Thin foil preparation of metal particles in brittle ceramic matrices

Predisposing germline mutations in the BRCA1 gene were identified recently in families with 17 q-linked breast and ovarian cancers. Using single-strand conformation polymorphism (SSCP) analysis, we examined primary breast cancers for mutations in coding exons of BRCA1 in a panel of 103 patients, of whom all either represented early-onset cases (< 35 of age), were members of multiply-affected families, and/or had developed bilateral breast cancers. Mutations were detected in tumors from four patients, all of whom had developed breast cancers bilaterally: a frame-shift due to a 2-bp deletion at codon 797; a nonsense mutation at codon 1214; and two missense mutations, one at codon 271 leading to Val-->Met substitution, and the other at codon 1150 leading to Pro-->Ser substitution. In each case the same mutation was present in constitutional DNA. The mean age of onset was 49 years among the Japanese carriers of BRCA1 mutations identified in this study, in contrast to the mean age of 35 observed among carriers of BRCA1 mutations in a similar U.S. study (Futreal et al., 1994). The evidence reported here supports a rather limited role of BRCA1 in breast carcinogenesis.     

High-temperature compatibility of refractory metals with scandium oxide

Conclusions Chemical reaction between Sc₂O₃ and Ta, Mo, and W is not observed when they are heated to 2100°C in a protective medium for 4 h. The depth of diffusion of the metal into the oxide is less than the resolving power of the microscope (1). It is, therefore, theoretically possible to use scandium oxide as a dispersion-strengthening phase for metal artifacts of Ta, Mo, and W, for coating these artifacts with Sc₂O₃, etc.Translated from Poroshkovaya Metallurgiya, No, 1, pp. 83–87, January, 1968.     

High-temperature friction of refractory compounds

The paper overviews long-term studies into the behavior of metallic (carbides, borides, and nitrides of transition metals), and nonmetallic (boron and silicon carbides, aluminum nitride) refractory compounds as well as composite materials based on them in high-temperature friction in vacuum and air. The friction characteristics (wear rate and friction coefficient) are indicated as a function of temperature in the range from room temperature up to 1000–1400 °C. Data of x-ray examination and electron microscopy of friction surfaces are cited. The fracture mechanism for contacting surfaces of materials in friction is considered. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 167–178, 2008.     

The Effect of ceramic reinforcements during spray atomization and codeposition of metal matrix composites: part i. heat transfer

The effects of ceramic participates on microstructure during spray atomization and codeposition of metal matrix composites (MMCs) were investigated, with particular emphasis on the transfer of thermal energy from the atomized matrix to the ceramic particulates. A thermal energy model, based on fundamental heat-transfer considerations, was formulated, and the numerical results were compared to the microstructural findings. In this model, the transfer of thermal energy from the atomized metal to the ceramic phase was computed for two separate stages: (a) atomization and (b) deposition. The numerical results obtained using SiC particulates in an aluminum matrix show that 10 pct of the enthalpy of the atomized spray is transferred to the ceramic particulates during atomization, whereas 10 pct of the thermal energy available after deposition will be consumed in the process of equilibrating the temperature of the particulates to that of the matrix. The enhanced heat transfer achieved as a result of the presence of ceramic reinforcement was correlated with the grain sizes of various unreinforced and reinforced spraydeposited MMCs.     

High-temperature interaction of uranium mononitride with refractory metals. Interaction with rhenium

The interaction of uranium mononitride UN with a refractory metal (rhenium) is studied in the temperature range 1773–2273 K. The coefficients of uranium diffusion from UN into polycrystalline and single-crystal rhenium and their temperature dependences are determined. The diffusion mobility of uranium in rhenium is shown to be lower than that in molybdenum and to be higher than in tungsten.     

High-temperature oxidation of a silicon nitride constructional ceramic

Conclusions An account is given of an investigation into the high-temperature oxidation of a silicon nitride base constructional ceramic. It is shown that the mechanism of the oxidation process for this ceramic depends on temperature. The ceramic is superior in oxidation resistance to similar materials studied earlier.Translated from Poroshkovaya Metallurgiya, No. 11(263), pp. 50–54, November, 1984.     

The Effect of ceramic reinforcements during spray atomization and codeposition of metal matrix composites: Part II. Solid-state cooling effects

In the present study, the mechanisms governing the evolution of microstructure during spray atomization and codeposition of metal matrix composites (MMCs) were investigated, with particular emphasis on the effects of the ceramic phase on the resulting microstructure during solidstate cooling. The grain size refinement that is commonly observed when a distribution of ceramic particulates is coinjected into a metallic spray during spray atomization and deposition processing was rationalized in terms of three distinct effects: (a) solidification effects, (b) heattransfer effects, and (c) solid-state cooling effects. The solidification and heat-transfer effects were discussed in Part I. [1] Regarding solid-state cooling effects, the present results show that the presence of a dispersion of ceramic particulates in the aluminum matrix effectively reduces the rate of grain growth during solid-state cooling. Experimental support to this suggestion was provided by the results of an investigation on the changes in grain size following isochronal thermal anneals.     

