用分离共晶法制备表面复合材料

根据电磁搅拌下定向凝固时形成分离共晶的原理,制备了表面为Ｓｉ和Ａｌ３Ｆ３,Ａｌ３Ｎｉ,Ａｌ６Ｍｎ等金属间化合物的表面复合材料。分析了复合材料的组织,探讨了转速、晶体生长速度等参数与分离层厚度之间的关系。分析了分离共晶层在轴向和周向分布的特点,测定了分离层的耐磨性。     

Carbide morphology in bulk and unidirectionally solidified Fe-C-V eutectics

Abstract

Investigations on the development of eutectic structures in Fe-C-V are of considerable interest as a result of the unique properties exhibited by these alloys. In this work a series of Fe-C-V alloys were prepared in order to investigate the solidification conditions and sequence, eutectic morphology, and the development of in situ eutectics. It was found that near perfect eutectic structures can be achieved by slow cooling of an Fe-C-V alloy. The eutectic obtained consisted of semispherical grains with fibrelike VC_1–x carbides. These fibres were found to develop appreciable ramifications during the solidification process. Assuming a critical area of liquid per fibre at the solidification front, as needed for stable eutectic growth, yielded a parabolic type of expression N_b ∝ t² for the number of branches (N_b) developed as afunction of the solidification time t. A qualitative model is proposed in this work to explain the different stages involved during the solidification of alloys of hypo-, hyper-, and eutectic composition. In addition, unidirectional solidification gave rise to in situ eutectics with aligned fibres. Finally, a solidification constant (u_eλ² = K) of 202 μm³ s^?1 for stable eutectic growth was experimentally determined.     

Silicon- and germanium-based eutectics

A survey has been made of the microstructures produced by unidirectional solidification of selected eutectic systems based on the semiconductors silicon and germanium. The aim of the work was to identify those systems which produce an aligned rod-type structure consisting of metallic rods in a semiconducting matrix.The systems NbSi₂-Si, TaSi₂-Si and Ti Ge₂-Ge have been found to produce structures of this type which may be of use in future electronic applications.     

Irreversible hydrogen effects on resistivity of sputtered copper films

Can hydrogen trapped within the lattice of copper film produce irreversible effects on the electrical resistivities of copper film at room temperature? In order to answer this question, copper films were sputtered in the presence of hydrogen and resistivities were measured in vacuum at room temperature. A series of sputtering depositions were carried out at different hydrogen partial pressures to confirm irreversible hydrogen effects. Films sputtered in argon only, were used as controls. The electrical resistivities of copper films were measured as a function of hydrogen partial pressure. Saturation is reached for the electrical resistivity in high hydrogen partial pressures. The saturation is at around 5.0% hydrogen partial pressure of total sputtering pressure. The electrical resistivities of copper films are lowered irreversibly by hydrogen, because the films were sputtered in the gas mixtures of argon and hydrogen and the electrical resistivities of films were measured in the air. The sputtering rate decreases as the hydrogen partial pressure increases. The sputtering rate is found to be proportional to the average mass of the incident ion.     

Transition between two steady states of unidirectional solidification of lanthanum modified Al–Si eutectic

Abstract

The transition between two steady states of unidirectional solidification of Al–Si eutectic modified with 0·5 wt-%La has been investigated experimentally by abruptly changing the solidification rate. The addition of lanthanum results in only partial modification of the eutectic microstructure, fiakelike and fibrelike silicon phases being always present after solidification. The interflake spacing and the interfibre spacing are shown to have a continuous but retarded response to an abrupt change of solidification rate, the retardation of the interflake spacing being the greater. A model of the response dynamics governing the transition has been developed to interpret the results of the experiments.

MST/1237     

Solidification Microstructures of a Single-crystal Superalloy under Ultra-high Temperature Gradient Conditions

The solidification microstructures and solute segregation of a newly developed hot corrosionresistant single-crystal Ni-base superalloy were investigated with a zone-melting and ultra-highthermal gradient unidirectional solidification apparatus.Compared with the microstructures solidifiedat conventional low thermal gradient conditions,the dendrite arm spacings,the interdendriticmicroporosity and γ/γ' eutectic,and the severity of solute segregation of the single-crystalsuperalloy solidified at ultra-high thermal gradient conditions were considerably reduced.It wasshown that the microstructure solidified under ultra-high thermal gradient condition is ideal for thefull exploitation of the excellent property potentials of single-crystal superalloys.     

