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•Performing the laser shock peening without coating process on high purity copper.•Increment of micro-hardness and formation of compressive residual stress.•Microstructures ...modification; Dislocation re-arrangement and grain refinement.•Showing superior wear resistance during the fretting test.•Maintaining a low contact resistance, resulting in electrical contact failure delay.
The effects of laser shock peening without coating (LSPwC) on the degradation of copper electrical contact was investigated. A Nd:YAG laser with laser energy densities of 5.3 and 10.6 GW/cm2 was used for the LSPwC process. Surface hardness was enhanced from 55 HV to 110 and 120 HV for the laser shock-peened copper at 5.3 GW/cm2 and 10.6 GW/cm2, respectively. Moreover, near the copper surface, LSPwC introduced the max. compressive residual stress of 387.5 and 385.5 MPa for laser energy densities of 5.3 and 10.6 GW/cm2, respectively. Electron backscatter diffraction and transmission electron microscopy revealed that LSPwC introduced dislocation rearrangement, deformation twins, and grain refinement. The laser shock-peened copper exhibited superior wear resistance compared with the base metal. During the fretting test, the wear loss of the base metal was 1.61 × 10-3 mm3, and this decreased to 0.99 × 10-3 and 0.94 × 10-3 mm3 for the laser shock-peened copper at 5.3 and 10.6 GW/cm2, respectively. Thus, the laser shock-peened copper maintained a low electrical contact resistance during the fretting test, resulting in electrical contact failure delay from 2790 cycles for the base metal to 5011 and 5210 cycles for laser shock-peened copper at 5.3 and 10.6 GW/cm2, respectively.
Like other manufacturing processes, controlling the microstructure of additively manufactured parts is essential to reach the desirable mechanical properties. However, available reports on the ...control of as-build microstructure and mechanical properties of Ni-base superalloys during laser powder-bed fusion (LPBF) process are not comprehensive. This article aims at a systematic approach to study the effect of scanning strategies and build orientations on solidification patterns in the printed LPBF Hastelloy X parts. The as-built microstructure (grain size, texture) and mechanical responses (yield strength, ultimate tensile strength (UTS), and elongation) are also presented. Results reveal that the stripe unidirectional scan pattern leads to the largest grain size (>850 μm) with the lowest mechanical strength. These samples also exhibit the strongest crystallographic texture, resulting in a planar anisotropic mechanical response (~22 MPa difference in UTS). On the other hand, the stripe rotation scan strategy (67° rotation) leads to a randomly oriented and finer grain structure (~110 μm) with a higher UTS (~800 MPa) due to grain refinement observed in these samples. In addition, the aspect ratio of the columnar grain structure was observed to influence the mechanical response of these parts. UTS of horizontally printed parts were ~26% more than the vertical parts for the stripe scan strategy (67° rotation). However, changing the solidification pattern (stripe XY with 90° rotation) was observed to reduce this difference to ~18%. These findings can be used to tune the microstructure of as-built LPBF parts to obtain an optimal mechanical behaviour.
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The present work aims to fabricate CrMnFeCoNi high-entropy alloy (HEA) possessing outstanding wear and corrosion properties via laser additive manufacturing (LAM) and subsequent laser shock peening ...(LSP). The surface morphology, microstructure, microhardness and residual stress of LAM-fabricated specimen were characterized before and after LSP. Additionally, sliding wear and electrochemical corrosion experiments were conducted to evaluate the suitability of LSP for improving wear and corrosion resistance. Results indicated that friction coefficients and wear rates of LAM-fabricated specimens obviously decreased after LSP. Both untreated and LSP-treated specimens displayed uniform wear mechanisms, including abrasive and adhesive wear, while the wear damage level of the high-energy LSP-treated specimen was the mildest. Moreover, LSP-treated specimens exhibited lower corrosion current density and higher corrosion potential as compared with the untreated specimen, suggesting an enhancement in corrosion resistance. The hardened surface layer had positive effects on inhibiting furrow and spalling to resist material removal, and the compressive residual stress enhanced the adhesion of tribo-layers on the worn surface to protect the underlying layer from further damage. The grain refinement and compressive residual stress synergistically contributed to form compact passive films, thereby restraining the aggression of corrosive ions to enhance the corrosion resistance.
