Zirconium-Induced Softening in Hyperstoichiometric Ni3Al

The room temperature compressive properties and microhardness of Ni3AI alloys doped with Zr were studied. For the hypostoichiometric Ni3AI alloys, the compressive strength and microhardness increased with an increase in Zr content, while softening behavior induced by doping with a certain amount of Zr was observed in hyperstoichiometric Ni3AI alloy. Possible mechanisms for the softening effect were suggested.     

Effects of composition on microstructures of rapidly solidified Ni–Al alloys

Microstructures of melt-spun Ni–Al alloys with compositions from 61–85 at% Ni were studied by means of transmission electron microscopy, X-ray diffraction analysis and optical microscopy. The microstructures of as-quenched ribbons exposed to cooling rates of the order of 106 K s-1 reflect the transition from primary -NiAl to -Ni solidification with increasing nickel content. In 70 at% Ni alloy ribbons, martensitic NiAl grains were detected near the wheel-side surface contrasting with anomalous and lamellar eutectic microstructure in the top part. Directly ordered Ni3Al grains with single (or large) antiphase domains (APDs) and a minor eutectic fraction were observed in 75 at% Ni alloy ribbons. Samples containing 80 at% Ni exhibit mainly single-phase Ni3Al grains with 10–20 nm sized APDs indicating sequential ordering. Weak L12 ordering was even detected in 85 at% Ni ribbons which displayed ordered antiphase zones of 1 nm size. Disordered -(Ni) films on grain boundaries can be discounted for 80 at% Ni ribbons, but occurred near the top of 85 at% Ni samples. The results are explained in terms of the reassessed Ni–Al phase diagram employing recent corrections near to the Ni3Al composition and new results on phase formation in undercooled Ni–Al melts. © 1998 Kluwer Academic Publishers     

Antiphase domain morphologies in Ti3Al-Si alloys

Ti₃Al based alloys with additions of Si, V, and V + Si were prepared in ingot form by argon arc co-melting and in the form of rapidly solidified ribbons by chill block melt spinning. Binary Ti₃Al and ternary Ti₃Al-Si arc-melted ingots showed equiaxed antiphase boundaries (APBs) in the ₂ (DO₁₉) grain interiors with columnar APBs adjacent to the grain boundaries. In the melt spun ribbons, which undergo high cooling rates, three types of antiphase domain (APD) morphologies (fine, columnar, and coarse equiaxed APDs) were observed in any single ₂ grain. Addition of 15 at.%V to these alloys led to retention of the ordered (B2) phase with a relatively large antiphase domain size.     

激光熔化沉积Mo/ Mo2Ni3 Si 金属硅化物合金显微组织与耐磨性

以Mo 、Ni、Si 金属粉末为原料, 利用激光熔化沉积工艺制备出以难熔金属Mo 初生树枝晶为增韧相,以三元金属硅化物Mo₂Ni₃ Si 为基体的金属硅化物耐磨合金, 在室温干滑动磨损条件下测试了合金的耐磨性能。结果表明, 初生树枝晶的体积分数随着Mo 含量的增加而增加, 而硬度却随之降低。由于金属硅化物Mo₂Ni₃ Si的高硬度和难熔金属Mo 树枝晶的高强韧性, 合金在室温干滑动磨损条件下具有良好的耐磨性能。      

Effect of rapid quenching on the magnetic and structural properties of Bi-MnBi composites

Rapid quenching of hypereutectic Bi-Mn alloys with compositions ranging from Bi-1.5wt% Mn (Bi-5 at% Mn) to Bi-20 wt% Mn (Bi-50 at% Mn) was carried out to achieve an optimum constitution of the ferromagnetic MnBi phase. Microstructural investigations by optical and electron microscopy techniques revealed the presence of very fine MnBi particles in the as-spun samples. The results of the microstructural and thermal analysis studies have indicated that it is possible to achieve control over the size and amount of the ferromagnetic phase by melt spinning. Some initial results of magnetic properties of melt-spun ribbons are also presented.     

超微晶NiTiNb合金微观结构与演变

采用快淬法将NiTiNb记忆合金制备成超微晶薄带,晶粒尺寸为400nm～1.5μm,研究了晶粒的微观结构特征及演变过程.结果显示,NiTiNb薄带的微观组织由NiTi和少量的氧化物或碳化物颗粒组成,组织中无富Nb相.富Nb相在高温退火时析出,退火前后的薄带均不发生马氏体转变.     

