A Novel Micro-Scale Plastic Deformation Feature on a Bulk Metallic Glass Surface under Laser Shock Peening

Abstract

Laser shocking peening is a widely applied surface treatment technique that can effectively improve the fatigue properties of metal parts. We observe many micro-scale arc plastic steps on the surface of Zr47.9Ti0.3Ni3.1Cu39.3Al9.4 metallic glass subjected to the ultra-high pressure and strain rate induced by laser shock peening. The scanning electronic microscopy and atomic force microscopy show that the arc plastic step (APS) has an arc boundary, 50-300 nm step height, 5-50 m radius and no preferable direction. These APSs have the ability to accommodate plastic deformation in the same way as shear band. This may indicate a new mechanism to accommodate the plastic deformation in amorphous metallic glass under high pressure, ultra-high strain rates, and short duration. As one of the most promising structural materials, bulk metallic glasses (BMGs) have drawn much attention due to their unique properties such as high strength/weight ratio and large elastic deformation capability. PACS[1−3] Recently, in order to improve the performance in specific application areas, several surface modification methods have been applied on BMGs. For example, sand blasting [4] is used to improve the wettability of BMG for biomedical applications. Laser melting is utilized to induce residual stress [5] or to form nano-crystals [6] in a subsurface to improve the mechanical properties. Zhang et al. [7] successfully treated a BMG's surface with shot peening to generate a ∼80-µm-thick affected zone which contained many slight shear bands. It is speculated that these pre-existing shear bands are favored locations for resumed plastic flow, so that the plasticity is increased while fewer main shear bands are generated. Similar to but having more advantages over shot peening, laser shock peening (LSP) [8] has been widely used to improve wear resistance and fatigue performance in the metallic components of bulk materials. In the LSP process, a shock wave is generated and propagates into the target through the interaction of a pulsed high-intensity laser beam and absorption layer on the metallic target surface. If the amplitude of the shock wave exceeds the Hugoniot elastic limit (HEL) of the target material, plastic deformation occurs and residual compressive stresses are induced near the material surface, resulting in the enhancement of fatigue life. Since the beam size could be easily adjusted, a localized micro-scale peening technique [9] has been developed and applied on the metal films in the semiconductor industry. In addition, LSP is suitable in processing materials with complex structural geometry by manipulating laser beams and utilizing liquid confining media like water.[10] To our knowledge, LSP processing on BMGs is rarely reported. In this Letter, we report a novel micro-scale plastic deformation feature observed on the surface of Zr-BMG treated by LSP.A Zr 47.9 Ti 0.3 Ni 3.1 Cu 39.3 Al 9.4 BMG rod in diameter 5 mm was prepared by melting a mixture of elemental metals with purities ranging from 99.5% to 99.99% in an argon atmosph...

Deformation feature and properties of Zr based bulk metallic glass treated by laser shock peening

“…These features are consistent with our previous results for the sample alloy with 5 mm thickness. 11 The morphology of the deformed region for the thin sample after peening is shown in Fig. 2.…”

“…With a coupling pressure analytical method, the pressure transmitted to the BMG through shock wave was estimated to have a peak value about 8?2 GPa and full width at half maximum about 35 ns. 11,12 Moreover, the time (t), when the elastic precursor wave reaches the free back end of the sample, is calculated by t~h c~h…”

“…However, less attention has been paid on the LSP effect on the BMGs up to now. 11 In this work, LSP was applied to treat a Zr based BMG. The deformation feature and properties evolution in the BMG after LSP were investigated.…”

Softening of Zr-based metallic glass induced by nanosecond pulsed laser irradiation

“…Taking into account the laser-MG interaction, the explanation based on the re-activation of pre-existing shear bands inside the sample could also be adopted to rationalize the observed behavior of the laser-irradiated surface. Previous studies [20,37,38] reported that after laser shock peening of a MG coated by aluminum foil as absorption layer and immersed in water to limit the plasma expansion, large amounts of shear bands appeared on the MG surface. Fig.…”

Nanoindentation response of laser shock peened Ti-based bulk metallic glass

“…Wei et al performed LSP on Zr-based BMG, finding that numerous arc shearing steps with height of 50-300 nm formed on the treated surface. 11,12 The distribution of the residual stress characterized by Finite element analysis (FEA) revealed that the LSP could obviously improve the plasticity of BMGs. 13 Based on the results mentioned above, it is expected that the LSP could induce an extremely deep deformation region within BMGs, thus LSP could not only improved the plasticity of BMGs obviously, but also give the chance to investigate the structure evolution in the deformation region.…”