Generally for materials with good plastic deformation ability
Generally, for materials with good plastic deformation ability, when the indenter penetrates their surface, the subsurface materials near the indenter tip are deformed due to hydrostatic pressure and are hardened subsequently by the applied plastic deformation. Under such conditions, the stress is not enough to produce further plastic deformation in this region. However, this hardened area could compress the near materials and cause this area to deform plastically which results in the formation of shear bands. Likewise, once this part also becomes hardened, it KY02111 could produce plastic deformation in the adjacent materials, therefore shear bands formation could extend to adjacent areas beneath the indented surface . In this work, Ti–7Fe–11Nb alloy presents a larger deformation zone, with more primary and secondary shear bands beneath indent, than Ti–7Fe and Ti–7Fe–4Nb alloys (Fig. 9(c)). This is due to its microstructure which consists of β phase with higher plastic deformation ability than α″ phase . Notably, in the Ti–7Fe–4Nb alloy with a lower β-stabilizer Nb content, the size of the plastic deformation zone and the number of primary and secondary shear bands observed are reduced (Fig. 9(b)). This can be attributed to its higher concentration of α″ martensitic phase and an associated lower plastic deformation ability than β phase  vessel elements causes plastic deformation to be concentrated only in a smaller region beneath the indenter tip. Finally, in case of Ti–7Fe alloy, with highest volume fraction of α″ phase, the size of the deformation zone and the amount of the observed primary shear bands are minimised while no secondary ones can be seen in Fig. 9(a).