Microstructural changes of Zr702 induced by pulsed laser surface treatment

摘要

In this work, the surface of a fully recrystallized Zr702 is treated by pulsed laser following which microstructural changes are investigated by use of electron backscatter diffraction and electron channeling contrast imaging techniques. The pulsed laser treatment results in three distinctly different microstructural features from the surface to the substrate: fine alpha plates with a few hundred nanometers in width (zone I), irregular-shaped grains with varied sizes (zone II), and essentially unchanged equiaxed grains (zone III). The alpha plates result from rapid phase transformation due to easy heat extraction of the pulsed laser with dense nanoscale twins inside those plates closer to the surface. The origin of the irregular-shaped grains is found to be related to insufficient recrystallization of antecedently formed alpha plates near the substrate. Hardness tests reveal highest value (similar to 356.7 HV) near the surface in zone I and the lowest value (similar to 165.2 HV) in zone II. Reasons accounting for the difference are discussed in terms of various microstructural characteristics induced by the pulsed laser surface treatment. (C) 2015 Elsevier B.V. All rights reserved.