Microstructures and hardness of ultrafine-grained Ni3Al

The microstructural evolution of the ultrafine-grained intermetallic compound Ni₃Al is studied as a function of annealing at different temperatures. The ultrafine microstructure is produced by a high plastic torsional straining. Transmission electron microscopy, X-ray diffraction and differential scanning calorimetry are used to characterize the microstructural evolution and microhardness is used to determine mechanical behaviour. The as-deformed microstructure exhibits an almost fully disordered crystalline structure with coherent domain size of about 18 nm, a strong torsional texture and high internal elastic strains. On annealing the as-deformed samples at different temperatures, the recrystallization of the material into a granular type structure containing non-equilibrium grain boundaries is first observed. This is followed by the transformation from non-equilibrium grain boundaries with simultaneous grain growth. This transformation is correlated with an increase of hardness. A new concept of non-equilibrium grain boundaries transparency is presented to interpret this singular behaviour. The results are compared to those obtained on an ultrafine-grained Al-1.5% Mg alloy produced by the same technique and which exhibits the same mechanical behaviour.     

Microstructure and mechanical properties of Mg-7Zn-3Al alloy with Nd and Y additions

The effects of combined addition of 0.6 wt.% Nd and 0.4 wt.% Y on the microstructure and mechanical properties of Mg-7Zn-3Al alloy were investigated.The results indicated that the Nd and Y addition led to obvious dendrite coarsening.However,it could modify the morphology and distribution of-Mg 32(Al,Zn) 49 intermetallics.Moreover,Al 2 REZn 2 phase could be introduced into the alloy with the Nd and Y addition.With the effective second-phase strengthening,the ultimate tensile strength and elongation in as-cast state can be improved by the Nd and Y addition.After ageing treatment,the alloy with the Nd and Y addition exhibited better precipitation strengthening effects by forming finer MgZn 2 and Mg 32(Al,Zn) 49 precipitates into the-Mg matrix.As a result,the yield and ultimate strength of Mg-7Zn3Al-0.6Nd-0.4Y alloy could be increased to 182 and 300 MPa by peak-ageing treatment.     

Microstructure and mechanical properties of copper alloyed austempered grey cast iron

Austempered grey cast iron (AGI) has emerged as a major engineering material in recent years because of its attractive mechanical properties. The main aim of this investigation is to assess the mechanical properties of copper alloyed AGI. Alloyed grey cast iron specimens are subjected to austempering heat treatment at six different temperatures for four different time periods. The resulting microstructures have been evaluated and characterised by means of light microscope and scanning electron microscope and X-Ray diffraction analysis. The microstructural features of AGI such as austenite content and its carbon content have been also found to influence the hardness, tensile properties and elongation. Both duration of the austempering time and the austempering temperature affect the mechanical properties of AGI. The hardness, tensile strength and ductility initially increase, and thereafter it decreases on longer periods of austempering. On the other hand hardness, tensile strength decreases as increasing austempering temperature, while ductility increases. The best combination of hardness 380BHN and strength 332?MPa; observed at 927°C of austenitising and 260°C of austempering temperature for 60?min.     

Effect of copper additions on the mechanical properties of iron

The effect of copper alloying on the mechanical properties of iron is studied. Alloying of a model material (armco-iron) with 0.2–2.0% Cu is shown to increase the strength characteristics by a factor of 1.5–2.5 and to decrease the ductility by 8–60%.     

