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High strain rate plastic deformation under laser shock processing (LSP) has been applied to the AlCoCrFeNi dual-phase high entropy alloy (HEA) for optimizing the microstructure and properties. Phase constituents, microstructure evolution of the HEA before and after LSP were investigated. Microstructures of the HEA samples were examined using scanning electron microscopy and transmission electron microscopy. Results showed that the microstructure in the LSPed region was obviously refined. High density dislocations were produced in the alloy and dislocation slip was the main plastic deformation mode during LSP treatment. When the laser energy increased to 5 J and 7 J, nano-precipitates, twins and stacking faults appeared, and the plastic deformation mode was a mixture of deformation twinning and dislocation slip. The refined grains, dislocation structures, deformation-induced twins and stacking faults were analyzed and associated with the microhardness. The microhardness of the HEA was significantly improved after LSP, which can be attributed to the synergistic strengthening of grain refining strengthening, precipitation strengthening and dislocation strengthening. • Severe plastic deformation under LSP is applied to the AlCoCrFeNi dual-phase HEA. • Precipitates, twins, stacking faults and dislocations after LSP are discussed. • Synergistic strengthening of refined grain, precipitate, dislocation is revealed. [ABSTRACT FROM AUTHOR]

Microstructural evolution and mechanical properties of an aging 6061 Al alloy subjected to laser shock processing treatment (post-aging LSP treatment) were investigated by transmission electron microscopy (TEM) and mechanical tests. Results showed that the precipitates formed during aging treatment still remained, and the grain was refined by the ultra-high plastic strain plastic deformation during subsequent LSP treatment. Moreover, the precipitates effectively interacted with the dislocations induced by LSP. These typical microstructures contributed to the improvement in mechanical properties of the Al alloy. Relatively higher microhardness and strength were observed for the post-aging LSP Al sample. Furthermore, the synergistic strengthening mechanism involving the interaction of precipitate with dislocation, dislocations, and refined grains were clearly revealed. • The Research Highlights in this paper are as follows: • Novel process combining aging and LSP, i.e., post-aging LSP treatment, is reported. • Grain refinement, interaction between dislocation and precipitate, are discussed. • Synergistic strengthening mechanisms during post-aging LSP treatment are revealed. [ABSTRACT FROM AUTHOR]

The effects of massive laser shock peening (LSP) treatment with different coverage layers on residual stress, pitting morphologies in a standard corrosive solution and electrochemical corrosion resistance of AISI 4145 steel were investigated by pitting corrosion test, potentiodynamic polarisation test, and SEM observations. Results showed massive LSP treatment can effectively cause an obvious improvement of pitting corrosion resistance of AISI 4145 steel, and increased coverage layer can also gradually improve its corrosion resistance. Massive LSP treatment with multiple layers was shown to influence pitting corrosion behaviour in a standard corrosive solution. [ABSTRACT FROM AUTHOR]

The surface microstructure of (Nb,Ta)C/Ni composite cladding coatings containing in-situ synthesized composite carbides (ISSCC-LCed coatings) was regulated by laser shock peening (LSP). The regulation mechanism of laser shock waves (LSW) on the microstructure evolution and electrochemical corrosion behavior of the ISSCC-LCed coatings was emphatically revealed. Correspondence between corrosion morphology and microstructure was established. Meanwhile, the phase evolution and residual stress variation laws were also tested and analyzed. The obtained results indicated that the LSW-induced surface structure exhibited interphase distribution characteristics of large and small grains through plastic deformation mechanisms such as extrusion, slip, folding, fracture, and cracking. Plastic deformation caused the relative movement of (Nb,Ta)C at the subsurface out of the surface, and the large (Nb,Ta)C fractured and extended over the entire carbide. Furthermore, element interdiffusion phenomenon existed between (Nb,Ta)C and Fe–Ni alloy. The coupling effect of LSW-induced surface fine grains and residual compressive stress inhibited corrosion propagation and improved electrochemical corrosion resistance. [ABSTRACT FROM AUTHOR]

Abstract Effects of service temperature on the tensile properties and microstructural evolution of tensile specimens manufactured by commercial pure (CP) titanium subjected to laser shock peening (LSP) were investigated. Special attention was paid to the microstructural features at the top surface close to the fracture zone of the failed LSPed specimens at 20 °C, 150 °C, 250 °C, and 350 °C by means of transmission electron microscopy (TEM) observations. Results indicated that the ultimate tensile strength (UTS) of LSPed specimens gradually decreased, but the area reduction and elongation of LSPed specimens increased with the increment of service temperature. Furthermore, the influence mechanism of service temperature on the microstructural evolution of the LSPed CP titanium consisted of two modes: (a) ultra-high strain rate inhibited the dislocation motion at a lower temperature which was more prone to the occurrence of deformation twinning, and (b) ultra-high strain rate was easier to activate dislocation motion at a higher temperature, making deformation twinning disappear in the plastic deformation layer of CP titanium. Graphical abstract Image 1 Highlights • Increasing temperature is easier to generate necking phenomenon of LSPed CP titanium. • Ultimate tensile strength of LSPed specimens decreased with increasing temperature. • Microstructural features of failed specimens at various temperatures were presented. • Influence mechanism of temperature on microstructure of LSPed specimen was revealed. [ABSTRACT FROM AUTHOR]

