查看更多>>摘要：We have investigated the phase stability,mag-netic properties,and martensitic transformation thermo-dynamics/kinetics of the Ni24-xMn18+x+ySn6-y(x,y=0,1,2)system by combining the first-principles calculations and experiments.The calculation results show that the optimized lattice parameters are consistent with the experimental data.Respectively,we obtain the relation equation for the austenite formation energy(Eform-A)and Mn content(XMn):Eform-A=507.358XMn-274.126,as well as for the six-layer modulated(6M)martensite for-mation energy(Eform-6M)and Ni content(XNi):Eform-6M=-728.484XNi+264.374.The ternary phase diagram of the total magnetic moment was established.The excess Mn will reduce the total magnetic moment of 6M(Mag6M)and non-modulated(NM)(MagNM)martensites,with the following equations relating the total magnetic moment and Mn content:Mag6M=-15.905XMn+7.902 and MagNM=-14.781XMn+7.411,while the effect on austenite is complex.The variation of total magnetic moment is mainly dominated by the Mn atomic magnetic moment.The 3d electrons of MnSn(Mn at Sn sublattice)play an important role in magnetic properties from the perspective of the electronic density of states.Based on the thermodynamics of martensitic transformation,the alloys will likely undergo austenite(←→)6M(←→)NM transforma-tion sequence.Combining the thermodynamic and kinetic results,the martensitic transformation temperature decreases with x increasing and increases with y increasing.These results are expected to provide reference for pre-dicting the phase stability and magnetic properties of Ni-Mn-Sn alloys.
查看更多>>摘要：The effects of cryogenic treatment(CT)and tem-pering-cryogenic treatment(TCT)on the microstructure and properties of coarse-grained WC-10Co cemented carbides with different carbon contents were researched.The binder phase,WC mean grain sizes,W solubility in the binder,rel-ative magnetic saturation,densities,hardness,wear resistance and second phase precipitation of cemented carbides with different heat treatments were discussed.The results show that there are significant changes of microstructure and properties in the samples with CT and TCT,especially due to the pre-cipitation of metastable nanoparticles WxCoyCz in the binder during the heat treatments of CT and TCT.With the simul-taneous combination of microstructure and nanoparticle-re-inforced binder,a dramatically improved combination of hardness and wear resistance of the samples after TCT has been achieved.
查看更多>>摘要：A new two-step spark plasma sintering(TSS)process with low-temperature pre-sintering and high-tem-peraturefinal sintering has been successfully applied to prepare the tungsten-particle(Wp)-reinforced bulk metallic glass composites(Wp/BMGCs).Compared to normal spark plasma sintering(NS),the densification rate and relative density of Wp/BMGCs can be improved by selecting TSS with appropriate sintering pressure in the low temperature pre-sintering stage.However,the compressive strength and plastic strain of 30％Wp/BMGCs prepared by TSS are both higher than those of the samples prepared by NS.The TSS process can significantly enhance the compressive strength of 30％Wp/BMGCs by 12％ and remarkably increase the plastic strain by 50％,while the trend is completely opposite for 50％Wp/BMGCs.Quasi-in situ experiments and finite element simulations reveal that uneven temper-ature distribution among particles during low-temperature pre-sintering causes local overheating at contact points between particles,accelerating formation of sintering neck between particles and plastic deformation of Wp.When the volume fraction of Wp is low,TSS can improve the interface bonding between particles by increasing the number of sintering necks.This makes the fracture mode of Wp/BMGCs being predominantly transgranular fracture.However,as the volume fraction of Wp increases,the adverse effects of Wp plastic deformation are becoming more and more prominent.The aggregated Wp tends to form a solid"cage structure"that hinders the bonding between particles at the interface;correspondingly,the fracture behavior of Wp/BMGCs is mainly dominated by intergranular fracture.Additionally,reducing the sintering pressure during the low-temperature pre-sintering stage of TSS has been shown to effectively decrease plastic defor-mation in Wp,resulting in a higher degree of densification and better mechanical properties.
查看更多>>摘要：(Zr0.53Al0.1Ni0.05Cu0.3Ti0.02)99Y1(at％)coating with amorphous layer of about 180 μm thick was prepared on a steel substrate by using laser cladding method.The coating is compact and shows good metallurgical bonding with substrate.The microstructure,microhardness and corrosion behavior along the depth from the coating sur-face to the substrate were investigated.It is found that a gradient structure consisted of amorphous surface layer,amorphous-crystalline transitional layer and substrate is formed after the laser cladding.The microhardness and corrosion behavior exhibit variation with the microstruc-tural evolution at different depths from the coating surface.The microhardness and corrosion resistance in 3.5 wt％NaCl solution of the amorphous surface layer are compa-rable to those of the as-cast Zr-based BMG with the same composition,and higher than those of the steel substrate.
查看更多>>摘要：To improve the wear performance of CoCrA-lYTa coating,part of the carbon nanotubes(CNTs)chemically reacted with Ta to form reinforcement phase(TaC),while the other CNTs were retained as lubrication phase.Subsequently,the CoCrAlYTa-xCNTs(x=0,1,2,and 4;wt％)composite coatings were prepared by laser-induction hybrid cladding(LIHC),and the microstructure and wear resistance of coatings were systematically ana-lyzed.Results show that the coatings are mainly composed of TaC,y-(Co,Cr)and β-(Co,Cr)Al.As the CNTs content increases from 0 wt％ to 4 wt％,the volume fraction of TaC increases from 13.11 vol％ to 16.12 vol％.Meanwhile,the nano-hardness of y-(Co,Cr)and β-(Co,Cr)Al are improved from 7.49 and 9.72 to 9.36 and 11.19 GPa,respectively.As a result,the microhardness of coating increases from HV 536.25 to HV 738.16,the wear rate decreases from 32.4 x 10-3 to 6.1 x 10-3 mg·m-1,and the average fric-tion coefficient decreases from 0.55 to 0.44.The good wear performance of the coating is attributed to the formation of TaC and the existence of remained CNTs lubricant film.
查看更多>>摘要：Superior compound coatings were prepared on CK45 steel surface by vanadium-nitrocarburizing duplex treatment in low-temperature salt bath.In this study,the microhardness,the phase constitution and the composi-tional distribution in the coatings prepared under different conditions were systematically characterized.The results indicated that the reactions among activated vanadium,carbon and nitrogen atoms occurred on the steel surface,leading to the formation of compound coatings composed of outermost and compound layers.The mechanism for the formation of compound layer as well as the growth kinetics of the layer was also discussed.Upon the duplex treatment,the wear and corrosion resistances of steel surface were significantly improved.It was found that the growth kinetics of compound layer obeyed the parabolic law,with the activation energy of 122.82 kJ·mol-1.
NETL
NSTL
万方数据