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[PtMnSb 15 nm /Si 10 nm ] *7 ferromagnet/semiconductor multilayered films were synthesized by solid-state reaction of [(Pt 0.69 nm /Mn 0.44 nm /Sb 0.37 nm ) *10 /Si 10 nm ] *7 elemental multilayers. Two different thermal treatments, i.e . the post-annealing and the simultaneous annealing (substrate heating during deposition) were employed to control the interdiffusion and the compound phase formation. Structural characterizations revealed that these films were composed of the PtMnSb, amorphous Si and interdiffusion layers. Moreover, the films produced by simultaneous annealing had the relatively thick interdiffusion layers rather than the films by the post-annealing. According to the magnetization measurements, we obtained the larger value of saturation magnetization for the simultaneous annealed film rather than that for the post-annealed one. We will discuss the structural and magnetic properties of the samples in conjunction with the extent of the interdiffusion as well as the crystallinity of the magnetic compound.

A novel synthesis method of Ba–Ga–Ge type-I clathrates is proposed. It enables us to use BaCO 3 for one of the starting materials in place of Ba metals, which should be the greatest advantage of handling the materials, from the viewpoint of possible industrial application in the near future. By using this method, we have successfully produced the Ba 8 Ga 16 Ge 30 compounds from the starting materials BaCO 3 , Ge and Ga. The synthesis reaction should occur simultaneously with the reduction reaction of BaCO 3 , which requires rather high reaction temperature beyond 1573 K. However, the resulting reactant still contains additional phases, such as Ge and Ba–Ga–O phases. The samples exhibited a positive value of the Seebeck coefficient from room temperature to 973 K, in spite of the fact that the Ba–Ga–Ge type-I clathrates were usually reported to show negative Seebeck coefficient.

To study dry sliding wear behavior and its relation to microstructure, Ti–50Al alloys and Ti–47Al–3W alloy and its composite with varying reinforcement of Ti2AlC were prepared by reactive arc-melting. Dispersion of fine B2 particles is obtained by the addition of tungsten to TiAl alloy, which improves both the hardness and wear resistance of the matrix. By adding carbon to Ti–47Al–3W alloy, composite can be produced having a random distribution of reacted rod-like Ti2AlC particles and smaller Ti2AlC precipitates with fine B2 particles in the matrix. The Ti–47Al–3W/3.5 vol%Ti2AlC intermetallic composite features excellent wear resistance compared to 10 and 18 vol% composites, and fine dispersion of the Ti2AlC and B2 particles in the matrix has improved the wear resistance properties.

Ti-B-N cast alloys were prepared by a reactive arc-melting technique using elemental titanium and boron nitride powders. The alloys obtained were composites of titanium matrix containing nitrogen of 3 mol% or less and a small amount of TiB reinforcement. The microstructure of the matrix was a cellular structure consisting of elongated dislocation cells with 1-2 μm in width and 5-10 μm in length, for Ti-1B-1N alloy. The TiB particles were rod-like in shape with size of less than 0.5 μm in diameter and agglomerated to form clusters along the grain boundary. The mechanical properties were mainly dependent on the content of nitrogen and the influence of TiB on the mechanical properties was relatively small. The Ti-B-N cast alloys containing suitable concentration of nitrogen, Ti-0.58-0.5N alloys, had a high strength of 920 MPa with adequate ductility of more than 5%.

TiAl(Cr)/Ti 2 AlC composites have been prepared by a reactive arc-melting technique using elemental powders of Ti, Al, Cr and C. Resulting composites have been reinforced using 3.5, 10 and 18 vol% Ti 2 AlC in a matrix of TiAl with and without addition of Cr. The axial ratio of γ-phase has been lowered through the complete solid solution of chromium. The grain size of the matrix has been found to decrease whereas its distribution converges along the content of Ti 2 AlC. The lamella grains in the matrix have been changed both into TiAl and very fine Ti 2 AlC particles by a homogenizing treatment. Compared to TiAl single-phase alloy, studied composite materials have revealed superior mechanical properties, such as bending strength, compressive strength and fracture toughness. This improvement is caused by the formation of Cr solid-solution for hardening, dispersion of the Ti 2 AlC particles and the fine grain of the TiAl matrix.