•LAM-fabricated CrMnFeCoNi HEA is treated by LSP.•LSP improves the wear and corrosion resistance of LAM-fabricated CrMnFeCoNi HEA.•The wear and corrosion mechanisms of CrMnFeCoNi HEA treated by LSP are discussed.
Non-conventional differential speed and confined hot rolling methods were employed to process two binary magnesium-aluminum-alloys, Mg-xAl (x = 6 and 9 wt%), with conventional rolling being used as a ...comparative control. The study focused on the effect of the processing methods and parameters on the efficacy of grain refinement and texture evolution through dynamic recrystallization, and eventually on the mechanical properties of the as-processed materials. Key results are summarized as follows: (1) The grain size of the Mg–6%Al and Mg–9%Al alloy plates was greatly refined after rolling; the microstructure of the plates processed by differential speed rolling (DSR) showed greater refinement than those processed by conventional rolling (CR) or confined rolling. (2) For both alloy compositions, the as-rolled plates exhibited a strong {0001} basal texture, regardless of CR, DSR, or confined rolling conditions. Moreover, the basal texture intensity of the plates via DSR was lower than that of the plates processed by other rolling methods. (3) The mechanical properties were significantly improved after rolling for both alloy compositions. In particular, the anisotropy of the plates processed by DSR was reduced compared to that of the plates processed by CR.
As such, our research showed that DSR holds great potential in the fabrication of bulk metal components with enhanced mechanical properties and formability.
•Mg–6Al and Mg–9Al were processed by differential speed (DSR) and confined rolling and compared to conventional rolling (CR).•Elevated temperature DSR and confined rolling result in a fully dynamically recrystallized microstructure.•The microstructures are refined through DRX, with tilted basal poles to the rolling direction and weakened texture intensity.•The DSR and confined rolled samples exhibit greater ductility than those of the CR samples, without a sacrifice of strength.
A series of novel β-type Ti-Zr-Nb-Mo alloys was fabricated to develop potential biomedical materials. The effects of the Mo content on microstructure, mechanical properties and electrochemical ...behavior were investigated in depth. The phase composition of all Ti-Zr-Nb-Mo alloys consists of a single β phase. The grains are obviously refined due to the addition Mo. The average grain size of the (TiZr)72Nb15Mo13 alloy is the smallest. The yield strength and hardness of the alloys are significantly improved as the content of the Mo element increases. Due to the contributions of the fine-grained and solution strengthening, the (TiZr)70Nb15Mo15 alloy exhibits the highest yield strength (834 MPa) and hardness (486 HV). The elastic modulus of the Ti-Zr-Nb-Mo alloys ranges from 96 GPa to 105 GPa, which is lower than that of the Ti-6Al-4V alloy. The potentiodynamic polarization curves and electrochemical impedance spectroscopy show that each sample exhibits a great corrosion behavior in the simulated body fluid at 37 °C. The corrosion resistance of Ti-Zr-Nb-Mo alloys is markedly altered by adding the Mo element. In particular, the (TiZr)72Nb15Mo13 alloy exhibits the best corrosion resistance of all the samples, ant its corrosion potential and corrosion current density are −0.344 ± 0.005 V and 71.9 ± 5.3 nA•cm−2, respectively. This finding is potenially explained by the fact that grain refinement leads to the formation of a compact and stable passive film on the surface of the alloy.
•A series of novel β type Ti-Zr-Nb-Mo biomedical alloys were fabricated.•The grain size was obviously refined due to the addition of Mo element.•The Ti-Zr-Nb-Mo alloys possess excellent mechanical properties.•The Ti-Zr-Nb-Mo alloys exhibit great corrosion resistance in the SBF.
Hydrogen embrittlement behaviors of a high-Mn TWIP (twinning induced plasticity) steel with various grain sizes from coarse grains to ultra-fine grains were studied by hydrogen pre-charging and ...subsequent slow stain rate tensile tests. The results of the tensile tests showed that the yield strength and tensile strength were not influenced by hydrogen-charging, whereas the total elongation reduced with hydrogen-charging in coarse-grained specimen but no change in the ultrafine-grained specimen. Fracture surfaces showed dimple patterns in all specimens. The present results suggested that the grain refinement suppressed hydrogen embrittlement in the high-Mn TWIP steel, even though the diffusible hydrogen content increased by grain refinement.
