Microstructural evolution and grain refinement mechanism of pure tungsten under explosive loading condition

•The deformation mechanism of CVD W during ultra-high strain rate deformation process was revealed.•Dislocation walls induced grain refinement mechanism of CVD W under ultra-high strain rate condition was revealed.•The microstructure evolution of CVD W under ultra-high strain rate condition was revealed.

The microstructural evolution and grain refinement mechanism of pure tungsten prepared by chemical vapor deposition under explosive loading condition were systematically investigated. Results show that dynamic recrystallization is the main deformation mechanism of pure tungsten under explosive loading condition, and new refined tungsten grains were observed in the deformed tungsten. However, the grain refinement mechanism of tungsten is obviously different from that of subgrain rotational dynamic recrystallization (RDR) mechanism and progressive subgrain misorientation recrystallization (PriSM) mechanism. Under the explosive loading condition, the tungsten grains are severely elongated into fibrous grains. Because the deformation time is ultra-short, dislocation slips are conducted through single slip system within the elongated tungsten grain, resulting in the formation of high density dislocation walls consisting of parallel dislocation lines. With continuous deformation, the high density dislocation walls are transformed into subgrain boundaries, which further evolve into refined boundaries. Then the fibrous tungsten grains are fragmented into equiaxed grains. No deformation twins were observed in the deformed pure tungsten.