The metallurgical structure of as-solidified Ni-Cr-B-Si-C hardfacing alloys

The crystallization of complex nickel-base hardfacing alloys is studied with reference to the ternary Ni-Si-B and quaternary Ni-Cr-B-Si systems. Quenched interrupted, directional solidification is employed to establish the solidification sequence. The transformation temperatures are measured by differential thermal analysis. Solid-state transformations occurring during the cooling process are described. A model of the solute exchanges during solidification is proposed in order to predict the amount of liquid remaining at each stage in the process, particularly at the last stage when all the eutectic liquid is frozen in.     

Interface temperature measurement of M2C and M6C eutectic carbides in the Fe–Mo–C system

The High speed cast iron, which is used for hot rolling parts, needs high fracture toughness and wear resistance. To improve these properties, the control of eutectic carbides, M₃C, M₇C₃, M₆C and MC is important by adding elements such as Cr, W, V and Mo.The aim of this study is to estimate which carbide will solidify under certain solidification conditions and compositions. This prediction criterion can be gained by measuring the interface temperature of each carbide in various samples with different solute elements, composition and growth rate.In this report, the solidified temperature of γ+M₂C and γ+M₆C eutectic carbide in the Fe–Mo–C ternary system in the composition range near to the eutectic monovariant line, was measured during the unidirectional solidification process. The relationship between solidified interface temperature and growth rate was obtained. In eutectic solidification along the γ+M₆C monovariant line, a coefficient of undercooling, the k value, was obtained.The authors have already measured the k values of other eutectic carbides, such as γ+M₃C, austenite+M₇C₃, and γ+VC in Fe–Cr–C and Fe–V–C system. The paper also discusses the relationships between these properties of eutectic carbides.     

Some amorphous alloys in Zr-Ru-Mo and Zr-Ru-W systems prepared by rapid solidification

All binary systems of the ternary systems Zr-Mo-Ru and Zr-W-Ru show at least one eutectic point. This indicates the existence of low melting eutectic alloys in these ternary systems (∼ 1200–1300°C). As starting materials, homogeneous Zr-Mo-Ru and Zr-W-Ru samples of different compositions were prepared by rapid solidification (∼10⁶Ks⁻¹) in a splat-cooling apparatus with a rf levitation coil and a high-velocity two-piston arrangement driven by solenoids. The possibility of obtaining alloys in amorphous state from low-melting areas of these ternary systems with the addition of boron or silicon has been investigated.     

高钒铁碳合金凝固过程及元素的分布

通过定向凝固 液淬试验、金相分析、电子探针面扫描、微区成分能谱分析和差热分析等手段,研究了高钒铁碳耐磨合金的凝固过程。结果表明:该合金在凝固时首先从液相中析出初生VC相;随着VC的析出,液相中V含量降低,达到共晶成分时,合金将发生共晶反应L→γ+MC;之后将按照L→γ+MC+MC2的反应进行三元共晶凝固。V主要分布于MC型的碳化物,Mo和Cr主要分布于MC2型的碳化物中。     

Effect of magnesium content on thermal and structural parameters of Al–Mg alloys directionally solidified

In this study, the influence of magnesium content on thermal and structural parameters during the unsteady-state unidirectional solidification of Al–Mg alloys is analyzed. Using a special device, Al–Mg alloys containing 5, 10, and 15 wt% Mg were submitted to unidirectional solidification. Using a data acquisition system, the temperature variations along the casting during solidification were measured. From these results, the variations of solidification parameters as growth rate of dendrite tips, thermal gradient, cooling rate, and local solidification time were determined. The variation of global heat transfer coefficient at metal/mould interface was estimated through the adjustment of experimental temperature variation close to the interface and numerical predictions. Primary and secondary dendrite arms spacing variations during solidification were measured by optical microscopy. From these results, comparative analysis were developed to determine the influence of magnesium content.     

