Mechanical behaviour of excimer laser irradiated polycrystalline zirconium

The effects of laser irradiation on the mechanical response of polycrystalline zirconium (Zr) have been investigated. Zr samples were irradiated with an excimer (KrF) laser (lambda approximate to 248 nm, tau approximate to 18 ns and repetition rate approximate to 30 Hz). The irradiation was performed in the ambient environment of a gas mixture containing (CO2: N-2: He) under a filling pressure of 20 Torr by varying laser fluences ranging from 3.8 to 5.1 J cm(-2). The surface and structural modification of the irradiated targets were investigated using a scanning electron microscope (SEM) and x-ray diffractometer (XRD). In order to explore the mechanical properties of the irradiated Zr, the tensile testing and Vickers microhardness testing techniques were employed. SEM analysis reveals the grain growth on the irradiated Zr surfaces; however, for increasing fluence up to 4.7 J cm(-2), the appearance of the grains becomes more distinct with an increase in their number density and decrease in size. For the maximum fluence of 5.1 J cm(-2), the grains completely vanish and the surface becomes diffusive. XRD analysis reveals the appearance of new phases of ZrN and ZrO2. The variation in the peak intensity is observed to be anomalous, whereas the decreasing trend in the crystallite size and residual stresses is observed with increasing fluence. The microhardness analysis reveals the increasing trend in surface hardness with increasing fluence. The tensile testing demonstrates the anomalous behaviour of the yield stress and ultimate tensile strength with increasing fluence.