When a nanoparticle layer was placed between the absorbing layer and the top surface of a 5A06 aluminum alloy during laser shock peening (LSP), nanoparticles close to the top surface were implanted into the surface layer of the 5A06 aluminum alloy because of the mechanical effect of laser shock wave (LSW). This technology was dubbed LSW-driven nanoparticle implantation (LSWNI) into the surface layer of light alloy. This work applied the finite element method to demonstrate the dynamic movement of LSW-driven nanoparticles implanted into a 5A06 aluminum alloy. Based on the penetration process, an implantation depth model was developed for a nanoparticle into a 5A06 aluminum alloy subjected to a single and two LSWNI impacts. Results showed that the nanoparticles were implanted into the surface layer of the 5A06 aluminum alloy by an ultra-strong LSW and were distributed uniformly. The calculated implantation depth of the nanoparticle agreed well with the experimental data, verifying the validity of the implantation depth model. [ABSTRACT FROM AUTHOR]

The microstructural response and grain subdivision process in commercially pure (CP) titanium subjected to multiple laser shock peening (LSP) impacts were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. The micro-hardness curves as a function of the impact time were also determined. The deformation-induced grain refinement mechanism of the close-packed hexagonal (hcp) material by laser shock wave was subsequently analyzed. Experimental results showed that uniform equiaxed grains with an average size of less than 50 nm were generated due to the ultra-high plastic strain induced by multiple LSP impacts. Special attention was paid to four types of novel deformation-induced microstructural features, including a layered slip band in the tension deformation zone, and inverse-transformation martensite, micro-twin grating and micro-twin collision in the compression deformation zone. Furthermore, the grain refinement mechanism in the near-surface layer of CP titanium subjected to multiple LSP impacts contains two types of simultaneous subdivision modes: multi-directional mechanical twin (MT)-MT intersections at (sub)micrometer scale, and the intersection between longitudinal secondary MTs and transverse dislocation walls at nanometer scale. In addition, both grain refinement (nanocrystallization) and the existence of a small amount of inverse-transformation martensite induced by multiple LSP impacts contribute to an increase in the micro-hardness of the near-surface layer. [ABSTRACT FROM AUTHOR]

Surface topography of an upsetting wrought superalloy processed by laser shock peening was observed in microscale and a series of morphological characteristics such as surface reliefs with special orientation, destructive dimples were found. The longitudinal sizes of the micro surface structures are within 100 nm to 1000 nm generally. The mechanical response laws of metal materials under laser shock were proposed to explain the emergence of the special micro-structure characteristics. It can be concluded that the formation of surface reliefs is a release way of the internal stresses under laser shock and small dimples are deemed as an external representation of the release of impact energy in the mode of fracture damage. [ABSTRACT FROM AUTHOR]

The influence of massive laser shock peening (LSP) impacts with coverage area on tensile properties of AM50 magnesium alloy was investigated using MTS880-10 servo-hydraulic material testing machine system. Microstructure in the surface layer and fracture morphologies of as-machined and LSPed tensile specimens were also characterized and analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cross-sectional optical microscopy (OM). Special attention is paid to the crack initiation location as a function of LSPed coverage area in the gauge part of tensile specimen. Experimental results and analysis indicate that coverage area significantly influenced tensile properties of the tensile specimen. In addition, the grain refinement process in the top surface layer of AM50 magnesium alloy caused by massive LSP impacts is presented. Furthermore, the underlying influence mechanism of LSPed coverage area on tensile properties and crack initiation location of tensile specimen was clearly revealed. [ABSTRACT FROM AUTHOR]

Abstract: Laser shock processing (LSP) is used to enhance the fatigue behavior of the structures. The effects of residual stress on fatigue behavior and crack propagation from LSP-worked hole were performed in this investigation. The influence of compressive stress on fatigue behavior and crack propagation of the hole was revealed, and a parametric study on residual stress and stress intensity factor was performed in order to determine their effect on crack growth propagation. The dislocation microstructure of 7050 aluminum at different laser intensities shows similar results, which indicated that LSP had an obvious inhibitory action to fatigue crack initiation and growth of the hole crack. [Copyright &y& Elsevier]

Abstract: The aim of this article is to address the effects of a single laser shock processing (LSP) impact on the nano-hardness, elastic modulus, residual stress and phase transformation of ANSI 304 austenitic stainless steel. Residual stress distribution of the LSP-shocked region is determined by X-ray diffraction (XRD) with sin2 ψ method, and the micro-structural features in the near-surface layer are characterized by using cross-sectional optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). By comparing with the untreated samples, LSP can clearly improve nano-hardness, elastic modulus, and residual stress in the LSP-shocked region. The underlying enhancement mechanisms of LSP on nano-hardness, elastic modulus and residual stress of stainless steel ANSI 304 are also revealed. These studies may provide some important insights into surface modification for metal materials. [Copyright &y& Elsevier]

Abstract: The tensile samples manufactured by 7050 aluminum (Al) alloy were treated by different shocked paths during two-sided laser shock processing (LSP), and the samples were divided into two groups according to these different paths. The first group was treated by two paths, while the second group was treated by four paths. The fatigue tests were performed on a servo-hydraulic material testing machine system by using the stepped loading method named Locati. The fracture morphology was observed by scanning electron microscopy (SEM). Experimental results showed that the fatigue lives of the second group increased compared to those of the first group. The effects of different shocked paths on fracture morphology during two-sided LSP were discussed. Furthermore, the enhancement mechanism of different shocked paths on fatigue crack initiation and growth two-sided LSP was also addressed during. [Copyright &y& Elsevier]