查看更多>>摘要：In this work,the Al-Cu-Mg alloy with different Y(0-0.2 wt％)and Ce(0.5-1.5 wt％)are designed.The effect of mixed addition of Y and Ce on the grain structure and hot tearing for Al-4.4Cu-1.5Mg-0.15Zr alloy was investigated using"cross"hot tearing mould.The results indicate that as rare earth Y and Ce increases,the grain size becomes finer,the grain morphol-ogy changes from dendrite to equiaxed grain,and effectively reduce the hot tearing sensitivity coefficient(HTS1)and crack susceptibility coefficient(CSC)of the alloy.With the increase of Ce element(0.5-1.5 wt％),the hot tearing susceptibility of the alloy decreases first and then increases.With the increase of Y element(0-0.2 wt％),the hot tearing sensitivity of the alloy decreases.When the content of rare earth is 0.2 wt％Y+1.0 wt％Ce,the minimum HTS1 value and CSC value of the alloy are 68 and 0.53,respectively.Rare earth Ce refines the alloy microstructure,shortens the feeding channel,and reduces the hot tearing initiation.Meanwhile,the rare earth Y can form Al6Cu6Y phase at the grain boundary,improve the feeding capacity of the alloy.Therefore,appropriate addition of rare earth Y and Ce can effectively reduce the hot tearing tendency of the alloy.
查看更多>>摘要：Mg alloy seamless tubes(MASTs)were prepared through three-high rotary piercing process,effect of billet temperature,feed angle and plug advance on microstructure,texture and mechanical properties of tubes were investigated.The effect on the deformation mechanism and improving mechanical properties mechanism of this process for MASTs were studied.The results show that the grain size could be refined to 11.3-31.1％of the initial grain size and the microstructure was more uni-form due to the accumulation of strain.The formation of high strain gradient at the grain boundary activated the non-basal slip.This piercing process could change the grain orientation of as-extruded billet and eliminate the initial basal texture to produce new favorable texture.And the process could accelerate the continuous dynamic recrystallization process.After piercing,yield strength of pierced tubes decreased by 6.7％,ultimate tensile strength(UTS)and elongation increased by 32.4 and 45％,respectively,at optimal parameters.The plate-shaped β1-Mg17Al12 orientation transformed from basal plates to prismatic plates,facilitating the increase in UTS and ductility.The decrease size of nanoscale precipitates could reduce the cracking possibility.The critical resolved shear stress ratios of pyramidal(10-11)slip and(11-22)slip to basal slip for the sample including prismatic plates both decreased compared to that including basal plates.This could enhance the ductility of tube sample.Moreover,grain boundary sliding could contribute to a better ductility via coordinating deformation and reducing stress concentration during piercing process.
查看更多>>摘要：Through carrying out the high-temperature tensile experiments on an as-extruded Mg-11wt％Y alloy at 350 ℃,400 ℃,450 ℃,500 ℃ and 550 ℃,the mechanical behavior and fracture mechanisms at elevated temperatures are investigated and compared.Tensile results show that with the increase of temperature,the yield strength and ultimate tensile strength of the alloy increase at first and then decrease,while that the elongation ratio decreases firstly and then increases.For the sample being tested at 350 ℃,the values of yield strength,ultimate tensile strength and the elongation ratio are 188 MPa,266 MPa and 11％,respectively.At 400 ℃,the yield strength and ultimate tensile strength reach the maximum values of,respectively,198 MPa and 277 MPa,but the elongation ratio is the lowest and its value is only 8％.When the applied tem-perature is increased to 550 ℃,the values of yield strength and ultimate tensile strength,respectively,decrease to 140 MPa and 192 MPa and the elongation ratio increases to 38％.Failure analysis demonstrates that the fracture surfaces of different samples are mainly composed of plastic dimples and exhibit the typical characteristic of ductile fracture.The observation to the fracture side surfaces indicates that at the temperatures of 350 ℃ and 400 ℃,microcracks mainly initiate in the interior of Mg24Y5 particles.When the temperatures are 450 ℃,500 ℃ and 550 ℃,the cracks preferentially initiate at the Mg24Y5/α-Mg interfaces.
