查看更多>>摘要：Directed energy deposition-arc(DED-Arc)technology has the advantages of simple equipment,low manufacturing cost and high deposition rate,while the use of DED-Arc has problems of microstructure inhomogeneity,position dependence of macroscopic mechanical properties and anisotropy.Therefore,it is necessary to carry out a subsequent heat treatment to improve its microstructure uniformity,mechanical properties and superelasticity.In this investigation,the DED-Arc 15-layer NiTi alloy thin-walled parts with the solution treatment at different process parameters were studied to analyze the effects of solution heat treatment on microstructure,phase composition,phase transformation,microhardness,tensile and superelasticity.The temperature range of solution treatment is 800-1050 ℃,and the treatment time range is 1-5.5 h.The results show that after solution treatment at 800 ℃/1 h,the content of precipitated phase decreases,the grain is refined,the microhardness increases,and the mechanical properties in the 0° direction are improved.The strain recovery rate after 10 tensile cycles has increased from 37.13％(as-built)to 49.25％(solid solution treatment).This research provides an effective post treatment method for high-performance DED-Arc NiTi shape memory alloys.
查看更多>>摘要：In order to improve the properties of titanium alloys manufactured by laser melting deposition(LMD),the electroshock-ing treatment(EST)was proposed in this work.The effects of EST on microstructure and mechanical properties of LMD Ti-6.5Al-3.5Mo-1.5Zr-0.3Si were investigated.The results showed that the width of the heat affected band decreased and disappeared under the thermal and athermal effects of EST,resulting in the uniform microstructure.In the microstructure,the α laths became coarser gradually,and the quantity of α/β interface was reduced.The reduction of the quantity of α/βinterface leads to make less resistant to dislocation,resulting in the reduction in hardness and strength.The discontinuous grain boundary α phase and nucleation α colony near grain boundary inhibited the crack propagation and improved the ductility.Summary,EST can manipulate the microstructure and improve the mechanical properties of LMD titanium alloys.
查看更多>>摘要：The electrochemical behavior of Ti-6Al-4V with 1 mm and 16 mm thickness prepared by electron beam powder bed fusion(EB-PBF)was investigated in phosphate buffered saline.Electrochemical results showed that EB-PBF Ti-6Al-4V with a larger component size was more resistant to corrosion compared to the smaller component,because of less acicular α'phase content and more β phase content.As a non-equilibrium phase in the"high-energy state",α'phase has a greater susceptibility to corrode and reduces the corrosion resistance of the material,while β phase improves corrosion resistance of titanium alloys.The results show that the phase composition has a more significant effect on the corrosion performance than the grain size.
查看更多>>摘要：Cu-bearing stainless steels(SSs)with high strength,excellent plasticity,and effective antimicrobial properties hold significant potential for applications in the marine industry.In this study,Cu-bearing SSs with copper ranging from 0 to 6.0 wt％were successfully prepared using selective laser melting(SLM)technology.For the Cu-bearing SSs with different copper contents,the effect of heat treatment on the microstructural and mechanical behaviors was studied systematically.Microstructural observations revealed that the subgrain size of Cu-bearing SSs increased with heat treatment at 500 ℃ and 700 ℃ for 6 h.Furthermore,the tensile strength and elongation increased after the heat treatment temperature due to the combined effect of dislocations,twins,and ε-Cu precipitated phases.Notably,after heat treatment at 700 ℃,the SLM4.5Cu sample exhibited an abnormal rise in tensile strength and elongation.This finding suggests that the diffusion strengthening caused by ε-Cu precipitates exceeded the stacking fault energy.Consequently,the tensile strength and elongation reached 693.32 MPa and 56.94％,respectively.This work provides an efficient approach for preparing Cu-bearing SSs with exceptional strength and plasticity.
查看更多>>摘要：This work investigated the gradient microstructure evolution and tensile property of LPBF fabricated 15-5 precipitation hard-ening stainless steel in post-process direct ageing(DA)and solution treating & ageing(STA).The varied microstructures for austenite and small-sized oxide inclusions at different sample heights in the as-built(AB)condition was generally preserved after DA treatment.However,austenite was almost disappeared,and oxide particle grew significantly after the STA treat-ment.As a result,the tensile property differences in sample top and bottom for AB and DA conditions did not occur in the STA samples.For the influence of post-process heat treatment,the STA condition had the highest yield strength due to the highest volume fraction of nano-sized Cu precipitates.However,the DA specimen had the highest ultimate tensile strength and elongation owing to the considerable amount of austenite phase and associated transformation induced plasticity effect.
查看更多>>摘要：Laser 3D printing,also known as laser additive manufacturing(LAM),is favored for its ability to form bulk metal-lic glass(BMG)and its composite materials(BMGcs)with freeform geometries.In this work,two different kinds of Fe41Co7Cr15Mo14C15B6Y2 amorphous coatings(A and B)were prepared by using LAM technology under air-and water-cooled conditions,respectively;meanwhile,to reduce the cracks generated due to the residual thermal stresses,coating C obtained by air-sweep annealing of B with a low energy-density laser.The morphology and amorphous content and microstructure of the coatings were investigated,the results show many cracks in coating B deposited under water-cooled conditions,and its microstructure shows an amorphous-crystal-nanocrystalline mixed structure.Cracking was suppressed in coating C,obtained by air-sweep annealing based on coating B,but the amorphous content was reduced from 32.6 to 13.4％.And the hardness and corrosion resistance of the coating will increase with the increase in the amorphous content.Finally,the internal friction behavior of a BMGcs was prepared on the basis of the process of sample C is compared with that of as-cast amorphous alloys.The results show that the low temperature internal friction behavior of BMGcs is affected by the defects produced during printing,and the high temperature internal friction behavior is affected by the precipitated hard phase.
查看更多>>摘要：A negative Poisson's ratio(NPR)structure represents optimal impact-resistance with applications in various fields,including the crash box in vehicles,which absorbs impact kinetic energy.The crash box is designed to deform in response to impact,increasing local structural density,which enhances impact resistance performance.Current studies have only focused on the NPR effect in the plane dimension at low-speed loads.Few studies have considered high-speed impact loads on three-dimensional NPR structures.We have developed two types of AlSi10Mg alloy energy-absorbing structures with NPR using three-dimensional printing technology,and have compared our systems with a conventional hexagonal mesh structure.Sam-ple testing involved split-Hopkinson pressure bar measurements,which showed good agreement with dynamic numerical simulations.When subjected to an impact load,the NPR structure exhibited better impact resistance and energy absorption compared with the positive Poisson's ratio structure.The proposed dual-layer hexagonal structure ensures an NPR effect while exhibiting higher strength and improved stability relative to the conventional concave hexagon structure.
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