纳米SiC增强纯Al基复合材料的微观组织和力学性能

与采用微米尺度SiC颗粒为增强相制备的Al基复合材料相比,以纳米SiC颗粒为增强相制备的Al基复合材料具有更加优异的力学性能,可极大提高SiC增强Al基复合材料的服役可靠性及应用范围。采用传统粉末冶金方法制备纳米SiC颗粒增强纯Al基复合材料,研究烧结温度和增强相体积分数对复合材料微观结构和力学性能的影响。研究表明,烧结温度和增强相体积分数均对复合材料的微观结构和力学性能有重要影响。随烧结温度升高,复合材料中的残留微孔减少,密度和强度均得到显著提高。含体积分数为3%纳米SiC颗粒的复合材料在610℃具有最高的强度,进一步提高纳米SiC颗粒的含量并不能提高材料的力学性能,这主要是由于当纳米SiC颗粒的体积分数超过3%时将出现明显的团聚,从而降低强化效应。     

Room-temperature mechanical properties of cold-rolled thin foils of binary,stoichiometric Ni3Al

In our previous works, thin foils of boron-free stoichiometric Ni₃Al, with thicknesses ranging from 57 to 315 μm, were fabricated by cold rolling of single-crystalline sheets which were sectioned from directionally solidified ingots. In this article, the room-temperature mechanical properties of the 83 and 95 pct cold-rolled foils were examined. Depending on the initial rolling direction, the foils exhibited two types of deformation microstructures: a banded structure with dual {110} textures and a band-free structure with a single {110} texture. The 83 pct cold-rolled foils showed very high Vickers hardness numbers: 649 and 604 for the banded and band-free structures, respectively. The foils possessed very high tensile fracture stress (1.7 to 2.0 GPa), with no appreciable plastic elongation along the rolling direction. The fracture stress of the 95 pct cold-rolled foils was slightly higher than that of the 83 pct cold-rolled foils. The banded-structure foils showed slightly higher fracture stress than the band-free-structure foils at the 83 pct reduction, but there was no difference between both the structures at the 95 pct reduction. Although there was no appreciable tensile elongation, slip traces were clearly observed on the surfaces of the foil specimens after the tensile test, indicating traces of some plastic deformation. The 95 pct cold-rolled foils possessed bending ductility, which was estimated as about 12 pct elongation on the tension-side surface of the bent specimen.     

烧结温度对Al_3Ni金属间化合物增强铝基复合材料力学性能的影响

通过粉末冶金原位合成法制备Al3Ni金属间化合物增强铝基复合材料。采用X射线衍射,扫描电镜,硬度测试和压缩强度测试,研究烧结温度对复合材料微观结构和力学性能的影响。结果表明:在铝基体中成功获得了均匀分布的金属间化合物Al3Ni增强相;随烧结温度从570℃上升到590℃,复合材料的密度从2.435 g/cm-3上升到2.990 g/cm-3,维氏硬度从~24升高到~37;经590℃烧结制备的复合材料表现出了高的压缩强度(255 MPa)和伸长率(~40%)。     

Structure and mechanical properties of chromium alloyed with magnesia and boron

Conclusions By alloying chromium simultaneously with magnesia and borides, it is possible to increase its high-temeprature strength and at the same time improve its low-temperature ductility. The best combination of mechanical properties is exhibited by alloys with boron contents of not more than 0.1 wt. %. The greatest increase in the short-time strength of chromium is brought about by alloying with tungsten. In longer periods of operation higher strength is shown by chromium alloyed with vanadium boride.Translated from Poroshkovaya Metallurgiya, No. 7(223), pp. 78–82, July, 1981.     

添加Dy2O3的烧结钕铁硼磁体的磁性能与力学性能

应用常规粉末冶金工艺制备添加不同质量分数Dy2O3的32(Pr-Nd) -0.60Gd -0.55Nb -0.20Cu -0.45Al - 1.12B - Fe烧结磁体,分析了磁性能、抗弯强度、显微组织的变化规律.结果表明,添加Dy2O3使磁体内禀矫顽力近似线性地上升,而剩磁与磁能积则近似线性地下降;添加1.0％的Dy...     

