查看更多>>摘要：The effect of adding MgO nanoparticles(0％,0.01％,0.05％,and 0.10％)on the inclusion and acicular ferrite(AF)formation in 1.8％Ni low carbon Al-killed(LCAK)steel was explored.The inclusion analysis reveals that MgO nanoparticles react with dissolved Al or Al2O3 inclusions and finally change to fine MgAl2O4 wrapped by MnS in the case of adding 0.05％MgO nanoparticles.In contrast,MgO nanoparticles are agglomerated and form Mg-bearing inclusion clusters in the case of 0.10％or reduced to high Al2O3 inclusions by dissolved Al in the case of 0.10％.The microstructure observations show that the AF formation was promoted in the case with addition of 0.05％MgO nanoparticles.The process of inclusion-inducing AF nucleation is essentially characterized via the high-temperature confocal scanning laser micro-scopy experiment.δmin(δ denotes disregistry)of Al2O3/α-Fe,MgAl2O4/α-Fe,and MnS/α-Fe is evaluated to be 11.5％,6.5％,and 7.4％,respectively.The high AF fraction in the case of 0.05％MgO addition can be attributed to the low disregistry of MnS-MgAl2O4/ferrite and Mn-depleted zone adjacent to the MnS layer.Based on the results,0.05％was recommended as the proper addition amount of MgO nanoparticles in 1.8％Ni LCAK steel.
查看更多>>摘要：The distinctive distribution of acoustic emission(AE)characteristic parameters generated during tensile testing of low-temperature tempered AISI4140 steel was investigated.Two clusters of acoustic emission signals were distinguished using power-law distribution fitting and k-means clustering methods.These clusters were identified as resulting from dislocation motion during yielding and dislocation entanglement during uniform plastic deformation.The conclusion is further confirmed by transmission electron microscopy images at different strains.In particular,the unique"arch-shaped"dis-tribution of the acoustic emission energy during yielding implies a change in unusual dislocation motion modes.The effect of carbide precipitation was qualitatively discussed as not considering the primary cause of the formation of this arch-shaped distribution.The evolution of dislocation motion modes during yielding of low-temperature tempered martensite was elucidated by comparing the significant difference in cumulative energy values during yielding of annealed and low-temperature tempered specimens.Dislocations emit from Frank-Read or grain boundary sources and slip along short free paths,contributing to the initial increase in AE signals energy.Subsequently,the primary source of acoustic emission energy"arch-shaped"peak during yielding was generated by the avalanche behavior of accumulated dislocations,leading to the accelerated dislocation motion.
查看更多>>摘要：The second phase dissolution and elements migration behavior of a nickel-based single crystal superalloy during solution heat treatment with direct current were investigated for simplifying and shortening the solution heat treatment of the Ni-based single crystal superalloy.The results showed that the electric current solution heat treatment improved microstructural homogenization as well as the distribution of alloying elements,especially for the refractory metal W and Mo.The microsegregation ratios for Mo and W after electric current solution heat treatment at 1230 ℃ for 4 h are near those without electric current at 1250 ℃ for 4 h.The electric current accelerated the yphase dissolution process,and the yphase could be completely dissolved at a lower treatment temperature or within a shorter treatment time under electric current solution heat treatment with direct current.A microcosmic current model was proposed to analyze the effect of the electric current on the solution heat treatment of the Ni-based single crystal superalloy.
