Daniel Yousaf

Laser irradiation effects on the surface, structural and mechanical properties of Al–Cu alloy 2024

Laser irradiation effects on surface, structural and mechanical properties of Al–Cu–Mg alloy (Al–Cu alloy 2024) have been investigated. The specimens were irradiated for various fluences ranging from 3.8 to 5.5 J/cm2 using an Excimer (KrF) laser (248 nm, 18 ns, 30 Hz) under vacuum environment. The surface and structural modifications of the irradiated targets have been investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. SEM analysis reveals the formation of micro-sized craters along the growth of periodic surface structures (ripples) at their peripheries. The size of the craters initially increases and then decreases by increasing the laser fluence. XRD analysis shows an anomalous trend in the peak intensity and crystallite size of the specimen irradiated for various fluences. A universal tensile testing machine and Vickers microhardness tester were employed in order to investigate the mechanical properties of the irradiated targets. The changes in yield strength, ultimate tensile strength and microhardness were found to be anomalous with increasing laser fluences. The changes in the surface and structural properties of Al–Cu alloy 2024 after laser irradiation have been associated with the changes in mechanical properties.

Effect of excimer laser fluence on the surface structuring of Ti under vacuum condition

The effect of variation of excimer laser fluences on the surface structuring of titanium (Ti) targets has been investigated. The KrF excimer laser (λ = 248 nm, t = 20 ns, repetition rate 20 Hz) has been employed for this purpose. The targets were irradiated for various laser fluences ranging from 0.86 J cm−2 to 1.27 J cm−2 under vacuum condition. Various diagnostic techniques like scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD) have been utilized to investigate the surface topography and structural changes of laser ablated targets. SEM analysis reveals the formation of laser-induced periodic surface structures (LIPSS) at the central ablated region. The periodicity of LIPSS increases from 5 μm to 88 μm with the increase of fluence from 0.86 J cm−2 to 1.27 J cm−2. The formation of grains is observed at the peripheral ablated region for all laser fluences. Reduction in grain size from 7.7 μm to 3.8 μm is observed with increasing fluence from minimum to maximum v...

The generation, detection and measurement of laser-induced carbon plasma ions and their implantation effects on brass substrate

ABSTRACT The generation, detection and measurement of laser-induced carbon plasma ions and their implantation effects on brass substrate have been investigated. Thomson parabola technique was employed to measure the energy and flux of carbon ions. The magnetic field of strength 80 mT was applied on the graphite plasma plume to provide an appropriate trajectory to the generated ions. The energy of carbon ions is 678 KeV for laser fluence of 5.1 J/cm2 which was kept constant for all exposures. The flux of ions varies from 32 × 1011 to 72 × 1014 ions/cm2 for varying numbers of laser pulses from 3000 to 12,000. In order to explore the ion irradiation effects on brass, four brass substrates were irradiated by carbon ions of different flux. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) are used to analyze the surface morphology and crystallographic structure of ion-implanted brass, respectively. SEM analysis reveals the formation and growth of nano-/micro-sized cavities, pores and pits for the various ion flux for varying numbers of laser pulses from 3000 to 12,000. By increasing ion flux by increasing the number of pulses up to 9000 shots, the dendritic structures initiate to grow along with cavities and pores. At the maximum ion flux for 12,000 shots, the unequiaxed dendritic structures become distinct and the distance between the dendrites is decreased, whereas cavities, pores and pits are completely finished. The XRD analysis reveals that a new phase of ZnC (0012) is formed in the brass substrate after ion implantation. Universal tensile testing machine and Vickers microhardness tester are used to explore the yield stress, ultimate tensile strength and microhardness of ion-implanted brass substrate. The mechanical properties monotonically increase by increasing the ion flux. Variations in mechanical properties are correlated with surface and structural modifications of brass.

Modifications in surface, structural and mechanical properties of brass using laser induced Ni plasma as an ion source

Laser induced Ni plasma has been employed as source of ion implantation for surface, structural and mechanical properties of brass. Excimer laser (248 nm, 20 ns, 120mJ and 30 Hz) was used for the generation of Ni plasma. Thomson parabola technique was employed to estimate the energy of generated ions using CR39 as a detector. In response to stepwise increase in number of laser pulses from 3000 to 12000, the ion dose varies from 60 × 1013 to 84 × 1016 ions/cm2 with constant energy of 138 KeV. SEM analysis reveals the growth of nano/micro sized cavities, pores, pits, voids and cracks for the ion dose ranging from 60 × 1013 to 70 × 1015 ions/cm2. However, at maximum ion dose of 84 × 1016 ions/cm2 the granular morphology is observed. XRD analysis reveals that new phase of CuZnNi (200) is formed in the brass substrate after ion implantation. However, an anomalous trend in peak intensity, crystallite size, dislocation line density and induced stresses is observed in response to the implantation with various dos...

Effect of laser pulses on the surface and structural modification of ablated titanium in a liquid-confined environment

The effect of laser pulses on surface morphology, chemical composition and crystallinity of titanium samples after irradiation in ethanol environment has been investigated. KrF Excimer laser (248 nm, 20 ns and 20 Hz) was employed for this purpose. Targets were exposed for various number of laser pulses ranging from 500 to 2000 in ambient environment of ethanol at a fluence of 3.6 J/cm2. In order to explore the modification in surface morphology, chemical composition and crystallinity, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) techniques were employed, respectively. SEM analysis reveals the formation of grains. The grain size initially decreases for increasing number of laser pulses up to 1500 and then increases with further increase in number of laser pulses up to 2000. The grain boundaries become diffused with increase in number of laser pulses from 500 to 1500. Further increase in number of pulses, up to 2000, results in much wider and distinct grain boundaries. At peripheral ablated areas, small-sized diffused grains are revealed. EDS analysis reveals an increase in the content of oxygen up to 29.25 wt.% at the central ablated area. Whereas the value of oxygen content increased to 33.08 wt.% in the peripheral ablated area, which caused the decrease in the grain size as observed in the SEM results of the peripheral ablated area. XRD analysis reveals the formation of titanium hydride along with the development of various phases of titanium oxide (Rutile: TiO2). For various number of laser pulses, the variation in the peak intensity, crystallinity and d-spacing is observed for irradiated titanium.