多晶Ni_3Al合金硼致塑性研究进展

本文综述了十余年来国内、外多晶Ni_3Al加硼致塑现象和机理的研究概况。讨论了多晶Ni_3Al的内禀脆性,硼在多屍Ni_3Al中的存在状态与作用,硼对晶界区化学有序的影响,硼致多晶Ni_3Al合金塑性机理的实验结果与观点,并提出了有待进一步研究的问题。     

Morphology and mechanical properties of melt-spun and conventionally cast aluminium,AlMg and AlSi alloys before and after hot extrusion

Rapidly solidified aluminium, AlMg (0 to 16.5 at % Mg) and AlSi (0 to 20.2 at % Si) alloys were produced by melt spinning. The AlMg ribbons were single-phase, whereas the AlSi ribbons were dual-phase. In the ribbons of both alloy systems the fineness of the microstructure increased with increasing alloying element content. The melt-spun ribbons were consolidated by hot extrusion. For comparison, conventionally cast alloys of corresponding compositions were extruded analogously. During the extrusion process in AlMg (16.5 at % Mg) and in the AlSi alloys precipitation occurred. The consolidation of the ribbons was markedly influenced by the oxide layer on the ribbon surfaces: in the AlSi consolidates a more intimate contact between the ribbons was apparent than in the aluminium and AlMg consolidates. In the extrudates of the conventionally cast alloys the grains and second-phase particles were much larger than in the consolidates. The observed dependence on alloy composition of hardness, ultimate tensile strength and elongation at fracture of both consolidated ribbons and extrudates of the conventionally cast alloys are discussed in terms of matrix grain size, solute content of the matrix, amount and size of second-phase particles and recrystallization behaviour. For all compositions of the alloys the Vickers hardness of the as-melt-spun ribbons was higher than that of the consolidated products, owing to recrystallization and precipitation provoked by the hot consolidation process. The ultimate tensile strength as well as the elongation at fracture of both consolidated ribbons and extruded conventionally cast alloys did not differ significantly for AlMg. However, due to a finer microstructure and a stronger inter-ribbon bonding, for AlSi alloys with a high silicon content the rapid solidification processing route did yield a product with significantly improved mechanical properties as compared with the extruded conventionally cast alloys.     

Improvement of Shape-Memory Characteristics and Mechanical Properties of Copper-Zinc-Aluminum Shape-Memory Alloy with Low Aluminum Content by Grain Refinement

Shape-memory alloys (SMAs) are used as sensors and actuators in most engineering and medical applications and are optimized to exhibit either high stress recovery or high strain recovery. But most binary and ternary Cu-base SMAs are brittle and show low strain recovery due to the coarse grains obtained during solidification. Many new methods, such as powder metallurgy, rapid solidification, multipass rolling and equal-channel angular extrusion, are now being used to produce Cu-base shape-memory alloys with fine grains. However, these methods usually yield the alloys in small quantities despite the fact that each of them has its own advantages and limitations. Casting continues to be the most common and easiest method that helps produce SMAs in large quantities. To overcome the formation of coarse grains during casting, grain-refining additions were made to the liquid alloy. But the extent of grain refining achieved and, in turn, its effect on the shape recovery strain, varies from one study to another. The present work shows that by very small additions of Zr and Ti to a CuZnAl SMA with a low Al content, the shape-recovery strain can be increased to as high as 8%. The alloy also shows higher hardness and ductility after grain refinement.     

Mechanical Model on Brittle Crack Initiation and Propagation

A mechanical model is presented in this paper to describe the initiating and propagating of brittle cracks. Two criteria have been deduced from the model to determine the effects of such factors as local stress state, surface and grain boundary energies as well as local grain boundary orientation on the initiating and propagating of both intergranular and transgranular brittle cracks. By which the role of adding B in Ni3Al base alloys to improve their ductility,temper and hydrogen embrittlements in steels and other alloys as well as the random feature of brittle crack initiation could be explained     

Morphological characteristic of the conventional and melt-spun Al-10Ni-5.6Cu (in wt.%) alloy

