Microstructure and mechanical properties of rapidly solidified Al-Cr alloys

The microstructure and mechanical properties of rapidly solidified Al-Cr alloys were investigated by XRD, TEM and microhardness testing instrument. The results indicate that the matrix of rapidly solidified Al-Cr alloys is α-Al solid solution when the Cr content is lower than 4 wt%. However, when the Cr content is above 4 wt%, the microstructures of rapidly solidified Al-Cr alloys are different along cross section. The microstructure of alloy contacting copper roller consists of α-Al and a few intermetallic compounds. With the increase of distance from copper roller, the matrix consists of α-Al and spherical intermetallic compounds which conglomerate in α-Al matrix. These intermetallic compounds are Al₇Cr, Al₁₁Cr and Al₄Cr. The tensile strength has the maximal value when the Cr content is about 8 wt%. The annealed microstructures show that supersaturated α-Al solid solution dissolved with increasing anneal temperature. The starting temperature of the second phase precipitated from the supersaturated α-Al solid solution desponds on the supersaturation. Meanwhile, the microhardness of rapidly solidified Al-Cr alloy reaches maximal value after annealing at 300 °C. Funded by the Innovation Fund for Outstanding Scholar of Henan Province (No. 0621000700)     

Devitrification behaviour of rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy prepared by melt spinning method

Rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy was prepared by using melt spinning. Its calorimetric behavior was characterized by using differential scanning calorimeter in a continuous or isothermal heating mode. phase transformation was investigated, with a special interest in primary crystallization, by using an in-situ examination of X-ray diffractometry （XRD） and high resolution transmission electron microscopy （HRTEM）. The results show that, the whole devitrification of rapidly solidified Al87NiyCu3Nd3 amorphous alloy involves two main processes of primary crystallization and secondary crystallization that consist mainly of two reactions. For primary crystallization, the apparent activation energies, EIso and EKis and growth activation energies Eg are about 153, 166 and 288 kJ/mol, respectively. The interdiffusion of Al atoms is a rate-controlled step of formation of the a（Al） particles, but slow diffusion of Ni and Nd atoms plays a significant role in retarding growth of the α （Al） particles. For secondary crystallization, EIso, EKis and Eg of the first reaction are about 291,208 and 290 kJ/mol, and those of the second reaction are about 367, 269 and 372 kJ/mol. The two reactions of secondary crystallization are controlled mainly in an interface-controlled three-dimensional mode, depending mainly on slow diffusion of Ni and Nd atoms.     

Microscopic phase-field simulation of Cr atom substitution character during formation of Ll2 and DO22 phases in Ni-Cr-Al alloy

The simulations of Cr atom substitution character during the formation of L12 and DO22 phases in Ni-Cr-Al alloy were performed at 873 K based on microscopic phase-field model. It is found that the substitution of Cr is affected by Cr and Al contents and limits of occupation probabilities of Cr atom in L12 phase are present. The precipitate is single L12 phase when the component is less than the limit, Cr atoms substitute the Al sublattices in Ll2 phase, and both of atoms Al and Cr occupy the β-sites and complex phases Ni3（Al1-xCrx） are formed; Cr atoms enter Ni sites when Al and Cr contents exceed the limit, and substitute β-sites or both of α- and β-sites. The DO22 phase is formed at the boundary of Ll2 phase.     

Statistical values of valence electron structure parameters applied to research on phase transition temperature and eutectoid reaction of titanium alloy

Based on the empirical electron theory of solids and molecules (EET), the statistical values of valence electron structure parameters Sn _A and SE _A which can characterize the properties of alloy phases are calculated, and influences of alloying elements (e.g., V, Nb, Mo, Hf, Zr, Fe, Mn, Co, Cr, Si, and so on) on the phase transition temperature and eutectoid reaction of titanium alloy are discussed with the statistical values of valence electron structure parameters. The research results agree well with real situations. Supported by the National Natural Science Foundation of China (Grant No. 50471022, 50741004) and National Key Basic Research Program of China (“973”) (Grant No. 2007CB613807)     

Microscopic phase-field simulation for coarsening behavior of L12 and DO22 phases of Ni75Cr x Al25? x alloy

