查看更多>>摘要：The oxidation behavior of the AlCoCrFeNiY-Tax high entropy alloy(HEA)doped with different Ta contents at 1100 ℃ is investigated.In this study,different reasons for the spallation of the oxide scales of HEAs without/with excessive Ta addition after 1000 h of oxida-tion are discussed,and the most suitable Ta doping content for this HEA is explored,in which the HEA exhibits both an exceptionally low oxidation rate,and the formation of oxide scales composed of intact α-Al2O3.Meanwhile,it is found that the addition of Ta can effectively inhibit the phase transition of β phase,which makes the surface of the oxide scale smoother.By combining our experimental results with Wagner-Hauffe theory,the influence of Ta drag effect on oxide scale growth is explained,which provides some theoretical guidance for the subsequent design of AlCoCrFeNi HEAs,and can lead to the devel-opment of thermal barrier coatings at higher service temperature.
查看更多>>摘要：Designing microstructures and unveiling dynamic erosion mechanisms remain important challenges for Ag-based contacts.To simultaneously enhance erosion and compression resistance,an AlCoCrFeNi high-entropy alloy(HEA)is introduced into Ag-based materials to fab-ricate novel Ag-HEA contacts with island-and skeleton-restricted microstructures.The arc erosion experimental results reveal that the skeleton-restricted HEA microstructure is the key factor in reducing the hill and crater morphologies of the contact surface,effectively delaying material transfer between the movable and sta-tionary contacts.The molten bridge evolution and com-pressive deformation behavior of Ag-HEA contacts with various microstructures are investigated using molecular dynamics(MD)simulations.MD results indicate that the constraint of Ag atom diffusion in the molten pool and the involvement of HEA atoms in the molten bridge are the primary mechanisms for improving erosion resistance.The skeleton-restricted HEA microstructure reduces the total energy and structural stability of the molten bridge system and promotes its fracture and disintegration.Moreover,the synergistic effect of the twin and Lomerz-Cottrell lock structures can hinder dislocation glide,generating dis-persed and small-area stacking faults in the Ag matrix and mitigating the concentration of shear strains.Thus,the skeleton-restricted HEA microstructure contributes posi-tively to compression resistance.This study presents a novel approach to designing Ag-based contacts.
查看更多>>摘要：Cryogenic pre-deformation treatment has been widely used to effectively improve the comprehensive mechanical properties of steels and novel metals.However,the dislocation evolution and phase transformation induced by different degrees of deep cryogenic deformation are not yet fully elucidated.In this study,the effects of multiple cryogenic pre-treatments on the mechanical properties and deformation mechanisms of a paramagnetic Fe63.3Mn14-Si9.1Cr9.8C3.8 medium-entropy alloy(MEA)were investi-gated,leading to the discovery of a pretreated MEA that exhibits exceptional mechanical properties,including a fracture strength of 3.0 GPa,plastic strain of 26.1％and work-hardening index of 0.57.In addition,X-ray diffrac-tion(XRD)and transmission electron microscopy(TEM)analyses revealed that multiple cryogenic pre-deformation treatments significantly increased the dislocation density of the MEA(from 9 × 1015 to 4 × 1016 m-2 after three pre-treatments),along with a transition in the dislocation type from predominantly edge dislocations to mixed disloca-tions(including screw-and edge-type dislocations).Nota-bly,this pretreated MEA retained its paramagnetic properties(µr＜1.0200)even after fracture.Thermody-namic calculations showed that cryogenic pretreatment can significantly reduce the stacking fault energy of the MEA by a factor of approximately four(i.e.,from 9.7 to 2.6 mJ·m-2),thereby activating the synergistic effects of transformation-induced plasticity,twinning-induced plas-ticity and dislocation strengthening mechanisms.These synergistic effects lead to simultaneous strength and duc-tility enhancement of the MEA.