查看更多>>摘要：In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusting the content of long-period stacking ordered(LPSO)phases.It was found that the content of LPSO phases in the alloys differed the most after heat treatment at 530 ℃ for 16 h and 24 h,with values of 13.56％and 3.93％respectively.Subsequently,high-temperature tensile experiments were conducted on these two alloys at temperatures of 150 ℃,200 ℃,250 ℃,and 300 ℃.The results showed that both alloys exhibited the PLC effect at temperatures ranging from 150 to 250 ℃.However,at a temperature 300 ℃,only the alloy with a greater concentration of LPSO phases exhibited the PLC effect,whereas the alloy with a lower proportion of LPSO phases did not exhibit this phenomenon.Additionally,both alloys exhibited remarkable high-temperature stability,with the alloy containing a greater percentage of LPSO phases also demonstrating superior strength.The underly-ing mechanism for this phenomenon lies in the exceptional high-temperature stability exhibited by the second phase within the alloy.Furthermore,the LPSO phase effectively obstructs the movement of dislocations,and it also undergoing kinking to facilitate plastic deformation of the alloy.The results indicate that the PLC effect can be suppressed by reducing disloca-tion pile-up at grain boundaries,which leads to a decrease in alloy plasticity but an increase in strength.The presence of the PLC effect in the WA121 alloy is attributed to the abundant dispersed second phase within the alloy,which initially hinders the movement of dislocations,leading to an increase in stress,and subsequently releases the dislocations,allowing them to continue their movement and thereby reducing in stress.
查看更多>>摘要：In this work,the microstructure and mechanical properties of large cross-sectioned Mg-9Gd-3Y-1.2Zn-0.5Zr(VWZ931)samples produced by the small extrusion ratio has been investigated.The as-extruded VWZ931 sample with diameter of～30 mm can exhibit the high yield strength(YS)of 339 MPa,ultimate tensile strength(UTS)of 387 MPa and elongation of 8.2％,respectively.After peak-aged,the YS and UTS of the Mg samples were significantly increased to 435 MPa and 467 MPa.The small extrusion ratio leads to the low fraction of dynamic recrystallized(DRX)grains in VWZ931 sample,and the texture hardening effect can be fully utilized to achieve high strength.The combined effect of precipitation strength-ening due to the long-period stacking ordered phases and the β'phase,grain boundary strengthening due to the fine DRX grains,heterogeneous deformation-induced strengthening caused by bimodal microstructure,can together contribute to the high strength of present Mg alloy.The findings can shed light on designing other large-sized Mg wrought alloys with high mechanical performance.
查看更多>>摘要：Interstitial strengthening with nitrogen(N)is one of the effective ways to improve the mechanical properties of HEAs,but the effects of N on the microstructures and mechanical properties of the irradiated HEAs have not been studied extensively.Here,the microstructures and mechanical properties of N-free and N-doped Ti2ZrNbV0.5Mo0.2 HEAs before and after He irradiation were investigated.The results showed that the solid solution strengthening caused by interstitial N improved the yield strength at room temperature and 1023 Kwithout significantly reducing plasticity.N doping significantly promoted the growth,aggregation and wider spatial distribution of He bubbles by enhancing the mobility of He atoms/He-vacancy complexes,with the average size of He bubbles increasing from 10.4 nm in N-free HEA to 31.0 nm in N-doped HEA.In addition,N-doped HEA showed a much higher irradiation hardness increment and hardening fraction than N-free HEA.Contrary to conventional materials doped with N,the introduction of N into Ti2ZrNbV0.5Mo0.2 HEA had adverse effects on its resistance to He bubble growth and irradiation hardening.The results of this study indicated that N doping may not improve the irradiation resistance of HEAs.
查看更多>>摘要：In this work,the phase evolution mechanism and nanomechanical properties of(CoCrNi)82Al9Ti9 high-entropy alloy(HEA)prepared by selective laser melting(SLM)in the molten pool were studied.This HEA contains multiple primary elements and undergoes high-temperature gradient and rapid cooling during SLM.This leads to significant inhomogeneity of nano-scale microstructure characteristics and instability of properties.After optimizing process parameters,the microstructure evolution at the optimal parameter volume energy density of 440 J/mm3 was studied.A phase transition from BCC to FCC occurred in the melt micro-zone.Remelting the micro-area of the melt pool results in a temperature rise and the combustion-induced loss of Al elements.Moreover,the Ni element content increases significantly outside the melt pool.This process enhances the phase stability of FCC and facilitates phase transitions.Additionally,rapid cooling leads to the formation of distinctive ultrafine equiaxial crystals inside the melt pool,accompanied by the generation of intracrystalline needle-like nano-scale phases.Outside the melt pool,the accumulation of energy results in the formation of coarse dendrites.Therefore,the nano-hardness inside the molten pool is remarkably high at 11.79 GPa,while the outside the molten pool is reduced to 9.58 GPa.And the fracture toughness outside the melt pool also decreased.Comparing with inside the melt pool,the residual stress outside the melt pool changed from compressive to tensile stress and decreased from 603.28 to 322.84 MPa.