Antimony-doped MnPt 3 thin films have been successfully fabricated by solid-state reaction of thin multilayered Mn/Sb/Pt films. It was found that the (100) preferential orientation of the MnPt 3 phase was developed with increasing antimony content. In addition to this, an anomalous crystalline growth with (100) oriented grains was observed, which resulted in a wide distribution of the grain size of the annealed samples. This behavior is considered to be secondary grain growth, which is usually caused by a surface free energy minimization rule. However, the (100) planes of MnPt 3 do not have the lowest surface free energy. We discuss the mechanism of this anomalous grain growth from the view-point of strain energy minimization, in conjunction with the anisotropy in the strain energy density for each crystallographic plane of MnPt 3 .

TiAl/Ti2AlN composites were prepared by a reactive arc-melting technique using elemental powders of Ti, Al, and AlN . Ti2AlN particles synthesized by the combustion reaction synthesis were dispersed in the lamella grains, with rod-like shapes with sizes of 1–3 \\micron width and 5–15 \\micron length. The grain size of the matrix was decreased and the deviation of the grain size was converged by the distribution of the Ti2AlN . The lamella grains in the matrix were decomposed both into TiAl and very fine Ti2AlN particles by the homogenizing treatment. The bending strength of these composites was larger than that of TiAl single-phase material and it was improved by increasing the Ti2AlN content. Their ductility kept the same level of that of TiAl. Fracture toughness values were enhanced by the dispersion of Ti2AlN, since crack propagation can be deviated by such dispersoids in the composite materials.

We have investigated the structural and electric properties of TiB 2 thin films produced by RF sputtering on glass substrates. The films are composed of the TiB 2 small crystallites as well as the Brich amorphous phase, which is resulting from the Brich composition of the films. The resistivities of the films vary from 239 to 323 μΩ cm depending on the RF power and the sputter time. These values are considerably larger than that of a bulk sample. The temperature dependence of the resisitivities is found to be carrier concentration dependent. However, the very high carrier densities (0.7–1.2×10 22 /cm 3 ) and the relatively small mobilities (2.3–5.7 cm 2 V −1 s −1 ) were obtained, suggesting that the conduction carrier might behave like nearly free electrons. We discuss these features in conjunction with the microstructure of the films.

Gamma titanium aluminides ({gamma}-TiAl alloys), having an L1{sub 0}-type structure, are candidate materials for use in future gas turbine aero-engines and automotive engines because of their low density, high specific strength and high stiffness. In air, however, it is well known that titanium aluminide oxidizes at a more rapid rate at temperatures above 1,123 K; therefore, the oxidation resistance becomes a critical factor for TiAl alloys to be used at high temperatures (perhaps above 1,073 K). Coatings for the TiAl alloy are essential to high temperature oxidation resistance. The Al-Ti-Cr ternary phase diagram at 1,423 K indicates that the L1{sub 2} phase field is in equilibrium with the TiAl(L1{sub 0}) phase field. Furthermore, the L1{sub 0}- and L1{sub 2}-alloys in this ternary system resemble each other very closely in crystal structure and lattice parameter (TiAl(L1{sub 0}); a = 0.4005, c = 0.4070 nm (27), Ti-67Al-8Cr(L1{sub 2}); a = 0.3960nm (25)). Therefore, the L1{sub 2}-(Al,Cr){sub 3}Ti alloy can be considered applicable to L1{sub 0}-TiAl alloys as an optimum material for coatings. The purpose of this study is to apply L1{sub 2} alloy coatings to the TiAl alloys by pack cementation techniques, and to evaluate the oxidation resistance of the coated alloys.

Diffusion bonding of L10-type and L12-type alloys in the Ti-Al-Cr system was carried out to study graded diffusion layer. The Ti52Cr5Al43(L10) and Ti25Cr14Al61(L12) alloys were bonded at 1473 K for 1 h under 30 MPa, and annealed at 1423 K for 48 h in a vacuum(-10-4Pa). The resulting diffusion layer had Al-rich L10 phase layer of about 50μm and L12/L10 (coherent precipitated) two phase layer of about 50μm. The formation of the L12/L10 two phase layer is caused by the presence of the Ti-rich L12 phase field at higher temperatures. It was found that such diffusion layers have a preferable composition gradient and a graded linear expansion coefficient for functionally graded materials.

