A hybrid post-processing method that synergistically combines cavitation peening and electrochemical polishing to achieve superior surface quality of solid and lattice structured additively ...manufactured (AM) metal parts is analysed. The method enables surface strengthening of AM parts through plastic deformation caused by cavitation while simultaneously improving the surface finish through electrochemical dissolution of surface asperities. Compared to sequential processing, the hybrid process produces higher microhardness and comparable surface roughness in a single step. Results show that coupling of the physical-chemical effects accompanying cavitation and electrochemical reaction can enhance the cavitation intensity and dissolution efficiency in hybrid processing.
Mechanical surface modification such as shot peening offer powerful enhancement of fatigue properties of metals and other materials. Cavitation usually causes surface damage in hydraulic machineries. ...However, careful selection of process parameters allowed developing an approach known as “cavitation peening.” Its advantage is surface roughness increase is lower than in conventional shot peening as there are no solid collisions involved. As cavitation is a hydrodynamic phenomenon, an understanding of both fluid dynamics and materials science is required. Cavitation peening is distinguished from “water jet peening,” in which water column impulse is used. Another flavor is “Submerged laser peening” that involves the use of a pulsed laser and can be considered a type of cavitation peening where cavitating bubbles are generated due to laser ablation. Ultrasound vibration, a popular method for generating cavitation for cleaning, has also been adapted for cavitation peening. The present comparative review presents key insights and achievements and addresses future directions that are required for advancing cavitation peening technology by considering the mechanisms of cavitation peening based on the reported data for water jet, pulsed laser, and ultrasonic cavitation peening. The data and methods are critically considered and summarized in comparison with shot peening. Strategic view of future challenges is presented.
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•Fatigue resistance enhancement using water jet, pulsed laser and ultrasonic cavitation peening was quantified•Cavitation peening using jet, pulsed laser & ultrasonic enhanced fatigue properties•Cavitation peening clearly distinguished from water jet peening•Cavitation peening benefits shown to exceed those by shot peening•Dislocation density induced by cavitation peening was lower than by shot peening•Importance of vortex cavitation is shown for experimental and numerical future work
Surface roughness, residual stress, grain boundary microstructure of the surface layer, the electrochemical corrosion behavior and the surface chemical state after the electrochemical test in alloy ...600 in 3.5 wt% NaCl medium was investigated. After the WJP treatment, the surface roughness was increased and residual compressive stress was introduced. A low angle grain boundary layer and a lamellae-shaped layer were formed on the surface. A passivation film with higher Cr content was formed on the WJP treated surface after the electrochemical test. After the WJP treatment, the electrochemical corrosion potential changed from −151 ± 4.6 mV to −133 ± 3.1 mV, the corrosion current density changed from 0.298 ± 0.003 μA/cm2 to 0.052 ± 0.001 μA/cm2, the pitting potential increased from 258 ± 13 mV to 350 ± 8 mV, and the film resistance increased from 4283 ± 158 Ω/cm2 to 124,850 ± 187 Ω/cm2. The superior corrosion resistance was attributed to the change in stress state and microstructure of the surface layer.
•WJP could introduce low angle grain boundary and grain refinement.•Pitting resistance of 600 MA in NaCl solution was enhanced.•Superior corrosion resistance in 600 MA was attributed to the change in microstructure and stress state.
•Mechanism of laser cavitation peening (LCP) was investigated.•Understanding into the dynamic characteristics of cavitation bubble in LCP.•Q235 steel was impacted by LCP and the strengthening ...mechanism was analyzed.•Degradation of Methylene blue solution by LCP was discussed.
The mechanism of laser cavitation peening (LCP) including laser shock wave, bubble collapse shock wave, and water-jet was investigated at various stand-off distances (γ) combined with experiment and simulation. The dynamic characteristics, pressure field, and temperature field of cavitation bubble were investigated. The Q235 steel was impacted by LCP and the strengthening mechanism was analyzed, and the chemical effect in LCP was discussed. The results found that the pressure intensity of shock wave and water-jet decreases with increasing the γ. At γ=0, the laser shock wave, bubble collapse shock wave, and water-jet are 989 Mpa, 763 Mpa, and 369 Mpa respectively. The pressure and temperature of the bubble decrease obviously in the second and third pulsations. The impact of LCP causes plastic deformation on the Q235 steel surface and refines the grains on the surface layer within a depth of 20–30 μm. The enhancement of microhardness and the residual stress increases with the increase of γ, and the optimal value for LCPwc is 0.4. The degradation rate of MB solution in the infinite domain, LCPwc, and LCP is 26.4%, 41.7%, and 34.5%.
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•Mild steel is processed by massive laser cavitation peening (LCP).•Plastic deformation, residual stress, microhardness, and microstructure after treatment are analyzed.•Understanding ...into the effects of impact times on work hardening and grain refinement.•LCP processing and material strengthening mechanisms are revealed.
A method of laser cavitation peening (LCP) was employed to strengthen the Q235 steel. The plastic deformation, residual stress, microhardness, phase, and microstructure of Q235 steel subjected to laser cavitation peening were investigated through a combination of experiments and simulations. The processing and strengthening mechanisms (LCP impact, plastic strain, grain refinement) were analyzed. Laser-induced cavitation bubble experiences three periodic pulsations during the process of LCP. The strengthening of Q235 steel by LCP can be attributed to the impact of the laser shock wave, bubble collapse shock wave, and water-jet. LCP causes plastic deformation in the surface layer of material and thereby introducing compressive residual stress and enhancing the microhardness. Dislocation structures including dislocation tangles, dislocation walls, and dislocation cells generate within the grains and near grain boundaries after LCP impact. Residual stress, microhardness, and dislocation density increase significantly with the increase of impact times. The high-density dislocation tangles and the sharing of dislocation cells refine the original coarse grains into equiaxed fine grains. The process of grain refinement is accompanied by the dissolution of cementite.
