K.M. Chang(Department of Mechanical and Aerospace Engineering
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West Virginia University
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P.O. Box 6160
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Morgantown
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WV 26506
,
USA Manuscript received 26 August 1996)
金属学报(英文版)
P/M superalloy disks obtain their final strength by appropriate heat treatments; the maximum attainable strength depends on the rapid cooling rate from the solution annealing. A rapid quench of a large disk forging can cause two problems, surface cracking and shape distortion.In the past,many attempts employ the finite element code to model and to predict temperature evolution and induced stress distribution in a large turbine disk. The major difficulty was the correct description of alloy behavior; particularly the thermomechanical properties and the failure criteria of material during the cooling. High temperature fatigue resistance is always the key requirement for disk materials. New methodology of residual life management emphasizes the initiation as well as the propagation of the cracks developed under the service conditions. One of major challenges to P/M superalloys is the time-dependent behavior of fatigue cracking, which relates to the well-known SAGBO (stress-assisted grain boundary oxidation) phenomenon.A great effort has been done to understand the micro-mechanism of time-dependent fatigue crack propagation resulted in the second generation of P/M superalloys. Further improvement on temperature capability of disk alloys at rim area may lead to the idea of dual-property disks.Different grain structures at different portions of a large disk are possible,as the property requirements for different locations are different. This goal is achievable if the thermal history at specific disk locations can be controlled to develop desirable microstructures and properties.Some suggestions on the future direction of research efforts will be discused.
关键词:
:superalloy disk
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T. Khan(Onera
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B.P. 72
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92322 Chatillon Cedex
,
France Manuscript received 26 August 1996)
金属学报(英文版)
This paper describes the key role played by superalloys in aerospace propulsion. Turbopump blades in liquid rocket engines operating under severe thermal and environmental conditions require the development of specific materials.A new superalloy,THYMONEL 8, developed by ONERA in collaboration with SEP is shown to possess a set of properties required for advanced rocket engines. For future civil aircraft engines, the development of compressor and turbine disk materials operating at still higher temperatures requires a greater contrul of the grain size,which has to be increased for improved creep resistance and higher damage tolerance. Work carried out at ONERA emphasizes the importance of high temperature deformation conditions, especially the strain rate, for obtaining a uniform grain growth.
关键词:
:superalloy
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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
Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
The influence of solution temperature on the microstructure and mechanical properties of TMW-4M3 superalloy has been investigated. Comparisons of mechanical properties have also been made between the heat-treated TMW-4M3 variants and the commercial U720Li. The key microstructural variables examined were grain size and the volume fraction and size of the strengthening gamma' precipitates that control the mechanical properties of these alloys. By increasing the solution temperature from 1373 K to 1393 K (1100 A degrees C to 1120 A degrees C), the volume fraction of primary gamma prime dropped from 16.9 pct to 14.5 pct, whereas the average grain size increased from 8.7 mu m to 10.6 mu m. Compared with an alloy with a smaller grain size, the alloy with a larger grain size exhibited superior resistances to creep and fatigue crack growth without the expense of reduced tensile strength and low-cycle fatigue resistance. This suggested that a higher solution temperature may benefit TMW-4M3 in terms of superior overall properties. The greater overall properties of TMW-4M3 variants than that of commercial U720Li were also demonstrated experimentally. The possible explanations for the improvement of mechanical properties were discussed.
关键词:
ni-base superalloy;low-cycle fatigue;heat-treatment;cooling;precipitation;stainless-steel;yield strength;udimet 720li;creep;behavior;alloy
Z.M.Sun
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H.Hashimoto
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S.Sumi
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Y.H.Park and T.Abe (Materials Engineering Division
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Tohoku National Industrial Research Institute 4-2-1 Nigatake
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Miyagino-ku
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Sendai 983-8551
,
Japan) Z.H. Shan (Research Fellow of Science and Technology Agency of Japan STA)
金属学报(英文版)
Two intermetallic compounds of Ti-50at.% Al and Ti-48at.% Al-2at.% Cr were prepared with a mechanical alloying and pulse discharge sintering process. The as-sintered material showed a microstructure of equiaxed gamma grain with sub-micron size. Heat treatments in vacuum at different temperatures up to 1573K were conducted on the sintered materials. The microstructure of the material coarsened considerably after heat treatment at temperatures higher than 1523K. The mechanical properties of the as-sintered and the heat treated materials were measured at temperatures of up to 973K, with four-point bending tests. Experimental results indicated that the addition of Cr increased the fracture strength of the intermetallic compound at room temperature and at elevated temperatures as well. The bending fracture strength increased with increasing testing temperature up to about 873K and a decreasing followed up. Both fracture strength and fracture strain of the material were found to be improved by heat treatment.
关键词:
titanium aluminide
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PEI Zhong-ye
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HAN Wei
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ZHAO Gang
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CHEN Xing-fu
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LI Jun-tao
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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
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