Based on the microscopic phase-field dynamic model and the microelasticity theory, the coarsening behavior of L1₂ and DO₂₂ phases in Ni₇₅Cr _x Al_25−x alloy was simulated. The results show that the initial irregular shaped, randomly distributed L1₂ and DO₂₂ phases are gradually transformed into cuboidal shape with round corner, regularly aligned along directions [100] and [001], and highly preferential selected microstructure is formed during the later stage of precipitation. The elastic field produced by the lattice mismatch between the coherent precipitates and the matrix has a strong influence on the coarsening kinetics, and there is no linear relationship between the cube of the average size of precipitates and the aging time, which does not agree with the results predicted by the classical Lifshitz-Slyozov-Wagner. The coarsening processes of L1₂ and DO₂₂ phases are retarded in elastically constrained system. In the concurrent system of L1₂ and DO₂₂ phases, there are two types of coarsening modes: the migration of antiphase domain boundaries and the interphase Ostwald ripening. Foundation item: Project(50671084) supported by the National Natural Science Foundation of China; Project(20070420218) supported by China Postdoctoral Science Foundation     

Electronic structure and FIM imaging mechanism of Fe-Al intermetallic compounds

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Simulation of the precipitation process of Ni75AixV25-x alloys incorporated in the microelasticity field

The microelasticity field was incorporated into the microscopic phase-field equation for the ternary alloy systems, the morphology evolution and coarsening behavior of the Ni75AixV25-x alloy were simulated. The γ phase precipitates initially for Ni75Al7aV17.9 and Ni75Al5.5V19.5 alloys and the two phases transform from the equiaxed or strip-like to the quadrate as the growth and coarsening processes. For the anisotropic elasticity interaction of the system, the orientation of γ is along the 〈001〉 directions and the θ phase is along the short axis direction of [10]. Analysis of the structure and the pair-correlation functions indicate that the average precipitate length scale of the particles increases at the late-stage coarsening, and the dynamical scaling behavior is obeyed.     

AFM research on Fe-based nanocrystal crystallization mechanism

The cross-section pattern of Fe-based alloy ribbon (Fe_73.5Cu₁Nb₃Si_13.5B₉) annealed at different temperatures was investigated by AFM (atomic force microscope), and the effect mechanism of Nb and Cu in Fe-based alloy ribbon annealing was analyzed with XRD diffraction crystal analysis technique and other research results. New concepts of encapsulated grain, Nb vacancy cluster, Nb-B atom cluster and so on were proposed and used to describe the formation mechanism of α-Fe (Si) nanocrystal. Finally, a three-phase (separation phase, encapsulated phase and nanocrystalline phase) interconnected structure model in Fe-based nanocrystalline alloy was established. Supported by the Natural Science Foundation of Zhejiang Province (Grant No. Y405021), Zhejiang Provincial Science and Technology Key Project (Grant No. 2006C21109) and Key Project of Science and Technology Research of China Ministry of Education (Grant No. 204059)     

Effects of Si and Ce on the microstructure and hydrogen storage property of Ti_(26.5)Cr_(20)V_(45)Fe_(8.5)Ce_(0.5) alloy

In this paper, the effects of Si and Ce on the microstructure and hydrogen storage property of Ti26.5 Cr20V45Fe8.5Ce0.5 alloy were studied, respectively. First of all, effects of Si on the microstructure and hydrogen storage properties of Ti26.5Cr20(V45Fe8.5)1?xSixCe0.5 (x = 0, 0.5, 1.0, 1.5 and 2.0 at%) alloys were studied by X-ray diffraction, scanning electron microscopy and P-C isotherm measurements. As the Si addition increases, the hydrogen absorption capacities of alloys decrease but the equilibrium pressure increases, due to the formation of Laves phase. Secondly, the effect of Ce on Ti26.5Cr20 (V45Fe8.5)0.98Si2 alloy was studied. It was found that Ce addition is an effective way to eliminate the effect of Si on the hydrogen storage properties of the alloy.     

Devitrification process in rapidly solidified Al-Ni-Cu-Nd metallic glass

In the present study, rapidly solidified ribbons of A187 Ni7 Cu3 Nd3 metallic glass was prepared by using melt spinning. Devitrification process of the totally amorphous ribbons was investigated by high temperature X-ray diffraction analysis, combining with differential scanning calorimetry, under continuous and isothermal heating regime. The X-ray diffraction intensity and full width at the half maximum (FWHM) were analyzed to investigate the increase of crystallized amount and growth of α-Al crystal particles. The results show that under continuous heating regime, the metallic glass devitrifies via two main stages: primary crystallization, resulting in two-phase mixture of α-Al plus residual amorphous phase, and secondary crystallization, corresponding to rapid precipitation of some inter-metallic phases in the form of dispersion or eutectic mixture. Under isothermal heating regime, only Al crystal precipitates from the Al-rich amorphous matrix at low temperature, and when heating at 280 ℃ only Al     