Using elemental powders, reactive hot-pressing was carried out to prepare Si3N4/SiC composite ceramics. Silicon and graphite powders with additives (Al2O3 and Y2O3) were reacted at 1873K in gaseous nitrogen (0. 15MPa) and hot-pressed at 2073K for 7.2ks with applied pressure of 70MPa, and finally formed a Si3N4(β-Si3N4)-SiC(β-SiC) composite with a small amount of glassy and crystalline phases from additives. The resulting composites had 12-34vol%SiC, and the SiC grains were granular with sizes of about 0.1-1μm, and homogeneously distributed and well bonded to the matrix Si3N4. On the other hand, the Si3N4 matrix grains were rod-like in shape with sizes of 0.3-3μm. It was found that the composite ceramics had a relatively higher bending strength at both ambient and elevated (at 1423K) temperatures; about 1000 and 700 MPa, respectively. Fracture toughness of 5.3 MPam1/2 was obtained by indentation fracture tests. It was evident that reactive hot-pressing was very effective process for in-situ synthesis of Si3N4/SiC composite ceramics.

To improve low room-and high-temperature strength of titanium alminides, TiAI based composites reinforced with TiB2 and Ti2AIN particles were made by combustion reaction process using Ti-AI-BN powder mixtures, and arc-melted for densification. The powder compositions included Ti47.4Al44.2(BN)8.4, Ti49.0Al42.6(BN)8.4 and Ti50.5Al41.1(BN)8.4 in at%, corresponding to matrix composition of Ti48Al52, Ti50Al50 and Ti52Al48, respectively. The volume fraction of reinforced particles was about 18%. The as cast specimens had a matrix of TiAl(γ) with a lamellar structure of Ti3Al(α2). In the annealed specimens, such lamellar structures were completely or partially disappeared, while smaller particles (about 100-200nm) were observed in the matrix of all specimens. These particles were found to be MAIN and mainly formed in place of disappeared Ti3Al in the lamellae. The formation of these particles was attributed to different solubility limit for nitrogen in yand α2 and solutionizing α2 phase by heat treatment. It was found that the composite materials had a high strength at both room and elevated(1173K) temperatures; 800-1100MPa and about 600MPa, respectively. The bending and fracture toughness tests also proved that the composite annealed is better than the as cast, and values were about 0.4% in ductility and 13-15 MPam in fracture toughness.

To enhance the negligible low-temperature strength and ductility and low high-temperature strength of titanium aluminides, TiAl-(TiB2+Ti2A1C) composites were made by the combustion reaction processing using Ti, Al, and B4C powders, and homogenized by arc melting. The alloy composition included Ti52.2A145.6(B4C)2, 2 in at.%. The resulting composites had about 14 vol.% (TiB2+Ti2AIC) in the matrix TiAl with a lamellar structure of Ti3Al. In the homogenized specimens, such lamellar structures were not observed, therefore, the matrix after the homogenizing treatment consisted predominantly of the TiAl phase which is expected from the Ti-Al equilibrium phase diagram. On the other hand, smaller particles were visible in the matrix, and appeared to form in place of solutionizing lamellae. These particles have also identified as a Ti2A1C phase with an average particle size of about 100-200 run. This suggested that carbon atoms in the matrix, probably in the Ti3Al phase, formed carbide Ti2Al particles when the lamellar Ti3Al phase was disappeared during the homogenization treatment. It was found that the composite material has a high strength at both ambient and elevated (at 1173 K) temperatures ; about 900 and 500 MEN, respectively, and ambient-temperature ductility as large as 0.8% was obtained in bending.

BaTiO3 thin films having a fine grain size

In this work, the effects of deposition and annealing conditions on the dielectric properties and dc conductivity were investigated on the thin amorphous SrTiO3 films prepared by a sputtering method using neutralized argon-ion beams. It was demonstrated that the dielectric constant and dc conductivity increased markedly by vacuum annealing and by increasing the target-substrate distance during deposition. The amorphous SrTiO3 films have the optical band gap of about 2.5eV, accompanying with rather wide band tails. This suggests the existence of structural defects which may be caused by oxygen deficiency in the amorphous structure. The amounts of the oxygen deficiency were considered to be dependent on the annealing atmosphere as well as the target-substrate spacing. It is supposed that the ionization of oxygen vacancies, Vo→Vo¨+2e', plays an important role for the dielectric properties and dc conductivity of the amorphous SrTiO3 thin flms. The relative dielectric constants obtained ranged from 20 to 550.

