultrafine grains with representative low-angle grain boundaries by subsequently annealing or electron beam bombardments. This leads to uniform and ubiquitous ultrafine grains with the size <500 nm and covering a thickness of 1–2 ultrafine grains on the surface layer. Importantly, these ultrafine-grained structure exhibits outstanding creep resistances, as evidenced by reduced creep displacement and strain rate sensitivity when compared to the coarse-grained W matrix. The present study demonstrates a practical route to achieving surface nanocrystallization by combining surface mechanical attrition with surface heat treatments, and it opens up significant potential for the development of high-performance metallic metals and alloys through surface engineering.