HAN Yafang M. C. Chaturvedi Institute of Aeronautical Materials
,
Beijing
,
Chi na. Department of Mechanical Engineering
,
University of Manitoba
,
Canada.
材料科学技术（英文）
The steady state creep rate equdtion of a nickel base superalloy Inconel 718, strengthened by coherent ordered disc-shaped bct γ~(11) phase and coherent spherical fcc γ~1 phase precipitates, has been established in the stress and temperature ranges of 620-840 MN m~(-2) and 853-943K, respecti- vely. Constant stress tensile creep tests were used to medsure the values of steady state creep rate, ε_s, and the consecutive stress reduction method was used to measure the back stress during creep deformation. The values of effective stress exponent, n_e, were detemined from the slopes of the lgε_s vs. lg(σ_a-σ_0)/G plots. The effect of grain size, d, on steady state creep rdte has been also studied in this investigation, and the grain size sensitive exponents m were detemined from the slopes of lgε_s vs. lg(b/d) plots. The creep rate equations of Inconel 718, in the above stress and temperature ranges, have been proposed to be ε_s=1.6×10~(-5)(D_1Gb/KT) (b/d )~(0.19)[(σ_a-σ_0)/G]~(1.35) in diffusional creep region, and ε_s =75(D_1Gb/KT) (b/d)~(-0.42)[(σ_a-σ_0)/G]~(5.5) in dislocation power law creep region.
关键词:
Inconel 718
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null
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Materials Science and Technology
The relationship between degeneration of the primary M7C3 carbide and precipitation of the secondary M23C6 carbide has been investigated in a cobalt base superalloy after 100 h aging at 850 degrees C. The results indicated that the primary M7C3 carbide could not transform in situ into the secondary M23C6 carbide. The M23C6 formed by a direct reaction between chromium and carbon atoms. The dissolution of M7C3 provided the precipitation of M23C6 with essential carbon, which acted as a carbon reservoir. Near M7C3, the chromium content is a controlling factor of M23C6 precipitation while away from it, the carbon content dominated the reaction. The precipitate free zone around M7C3 is attributed to chromium depletion which is inherited from the as cast condition. MST/4174
关键词:
Materials Letters
Mechanical alloying (MA) of elemental powder mixtures of Fe50Nb35C15, Fe60Nb30C10 and Fe50Nb40C10 was performed using a high energy ball mill. In the MA processing, ball milling first leads to a Fe-Nb-C amorphous phase and nanocrystalline NbC. Further milling results in the formation of a nanocrystalline solid solution of Fe(Nb, C) and nanocrystalline NbC in Fe50Nb35C15 and Fe60Nb30C10, while the final product for Fe50Nb40C10 is a mixture of amorphous Fe-Nb-C and nanocrystalline NbC.
关键词:
mechanical alloying;Fe;Fe, Nb and C powders;amorphous;nanocrystalline;solid solution
Journal of Applied Physics
The dependence of yield strength, uniform elongation, and toughness on grain size in metallic structural materials was discussed. The toughness is defined as the product of yield strength and uniform elongation. The yield strength versus grain size can be well described by the Hall-Petch relation; however, the uniform elongation versus grain size is not well understood yet. A simple model involving the densities of geometrically necessary dislocations and statistically stored dislocations was proposed to estimate the uniform elongation versus grain size. Existing data for low carbon steels and aluminum indicate that, in the grain size less than 1 mu m, the materials usually exhibit high strength and low uniform elongation and, in the grain size greater than 10 mu m, the materials usually exhibit low strength and high elongation; in either case the toughness is low. However, in the grain size of several micrometers, the toughness is the highest. It is suggested that we should pay more attention to develop the metallic materials with grain size of several micrometers for structural applications. (c) 2007 American Institute of Physics.
关键词:
nanocrystalline copper;nanostructured metal;steels;deformation;ductility;law
Ieee Transactions on Components and Packaging Technologies
Silver-carbon (Ag/C) contact materials with different types of carbon, including diamond, graphite, carbon black, and carbon nanotubes were,fabricated by high-energy ball milling and hot-pressing. Their microstructures, arcing properties, and stability of the carbon structures were investigated. The results show that Ag/C nanotubes material displays a scallop-like morphology, which is significantly different from the microstructure of other Ag/C materials with dispersed particles. During the process of discharge, the diamond and carbon black in Ag/C materials are partially graphitized, while the morphology and crystal structure of graphite component have little change, indicating the graphite structure of Ag/C materials is the most stable of all.
关键词:
electrical contacts;Raman spectra;silver-carbon (Ag/C) black;silver-carbon (Ag/C) nanotubes;silver-diamond (Ag/diamond);silver-graphite (Ag/graphite);nanotubes;raman
新型炭材料
SiC/C foams and their monoliths of the same compositions, with various electrical Conductivities were prepared by polymer sponge replication/carbonization and hot-press solidification/carbonization respectively. Both materials have a three-dimensionally connected pore Structure with the former on a macroscopic scale and the latter a microscopic scale. The electromagnetic parameters of the SiC/C foams and the monoliths Versus their electric conductivities were measured at a frequency of 2 450 MHz by the TE(10) resonant cavity perturbation method. Results show that when the electrical conductivities of the SiC/C foams and the monoliths increase gradually, their dielectric constants epsilon(r') increase gradually and their dielectric losses tg delta(e) exhibit a maximum. The magnetic loss tg delta(m) of the SiC/C foams increases Continually while that of the monoliths first increases quickly then decreases slowly with increasing electric conductivities. When the effective electric conductivities of the SiC/C foams and the monoliths are the same, the epsilon(r') Values of the SiC/C foams are about a half and the to partial derivative(e) values are at least 2 times larger than those of the monoliths, while the tg delta(m) values of the monoliths are more than 4 times those of the SiC/C foams. The SiC/C foams and the monoliths are both non-magnetic, and their magnetic losses are found to be caused by their special structures interacting with the incident electromagnetic waves. Thus it is apparent that this kind of magnetic loss is extrinsic.
关键词:
SiC/C foams;Reticulated structure;Electromagnetic loss;Perturbation;method;extrinsically magnetic loss;carbon foams;dielectric-properties;x-band;composite;conductivity;black
Naqiong Zhu
材料科学技术（英文）
Three-dimensional atom probe (3DAP) technique has been used to study the nucleation and growth of M23C6 carbide in a supersaturated multi-component Fe-based alloy aged at 800°C. 3D images indicate that the radius of M23C6 carbide after ageing for 10 min is about 9 nm. Concentration profiles of alloy elements in the carbide are also obtained. Combined with PANDAT and Thermo-Calc software, attempts to model the early stages of precipitation are present. The calculated particle size and composition of M23C6 carbide is in good agreement with 3DAP data.
关键词:
Nucleation and growth
