材料期刊网

Hardness, Wear Resistance and nacture Toughness of Cast Hiduminium/Corundum Particulate Composites

K.H.W.Seah(Dept. of Mechanical Engineering , National University of Singapore , 10 Kent Ridge Crescent , Singapore 119260)R.S.Kulkarni and S.C.Sharma (Dept. of Mechanical Engineering , R.V.College of Engineering , Mysore Road , Bangalore-560-059 , Karnataka , Ind

材料科学技术（英文）

This paper reports some results obtained in an investigation to see how increasing the corundum dispersoid content from 0% to 7% in a matrix of as-cast and wrought hiduminium alloy affects the hardness. wear resistance and fracture toughness of the composite. The results show that as the corundum content is increased, the hardness and the wear resistance increase remarkably,whereas the fracture toughness drops significantly. It was found that Just a minute amount of corundum is sufficient to cause a fairly large change in these mechanical properties. The hardness of the material is also affected signifIcantly by the aging time. Moreover, if other factors are kept constant, hot extrusion improves both its hardness and its wear resistance. whereas the fracture toughness is decreased

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La对Ni-20Cr-18W-1Mo基高温合金1373K/100h氧化行为的影响

王健 , 袁亮 , 胡锐 , 张铁邦 , 李金山

稀有金属材料与工程

对有无La元素的Ni-20Cr-18W-1Mo基高温合金进行了1373 K/100h的等温氧化试验,分别采用扫描电镜(SEM),X射线能谱(EDX)和X射线衍射(XRD)分析了氧化试样的氧化膜表面和截面形貌特征.结果表明,La元素的添加能够极大地提高基体和氧化膜之间的结合力,使得Ni-20Cr-18W-1Mo基高温合金在1373 K时的抗氧化性提高,相比于未添加La元素的Ni-20Cr-18W-1Mo基高温合金,添加La元素的高温合金具有更小的抛物线氧化速率常数κ”和较弱的氧化膜剥落,同时,形成的表面氧化膜更加致密纤细.

关键词: Ni-20Cr-18W-lMo基高温合金 , 氧化 , La , 氧化膜 , 抛物线速率常数

Evaluating and Modeling the Mechanical Properties of the Prepared PLGA/nano-BCP Composite Scaffolds for Bone Tissue Engineering

Mehdi Ebrahimian-Hosseinabadi Fakhredin Ashrafizadeh Mohammadreza Etemadifar Subbu S. Venkatraman

材料科学技术（英文）

In this paper, preparation of nano-biphasic calcium phosphate (nBCP), mechanical behavior and load-bearing of poly (lactide-co-glycolide) (PLGA) and PLGA/nBCP are presented. The nBCP with composition of 63/37 (w/w) HA/β-TCP (hydroxyapatite/β-tricalcium phosphate) was produced by heating of bovine bone at 700°C. Composite scaffolds were made by using PLGA matrix and 10-50 wt% nBCP powders as reinforcement  material. All scaffolds were prepared by thermally induced solid-liquid phase separation (TIPS) at -60°C under 4 Pa (0.04 mbar) vacuum. The results of elastic modulus testing were adjusted with Ishai-Cohen and Narkis models for rigid polymeric matrix and compared to each other. PLGA/nBCP scaffolds with 30 wt% nBCP showed the highest value of yield strength among the scaffolds. In addition, it was found that by increasing the nBCP in scaffolds to 50 wt%, the modulus of elasticity was highly enhanced. However, the optimum value of yield strength was obtained at 30 wt% nBCP, and the agglomeration of reinforcing particles at higher percentages caused a reduction in yield strength. It is clear that the elastic modulus of matrix has the significant role in elastic modulus of scaffolds, as also the size of the filler particles in the matrix.