The influence of alloying on the microstructure and mechanical properties of P/M Ni3Al

The influence of alloying additions of iron and chromium alone and in combination with molybdenum and zirconium on the heat treatment response and mechanical properties of powder metallurgy processed Ni₃Al based materials have been characterized. Additions of 8 at.% Cr result in considerable solid solution strengthening, while 11 at.% Fe by itself has little effect on the yield strength. Additions of both iron and chromium result in an alloy with higher strength than either unalloyed Ni₃Al or alloys with either element alone, however, the ductility is reduced by formation of β′ phase. The alloys containing Fe or Cr alone and the unalloyed material are essentially single phase γ′ after heat treating at 1000°C for 1 h, while the more complex alloys have a significant volume fraction of disordered γ phase. The alloys with a high degree of order exhibit large yield drops and corresponding Lüders strains. As the amount of disorder increases the magnitude of both the yield drop and Lüders strain decreases. Values of the power law hardening exponent for the alloys are found to be as high as 0.8 and generally decrease as the amount of γ phase increases as a result of alloying. All of the materials have high strain rate sensitivity at elevated temperature combined with resistance to grain growth that suggests they will deform superplastically.     

钼-铼-镧合金微观组织及力学性能研究

通过固-液掺杂法在Mo-Re合金中加入稀土La₂O₃纳米颗粒制备得到Mo-Re-La合金, 将Mo-Re-La合金与Mo-Re合金、纯Mo的微观组织及力学性能进行对比研究, 得到如下结论: 在纯Mo中添加低含量Re元素(质量分数3.5%) 对Mo-Re合金有明显的细晶强化效果; 将La₂O₃纳米颗粒加入Mo-Re合金进一步细化和强化了Mo-Re-La合金。     

Microstructure and mechanical properties of PM Ni56Fe19Al25 alloy

Abstract

Scanning electron microscopy and X-ray diffraction analysis were used to study microstructure and mechanical properties of PM Ni₅₆Fe₁₉Al₂₅ alloy. The results indicate that as sintered specimen is (β+γ) dual phase structure, and its density is 6·54 g cm^?3 (the relative density is 94·0%), tensile strength is 771 MPa and the total strain is 4·3%. As quenched specimen presents a large superelasticity with the maximum recovery strain of 4·5%, and its tensile strength is 850 MPa and the total strain is 9·2%. The fracture modes of Ni₅₆Fe₁₉Al₂₅ alloy is transgranular, intergranular and tough mixed type.     

The mechanical properties of Al alloys reinforced with continuous Al2O3 fibers

The mechanical properties of aluminum matrix composites unidirectionally reinforced with Al₂O₃ fibers have been measured and characterized in longitudinal and transverse tension, as well as in shear. The flow strengths in transverse tension and shear are found to exceed those of the matrices, although the ductilities are lower. The strengthening is generally consistent with the development of plastic constraint in the matrix around well-bonded fibers, subject to the in situ properties of the matrix being known from independent measurements. The properties in longitudinal tension are found to involve interactions between fibers, such that fiber bundle strengths are not achieved, even when a low strength, pure Al matrix is used. Instead, the strengths are consistent with a crack growth controlled failure mechanism, wherein the strength is governed by the resistance of the material to crack extension from failed fibers.     

Effect of boron additions on the ductility and fracture behavior of Ni3Al single crystals

The effect of B additions on the ductility and fracture behavior of Ni₃Al single crystals has been investigated. Tensile tests at low and high temperatures were carried out in air at constant strain rate for two selected orientations. The results show a positive effect of B additions on both the ductility and the fracture stress at room temperature, but not at high temperatures. The largest improvement in ductility over that found for the pure material was found for additions of 0.2 at.% B. Scanning electron microscopy analysis of the fracture surfaces shows a combination of massive slip on {111} planes, some regions with cleavage-like appearance, and heavily dimpled areas. The improvement in ductility at room temperature has been explained in terms of the increased interfacial strength between the metal matrix and Ca-rich non-metallic inclusions on which the microvoids nucleate. The observations presented show that B additions improve the ductility of both polycrystalline and single crystalline Ni₃Al. It is suggested that a “bulk effect” should be considered in addition to the grain boundary strengthening effect of B when explaining the improvement in ductility of polycrystalline Ni₃Al due to B additions.