Investigation of the mechanism of polymorphic transformation in titanium under femtosecond laser pulse exposure

The change of structural-phase state of near-surface layers of technically pure $\alpha$-titanium (alloy VT1-0) under the influence of shock waves arising at femtosecond laser irradiation has been investigated. The formation of the near-surface layer hardened by finely dispersed particles of titanium carbides has been established. The elongated particles with HCC lattice ($\delta$-phase) have a certain orientation ratio with the $\alpha$-titanium HPC matrix: $\langle2\bar{11}0\rangle$ $\alpha$(HPC)|| $\langle$011$\rangle$ $\delta$(HCC) and $\{0001\}$ $\alpha$(HPC) || $\{111\}$ $\delta$(HCC). The mechanism of this transformation is discussed, which is related to the segregation of carbon atoms on the defects of the crystal structure induced by shock-wave action.