查看更多>>摘要：This study examines the microstructure,mechanical properties(with a focus on room-temperature toughness),and oxidation resistance of Ho-doped Nb-Si based in-situ composites.The base alloy consists of the coarse primary Nb5Si3 phase and the Nb5Si3+Nbss(Nb solid solution)eutectic cells.Ho doping influences the solidification path.When the Ho doping is higher than 0.2 at％,the alloys transform into eutectic alloys.Ho can be solid-solved in trace amounts in the Nbss phase.How-ever,most of Ho forms a stable Ho oxide phase,which alleviates oxygen contamination problem to some extent.Moreover,the interface separation between Ho oxide and other phases reduces the plastic deformation constraint.Thus,with 0.4 at％Ho doping,the KQ value is 18.03 MPa·m1/2,which is 31.1％higher than that of the base alloy.The strength of the Ho-doped alloys does not deteriorate with an increase in toughness.However,the large network-like Ho2O3 in the 0.8Ho alloy causes a decrease in toughness and strength.In addition,the Ho oxide phase effectively blocks the inward oxygen intrusion.With 0.8 at％Ho doping,the oxidation mass gain per unit area is 10.16 mg-cm2,which is 39.7％lower than that of the base alloy.
查看更多>>摘要：The high-temperature oxidation behavior of novel Co-Cr-Nb-W carbide-strengthened wear-resistance alloys with different Al contents(1wt％,2wt％and 3wt％)at 950,1000 and 1050 ℃ was thoroughly investigated by scanning electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy and field emission electron probe analyzer.The porous property of NbC in-situ oxi-dation products(Nb2O5,CoNb2O6 and Co4Nb2O9)induces a multi-layered oxide scale with micropores and cracks.Co-Cr-Nb-W alloy with 1 wt％Al undergoes catastrophic oxidation and spalling above 1000 ℃.The outward transportation of Cr and Co is effectively restrained by a continuous Al2O3 scale formed around NbC in-situ oxi-dation region when Al content reaches 3 wt％.The β-CoAl in Co-Cr-Nb-W alloy with 3 wt％Al has an oxidation priority over eutectic carbides and the alloy matrix which are both enriched with Cr,thereby preventing the formation of Cr-depletion area and improving the self-healing ability of the oxide film.A slight change in Al content has a remarkable influence on the cooperative effect of Al and Cr and multiplies the antioxidant capacity of Co-Cr-Nb-W alloy above 1000 ℃.
查看更多>>摘要：This study entailed an investigation of the mechanical properties,microstructural and texture orien-tation evolutions of Cu-Cr-Co-Ti alloys prepared via two-stage cryorolling and intermediate aging treatment.To this end,X-ray diffraction and electron backscatter diffraction were employed.The results indicate that the two-stage cryorolling and intermediate aging treatments led to the development of profuse twin bundles and significantly enhanced the mechanical properties.The initial cryorolling led to coplanar slip and developed a strong Y({111}<112>)orientation,accelerating the formation of Goss({011}<100>)orientation and a Brass-type texture.The intermediate aging treatment relieved the restriction on dislocation slip and reoriented the grains toward the Cop-per({112}<111>)and Z({111}<110>)orientations.The Z orientation,with a relatively high volume fraction,dominated the macrotexture.Secondary cryorolling intensified twinning and shear banding,transforming the Copper-type shear bands into Brass-type shear bands with rhomboidal prism morphology.The areas inside the Brass-type shear bands exhibited a Y orientation,and the areas outside the shear bands exhibited a stable Brass-type tex-ture.The evident decrease in the weighted Schmid factors demonstrated that the two-stage cryorolling and interme-diate aging treatment can modify the texture evolution and aid the design of high-performance Cu alloys.