关键词: Scaffold

Effect of Cooling Rate on Microstructure and Mechanical Properties of K465 Superalloy

PEI Zhong-ye , HAN Wei , ZHAO Gang , CHEN Xing-fu , LI Jun-tao , TIAN Yan-wen

钢铁研究学报(英文版)

K465 superalloy, as a material for production of turbine nozzle, shows high mechanical properties as well as microstructure stability in critical and severe service conditions. The alloy gains its appropriate microstructure and strength through solid solution strengthening mechanism. Heat treatment parameters such as: time and temperature of homogenization, partial solution and aging temperatures, and cooling rate from solid solution affect the microstructure of the alloy. Among these parameters cooling rate from solid solution is the most effective. Therefore, in this study the effect of cooling rate on microstructure and mechanical properties (tensile and stress properties) were investigated. For this purpose, three different cooling rates were applied on the cast K465 specimens after solution treatment at 1210℃ for 4 h. Microstructures of the specimens then were studied using optical and electron microscopy. Also, tensile tests were performed at room temperature and stress rupture tests were performed under the condition of 975℃ and 230 MPa. It was found out that with increasing cooling rate the size of the γ' precipitates decreases and the mechanical properties of specimens increases. Also, it was shown that the shape and volume fraction of primary γ' particles are largely influenced by the cooling rate following solution treatment at 1210℃ for 4 h.

关键词: cast superalloy;solution heat treatment;cooling rate;microstructure;mechanical properties

AMORPHOUS PHASE-TRANSITION MECHANISM BY THE MECHANICAL ALLOYING OF THE FE-W SYSTEM

Journal of Applied Physics

The Fe-W binary system exhibits a zero heat of mixing in the amorphous state. Thus, there is no chemical driving force for the crystal-to-amorphous transformation. However, the crystal-to-amorphous transition was observed in a mechanically alloyed mixture of pure Fe and W powders. A structural study by x-ray diffraction showed that supersaturated solid solutions of W in Fe [Fe(W) SSS] and Fe in W [W(Fe) SSS] were produced during the early stage of the mechanical alloying. Iron atoms were already totally involved in the solid-state amorphization reaction after 24 h of milling. The end products were W(Fe) SSS and amorphous Fe-W alloy. The amorphization by mechanical alloying of the Fe-W system is attributed to a solid-state amorphization reaction in which lattice distortion induced by supersaturation of W in Fe and a refinement of grain size may raise the free energy of Fe(W) SSS above that of the amorphous phase and make the Fe(W) SSS destabilize.

关键词: glass-formation;powders;amorphization;crystal;silicon;model

EFFECT OF W ON MECHANICAL PROPERTIES OF 12%Cr HEAT-RESISTANT STEEL

LIU Xingyang Northeast University of Technology , Shenyang , China FUJITA Toshio The University of Tokyo , Tokyo , Japan

金属学报(英文版)

The effect of W on mechanical properties of 12% Cr-W-V-Nb heat resistant steel at high temperatures and room temperature is reported.The experimental results indicated that if the W content was about 2.2—3.0 wt-%,there was no obviously change of R.T.tensile strength, but impact toughness decreased with the rise of W content.On the other hand,the increase of W content enhanced the short time stress rupture strength,but did not for the long time one. The increase of W have two effects on the precipitation behavior,promoting Laves formation of type Fe_2W,increasing the precipitated phase amount and speeding up the coarsening pro- cess of precipitated phase at high temperatures.The effect of W on the mechanical properties is closely associated with precipitation behaviors.When the rupture life is short,there has no enough time to coarsen the precipitated phases,so the increase of precipitated phases results in strengthening effect,i.e.the W increases the high temperature strength.After prolonged expo- sure,the evident coarsening took plaee,that decreased the effect of precipitation.