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•Ultimate tensile strengths of Al-Mn alloy at 25 °C and 350 °C are increased by 25.6% and 32.4%.•TiCB particles induce prominent α-Al grain refinement of Al-Mn alloy, from 410.1 μm to ...40.2 μm.•Novel TiCB particles could stabilize the deformation microstructure of Al-Mn alloy during hot extrusion.
In this work, novel TiC particles doped by trace amounts of B, referred to as TiCB, were introduced to an Al-Mn alloy with the Al-TCB master alloy. The effects of the TiCB particles on the solidification microstructure, extrusion behavior, and mechanical properties of the Al-Mn alloy were systematically studied. The results showed that TiCB particles could significantly refine α-Al grains by providing heterogeneous nucleation substrates and hindering the growth of α-grains. For example, when the amount of added TiCB particles was 0.5 wt%, average α-Al grain size could be refined to a minimum of 40.2 μm from 410.1 μm when no particles were added. After hot extrusion, TiCB particles and fractured α-Al(Fe, Mn)Si formed streamlines along the extrusion direction. More importantly, TiCB particles could inhibit the dynamic recrystallization process during hot extrusion and retain numerous geometrically necessary dislocations. Consequently, the mechanical properties of the Al-Mn alloy at room temperature (25 °C) and elevated temperature (350 °C) were significantly improved after adding TiCB particles. When the amount of added TiCB particles was 1.5 wt%, the ultimate tensile strengths at 25 °C and 350 °C were increased by 25.6% and 32.4%. This work sheds light on the grain refinement and strengthening of non-heat-treatable wrought Al-Mn alloys.
Twinning induced plasticity (TWIP) and phase transformation induced plasticity (TRIP) are two effective mechanisms for achieving good combination of strength and ductility in metallic materials, such ...as steels and high entropy alloys (HEAs). A further enhancement of the strength-ductility combination can be achieved by grain refinement owing to the grain boundary strengthening effect. In this work, we investigated the microstructure and mechanical properties of a TRIP HEA (Cr20Mn24Fe30Co20Ni6, at.%) and a TWIP HEA (Cr20Mn15Fe34Co20Ni11, at.%) after grain refinement by cold-rolling and short-time annealing. The results show a simultaneous increase of strength and ductility for the Cr20Mn15Fe34Co20Ni11 alloy after grain refinement, maintaining the TWIP effect. However, the Cr20Mn24Fe30Co20Ni6 alloy displays a significant enhancement of strength accompanied by a loss of ductility. Detailed microstructure analysis shows that nano-sized σ precipitates are formed in the Cr20Mn24Fe30Co20Ni6 alloy during the grain refinement process. While the nano-precipitates contributes significantly to the strength, they also lead to a spread of micro-voids and early fracture upon deformation. Our work provides some insights in balancing different strengthening mechanisms in alloy design and microstructural manipulation.
Surface mechanical attrition treatment (SMAT), an effective tool to refine the surface microstructure of materials, is based on the same concept of conventional shot peening; however, it is very ...difficult to relate its experimental data with those obtained from other SMAT studies or other impact based grain refinement methods. Herein, a detailed finite element model for SMAT is developed based on the well-defined coverage and Almen intensity parameters, which are the gold standard parameters world-widely used to characterize shot peening. The surface coverage was experimentally measured on pure Al and was implemented to build a realistic coverage assessment model. X-ray diffraction technique was used to measure the induced residual stresses and evaluate plastically deformed layer detected by peak broadening. The proposed model is shown to be able to accurately describe the trend of surface coverage by using a reasonable number of impacts. The comparison of residual stresses from the numerical model showed a good agreement with the experimental measurements. The thickness of deformed layer calculated by finite element method and measured by XRD peak broadening are in good conformity. This study establishes the basis for the direct comparison of any two SMAT or SMAT and other similar impact-based processes.
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•Numerical simulation of deformed layer and residual stresses induced by surface mechanical attrition treatment was studied.•Experimental coverage and Almen intensity of surface mechanical attrition treatment were successfully characterized.•The numerical coverage was in agreement with the experimental surface coverage.•The coverage of surface mechanical attrition treatment was found to follow the well-known Avrami model.•This study has established foundations for the direct comparison of samples with different parameter sets of the treatment.
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