The Al-10Ni-5.6Cu alloy was prepared by conventional casting and further processed melt-spinning technique. The resulting conventional cast and melt-spun ribbons were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy together with energy dispersive spectroscopy, differential scanning calorimetry and microhardness techniques. The X-ray diffraction analysis indicated that ingot samples were α-Al, intermetallic Al₃Ni and Al₂Cu phases. The optical microscopy and scanning electron microscopy results show that the microstructures of rapidly solidified ribbons are clearly different from their ingot alloy. Al-10Ni-5.6Cu ribbons reveal a very fine cellular structure with intermetallic Al₃Ni particles. Moreover, at high solidification rates the melt-spun ribbons have a polygonal structure dispersed in a supersaturated aluminum matrix. The differential scanning calorimetry measurements revealed that exothermic reaction was between 290 °C and 440 °C which are more pronounced in the ternary Al-10Ni-5.6Cu alloy.     

Corrosion behaviour and magnetic properties of melt-spun Nd-(Fe·Co·Ni)-B-(Al·Ti) ribbons

The corrosion behaviour of melt-spun Nd-Fe-B alloy ribbons in which Fe was replaced with Co and Ni and small quantities of Al and Ti added was investigated from the viewpoint of anodic corrosion, Although the addition of Ni degraded the magnetic properties of melt-spun ribbons, it improved corrosion resistance. According to EDXS and AES analyses, the corrosion products on the surface of Ni-free ribbons consisted of Nd and Fe oxides, but the Nd oxide corrosion product almost disappeared in the Ni-added samples. Also, the degradation of magnetic properties after the corrosion test was suppressed by the addition of Ni.From these results, it was thought that the improvement of corrosion resistance and the smaller degradation of magnetic properties of Nd-(Fe·Co·Ni)-B-(Al·Ti) ribbons after the corrosion test were associated with the suppressed dissolution of the Nd-rich phase at the grain boundaries.The oxidation of Ni-added melt-spun ribbons also showed similar characteristics and behaviour to the corrosion test in the morphologies of the ribbon surface and magnetic properties after the oxidation test.     

Atomistic Simulation of Interaction between Grain Boundary and Dislocations in Ni_3Al

The embedded atom type potentials and static relaxation method combined with a steepest decentcomputational technique have been used to simulate the interaction between the grain boundary(GB) and dislocations in Ni_3Al alloys.The focus has been placed on the energy feature of theinteraction,the distortion of GB structural units,and the dislocation core structure near the GB.Im-plication has also been made on the results for the understanding of the mechanism responsible forB-enhanced ductility.     

Correlation of the Mechanical Properties of Polycrystalline Ni_3Al Alloys with Their Electronic Structure

The electronic structure of Ni_3Al alloys with different B contents has been investigated by measuringthe positron lifetime spectra.The segregation of B atoms to defects could form strong covalentbondings with Ni and Al atoms and make the electronic structure in those locations similar to that inbulk,thus strengthen their cohesion.The interaction of B atoms,which were solid-solutioned in thecrystal lattice of Ni_3Al in a manner of occupying interstitial sites,with Ni and Al atoms resulted in theincrease of the density of valent electrons,thus increased the bonding cohesion in bulk.The im-provement of the mechanical properties of Ni_3Al alloys by B doping was due to both“grain bounda-ry effect”and“bulk effect”of B,which correlated with their electronic structure.     

热循环对快速凝固Al90Pb10合金结构形态的影响

利用差示扫描量热计(DSC)和透射电子显微镜(TEM),研究了用快速凝固法制备的Al90Pb10合金样品经三次DSC热循环处理前后的结构形态变化.结果表明,Al90 Pb10合金经热循环处理后,纳米镶嵌Pb颗粒发生了奥斯特瓦德(Ostwald)熟化,Al90Pb10合金中的位错形态也因此发生改变.也讨论了这种结构形态变化的内在机制.     

Fabrication and High Temperature Strength of Nb3Al by a Modified Reactive Sintering Process

Single phase Nb₃Al alloys and two phase Nb₃Al alloys containing a Nb solid solution (Nb_ss) or Nb₂Al are fabricated by a modified reactive sintering process. This process, called the clad chip extrusion (CCE) method, consists of clad-rolling Al/Nb/Al three layered plates, cutting the clad-rolled plates into pieces, extruding a container filled with the pieces and heat-treating the extruded Nb/Al composite rod with a very fine micro structure. Heat-treatments combined with HIPing are used to form high-density Nb₃Al compacts containing neither Kirkendall voids nor alumina particles. Nb₃Al alloys are brittle below 1300  K and fracture before yielding in compression tests in this temperature region. Single phase Nb₃Al alloys with the compositions from 20·2 to 23·3 at% Al possess very high yield strength in compression above 1473  K. The compressive strengths are almost independent of Al content, and the materials exhibit dynamic recrystallization around initial grain boundaries at large strains. Two phase alloys of Nb₃Al and Nb_ss deform, without cracking at lower temperatures, to larger strains, although they have lower yield strengths.     

