Formation of omega phase induced by laser shock peening in Ti-17 alloy

Abstract

Synchrotron-based high-energy X-ray diffraction and transmission electron microscopy were used to study the in-depth compressive residual strains and microstructure evolution in Ti-17 alloy subjected to two-sided laser shock peening (LSP). A noticeable difference was observed in the lattice strains and extents of peak broadening on the two sides of the sample. The compressive residual strain was smaller and the peak broadening was more pronounced on the bottom surface in comparison to the top surface. This is due to the β → ω phase transformation induced by LSP on the bottom surface. It was determined that the ω phase with fine particle morphology and incommensurate structure is located mainly in the 15 μm-thick layer under the bottom surface. The formation of the LSP-induced ω phase on the bottom surface can be attributed to the adiabatic increase in temperature due to the higher shock peak pressure on the bottom surface, and can result in the relaxation of the accumulated residual compressive strain in the original phases.