查看更多>>摘要：Si3N4-TiN-SiC composites were prepared by partial substitution of the Ti-Si-Fe alloy extracted from high-titanium blast furnace slag for Si under nitrogen atmosphere.The nitridation,microstructure and mechanical properties of the composites were investigated in detail.The results show that Ti-Si-Fe alloy facilitated the nitridation of Si and full nitridation of Si was achieved in the compacts with 3.6-5.4 wt.％Ti-Si-Fe alloy additive,and thus,densification and mechanical per-formances of the composites were improved obviously.Propagating of microcracks induced by the volume expansions accompanying with the conversion of Ti5Si3 and TiSi2 to nitrides at 950-1050 ℃ built new N2(g)transport channels in the compacts.In the following up nitridation process,adequate N2(g)was transported through these channels into the compacts to fundamentally enhance contact of N2 with Si,facilitate and ensure the complete nitridation of internal Si.Moreover,the Ti-Si-Fe-Mn-N eutectic liquid played an important role in the formation of both α-and β-Si3N4,and the Fe in the Ti-Si-Fe alloy was of great importance for the formation of fibrous Si3N4 by the reaction between SiO(g)and N2(g).
查看更多>>摘要：MnAl rare-earth-free permanent magnets exhibit excellent advantages from economic and resource perspectives,which have attracted extensive attentions in recent decades.We reported the evolution in phase formation and intrinsic magnetic properties of τ-phase in binary MnAl alloys with the variation in Mn:Al ratios.Ferromagnetic τ-phase can be generated within the compositional range of Mn50+xAl50-x(x=1-8),and pure τ-phase can only be obtained in the alloys with x=4-7.With Mn:Al ratio increasing,saturation magnetization Ms and magnetocrystalline anisotropy constant K1 are gradually weakened due to the incremental antiferromagnetic Mn-ldatoms,but Curie temperature of τ-phase is gradually increased induced by the strengthened d-d hybridization of Mn1a-Mn1d.An attempt of doping traces of Ti was carried out in order to eliminate the negative antiferromagnetic interaction derived from Mn-1d atom.Ti atoms tend to occupy 1d sites and replace the Mn-ld atoms due to the relatively fewer valence electrons compared with Mn,resulting in the reduction in Mn1a-Mn1d antiferromagnetic interactions,which is demonstrated by the higher Ms of Mn55-yAl45Tiy(y=1)than that of Mn55Al45.However,with further substitution of Mn by Ti,unfavorable κ-phase is unavoidably generated.Finally,the occupation preference and the corresponding influences on local magnetic interactions as well as the magnetizations of the different alloying atoms including interstitial element C,3d atoms Ti,Co and Cu,and main-group element Ga are systematically summarized,in order to offer the guidance of designing MnA1 permanent magnets with ideal magnetic properties.
查看更多>>摘要：In order to analyze the influence of the distance between heat sources(DLA)on the welding process,the effects of DLA on the droplet transfer behavior,weld formation characteristics and weld formation mechanism of AH36 in laser and cable-type welding wire gas metal arc welding arc hybrid welding were studied.Real-time photography was conducted using a high-speed camera to determine the droplet transfer and arc behaviors;the surface morphology and macroscopic cross-section of the weld obtained from the experiment were observed and analyzed.The arc height decreases with the increase in the DLA,the arc width shows the opposite change,and the welding current decreases.The allure of the laser to the arc increases with the increase in the DLA.The frequency of droplet transfer increases with the increase in the DLA,but the growth rate decreases.The continuous increase in the DLA leads to the tendency of the droplet size to decrease first and then increase,and the minimum value is obtained when the DLA is 4 mm.The DLA has obvious influence on the weld formation.The weld penetration and reinforcement change similarly,increasing first and then decreasing as the DLA increases,and the laser area of the weld also increases first and then decreases.
查看更多>>摘要：To achieve the new strategy of low cost and outstanding property,friction stir welding(FSW)was used to join AA2219-T6 alloy and AA2195-T8 alloy.The relationship between macro/microstructure and nanomechanical properties was estab-lished by using a nanoindentation instrument.During FSW,the grains in stir zone were refined by recrystallization,and the main mechanism of recrystallization was continuous dynamic recrystallization and geometric dynamic recrystallization.The overall micro-hardness value of AA2195 alloy was higher than that of AA2219 alloy due to the strength of the material,and the decrease in hardness value is attributed to the dissolution and coarsening of precipitation.Each zone of the dissimilar joint showed obvious indentation size effect,and the highest nano-hardness values of 2219-base metal(BM)and 2195-BM zones were 1.42 and 1.71 GPa,respectively.The nano-hardness is closely related to the precipitation behavior and follows the same law as the distribution of micro-hardness.The creep mechanism was mainly dislocation slip.The combined action of grain boundary,dislocation,and coarse precipitation can affect creep resistance,in which coarse precipitation plays a dominant role.
