QU Xuanhui HUANC Baiyun LEI Changming CHEN Shiqi Central South University of Technology
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Changsha
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China professor
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Powder Metallurgy Research Institute
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Central South University of Technology
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Changsha 410083
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China
金属学报(英文版)
Synthesis process of a TiAl+TiB_2 composite from the elemental powders was studied by means of differential scanning calorimetry and X-ray diffractometry.TiB_2 particles may form in TiAl matrix at temperature even below 700℃ owing to the exothermic reactions between Ti and Al powders.TiB_2 particles are very thermally stable,and they almost did not change in their relative amount,morphology and size after the synthesized composite was remelted.In addition,the existence of TiB_2 particles has obvious refining effect in the as-cast microstructure of TiAl-base alloys.
关键词:
TiAl alloy
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null
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自然科学进展﹒国际材料（英文）
The ZrO2 ceramic particles strengthened NiAl/Cr(Mo,Hf) composite was fabricated from the rapidly solidified NiAl/Cr(Mo,Hf) pre-alloyed powder and the ZrO2 powder by powder metallurgy technique. Microstructure examination revealed that in the prepared composite NiAl and Cr(Mo) phases distributed at the eutectic cell boundary become coarse but many Cr(Mo) platelets inside the eutectic cell were broken, which was different from the original powder. Moreover, fine Ni2AlHf and Hf solid solution particles distributed uniformly in the composite, and the ZrO2 particles mainly segregated along eutectic cell boundary. In addition, twin crystal and stacking faults were observed inside of ZrO2 grains. The experimental results showed that the ZrO2 ceramic particles strengthened NiAl/Cr(Mo,Hf) composite exhibited better room temperature and high temperature mechanical properties than the NiAl/Cr(Mo,Hf) alloy, which may be attributed to the fine structure and the strengthening effect of ZrO2 particles. (C) 2012. Chinese Materials Research Society. Production and hosting by Elsevier Ltd. All rights reserved.
关键词:
NiAl intermetallics;NiAl/Cr(Mo) composite;Powder metallurgy;ZrO2;strengthening;temperature compressive properties;mechanical-properties;eutectic;alloy;microstructure;behavior;nial-cr(mo)-hf
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
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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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Yong LIU
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Lifang CHEN
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Weifeng WEI
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Huiping TANG
,
Bin LIU
材料科学技术（英文）
Ti-4.5Al-6.0Mo-1.5Fe, Ti-6Al-1Mo-1Fe and Ti-6Al-4V alloys were prepared by blended elemental powder metallurgy (PM) process, and the effects of Nd on the microstructures and mechanical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was found out that the addition of Nd increased the density of sintered titanium alloys slightly by a maximum increment of 1% because small amount of liquid phase occurred during sintering. The addition of Nd shows little effect on the improvement of tensile strength, while the elongation is significantly improved. For example, the elongation of Ti-4.5Al-6.0Mo-1.5Fe can be increased from 1% without addition of Nd to 13% at a Nd content of 1.2 wt pct.
关键词:
Powder metallurgy titanium alloy
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null
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null
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Z.G.Liu
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B.Gabbitas
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D.L.Zhang
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J.Liang
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W.Gao
材料科学技术（英文）
The production and microstructural characterization of two types of ceramic particulate reinforced Ti matrix composites (TMCs): Ti-6Al-4V/10~vol. pct TiB and Ti(Al,O)/58 vol. pct Al2O3 were studied. The Ti-6Al-4V/10 vol. pct TiB composite with refined microstructure has been produced using a combination of high energy mechanical milling and hot isostatic pressing. The Ti(Al,O)/58 vol. pct Al2O3 in-situ composite powder has been produced using a novel powder processing process which involves high energy mechanical milling of a mixture of Al and TiO2 powders to produce an Al/TiO2 composite powder followed by thermal treatment of the composite powder. The Ti(Al,O)/58 vol. pct Al2O3 composite powder has been used to produce coatings. Selected mechanical properties of the Ti-6Al-4V/10 vol. pct TiB composite and the high temperature oxidation resistance have also been evaluated.
关键词:
Ti alloy
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Liqing CHEN
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Naoyuki Kanetake
材料科学技术（英文）
Ingot metallurgy (IM) aluminum has long been the subject and attracted the attention of many metallurgists and textural researchers of materials. Due to the introduction of large amounts of ex situ interfaces, however, the textures in powder metallurgy (PM) processed aluminum has been rarely reported. In this article, a pure aluminum plate was prepared $via$ PM route. The starting billet was first produced with uni-axially cold compaction and flat hot-extrusion and then followed by cold rolling processes. The hot-extruded and cold rolling deformation textures of the pure PM aluminum at 50%, 80% and 90% cold rolling reductions were studied by orientation distribution functions (ODFs) analysis. The finite element polycrystal model (FEPM) was finally utilized to simulate the cold rolling textural evolution at various stages of cold rolling. In FEPM simulation, the initial hot-extruded textures were taken into account as inputs. The results showed that typical β-fiber texture formed in pure PM aluminum with the cold rolling reduction increased till 80%, and there was not much change after excessive cold rolling deformation. Homogeneous slip is not the only deformation mode in PM processed pure aluminum plate at over 80% cold rolling reduction. The experimental results were qualitatively in good agreement with the simulated ones.
关键词:
Texture
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Carbon
Carbon nanotube (CNT)/aluminum composites were fabricated by a combination of powder metallurgy and subsequent friction stir processing (FSP). Microstructural observations indicated that the CNTs were singly dispersed in the composites. The CNTs tended to be dispersed along grain boundaries resulting in a much finer grain size. Although the CNTs were shortened and some Al4C3 formed in the matrix, the layer structures of the CNTs were well retained. Raman spectroscopy also showed that the damage to CNTs during FSP was not severe. Compared to that of unreinforced Al, the yield strength of 1 wt.% and 3 wt.% CNT/Al composites increased by 23.9% and 45.0%, respectively. A strength equation relating with load transfer and the grain refinement was proposed to describe the increase of the yield strength of the composites. (C) 2011 Elsevier Ltd. All rights reserved.
关键词:
reinforced aluminum composites;mechanical-properties;matrix;composites;nanotubes;strength;alloy
S Narayan
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A Rajeshkannan
钢铁研究学报(英文版)
An experimental investigation on the workability behaviour of sintered Fe-035C steel preforms under cold upsetting, have been studied in order to understand the influence of aspect ratio and lubrication condition on the workability process. The above mentioned powder metallurgy sintered preform with constant initial theoretical density of 84% of different aspect ratios, namely, 04 and 06 respectively were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press and sintered for 90 min at 1200 ℃. Each sintered preform was cold upset under nil/no and graphite frictional constraint, respectively. Under the condition of triaxial stress densification state, axial stress, hoop stress, hydrostatic stress, effective stress and formability stress index against axial strain relationship was established and presented in this work. Further more, attained density was considered to establish formability stress index and various stress ratio parameters behaviour.
关键词:
powder metallurgy
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failure analysis
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plastic behaviour
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workability