单辊旋铸CuCr25合金的显微组织及性能

研究了单辊旋铸CuCr25合金的显微组织和性能.结果表明,单辊旋铸CuCr25合金的显微组织呈现出球状富Cr相与枝晶状富Cr并存于Cu基体中的形貌,且富Cr相的大小随条带厚度的变化而变化,分析表明,单辊旋铸合金的快速凝固过程中发生了亚稳态的液相分离.与真空感应熔炼CuCr25合金的显微硬度相比,单辊旋铸CuCr25合金的显微硬度增大了57%,这主要是由于固溶度增加和晶粒细化的缘故.     

Al的添加对Mg2Ni储氢合金结构和氢扩散能力的影响研究

采用烧结-机械球磨二步法制备了Mg2-xAlxNi(x=0、0.3)储氢合金材料,研究了Al元素的加入对Mg2Ni储氢合金结构和氢扩散能力的影响.XRD和SEM研究表明Al 元素的加入会使储氢合金产生Al3Ni2和Mg3AlNi2新相,并且在表面覆盖分布各异的棱角多边形颗粒,利用循环伏安法测定了Mg2-xAlxNi(x=0、0.3)储氢电极的氢扩散系数,结果表明:Al元素的加入能显著改善Mg2Ni储氢合金结构,提高了氢扩散能力.     

La0.67Mg0.33Ni3.0-xAlx(x=0～0.3)贮氢合金的相结构及电化学性能的研究

研究了Al元素对合金La0．67Mg0．33Ni3．0中Ni的替代对舍金的微观组织结构及电化学性能的影响。X射线衍射(XRD)分析结果表明La0．67Mg0．33Ni3．0合金由PuNi3型(La，Mg)Ni3相和Ce2Ni2型(La，Mg)2Ni7相组成，Al元素加入后，开始出现CaCu5型LaNi5相，随着Al含量的增加，LaNi5相逐渐增多，当x=0．3时，LaNi5相成为合金的主相，合金La0．67Mg0．33Ni3．0中Al的X荧光元素面分布图像表明了Al元素主要进入LaNi5相中，说明Al是一种LaNi5相形成元素；电化学测试表明，随着Al含量的增加，合金的最大放电容量依次下降，4种合金的最大放电量分别为392、324、267和252mAh／g，活化次数变化不大(2～3次即可活化)，循环稳定性先增加后下降。     

Role of aluminium addition on structure of Fe substituted Fe73·5 − x Si13·5B9Nb3Cu1Al x alloy ribbons

The investigation has dealt with the structure and magnetic properties of rapidly solidified and annealed Fe_73·5???x Si_13·5B₉Nb₃Cu₁Al _x (x?=?0, 2, 4, 6 at%) ribbons prepared by melt spinning. Complete amorphous structure was obtained in as-spun ribbons of x?=?0 and 2 at% compositions, whereas structure of ribbons containing higher Al was found to be partially crystalline. Detailed thermal analyses of the alloys and the melt spun ribbons revealed that the glass forming ability in the form of ${{ \textit{T}}}_{\mathbf{x}}{/}{{ \textit{T}}}_{\mathbf{l}}$ (ratio between crystallization and liquidus temperature) is the highest for 2 at% Al alloys and decreases with further addition of Al. Annealing of all as spun ribbons resulted in the precipitation of nanocrystalline phase embedded in amorphous matrix in the form of either ${ \textit{DO}}_{{ 3}}$ phase or bcc ${\upalpha}$ -Fe(Si/Al) solid solution depending on the initial composition of the alloy. Only bcc ${\upalpha}$ -Fe(Si/Al) solid solution was formed in 2 at% Al ribbons whereas ordered DO₃ structure was found to be stabilized in other ribbons including 0 at% Al. A detailed study on determination of precision lattice parameter of nanocrystalline phase revealed that the lattice parameter increases with the addition of Al indicating the partitioning behaviour of Al in nanocrystalline phase.