微弧氧化改性电子束选区熔化Ti6Al4V合金的腐蚀与磨损性能

为了分析微弧氧化电压对Ti6Al4V(TC4)合金腐蚀和磨损性能的影响,分别在400、420和450 V对电子束选区熔化(SEBM)制备的TC4样品进行微弧氧化表面处理。结果表明,随着氧化时间和温度的增加,亚稳态锐钛矿型TiO2逐渐转变为金红石型TiO2。MAO膜表面形貌主要是尺寸分布均匀的大量微孔,仅在450V电压下出现裂纹和>10μm的孔隙;MAO膜厚度与施加电压呈正相关。MAO膜的耐腐蚀性能和磨损性能与其相成分、表面微孔尺寸分布及膜厚有关;当MAO电压为420 V时,腐蚀电流密度最小(0.960×10^-7 A/cm^2),阻抗最大(7.17×10^5Ω·cm^2),耐腐蚀性能最好;相同载荷条件下,涂层的摩擦因数及磨损量均大于基体的;随着MAO施加电压的增加,MAO膜的磨损机制由磨粒磨损转变为粘着磨损,且450V电压时粘着磨损加剧,摩擦因数也最大,为0.821。

A comparative study of surface characterization and corrosion behavior of micro-arc oxidation treated Ti-6Al-4V alloy prepared by SEBM and SLM

Additively manufactured Ti-6Al-4V(TC4)parts have been successfully employed as artificial implants in dental and orthopedic surgery due to their excellent mechanical properties.However,the suboptimal corrosion resistance limits their applications.The surface characterization and corrosion behavior of micro-arc oxidation(MAO)treated TC4 alloy prepared by selective electron beam melting(SEBM)and selective laser melting(SLM)technologies were compared.The corrosion resistance mechanism of SLM-MAO and SEBM-MAO was clarified through the analysis of the microstructure evolution,surface morphology,and electrochemical experiments.The results show that the anatase-type TiO_(2) is partially transformed into the slankite phase after MAO treatment.The surface roughness of SEBM sample was reduced by MAO coating,while the surface roughness of SLM sample increased after MAO,which is related to the difference between the microstructure of the deposited samples caused by different additive manufacturing technologies.When MAO time was 15 min,SLM-MAO and SEBM-MAO coating displayed the best and the worst corrosion resistance,respectively.

Subgrain microstructures and tensile properties of 316L stainless steel manufactured by selective laser melting

316L stainless steel samples were manufactured by selective laser melting(SLM).The microstructure of SLM-made 316L stainless steel and the room temperature tensile properties both perpendicular and along the building direction were studied and characterized.The static temperature field during the molten pool formation was simulated by finite element simulation.It indicates that the nonlinear asymmetrical inclined temperature gradient in SLM process produces a large surface tension gradient.The melt forms a Marangoni flow with different convection modes under the action of surface tension as well as a micro-molten pool morphology with subgrain structures such as strip,hexagonal and elongated cellular structures.In addition,there are also epitaxially grown columnar grains.The growth of columnar crystals is not affected by the boundary of the molten pool.Subgrain structures and low-angle grain boundaries make the tensile strength and the elongation of SLM-made 316L sample higher as compared to those of the cast and wrought samples.The room temperature tensile strength of the sample perpendicular to the building direction is higher than that of the sample along the building direction,while the elongation is lower than that of the sample along the building direction.

Through-thickness texture gradient of tantalum sputtering target

For sputtering targets, through-thickness texture is critical for assuring reliable sputtering performance.In this paper, through-thickness texture gradient of a rolled and subsequently annealed tantalum sputtering target was investigated. The results show that by carefully controlling the rolling process, shear-related components at the surface of the rolled sample could be avoided. Both the rolled sample and the annealed target develop a through-thickness texture gradient with the formation of a stronger {1 1 1}fiber in the center layer compared with that in the surface layer.