查看更多>>摘要：Laser powder bed fusion(LPBF)is considered to be one of the most promising additive manufacturing technologies for producing components with geometries and high geometrical precision that are unattainable by traditional technologies.The superalloy exhibits excep-tional mechanical and high-temperature performances,rendering it a prime candidate for advanced aero-engine applications.Despite the high demand for LPBF-manu-factured superalloys,the superalloy is one of the materials manufactured difficultly by LPBF due to their large laser absorptivity fluctuation,poor molten pool stability and sharp temperature gradient.Hence,superalloys are char-acterized by severe pores,undesirable coarse columnar grains and poor mechanical properties.In this work,the effect of nano-TiN particles on defects,molten pool char-acteristics and microstructure and performance of the composites were investigated.The 4.5 wt％TiN/Haynes 230 samples exhibited exceptional nanohardness and elastic modulus with maximum values reaching 5.53 GPa and 240.03 GPa,respectively.These superior mechanical properties were attributed to the combined effects of spatter and gas pore inhibition,grain refinement and duplex nano-phases strengthening.Moreover,the stability of molten pool was enhanced,and spatter was effectively suppressed by adding nano-TiN particles,while grain refinement and columnar to equiaxed transitions were promoted.Further-more,the matrix exhibited a high dislocation density due to a significant hindrance of dislocation movement caused by massive nano-phases(e.g.,TiN and M23C6),resulting in the formation of extensive dislocation tangles and rings.This work offers novel insights into the role of nanoparti-cles reinforced superalloy composites by LPBF.
查看更多>>摘要：In this paper,Si coatings were sprayed onto C/SiC composite substrates by atmospheric plasma spray-ing(APS).The high-temperature oxidation behavior of the substrate and coating at temperatures of 1100 and 1300 ℃was also studied.The C/SiC ceramic matrix composite will be damaged seriously and even failed due to the oxidation of carbon fibers in matrix.The Si coating effectively improved the oxidation resistance of the C/SiC substrate in the high-temperature oxidation test.The effect of the thickness of the Si coatings on the oxidation resistance was investigated.The 150-pm coating is proved to enable the substrate to have the lowest oxidation weight loss and the best oxidation resistance after static oxidation for 5 h.
查看更多>>摘要：The present study has proposed a compact process for the production of high-purity β-Ga2O3 powder by simply using gallium metal and water as the raw materials.The process basically consists of two essential steps including hydrothermal synthesis of GaOOH and calcination of GaOOH for the production of the target product of β-Ga2O3.Thermodynamic evaluation and sys-tematic experiments were conducted for process parameter optimization.X-ray diffractometer(XRD),scanning elec-tron microscopy(SEM),thermogravimetry-differential scanning calorimetry(TG-DSC)and X-ray photoelectron spectroscopy(XPS)were utilized to clarify the reaction mechanisms of the hydrothermal synthesis and transfor-mation of GaOOH to β-Ga2O3 by calcination.Chemical analysis of the final product of β-Ga2O3 obtained under the optimal conditions was carried out with inductively cou-pled plasma mass spectrometry(ICP-MS),and the results showed that the contents of the representative impurities such as Ni,Cu,In,Mn,Co,Zn and Cr are obviously lower than the requirement of 5N β-Ga2O3 standard,exhibiting excellent application prospect of the proposed process to produce high-purity β-Ga2O3.
查看更多>>摘要：Poly-p-anisidine could be easily fabricated via the oxidative polymerization reaction of p-anisidine using H2O2 as the green oxidant.It was unexpectedly found that zinc doping could significantly improve the adsorption ability of the material versus heavy metals such as Pb,Cu,Pd,Ag and Hg.Results of nitrogen adsorption-desorption experiments demonstrated that Zn doping could enhance the specific surface area and mesopore amount of the prepared material,which might facilitate its absorption to metals.This work not only provides a novel material for the treatment of heavy metal-polluted water but also leads to a nice mesoporous catalyst support for environment protection and organic synthesis,i.e.the Zn-doped poly-p-anisidine can be employed as the catalyst support to pre-pare Cu@PANI-OMe/Zn or Pd@PANI-OMe/Zn for the oxidative degradation reaction of phenol or Suzuki-Miyaura coupling reactions,respectively.It discloses a new strategy for fabricating the mesoporous polyaniline materials with profound application potential.
NETL
NSTL
万方数据