Nanotwins induced by pulsed laser and their hardening effect in a Zr alloy

A pulsed laser was employed to treat a Zr-2.5Nb alloy with laser-induced microstructures (especially dense nanotwins) characterized by electron channeling contrast imaging (ECC) imaging and electron backscatter diffraction (EBSD) techniques. Hardening effect of the nanotwins was derived by analyzing hardness contributions from various microstructural factors modified by the pulsed laser treatments (PLT). Results show that dense nanotwins, that are difficult to introduce into Zr alloys by conventional thermo-mechanical methods, can be readily produced by the PLT at laser powers of 50 and 100 W. The twinning system is determined to be the compressive type of {10–11}〈10–12〉 by orientation analyses using EBSD. After the PLT, specimen hardness is markedly increased, which could be attributed to not only grain refinement and solid solution of Nb but more considerably to the abundance of the {10–11} nanotwins, demonstrating their strong hardening effect. [Display omitted] •Dense nanotwins were introduced into Zr-2.5Nb alloy after pulsed laser surface treatment.•Twinning system of the nanotwins was determined to be the compressive type of {10–11}〈10–12〉.•The abundance of nanotwins in the laser-treated specimens can produce considerable hardening.