Effect of trace La addition on the microstructure and mechanical property of as-cast ADC12 Al-Alloy

The effects of addition of La on the microstructure of as-cast ADC12 Al-Alloy were investigated by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy disperse spectroscopy (EDS). The experimental results showed that the a-Al and eutectic Si crystals were modified with the addition of 0.3 wt% La. The eutectic Si crystals showed a granular distribution. At the same time, the alloy possessed the best mechanical property. When more than 0.3 wt% La was added to ADC12 aluminum alloy, the microstructure of as-cast alloy was coarsening gradually with the increase of the content of La and the mechanical property decreased. The effect of rare earth La which was added in ADC12 Al-Alloy for up to 0.9 wt% had been investigated in this study. The dendrites of ADC12 Al-alloy was refined obviously and the morphology of Si crystals showed a particle structure when the addition of La reached 0.3 wt%. Besides, the acicular La-rich intermetallics in the alloy deteriorated the mechanical property of alloy. To avoid this unwanted phase, the amount of added rare earth La must be less than 0.6 wt%.     

Micro-inhomogeneous structure of liquid Al-Fe alloys

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Preparation and sintering of nano Fe coated Si3N4 composite powders

Fe/Si₃N₄ composite powder was synthesized by the heterogeneous precipitation-thermal reduction process, and then pressed into flakes under a pressure of 10 MPa. Flakes were sintered by pressureless and hot-pressing at 1 600 °C under 0.1 MPa N₂. The chemical composition, phases and microstructure of composite powder and sintered flakes were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the structure of composite powders is Si₃N₄ coated by nano Fe. The crystal phases of sintered flakes by pressureless are Fe(Si) compound, SiC and Si₃N₄. The crystal phases of the sintered samples by hot-pressing are Fe, Fe(Si) compound and Si₃N₄. It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different. Foundation item: Project(50804016) supported by the National Natural Science Foundation of China     

Melt-spun Al<Subscript>70−<Emphasis Type="Italic">X</Emphasis></Subscript>Si<Subscript>30</Subscript>Mn<Subscript><Emphasis Type="Italic">X</Emphasis></Subscript> (<Emphasis Type="Italic">X</Emphasis>=0, 3, 5, 7, 10) anode in lithium-ion batteries

Al_70−X Si₃₀Mn _X (X=0, 3, 5, 7, 10, mol%) ribbons were prepared by melt spinning. A supersaturated solid solution of Si and Mn in fcc Al and some microstructures consisting of nano grains were obtained. Some alloys with nano-sized grains exhibited high discharge capacities and favorable cycle properties. The capacity of more than 400 mAh/g could be obtained in melt-spun Al₆₇Si₃₀Mn₃ alloy after 20 cycles and more than 300 mAh/g after 40 cycles. Li/Si and Li/Al compounds in the anodes of pure Al and pure Si were not detected in Al-Si-Mn alloys inserted by Li. It is considered that the formation of the supersaturated solid solution and refinement of microstructures have prevented the alloys from the forming the compounds with superfluous Li. As a result, the electrochemical properties have been improved. Supported by the National Natural Science Foundation of China (Grant No. 50371066)     

The wettability of Fe based alloy on TiO

For developing TiO based imitated gold materials, the wettabilities of Fe and Fe-Cr-Ni-Ti on TiO were studied. The results indicated that the wettabilities of Fe and Fe-Cr on TiO were poor, and their wetting angles were about 90° at melting point. The wetting angles reduced with the increase of wetting temperature, but the influence of temperature was small. Fe and Fe-Cr containing Cr 50% or less could react with TiO on the interface to form Fe₂Ti and Ti₂O₃, but this did not improve the wettability effectively. When Ni-Ti was added into Fe-Cr alloy, Ni₃Ti was formed on the interface, which can reduce the interface energy, improve the wettability, and prevent the formation of Fe₂Ti and Ti₂O₃. The wetting angles could go down to about 40° when 3% Ni-Ti was added to Fe-Cr alloy. Biography of the first author: LI Qing-kui, Dr., senior engineer, born in August 1966, majoring in rare metal materials.     