Iman AnsarianReza TaghiabadiSaeid AminiMohammad Hossein Mosallanejad...
1034-1046页
查看更多>>摘要：Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tri-bological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produced by the laser powder bed fusion(L-PBF)method.UIT considerably refined the L-PBF process-related acicular martensites(α'-M)and produced a well-homogenized and dense surface microstructure,where the porosity content of 1-,3-,and 5-pass UITed samples was reduced by 43,60,and 67％,respectively.The UITed samples showed an enhancement in their near-surface mechanical properties up to a depth of about 300 μm.The nanoindentation results for the 3-pass UITed sample revealed an increase of about 53,45,and 220％in its nanohardness,H/Er,and H3/Er2 indices,respectively.The stylus profilometry results showed that performing the UIT removed the L-PBF-related features/defects and offered a smooth surface.The roughness average(Ra)and the skewness(Rsk)of the 3-pass UITed sample were found to be lower than those of the L-PBFed sample by 95 and 223％,respectively.Applying the UIT also enhanced the material ratio,where the maximum load-bearing capacity(～100％)in as-L-PBFed(as-built)and 3-pass UITed samples was obtained at 60-and 10-μm depths,respectively.The tribological investigations showed that applying the UIT resulted in a significant reduction of wear rate and average.coefficient of friction(COF)of CP-Ti.For instance,under the normal pressures of 0.05 and 0.2 MPa,the wear rate and COF of the 3-pass UITed sample were lower than those of the L-PBFed sample by 65 and 58％,and 20 and 17％,respectively.
查看更多>>摘要：Improving the shape memory effect and superelasticity of Cu-based shape memory alloys(SMAs)has always been a research hotspot in many countries.This work systematically investigates the effects of Gyroid triply periodic minimal surface(TPMS)lattice structures with different unit sizes and volume fractions on the manufacturing viability,compressive mechanical response,superelasticity and heating recovery properties of CuAlMn SMAs.The results show that the increased specific surface area of the lattice structure leads to increased powder adhesion,making the manufacturability proportional to the unit size and volume fraction.The compressive response of the CuAlMn SMAs Gyroid TPMS lattice structure is negatively correlated with the unit size and positively correlated with the volume fraction.The superelastic recovery of all CuAlMn SMAs with Gyroid TPMS lattice structures is within 5％when the cyclic cumulative strain is set to be 10％.The lattice structure shows the maximum superelasticity when the unit size is 3.00 mm and the volume fraction is 12％,and after heating recovery,the total recovery strain increases as the volume fraction increases.This study introduces a new strategy to enhance the superelastic properties and expand the applications of CuAlMn SMAs in soft robotics,medical equipment,aerospace and other fields.
查看更多>>摘要：Previously,the in-plane mechanical anisotropy of Zr hot-rolled plates is ascribed mainly to the different activities of the deformation modes activated when loading along different directions.In this work,a quantitative study on the deformation behavior of a pure Zr hot-rolled plate under tension along the rolling direction(RD)and transverse direction(TD)reveals that both the activities of deformation modes and the anisotropy of grain boundary strengthening account for a tensile yield strength anisotropy along the TD and RD.Crystal plasticity simulations using viso-plastic self-consistent model show that prismatic slip is the predominant deformation mode for tension along the RD(RD-tension),while prismatic slip and basal slip are co-dominant deformation modes under tension along the TD(TD-tension).A low fraction of {1012} twinning is also activated under TD-tension,while hardly activated under RD-tension.The activation of basal slip with a much higher critical resolve shear stress under TD-tension contributes to a higher yield strength along the TD than along the RD.The grain boundary strengthening effect under tension along the TD and RD were compared by calculating the activation stress difference(ΔStress)and the geometric compatibility factor(m')between neighboring grains.The results indicate a higher grain boundary strengthening for TD-tension than that for RD-tension,which will lead to a higher yield strength along the TD.That is,the anisotropy of grain boundary strengthening between TD-tension and RD-tension also plays an important role in the in-plane anisotropy along the RD and TD.Afterward,the reasons for why there is a grain-boundary-strengthening anisotropy along the TD and RD were discussed.
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