The ceramic composites were prepared from elemental powders, i.e., titanium powders, aluminum powders and graphite powders. The powder mixtures, with a composition Ti50Al25C25 (in atomic% ) were cold pressed, and combustion reaction was carried out to form ceramic composites in Ti-Al-C system. However, the reaction products had extensive pores. Then the products densified by hot pressing for 1.8ks at 1473K under 70MPa in Ar gas atmosphere. It was found that the matrix phase (Ti2AlC) had good properties, e.g., microhardness and thermal expansion coefficient, as a composite phase for TiAl alloys. The processing technique in the present investigation is of interest as a new combustion reaction process to synthesize in-situ ceramics and ceramic composites.

Thin films of Mn2Sb were prepared by solid state mutual reactions in multilayered films consisting of Mn and Sb which were made by ion beam sputtering. Microstructure of the films was investigated by means of small and large angle X-ray diffraction (XRD), and cross-sectional transmission electron microscopy (TEM). Modulation wavelength of the multilayered films and discharging power for an ion source during sputtering determined the microstructural feature in the interdiffused region between the Mn and Sb layers, which was a dominant factor governing the texture development of the Mn2Sb phase on annealing. It can be concluded that the oriented nucleation process during deposition plays a significant role for the development of preferred orientation of the reacted compounds.

In this work, high-temperature reaction process with gaseous nitrogen led Si and Ti powders, Si and titanium silicide powders or titanium silicide powders to two phase ceramic composites consisting of Si3N4 (α-Si3N4 and β-Si3N4) and TiN. The results of X-ray diffraction analysis showed there are remarkable differences in the ratio of α-Si3N4/β-Si3N4 between the specimen used elemental powders and that used intermetalic powders. That is mainly caused by a difference in the starting temperature and reactivity of silicon nitridation. Thus, it is promising for synthesis of Si3N4-TiN composite powders to use intermetalic powders.

Thin multilayered films of Mn/Sb/Bi and Mn/ (Sb-Bi) were fabricated by ion-beam sputtering in order to synthesize the B81-Mn (Sb-Bi) phase by solid-state reaction and to examine the possibility of controlling the magnetic anisotropy of the films. Films which exhibited a strong (001) -preferred orientation of the B81 phase could be produced up to a bismuth content of y=0.06 for multilayered films of Mn/ (Sb1−yBiy). Texture development was greatly affected by the composition of the Sb-Bi solid-solution which formed in the Sb/Bi interface regions in the as-sputtered state, through the epitaxial growth process of the B81 phase. Although the films having a perpendicular magnetic anisotropy could not be obtained, the magneto-crystalline anisotropy of the B81 phase was estimated to change significantly with bismuth additions.

Superconducting transition behavior and phases evolved after sintering at 1145 K were studied on Si-doped Bi-based superconductors as a function of the doping level. The addition of Si in amounts of 0.29 to 0.57 wt% markedly improved the superconducting transition around 110 K; operating mechanisms are discussed based on DTA and microstructural analysis.

The TiAl‐Ti2AlC composites with and without impurities, Ni, Cl and P, were prepared by combustion reaction from the elemental powders and cast after arc melting. The resulting composites had about 18vol% Ti2AlC in the lamellar matrix consisting of -TiAl and Ti3Al (2). In the homogenized specimens, the2 phase decomposed to-TiAl and Ti2AlC. The composite material had a high strength both at ambient and elevated (1173K) temperatures; about 800 and 400MPa, respectively, with an ambient temperature ductility of 0.7% at bending test. The fracture toughness test also proved that the homogenized composite has higher toughness than the as cast one. The toughness value reached to 17.8MPam 1/2 . The zigzag cracks propagated in the homogenized composite and the reinforcement Ti2AlC particles and the finely precipitated Ti2AlC particles were main obstacles to the crack propagation. The composite with impurities showed a marginal improvement in the oxidation resistance over the composites without impurities. # 1999 Elsevier Science Ltd. All rights reserved.