凝固条件和镁对Al-Si11.0合金组织的影响

研究了宇向凝固时冷却条件和镁元素对Ａｌ－Ｓｉ１１．０合金树枝晶结构和共晶组织的影响。试验结果表明,随着冷却速度的增加,Ａｌ－Ａｉ１１．０合一次枝晶和二镒分枝间距都显著减小,在较小的冷却速度时,加入镁元素后合金的二镒分枝间距明显增大,而在冷却速度大于１６０Ｋ／ｍｉｎ时,则没有影响。试验还发现,加入镁元素后,冷却速度对共晶成分的影响显示减小,是合 共晶组织变细。在试验范围内,Ａｌ－Ｓｉ１１．０合金中加     

Globular-to-needle Zn-rich phase transition during transient solidification of a eutectic Sn-9%Zn solder alloy

The aim of this article was to investigate the microstructural evolution of a eutectic Sn-9%Zn solder alloy as a function of growth rate during transient unidirectional solidification. It was found that globular-like and needle-like Zn-rich phases prevail at growth rates ranging from 0.5 to 2 mm/s and 0.3 to 0.1 mm/s, respectively, with a transition region occurring between these growth rate ranges. The microstructure control in soldering processes can be accomplished by manipulating solidification processing variables such as the cooling rate and the growth rate, since the resulting morphological microstructure depends on heat transfer conditions imposed by solidification, and as a direct consequence will affect the final properties.     

Interface temperature measurement of M2C and M6C eutectic carbides in the Fe–Mo–C system

The High speed cast iron, which is used for hot rolling parts, needs high fracture toughness and wear resistance. To improve these properties, the control of eutectic carbides, M₃C, M₇C₃,M₆C and MC is important by adding elements such as Cr, W, V and Mo.

The aim of this study is to estimate which carbide will solidify under certain solidification conditions and compositions. This prediction criterion can be gained by measuring the interface temperature of each carbide in various samples with different solute elements, composition and growth rate.

In this report, the solidified temperature of γ + M₂C and γ + M₆C eutectic carbide in the Fe–Mo–C ternary system in the composition range near to the eutectic monovariant line, was measured during the unidirectional solidiication process. The relationship between solidified interface temperature and growth rate was obtained. In eutectic solidification along the γ + M₆C monovariant line, a coefficient of undercooling, the k value, was obtained.

The authors have already measured the k values of other eutectic carbides, such as γ + M₃C, austenite + M₇C₃, and γ + VC in Fe–Cr–C and Fe–V–C system. The paper also discusses the relationships between these properties of eutectic carbides.     

Microstructural defects and their origins in Cd–CuCd3 eutectic

Abstract

In this investigation, macrostructural and microstructural imperfections, formed in the fibrous Cd–CuCd₃ eutectic during unidirectional solidification, were characterized and the factors important in their formation were studied. The effect of growth rate R, imposed thermal gradient G, and natural convection on the defect morphology were investigated, and the important physical factors that determine the manner in which microstructural defects form were considered. Convection was found to play a minimal role in defect formation. The most important variable was found to be the ratio G/R, which determined the solid/liquid interface shape during solidification. When low values of G/R were used, eutectic cells were formed. For intermediate values of G/ R, the microstructure was found to contain features analogous to nodes in single–phase materials. Only when high values of G/R were used were all microstructural defects eliminated, producing a nearly perfect structure of parallel CuCd₃ rods in a matrix of cadmium. The morphology of branching and curving rods, which were found to be the primary microstructural defects, indicates that both the solid/solid interfacial free energy and its anisotropy are important factors in rod branching, and a branching mechanism consistent with the observations made was proposed. Anisotropy in the solid/solid interfacial free energy was considered to account for the formation of blades; however, kinetic considerations were required to account for the growth dependence of the rod-to-blade transition observed in this eutectic.

MST/130     

Microstructure and fracture toughness of the Bridgman directionally solidified Fe-Al-Ta eutectic at different solidification rates

Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates.Solidification microstructure transforms from regular eutectic to eutectic colony with the increase of the solidification rate.The solid/liquid interface of Fe-Al-Ta eutectic evolves from planar interface to cellular interface with the increase of the solidification rate.In addition,threepoint bending method was adopted to study the room-temperature fracture toughness of the as-cast Fe-Al-Ta eutectic alloy and the Fe-Al-Ta eutectic composites.Moreover,the fracture morphologies,the crack propagation path and the strengthening mechanism of Fe-Al-Ta eutectic were discussed.     

