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COMPOSITION TRIANGLE DIAGRAMS OF Ni-Mn-Ga MAGNETIC ShAPE MEMORY ALLOYS

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Acta Metallurgica Sinica(English Letters) 2006年第3期19卷 171-175页

作者： Y.F. Wang J.M. Wang C.b. Jiang h.b. xu School of Materials Science and Engineering Beijing University of Aeronautics and Astronautics Beijing 100083 China

A statistical work has been done to collect the composition ranges of Ni-Mn-Ga alloys exh.b.ting different structures and martensite start temperature （M,）, large magnetostrain or the co-existence of magnetic and structural transitions. The alloys with five-layered （5M）, seven-layered （7M） modulated and non-modulated （T） martensitic structures were mapped in the graph. An empirical formula has been presented to reflect the effect of elements nickel （Ni ）, manganese （ Mn ） and gallium （Ga）, on the martensite start temperature （M3）. The martensitic structure is sensitive to the composition and the martensitic transformation temperature is most drastically affected by the Ni content. The alloys with large magnetostrain or co-existence effect of the magnetic and structural transitions were also listed in a limited area.

关键词： Ni2MnGa alloy martensitic transformation magnetic shape memory alloy

ThE INFLUENCE OF Mo DIFFUSION ON ThE ThERMAL bEhAVIOR OF TbCs ON Ni_3Al bASED ALLOY IC-6

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Acta Metallurgica Sinica(English Letters) 2002年第1期15卷 45-48页

作者： D.b. Zhang S.K. Gong h.b. xu Y.F. han Dept. of Mat. Sci. and Eng. Beijing Univ. of Aero. and Astron. Beijing 100083 China

Conventional two-layered structure thermal barrier coatings (TbCs) were prepared onto γ'-Ni3Al based alloy IC-6 by electron beam physical vapor deposition (Eb-PVD). Isothermal oxidation and thermal cycling tests were carried out to investigate the effect of Mo content at the interface between bond coat and ceramic top coat caused by diffusion. It has been found that the alloy coated with TbCs presented the lowest oxidation weight gain value for the reason that the ceramic top coat in TbC system can effectively stop Mo oxides evaporating. The life time of TbCs has close relation with Mo content at the interface between the bond coat and top coat. Spaliation of ceramic top coat occurred during thermal cyclic testing when Mo atoms accumulated at the interface up to certain amount to decline the combination between the bond coat and top coat.

关键词： Eb-PVD thermal barrier coatings (TbCs) thermal cyclic diffusion

CODEPOSITION OF ALUMINUM AND SILICON ON PURE MOLYbDENUM SUbSTRATE USING hALIDE ACTIVATED PACK CEMENTATION TREATMENTS

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Acta Metallurgica Sinica(English Letters) 2002年第2期15卷 167-171页

作者： J.L. xu, F.S. Liu, C.G. Zhou, S.K. Gong and h.b. xu Department of Material Science and Engineering, beijing University of Aeronautics and Astronautics, beijing 100083, China Dept. of Mat. Sci. and Eng. Beijing Univ. of Aero. and Astron. Beijing 100083 China

A multi-component diffusion coating has been developed to protect Mo-based alloys from high temperature environmental attack. Aluminum addition was made during the coating process to improve the oxidation resistance by developing hexagonal Mo(Si, Al)2 through the development of the halide activated pack cementation coating process on pure Mo substrate. The results show that Mo(Si, Al)2 formed as a main phase on the surface and a little amount of Mo5Si3 also formed. The total thickness of coating is tens ofμm at 1373K. During the cyclic oxidation test at high temperature(at about 1323K in air), mullite (3Al2O3.2SiO2) and some SiO2 formed. The addition of Al is beneficial for MoSi2 coating and the Al-doped coating exh.b.ted only a small weight gain and protected the Mo substrate, while the MoSi2 coating without Al suffered a significant weight loss, indicating a loss of volatile MoO3 after cycles.

关键词： multi-component coating Mo(Si A1)2 halide activated pack cementation 3Al2 O3. 2SiO2 oxidation resistance

PREPARATION OF NANO-CRYSTALLINE Fe-Cu ThIN FILMS AND ThEIR MAGNETIC PROPERTIES

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Acta Metallurgica Sinica(English Letters) 2002年第1期15卷 109-112页

作者： X.F. bi S.K. Gong h.b. xu K.I Department of Materials Science and Engineering Beijing University of Aeronautics and AstronauticsBeijing 100083 China Research Institute of Electrical Communication Tohoku University Japan

Fe-Cu thin films of 0.2 mum in thickness with different Cu contents wereprepared by using r.f. magnetron sputtering onto glass substrate. The effect of sputteringparameters, including Ar gas pressure and input rf power, on the structure and magnetic propertieswas investigated. It was found that when the power is lower than 70W, the structure of the filmsremained single bcc-Fe phase with Cu solubility of up to 50at. percent. TEM observations for th.b.c-Fe phase showed that the grain size was in the nanometer range of less than 20nm. The coercivityof Fe- Cu films was largely affected by not only Ar gas pressure but also rf power, and reachedabout 2.5Oe in the pressure of 0.67-6.67Pa and in the power of less than 100W. In addition,saturation magnetization, with Cu content less than 60at. percent, was about proportional to thecontent of bcc-Fe. When Cu content was at 60at. percent, however, saturation magnetization was muchsmaller than its calculation value.

