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Interdiffusion within the beta-phase region of the Ni-Co-Cr-Al quaternary system

Journal of Alloys and Compounds

Interdiffusion coefficients within the beta-phase region of the nickel-cobalt-chromium-aluminum (Ni-Co-Cr-Al) quaternary system were estimated by square root diffusivity analysis. The obtained results indicated that the cross interdiffusion coefficients D(ij) (i not equal j, i, j = Al, Cr, Co) other than D(AlCo), were less than the main interdiffusion coefficients Do (i = j), and that the values of D(Ali) were greater than those of D(Cri) and D(Coi). This finding suggests that the addition of chromium decreases the interdiffusion coefficients of aluminum and cobalt, but the addition of cobalt did not cause an obvious change in the interdiffusion coefficients of aluminum and chromium in the beta-phase region. The different effects associated with the additions of chromium and cobalt were qualitatively discussed in light of the relationship between the thermodynamic properties of the system and Wagner's interaction parameter. The results revealed that the different effects could be ascribed to the stronger thermodynamic interactions between aluminum and cobalt compared to that between aluminum and chromium. (C) 2009 Elsevier B.V. All rights reserved.

关键词: Diffusion;NiAl phase;Electron microprobe;multicomponent diffusion couples;square root diffusivity;transfer-matrix method;zero-flux planes;intermetallic compound;coefficients;ternary;nickel;alloys;fe

MOCVD制备SiC:Al薄膜的导电类型调控研究

陈小庆 , 孙利杰 , 邬小鹏 , 钟泽 , 傅竹西

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用MOCVD方法在Si基片上生长了Al掺杂的SiC薄膜,发现三甲基铝(TMA)源载气流量与硅烷流量之比的大小,会决定薄膜的导电类型.用XPS方法测试样品后发现,TMA载气流量与硅烷流量比直接影响Al原子在SiC薄膜中的含量.Al含量在1.5%以下,Al原子在SiC薄膜中主要以填隙形式(Ali)存在,薄膜显示出n型;而Al含量在1.5%~3%之间的时候,Al原子主要以替位Si(AlSi)的形式存在,薄膜显示出p型.继续增加掺杂源的流量,所得SiC薄膜结晶质量会变得较差,电阻也变得较高.

关键词: 3C-SiC , SiC:Al , MOCVD , 导电类型

Synthesis of porous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis: Reaction mechanism and anisotropy in pore structure

Acta Materialia

Porous Ni-Ti shape-memory alloys (SMAs) have attracted a great deal of attention recently because they have a similar microstructure to human bone and have significant prospects in medical applications. In the present study, equiatomic porous Ni-Ti SMAs, especially those with an unusual kind of linear-aligned elongated pore structure, have been successfully prepared by self-propagating high-temperature synthesis (SHS) using elemental nickel and titanium powders. The porous Ni-Ti SMAs thus obtained have an open porous structure with about 60 vol.% porosity, and the channel size is about 400 mu m. The corresponding microstructural characteristics and the effect of preheating temperature on the microstructure have been investigated. It is found that the combustion temperature increases with increasing preheating temperature and results in melting of the NiTi compound above 450 degrees C. Moreover, the preheating temperature has been shown to have a significant effect on the microstructure of the SHS-synthesized porous Ni-Ti SMAs, and the mechanism of anisotropy in pole structure is attributed to the convective flows of Liquid and argon during combustion. (C) 2000 Acm Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.

关键词: self-propagating high-temperature synthesis (SHS);porous Ni-Ti;shape-memory alloys;combustion synthesis

Cyclic stress-strain response and surface deformation features of 011 multiple-slip-oriented copper single crystals

Acta Materialia

Cyclic deformation behavior and surface deformation features of [011] multiple-slip-oriented single crystals were investigated at constant plastic shear strain amplitude (gamma(pl)) in the range of 1.1x10(-4)- 7.2 x 10(-3) at room temperature in air. It was revealed that the cyclic deformation characteristic of [011] copper single crystal is quite different from that of [001] and [(1) over bar 11] multiple-slip-oriented copper single crystals. The [011] crystal exhibits a rather low initial hardening rate, which does not increase notably even under higher plastic strain amplitudes. The cyclic stress-strain (CSS) curve of the [011] crystal exhibit a clear plateau region over the range of plastic strain amplitude investigated. Surface observations indicated that the primary persistent slip bands (PSBs) already occur under a lower strain amplitude of 1.1x10(-4), but the operation of secondary slip was strongly suppressed by the corresponding dislocation interactions even at high strain amplitudes. This slip characteristic was suggested to be associated with the occurrence of the plateau region. When gamma(pl)greater than or equal to 2.5 x 10(-3), two types of deformation bands (DBI and DBII) formed on the specimen surface and their habit planes are perpendicular to each other strictly. An analysis based on the classical crystallographic deformation geometry was proposed to interpret the existence of an irreversible rotation of crystal in single crystal subjected to symmetrical push-pull loading. This phenomenon is assumed to be an essential reason for the formation of DBI and DBII. When gamma(pl)greater than or equal to 5.0 x 10(-3) another type of deformation band (DBIII) was observed on the specimen surface and its habit plane is exactly (001) with the maximum shear stress acting on it. The favorable macroscopic state of stress may be responsible for the formation of DBIII, giving rise to the cyclic softening in the cyclically deformed [011] copper single crystals at high strain amplitudes (y(pl) greater than or equal to 5.0 x 10(-3)). (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.

关键词: dislocation-structures;fatigue damage;behavior;amplitude;localization

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