结晶速度对InSb－NiSb共晶复合材料磁致电阻性能R_b／R_o影响的研究

研究了单向结晶速度Ｖ对ＩｎＳｂ－ＮｉＳｂ共晶磁致电阻性能Ｒ＿ｂ／Ｒ＿ｏ的影响。结果发现不同Ｖ，其Ｒ＿ｂ／Ｒ＿ｏ也不同。并且在Ｖ－Ｒ＿ｂ／Ｒ＿ｏ关系中存在着一个Ｒ＿ｂ／Ｒ＿ｏ最大值。这个最大值可由半导体的物理磁阻效应和几何磁阻效应的综合作用来说明。     

The Creep and Thermal Stability Characteristics of a Unidirectionally Solidified Al2O3/YAG Eutectic Composite

Compressive creep characteristics at 1773, 1873, and 1973 K, oxidation resistance over 1000 h at a temperature of 1973 K in ambient air, and the thermal stability characteristics at 1973 K in ambient air of a unidirectionally solidified Al2O3/YAG eutectic composite were evaluated. At a test temperature of 1873 K and a strain rate of 10–4/s, the compressive creep strength of a eutectic composite manufactured by the unidirectional solidification method is approximately 13 times higher than that of a sintered composite with the same chemical composition. The insite eutectic composite also showed greater thermal stability, with no change in mass after an exposure of 1000 hours at 1973 K in ambient air. The superior high-temperature characteristics are closely related to such factors as (1) the in-situ eutectic composite having a microstructure, in which single crystal Al2O3 and single crystal YAG are three-dimensionally and continuously connected and finely entangled without grain boundaries and (2) no amorphous phase is formed at the interface between the Al2O3 and the YAG phases.     

Effect of boron concentration on solidification structure and hardness of Fe–B–C wear‐resistant alloy

Fe–B–C wear‐resistant alloy, as a new type of iron‐based wear‐resistant materials, has drawn extensive attention of the researchers in materials at home and abroad. The boron concentration plays an important role in the microstructure and mechanical properties of Fe–B–C wear‐resistant alloy. In this paper, the solidification microstructure, volume fraction of eutectic, macro and micro hardness of Fe–B–C alloy are researched. The samples are measured by optical microscopy (OM), scanning electron microscopy (SEM), Rockwell‐hardness tester, Vickers‐hardness tester. Image processing software such as image‐pro and photoshop are used. The content of boron in experiment alloys are 1.0%, 1.5%, 2.0%, 2.5% and 3.0% respectively. As a result, the solidification microstructure of as‐cast Fe–B–C mainly consists of metallic matrix and eutectic structure. The eutectic phase is continuous netlike distribution along the grain boundary. As boron concentration increases, the volume fraction of borocarbide increases in the matrix, and the size is larger. The hardness of Fe–B–C also has a tendency to rise with the increase of boron concentration.     

Role of zirconium in the phase formation at the interdendritic zone in nickel-based superalloys

A commercial Alloy 80A and a modified alloy with lower titanium and zirconium contents, e.g. 1.4% and <0.01%, respectively, were subjected to unidirectional solidification followed by a rapid quench in water to preserve the structure at elevated temperatures. The slow solidification results in a coarse dendritic structure with a high enrichment of sulphur (up to 2%), aluminium (up to 4%), titanium (up to 13%) and zirconium in the interdendritic zones. In the commercial Alloy 80A, the zirconium and sulphur present in the interdendritic zone result in a eutectic containing ZrS and NiCrTi-matrix. Excess zirconium forms an NiZr-intermetallic. No TiS is formed in this case. In the absence of zirconium, the titanium enriched in the interdendritic residual melt forms a eutectic of TiS. In both cases the effective solidus temperature corresponding to the composition of the residual melt is 1170°C, compared to 1330 °C, which is the solidus temperature of the bulk material.