关键词： Fe-Cu thin film magnetic property sputtering condition nano-crystalline

ThE ChARACTERISTICS OF OXIDE SCALE FORMED ON LOW PRESSURE PLASMA SPRAYED NiCrAlY COATING IN ThE PRESENCE OF 5% WATER VAPOR

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Acta Metallurgica Sinica(English Letters) 2002年第1期15卷 123-126页

作者： J.S. Yu C.G. Zhou h.b. xu S.K. Gong Department of Materials Science and Engineering Beijing University of Aeronautics and AstronauticsBeijing 100083 China

The oxidations of low pressure plasma sprayed (LPPS) NiCrAlY coating on nickel base superalloy were studied at 1050℃ in flows of O2, and mixture of O2 and 5%h2O under atmospheric pressure. Oxide formed on the surface of LPPS NiCrAlY coating after oxidation at 1050℃ in pure O2 consisted of NiCr2O4, whereas oxide formed on the surface of LPPS NiCrAlY coating after oxidation at 1050℃ in a mixture of O2 and 5%h2O is mainly composed of NiO. The effect of water vapor on the characteristics of the oxide scale is attributed to the increase in Ni cation transport.

关键词： oxidation water vapor coating

PREPARATION OF Fe/Ni MULTILAYER FILMS AND ThEIR MAGNETIC PROPERTIES

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Acta Metallurgica Sinica(English Letters) 2002年第2期15卷 182-186页

作者： L.L. Liu, X.F. bi, S.K. Gong, h.b. xu and X. Y. Yuan Department of Materials Science and Engineering, beijing University of Aeronautics and Astronautics, beijing 100083, China Dept. of Mat. Sci. and Eng. Beijing Univ. of Aero. and Astron. Beijing 100083 China

FeNi multilayer films were prepared by Eb-PVD technique. A modified TG-DSC apparatus was used to measure their Curie temperatures, which were around 7600C, lower than that of pure Fe thin films. The easy magnetization axis was in-plane. high temperature annealing in vacuum decreased the coercivity sharply. The saturation magnetization also changed with heat treatment. After annealing at the temperature equal to the substrate temperature during deposition, the saturation magnetization decreased.

关键词： multilayer film Eb-PVD. Curie transition point saturation magnetization. coercivity

ThE CRYSTALLIZATION KINETICS OF AN AMORPhOUS Ti-RIChNiTi FILM

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Acta Metallurgica Sinica(English Letters) 2000年第6期13卷 1131-1135页

作者： X. Y. Jiang, h.b. xu and S.K. Gong (Department of Materials Science and Engineering, beijing University of Aeronautics and Astronautics,beijing 100083, China)

The crystallization kinetics of an amorphous Ti-rich NiTi film (Ni 46.34at.%, Ti 53.66at.%)prepared by DC magnetron sputtering was determined by non-isothermal techniques. The activation energy of crystallization and the mean value of the Avrami parameter are 382kJ/mol and 0.85, respectively. The calculated isothermal kinetic curse of amorphous film at 773K coincides with the result of X-ray *** formation of a Ti2Ni phase is accompanied with the crystallization of Ti-rich NiTi film.

关键词： amorphous NiTi film crystallization kinetics activation energy of crystallization

A STUDY ON ALUMINIDE COATINGS ON TiAl ALLOYS bY PACKCEMENTATION METhOD

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Acta Metallurgica Sinica(English Letters) 2000年第6期13卷 1148-1154页

作者： C.G. Zhou, h.b. xu and S.K. Gong (Department of Materials Science and Engineering, beijing University of Aeronautics and Astronautics,beijing 100083, China) K. Y. Kim (Department of Materials Science and Engineering, Pohang University of Science and Techn

The halide-activated pack cementation method is utilized to deposit aluminide coat- ings on TiAl alloys. Emphasis is placed on the effect of alloying elements on the aluminizing behavior of TiAl alloy. The addition of a small amount of Nb or Cr in the TiAl improves significantly the aluminizing kinetics of TiAl alloys by increasing the solid-state division of Al through the formation of stable TiAl3 layer. The TiAl3 layer formed on the TiAl alloyed with Nb or Cr has better toughness than the TiAl3 formed on the non-alloyed TiAl. The reason for better toughness of the coating formed on TiAl is that partial TiAl3 with tetragonal structure was changed to high symmetry cubic L12 structure since Nb or Cr was dissolved into TiAl3. The TiAl3 layer formed on the TiAl alloyed with Nb or Cr has much.b.tter oxidation resistance than the TiAl3 layer formed on the non-alloyed TiAl. It is attributed to change in the crystal structure of TiAl3 from the brittle tetragonal DO22 to the ductile cubic L12 by addition of small amount of Nb or Cr.

关键词： TiAl alloying element pack cementation aluminizing

EXPERIMENTAL AND ThEORETICAL INVESTIGATION OF PSEUDOELASTIC hYSTERESIS IN ShAPE MEMORY ALLOYS

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Acta Metallurgica Sinica(English Letters) 1999年第3期12卷 235-240页

作者： Gong, S.K. xu, h.b. beijing Univ of Aeronautics and Astronautics Beijing China

The pseudoelastic hysteresis loop associated with phase equilibrium and the stress relaxation on the yield line were investigated, and the theoretical description was confirmed by deformation controlled load-deformation measurements on CuZnAl single crystals. It was found that in a loading-unloading process, the states of shape memory alloys run through a hysteresis loop, and the points that trigger the internal yield and recovery inside the pseudoelastic hysteresis loop define a line that traverses the hysteresis loop from the upper left to the lower right corner. This line was interpreted as a line of unstable phase equilibrium according to the thermodynamic arguments, which determines also the tendency for stress relaxation on the yield line section and for a stress growth on the recovery line section.

关键词： Aluminum copper alloys hysteresis Stress relaxation