According to above results, the grain refinement mechanism of SFPB-treated CuW70 alloy can be achieved. When the depth of deformation layer is far from the treated surface, only a small number of dislocations are generated because of low strains. Dislocation motion as a major deformation mode. As the depth decreases, deformation strains and strain rate increase. The dislocation density increases with the concentration of strain and then dislocation pileup occurred, which resulting in the formation of lamellar twins. The deformation of twins as a major deformation 30 40 50 60 70 80 90 100 W(220) W(200) W(211) Cu(111) Cu(200) 60min 30min 15min intensity/arbunit 2Theta/deg 0min W(110) Fig. 2. XRD patterns of CuW70 alloy in different SFPB-treated time. Fig. 3. TEM images and SAED patterns of SFPB-treated CuW70 alloy (a) dislocation, (b) deformation twins. H. Gao et al. / Materials Letters 176 (2016) 181–184 183 mode. As closer from the surface, the high density of dislocations lead to the formation of dislocation walls, dislocation loops and
dislocation tangles, which segment the lamellar twins. Dislocation motion as a major deformation mode replaces the twins. Ultimately, nano-crystal formed in the surface of SFPB-treated CuW70 alloy under the influence of dislocations and twins motion.