定向硅基陶瓷型芯的高温强化

采用热压注法制备氧化硅基陶瓷型芯,以硅酸乙酯水解液为强化液对型芯进行高温强化,研究强化液浓度和强化次数对型芯的高温挠度、开气孔率以及室温抗弯强度的影响.结果表明:强化液浓度对型芯的高温挠度影响显著,而对型芯室温性能影响不大,随着强化液中硅酸乙酯体积分数增加,型芯的高温挠度呈先减小后增大的趋势,当硅酸乙酯的体积分数为90...     

High-temperature behavior of precious metal base composites

The high thermodynamic stability and exceptional mechanical properties of intermetallic compounds based on platinum group metals (PGMs) make them potentially exploitable as structural materials for elevated temperature service. In this study, the development of high-temperature strength was evaluated for a selection of eutectic composites based on Ru-Al, Ir-Al, Ru-Nb, Ir-Nb, and Ru-Al-Ni using compression tests. All the alloys tested were characterized by high strength at extreme tem-peratures, none more so than an Ir₈₄Nb₁₆ alloy which had a proof stress in excess of 600 MPa at 1300 ‡C. In addition, several alloys showed significant compressional ductility at room temperature. Of particular interest is the synergy of soft constituent phases in evolving strengths greater than that anticipated by simple rules of mixture. The potential of secondary phases to advance both strength and room-temperature ductility makes these composites worthy of further investigation.     

The effect of reinforcements on the densification of a metal powder

The consolidation of Cu powder with and without particulates has been investigated. It was found that the same deformation mechanism applies over a wide range of consolidation conditions and reinforcement contents. A formalism previously used to characterize the consolidation of metal powder has been successfully extended to the composite system. The results demonstrate densification retardation caused by the reinforcements that depends both on aspect ratio and on mixing heterogeneity. Furthermore, the effect is greater than the corresponding effect of the reinforcements on the creep-rate of the fully densified body.     

High-temperature dilatometry of Ti-46Al-8Nb refractory alloy

The temperature dependence of the linear thermal expansion coefficient K _L of the intermetallic Ti-46Al-8Nb (at %) alloy is experimentally determined for the first time within the temperature range from 373 to 1773 K (solidus point). The determined boundaries of phase fields are compared with the results of differential thermal analysis and the calculated phase diagram of the alloy. The high-temperature limit (1384 K) of the alloy structure thermostability is detected from signs of the α₂ + γ ? α + γ phase transition in dilatometric curves. The restructuring mechanism in the α + γ field is studied by scanning electron microscopy. It is shown that the α₂ + γ → α + γ phase transition is accompanied by selective structural degradation of single-crystalline α₂ lamellae and the related destruction of a fine lamellar α₂-Ti₃Al(Nb) + γ-TiAl(Nb) texture. The average values of K _L of the alloy are calculated within 100-K ranges in the low-temperature α₂ + γ phase field, which is of interest from a practical viewpoint, according to the State Standard GOST 8.018-2007.     

Enhancement of cell interactions with collagen/glycosaminoglycan matrices by RGD derivatization

The interaction of three cell types important to the wound repair process with collagen/glycosaminoglycan (GAG) dermal regeneration matrices covalently modified with an Arg-Gly-Asp (RGD)-containing peptide was characterized. Function-blocking monoclonal antibodies directed against various integrin subunits were used to demonstrate that human fibroblasts attached to the unmodified matrix through the integrin, alpha2beta1. Human endothelial cells and human keratinocytes, however, attached minimally to the unmodified matrix. After modification of the collagen/GAG matrix with RGD-containing peptide, endothelial cells and keratinocytes attached and spread well on the matrix. This attachment was RGD dependent as evidenced by essentially complete inhibition with competing soluble peptide. In terms of overall cell number, fibroblast cell attachment remained unchanged on the RGD peptide-modified matrix compared to the unmodified material. Antibody and peptide inhibition studies demonstrate, however, that attachment to the modified matrix was mediated by both alpha2beta1 and RGD-binding integrins. We have successfully introduced a specific RGD receptor-mediated attachment site on collagen/GAG dermal regeneration matrices, resulting in enhanced cell interaction of important wound healing cell types. This modification could have important implications for the performance of these matrices in promoting dermal regeneration.     

Identification of thermodynamically stable ceramic reinforcement materials for iron aluminide matrices

Aluminide-base intermetallic matrix composites are currently being considered as potential high-temperature materials. One of the key factors in the selection of a reinforcement material is its chemical stability in the matrix. In this study, chemical interactions between iron alu-minides and several potential reinforcement materials, which include carbides, oxides, borides, and nitrides, are analyzed from thermodynamic considerations. Several chemically compatible reinforcement materials are identified for the iron aluminides with Al concentrations ranging from 40 to 50 at. pct.