Compressive Behavior of Porous Titanium Fiber Materials

Porous titanium fiber materials with the fiber sizes of 70-120μm in diameter were prepared by vacuum sintering technology.The morphology and compressive properties of porous titanium fiber materials were investigated by using a scanning electron microscope(SEM)and an MST 858 compression testing machine in quasi-static condition.The results show that porous titanium fibers form complex micro-networks.The stress-strain curves of porous titanium fiber materials exhibit elastic region,platform region and densification region and no collapse during platform region.The yield strength of porous titanium fiber materials decreases with increasing the porosity and increasing the fiber diameter.

Sintering Behavior of Porous Titanium Fiber Materials

The porous titanium fiber materials with open porosity were successfully prepared by the vacuum sintering technology.The morphology characteristics of sintering neck of porous titanium fiber materials were investigated by scanning electron microscopy(SEM).The results show that the formation and growth of sintering neck of porous titanium fiber material approximately follow the rule that the primary mechanism is grain boundary diffusion and subsidiary mechanisms are other diffusion mechanisms during the sintering process.The formation and growth of the sintering neck depend mainly on the sintering temperature and slightly on the soaking time.The sintering system of porous titanium fiber material was determined and the equation of the sintering neck′s length was established.

Revealing substructure in clock-rolled Ta aided with triple focused ion beam

Clock rolling was developed to make deformation microstructure homogenize in high-purity Ta. The substructure of deformed Ta was revealed by electron back-scatter diffraction(EBSD) technique aided with triple focused ion beam(FIB). The results indicate that the triple FIB method can produce a mirror surface required by EBSD analysis. The clock rolling works well for the homogenization of deformed microstructure. Particularly,the local stored energy in {111} orientated grains is largely reduced by clock rolling, whereas it is enhanced in {100}orientated grains because of the occurrence of grain subdivision.

Effect of hydrogen addition on compression deformation behaviour of Ti-0.3Mo-0.8Ni alloy argon-arc welded joints

The effect of hydrogen addition on compression deformation behaviour of Ti-0.3Mo-0.8Ni alloy argon-arc welded joint has been investigated.Evolution mechanism of hydrogen-induced flow stress was discussed in detail.The results show that with increasing hydrogen content,the stretching and bending extent of fully lamellar microstructures including ot lamellas and acicular hydride continued to increase,the morphology of dynamic recrystallization(DRX)grains tended to change from approximately equiaxed to large lamellar shape,and the quantity of DRX grains and recrystallization degree of grains increased obviously.A large number of dislocations concentrated in the vicinity of the hydride.Steady stress was decreased continuously with increasing hydrogen content,while peak stress of the hydrogenated 0.12 wt.% H weld zone was decreased to the minimum value and then increased slowly.A slight decrease in flow stress of the hydrogenated 0.05 wt.% H weld zone was caused by limited increase in the volume fraction of softer βphase.Hydrogen-induced DRX of a phase and improved dislocation movement by strong interaction between the hydride and dislocation directly resulted in a sharp drop in flow stress of the hydrogenated 0.12 and 0.21 wt.% H weld zone.Solute hydrogen also finitely contributed to a sharp drop in flow stress of the hydrogenated 0.12 and 0.21 wt.% H weld zone by promoted local softening,which induced continuous DRX and more movable dislocations to participate in slipping or climbing.The reinforcement effect and plastic deformation of the hydride and solution strengthening of P phase induced by solute hydrogen finally led to the increase in flow stress of the hydrogenated 0.21 wt.% H weld zone in its true strain range from 0 to 0.36.

Heat transfer performance of porous titanium

Porous titanium fibre materials with different structural parameters were prepared by vacuum sintering method. The thickness,porosity and wire diameter of prepared materials were investigated to understand the effects of structural parameters on pool heat transmission performance of titanium fibre porous material. As a result,better heat transfer performance is obtained when overheating is less than 10 °C. In addition,when the wire diameter is smaller,the heat transfer is better. However,when superheating is above 10 °C,heat transfer performance can be improved by increasing the wire diameter. Moreover,thickness influences the superficial area of the prepared material and affects the thermal resistance when bubbles move inside the material; superficial area and thermal resistance are the two key factors that jointly impact the heat transfer in relation to the thickness of the materials. Experimental results also show that the materials of 3 mm in thickness exhibit the best performance for heat transmission. Furthermore,changes in porosity affect the nucleation site density and the resistance to bubble detachment; however,the nucleation site density and the resistance to bubble detachment conflict with each other. In summary,the titanium fibre porous material with a 50% porosity exhibits suitable heat transfer performance.