查看更多>>摘要：The effect of the amount of isothermal martensite and bainite on the microstructure and properties in a medium-carbon quenching and partitioning(Q&P)steel was investigated by designing the different Q&P treatment parameters.The results show that the amount of isothermal martensite increased gradually with the increase in quenching time.The increase in isothermal martensite amount improved the product of strength and elongation(PSE)of Q&P steels.In addition,the increase in carbides amount and the recovery in prior martensite with longer partitioning time led to an increase in PSE first and then,a decrease.It implies that a higher PSE could be obtained by the selection of a suitable partitioning time.Furthermore,the effect of bainite transformation during partitioning on PSE was investigated by designing the different partitioning temperatures,including 300,400(below bainite starting temperature,Bs)and 480 ℃(above Bs).The results show that compared with the samples partitioned at temperature above Bs,the bainite transformation was only detected when the samples were partitioned at temperature below Bs.The bainite transformation amount increased with the decreasing partitioning temperature,leading to the inhibition of carbides precipitation and more stable RA and thus,resulting in the highest PSE.
查看更多>>摘要：In order to elucidate the mechanism of the effect of Ta content on the high temperature behaviour of the alloys,the high temperature oxidation and thermal corrosion experiments were carried out on the three alloys with different Ta contents(2.72,3.10 and 4.00 wt.％).The results of high temperature oxidation and hot corrosion show that because Ta has a higher valence state than Al,it can reduce the indiffusion of O,and the rate at which Ta diffuses within the alloy matrix is relatively slow since it has a larger atomic radius.As a result,the diffusion of the Al element is inhibited as the Ta content increases.Therefore,adding Ta inhibits the formation of Al2O3 in the surface oxide and promotes the formation of Cr2O3.Thus,Ta promotes oxidised film growth on the sample surface,which inhibits the diffusion of S,O and other elements into the matrix.Additionally,Cr2O3 is not easy to dissolve in molten salt,which ultimately makes the alloy have high oxidation resistance and thermal corrosion resistance.
查看更多>>摘要：A novel Fe-Cr-Mo amorphous coating,a high-temperature corrosion-resistant material for water wall protection of power plant ultra-supercritical boilers,has been prepared via arc spraying.A systematic study was conducted to evaluate the high-temperature corrosion behavior of this coating,and its resistance to corrosion at high temperatures was scientifically assessed.The results indicate that the thickness of Fe-Cr-Mo amorphous coating is approximately 350 μm,exhibiting typical amorphous characteristics as confirmed by X-ray diffraction and transmission electron microscope characterization.During each stage of the 750 ℃ corrosion test,the oxygen content of the amorphous coating was significantly lower than that of the contrast coating(PS45 alloy coating),indicating a superior corrosion protection effect at high temperature.After 100 h of continuous testing,the corrosion mass gain of the amorphous coating was only 28.62％that of PS45 coating and 3.89％that of T12 steel substrate,indicating significantly depressed high-temperature corrosion kinetics.The excellent high-temperature corrosion resistance of Fe-Cr-Mo amorphous coating is primarily attributed to the stable Fe/Cr oxide film generated by the metastable state of the amorphous state,which serves as an excellent barrier.Furthermore,under the influence of heat in a high-temperature environment,the amorphous structure gradually transforms into a nanocrystalline structure.In contrast,the oxide film of the amorphous/nanocrystalline coating has low thermal stress,leading to better adhesion with the coating and resistance to cracking and peeling,thus providing excellent sustained protection.
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