Microstructures and mechanical behavior of PM Ti-Mo alloy

1　INTRODUCTIONTitaniumalloyshavebecomewidelyusedbioma terialsforhigh loadimplants ,becauseoftheirgoodbiocompatibility ,excellentcorrosionresistance ,lowdensityandhighspecificstrength .Ti 6Al 4V ,withahighstrengthandagoodmachine ability ,hasbeenthemostsuccessfullyusedTialloyinclinicalapplica tion [1 5] .However ,recentlyscientistshavefoundthatAlandVelementsinthisalloywilldoharmtohumanorganisms ,andshouldbesubstitutedbyothermorehost friendlyelements ,forexample ,Nb ,Zr ,FeandMo[6 10 ] …     

Influence of surface finish and annealing treatment on oxidation behavior of Ti-48Al-8Cr-2Ag alloy

The effect of surface finish and annealing treatment on the oxidation behavior of Ti-48Al-8Cr-2Ag (molar fraction, %) alloy was investigated at 900 and 1 000 °C, respectively in air. Thermal gravimetric analysis (TGA) was conducted for the characterization of oxidation kinetics. The microstructures of oxide scales were studied by scanning electron microscopy (SEM) and transmission election microscopy (TEM) techniques. Unfavorable effect of the annealing treatment on the oxidation behavior of the coating was also investigated. The results indicate that the oxidation behavior of the alloy is influenced by surface finish and annealing treatment. The oxidation rate of ground sample is lower than that of the polished alloy at 1 000 °C in air. The former forms a scale of merely Al₂O₃, and the latter forms a scale of the mixture of Al₂O₃ and TiO₂. Annealing can improve the formation of TiO₂. Foundation item: Project(2007430028) supported by the Science and Technique Foundation of Henan Educational Committee, China     

Effect of homogenization treatment on microstrucmre and properties of Al-Mg-Mn-Sc-Zr alloy

The effect of homogenization on the hardness, tensile properties, electrical conductivity and microstructure of as-cast Al-6Mg-0.4Mn-0.25Sc-0.12Zr alloy was studied. The results show that during homogenization as-cast studied alloy has obviously hardening effect that is similar to aging hardening behavior in traditional Al alloys. The precipitates are mainly Al3（Sc,Zr） and Al6Mn When homogenization temperature increases the hardness peak value is declined and the time corresponding to hardness peak value is shortened. The electrical conductivity of the alloy monotonously increases with increasing homogenization temperature and time. The decomposition of the supersaturated solid solution containing Sc and Zr which is formed during direct chilling casting and the precipitation of Al3（Sc, Zr） cause hardness increasing. The depletion of the matrix solid solubility decreases the ability of electron scattering in the alloy, resulting in the electrical conductivity increased. Tensile property result at hot rolling state shows that the optimal homogenization treatment processing is holding at 300-350℃ for 6-8 h.     

Microstructure evolution of AS41 magnesium alloy fabricated by ultrasonic vibration

The effects of ultrasonic vibration on the grain size and morphology of Mg2Si in Mg-4 wt% Al-1 wt%Si(AS41) alloys designed were evaluated. The results show that the major constituents of the alloy include β-Mg17Al12 and Mg2Si phase, and no difference in the type of constituents between without ultrasonic vibration and with ultrasonic vibration. Without any ultrasonic vibration, the grain size and Mg2Si phase in AS41 alloy are coare structure. However, the microstructure with fine uniform grains and Mg2Si particles are achieved with ultrasonic vibration. The crystal grains and Mg2Si particles refine with increase in the ultrasonic vibration intensity. When the ultrasonic vibration intensity was too low or too high, coarse structures could be obtained. The analysis of refinement mechanism indicates that the acoustic cavitation and flows induced by ultrasonic vibration lead to the fine uniform microstructure.     

Influence of secondary carbide precipitation and transformation on abrasion resistance of a 3Cr15Mo1V1.5 white iron

The relationship between the secondary carbide precipitation and transformation of the 3Cr15Mo1V1.5 white iron and abrasion resistance was investigated by using optical microscope （OM）, transmission electron microscopy （TEM） and X-ray diffrac- tion （XRD）. The results show that the properties of secondary carbides precipitated at holding stage play an important role in the abrasion resistance. After certain holding time at 833 K subcritical treatment, the grainy （Fe, Cr）23C6 carbide precipitated and the fresh martensite transformed at the holding stage for 3Cr15Mo1V1.5 white iron improve the bulk hardness and abrasion resistance of the alloy. Prolonging holding time, MoC and （Cr, V）2C precipitations cause the secondary hardening peak and the corresponding better abrasion resistance. Finally, granular （Fe, Cr）23C6 carbide in situ transforms into laminar M3C carbide and the matrix structure transforms into pearlitic matrix. These changes weaken hardness and abrasion resistance of the alloy sharply.