Quasi-In-Situ EBSD Observation of the Orientation Evolution in Polycrystalline Tantalum During Rolling Deformation

The evolution of crystallographic orientation of polycrystalline tantalum(Ta)during rolling was characterized by electron backscatter diffraction technique in a quasi-in-situ way,and the microstructure and microtexture before and after the deformation were characterized and analyzed,respectively.In the specimen,164 individual grains were exacted singly from the testing region and their corresponding orientations were reconstructed and analyzed,respectively.Results show that the heterogeneous deformation in a grain can be reflected by the accidented surface microstructure.Moreover,the orientations close to{111}orientations came closer to the{111}corner,while the orientation evolution is more complicated for the orientations close{100}corner,indicating that the evolution of these orientations close to{100}corner seemed to be irregular.

Effect of heat treatment on microstructural evolution,mechanical properties and tribological properties of H13 steel prepared using selective laser melting

H13 tool steel was successfully prepared by selective laser melting(SLM)technology.The effects of heat treatment on the microstructure,mechanical properties,and tribological properties of SLMed H13 steel were investigated.The heat treatment process involved a solution treatment and a double aging treatment of the deposited H13 tool steel prepared by SLM.The aim is to optimize the microstructure and mechanical properties of SLMed H13 steel.Due to the rapid heating and cooling effects of SLM,carbide precipitation in the deposited H13 steel was not uniform and residual stresses were present.The purpose of the solution treatment is to dissolve the solution at a high temperature to eliminate the residual stresses and defects introduced by the SLM-forming structure.The solution treatment and first aging treatment produced the precipitation of small carbides at the grain boundaries and inside the crystals,which increased the hardness of SLMed H13 steel.The hardness increased from 538±4.0 HV of the as-deposited sample to 548±5.8 HV of samples after the first aging treatment.Accordingly,the ultimate tensile strength and the elongation at break decreased from 1882 MPa and 11.5%in the as-deposited sample to 1697 MPa and 7.9%in those after the first aging treatment,respectively.Furthermore,the friction coefficient and wear rate in the as-deposited sample decreased from 0.5160 and 2.36×10^(–6)mm^(−3)N^(−1)m^(−1)to 0.4244 and 1.04×10^(–6)mm^(−3)N^(−1)m^(−1),respectively.However,the distribution of carbides inside the crystals was not uniform.The second aging treatment adjusted the morphology of carbide precipitation and made it more uniform,but the precipitation of carbides grew and settled at the bottom of the grain boundaries.The hardness decreased to 533±6.7 HV compared with that with the first aging treatment,but the ultimate tensile strength and plasticity reached a balance(1807 MPa,14.05%).Accordingly,the friction coefficient and wear rate also showed a stable and decreasing trend(0.4407,0.98×10^(–6)mm^(−3)N^(−1)m^(−1)).

Influence of powder oxidation on powder properties and formability in H13 hot-work steels processed by electron beam melting

The oxygen content of metal powder is decisive for the recyclability of powder.The research on the effect of oxygen content on powder properties and material formability has practical significance for economical production with additive manufacturing while preventing the waste of resources.Here,we deliberately oxidized the powder by baking at high temperature to increase the oxygen content in the powder and gave the calculation method of the oxygen content in the powder oxidation film.The majority of oxygen element was found in the oxide particles in the powder and the oxide flm on the powder surface,which did affect the flowability of the powder.It is worth noting that the increase in the oxygen content does not change the phase of H13 steel,but it can promote the molten pool flow and obtain a smoother surface.The increase in the oxygen content in the powder is not the decisive factor for the formability and defects of the printed samples.It is the combined effect of the powder deformation,the increase in the oxygen content,and the impurity pollution after repeated use,which leads to the limitation of repeated utilization of the powder.