Deformation-induced ω phase transition in polycrystalline tungsten under extreme shock loading

Tungsten(W) with the strongest metallic bonding and the highest melting point among metals, presents no phase transition before the melting temperature. Here we report the pristine body-centered cubic (BCC) α to metastable ω phase transformation in polycrystalline W under high-energy laser shock. The formation of ω phase is triggered by the collapse of atoms on two adjacent (111)α plane toward each other along <111>α direction. HADDF-STEM clearly shows the transition state hexagonal and the ideal ω phase form sequentially along the BCC/ω phase interface through different atomic displacement. First-principles calculations reveal that the energy required for BCC to ω transformation could be met at isostatic pressure lower than 200 GPa, which falls with the local stress concentration range of shock loading. Our findings not only unravel the new BCC/ω phase transition in W, but also shed lights to the plastic deformation mechanisms of strongly bonded materials under extreme shock loading.