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•The fatigue strength of AM Ti6A4V was improved by post-processing (surface peening)•Submerged laser peening (SLP), cavitation peening and shot peening were compared.•At SLP, laser ...ablation (LA) and laser cavitation (LC) were used.•At SLP, LA reduced surface roughness and LC introduced compressive residual stress.•Fatigue life improvements were estimated from surface roughness and residual stress.
This study demonstrates the improvement in the fatigue strength of additive manufacturing (AM) metals such as laser-based powder bed fusion of metals by post-processing. Titanium alloy samples manufactured by powder bed fused (PBF) Ti6Al4V produced through laser sintering (LS), treated by submerged laser peening (SLP), cavitation peening (CP), and shot peening accelerated via a water jet (SPwj), were subjected to torsional fatigue testing and compared with the as-built specimen. At SLP, the samples were treated by laser ablation (LA) and laser cavitation (LC) which was developed following LA. A cavitating jet was used for CP. For comparison, conventional post-processing using SPwj was also performed. To characterize the microstructural modification caused by the three post-processing methods, the cross-section of the treated surface was observed by electron backscatter diffraction. The fatigue strengths at 107 cycles were found to be 217, 361, 313, and 285 MPa for the as-built, SLP, CP, and SPwj specimens, respectively. The primary factors contributing to fatigue strength improvement by post-processing were surface smoothing and the introduction of compressive residual stress. The experimental observations were used to derive correlation formulas to estimate the fatigue life improvement due to post-processing as the function of the surface roughness and surface residual stress.
To demonstrate and compare the improving effects of cavitation peening and shot peening on the fatigue properties of additively manufactured metals, titanium alloy Ti6Al4V specimens prepared by ...direct metal laser sintering were treated by cavitation peening, using a pulsed laser or a submerged high-speed cavitating water jet, and shot peening and, subsequently, subjected to torsion fatigue tests. It was revealed that cavitation peening using a laser, shot peening, and cavitation peening using a cavitating jet prolong the fatigue life of AM Ti6Al4V at τa (applied stress) = 450 MPa by factors of 3.5, 3.2, and 1.4, respectively.
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•Cavitation peening (CP) improved fatigue properties of AM Ti6Al4V.•Fatigue properties of AM Ti6Al4V treated by CP was evaluated by torsion test.•Improvement by CP using laser was better than that of CP using cavitating jet.•Cavitation peening suppressed the crack initiation.•Cavitation peening and shot peening increased stiffness of the specimen.
Mechanical surface treatment technologies such as laser peening and cavitation peening require detailed characterization, including residual stress analysis, to optimize their processing parameters. ...Recent developments at neutron facilities allow non-destructive 2-dimensional residual strain mapping through Bragg edge imaging, which provides specific advantages over more established methods. The present work highlights the application of Bragg edge neutron imaging for the study of mechanical surface treatments, through determination of lattice spacing distributions by energy-resolved radiography. Through three different examples, the unique capabilities of the method are demonstrated, particularly for providing near surface residual strain maps within samples with complex geometries with relatively high spatial resolution. By providing a comparison with X-ray diffraction and neutron diffraction results, the present work emphasizes the potential of Bragg edge neutron imaging as a tool for surface treatment research.
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Hot corrosion studies were performed on pristine and abrasive water jet peened (AWJP) Ti–6Al–4V surfaces. Oxide scales form on the peened and pristine surfaces when coated with NaCl and exposed to ...600 °C for 100 h. Despite similar oxide compositions on both surfaces, the thickness and roughness of the oxide scale on the AWJ peened surface is lower. The hot corrosion rate of the pristine surface is 2.5 times higher than that on the AWJ peened surface. Enhanced hot corrosion resistance of the latter is attributed to compressive residual stresses on the surface that retards diffusion of chloride in the material.
•Hot corrosion behavior of abrasive water jet peened Ti–6Al–4V was investigated.•Surface microstructures are refined and compressive residual stresses were induced.•Peening had generated high density dislocations in Ti–6Al–4V components.•Hot corrosion resistance of peened sample was threefold times higher than pristine one.
•Fatigue strength of magnesium alloy AZ31B was improved by peening methods.•AZ31B was treated by submerged laser peening, cavitation peening and shot peening.•At submerged LP (SLP), laser ablation ...impact and laser cavitation impact were used.•At improvement of fatigue strength, SLP was best, cavitation peening was second.•SLP improved fatigue strength of AZ31B by 1.56 times.
To investigate the improvement in the fatigue strength of magnesium alloy by peening methods, magnesium alloy AZ31 was treated by submerged laser peening (SLP), cavitation peening (CP), and shot peening (SP), and the fatigue properties were evaluated by a plane bending fatigue test. In the case of SLP, both the impact induced by laser ablation (LA) and that caused by laser cavitation (LC), which developed after LA, were used. In the present study, the fatigue life at a constant bending stress was examined to determine the suitable coverage. It was found that the fatigue strengths at N = 107 for the SLP, CP, and SP specimens treated by each optimum condition were 56%, 18%, and 16% higher, respectively, than that of the non-peened (NP) specimen, which was 97 MPa. The key factors in the improvement of fatigue strength by peening methods were work hardening and the introduction of compressive residual stress.
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