关键词: 12%Cr-W-V-Nb steel , null , null , null

Evaluation of mechanical properties of structural materials by a spherical indentation based on the representative strain-an improved algorithm at great depth ratio

金属学报(英文版)

At great depth ratio, two methodologies based on the representative strain were improved to extract mechanical properties of metallic engineering structural materials from P-h curve of an indentation response. The improved aspects include: the combination of great ratio h(1)/R=0.1 and h(2)/R=0.4 replaced h(1)/R=0.01 and h(2)/R=0.06 (Cao's method) and h(1)/R=0.1 and h(2)/R=0.3 (Ogasawara's method); three types of metallic engineering structural materials with obviously different elastic modulus were dealt with to get their calculation parameters, respectively; a new parameter reflecting the effect of work-hardening exponent n was introduced to get the dimensionless function which is independent of n and a relationship between W/(h(3)sigma(r)S) and E*/(sigma(r)S) at great depth ratio. By using the results of finite element simulation, the efficiency and accuracy of the improved method have been proved, and it showed that the accuracy of the improved method is much better than the former method.

关键词: Spherical indentation;Representative strain;Metallic engineering;structural material;Mechanical property;Great depth ratio;measuring elastoplastic properties;energy-based method;plastic;properties;conical indentation;metal materials;hardness definitions;bulk materials;extract;tests

Biomimicry of bamboo bast fiber with engineering composite materials

Materials Science & Engineering C-Biomimetic Materials Sensors and Systems

Bamboo, one of the strongest natural structural composite materials, has many distinguishing features. It has been found that its reinforcement unit, hollow, multilayered and spirally-wound bast fiber, plays an extremely important role in its mechanical behavior. In the present work, on the basis of the study on bamboo bast fiber and wood tracheid, a biomimetic model of the reinforcing element, composed of two layers of helically wound fiber, was suggested. To detect the structural characteristics of such a microstructure, four types of macro fiber specimens made of engineering composites were employed: axially aligned solid and hollow cylinders, and single- and double-helical hollow cylinders. These specimens were subjected to several possible loadings, and the experimental results reveal that only the double-helical structural unit possesses the optimum comprehensive mechanical properties. An interlaminar transition zone model imitating bamboo bast fiber was proposed and was verified by engineering composite materials. In our work, the transition zone can increase the interlaminar shear strength of the composite materials by about 15%. These biomimetic structural models can be applied in the design and manufacture of engineering composite materials.

关键词: bamboo;bast fiber;biomimetics;engineering composites

Densification of the Tungsten Heavy Alloys at 1473 K and Fabrication of W-Mo System FGM with Density Gradient

Huaping XIONG , Lianmeng ZHANG , Junguo LI , Runzhang YUAN

材料科学技术（英文）

The tungsten heavy alloys with Ni-Al and Fe-Al additives were sintered by hot-press method at 1473 K for 1 h. It was found that the relative density of the W-Fe alloy could be increased evidently by addition of Al. However, the relative density of W-Ni-Al alloy with low content of Al was conversely decreased considerably compared with that of W-Ni alloy. The causes have been studied. The sintering experiments of Mo alloy and W-Mo alloys with 3 wt pct Fe-1.5 wt pct Al additives were also carried out under the same sintering condition of low temperature. Finally, W-Mo system FGM with density gradient was successfully fabricated. Its density changed gradually from 17.0´103 kg/m3 to 9.5´103 kg/m3 within the middle 1.1 mm thickness range.

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Prediction and improvement of mechanical properties of corrosion resistant superalloy K44 with adjusting minor additions C, B and Hf

Materials Transactions

The neural network (NN) method is applied to predict the influence of minor additions C, B and Won mechanical properties of cast superalloy K44 with heat treatment parameters considered. Furthermore, the influence of minor additions C B and Hf on phase stability is estimated using d-electrons theory. The results from these two methods indicate that decreasing C content, increasing B content and doping 0.2-0.3 mass% Hf can balance the desired mechanical properties and phase stability in K44 alloy, which also is confirmed experimentally through the relation between mechanical properties and phase stability of base/modified K44 alloys.

关键词: superalloy K44;neural network;d-electrons theory;mechanical;properties;phase stability;bayesian neural-network;nickel-base superalloys;creep-rupture life;behavior;phase