Language：English   Publisher：ELSEVIER SCIENCE SA  

Tensile creep tests were combined with detailed transmission electron microscopy in order to characterize the dislocation movements during creep of the die-cast AM50 magnesium alloy. TEM observations indicate that dislocations are introduced within the primary alpha-Mg grain interior in the die-casting process, which consist of both the basal and non-basal segments. The non-basal segments of dislocations, having smoother curvature in as die-cast state, partially exhibit steps parallel to the basal plane during high temperature exposure. The basal segments of dislocations are able to bow out and glide on the basal planes under the influence of a stress, and the non-basal segments and/or jogs follow the basal segments with the help of climb during creep. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matchemphys.2009.06.012

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Language：English   Publisher：JAPAN INST METALS  

The creep of die-cast Mg-Al-Ca alloys is characterized by the pronounced decrease in creep rate during the transient region. Higher creep rates immediately after the stress application for the alloys can result in the degradation of bolt-load retention in the automotive powertrain, applications. In this study, the effect of prior deformation on creep behavior was investigated for the Mg-Al-Ca AX51 (X representing calcium) die-cast alloy, where the prior deformation was introduced by using the creep machine at temperatures of 423 and 473 K. The creep curves of the specimens with the prior deformation were compared with that of the as die-cast specimen at the creep testing condition of 423 K and 80 MPa. It was found that the prior deformation introduced by the creep machine is not effective to decrease the creep rates for the alloy. The obtained results of creep behavior are discussed on the basis of dislocation movements during creep. [doi:10.2320/materirans.MAW200901]

DOI： 10.2320/matertrans.MAW200901

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Language：English   Publisher：ELSEVIER SCIENCE SA  

Creep rupture tests were performed for die-cast AM50 + xCa (x = 0.47, 0.95 and 1.72 mass pct) alloys at temperatures between 423 and 498 K. The creep curve for the alloys is characterized by a minimum in the creep rate, and the decrease in creep rate during transient stage becomes pronounced with calcium concentration. The minimum creep rate (epsilon over dot(m)) and the creep rupture life (t(rup)) follow the phenomenological Monkman-Grant relationship for each alloy; t(rup) = Co/epsilon over dot(m)(m). It is found that the exponent m is unity for the alloys and the constant Co is independent of creep testing temperature, which is reduced with increasing calcium concentration. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matchemphys.2008.09.015

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Language：English  

Thermal conductivity and thermal expansion for the intermetallic compounds Ir3X (X = Ti, Zr, Hf, V, Nb or Ta) were measured in the temperature range between 300 and 1100 K. The thermal conductivities of Ir3X are distributed in the range from 41 to 99 W m-1 K-1 at 300 K, while the difference of thermal conductivities becomes less emphasised at higher temperatures. The coefficient of thermal expansion (CTE) values of Ir3X are insensitive to temperature, and fall around 8 × 10-6 K-1 at 800 K. The Ir3X intermetallic compounds with X = Ti, Zr, Hf, Nb or Ta are suitable for ultra high-temperature structural applications due to their higher thermal conductivities and smaller CTE values.

DOI： 10.1595/147106708X361321

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Language：English   Publisher：JOHNSON MATTHEY PUBL LTD CO  

Thermal conductivity and thermal expansion for the intermetallic compounds Ir3X (X = Ti, Zr, Hf, V, Nb or Ta) were measured in the temperature range between 300 and 1100 K. The thermal conductivities of Ir3X are distributed in the range from 41 to 99 W m(-1) K-1 at 300 K, while the difference of thermal conductivities becomes less emphasised at higher temperatures. The coefficient of thermal expansion (CTE) values of Ir3X are insensitive to temperature, and fall around 8 x 10(-6) K-1 at 800 K. The Ir3X intermetallic compounds with X = Ti, Zr, Hf, Nb or Ta are suitable for ultra high-temperature structural applications due to their higher thermal conductivities and smaller CTE values.

DOI： 10.1595/147106708X361321

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Language：English   Publisher：JAPAN INST METALS  

Tensile creep tests have been carried out for the die-cast AM50 + xCa (x = 0.47, 0.95 and 1.72 mass pct) alloys in the temperatures between 423 and 523 K to elucidate the effect of calcium additions on creep properties for the AM50 alloy. The creep curve for the AM50 + xCa alloys is characterized by a minimum in the creep rate followed by an extended accelerating stage, and the decrease in creep rate during transient stage becomes pronounced with calcium concentration. The creep strengthening by calcium addition is emphasized at lower stresses and lower temperatures, resulting in the positive dependence of creep parameters, it and Q(c) against calcium concentration. It is found that the eutectic intermetallic phase covering the primary a grains detected in the AM50 + xCa alloys prevents the dislocation annihilation at grain boundaries. The creep strengthening by the addition of calcium results from both the solid solution strengthening of the a matrix by solute calcium and the retardation of dislocation annihilation attributed to the eutectic intermetallic phase. [doi: 10.2320/matertrans.MAW200830]

DOI： 10.2320/matertrans.MAW200830

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Language：English  

Creep rupture tests were performed for a die-cast Mg-Al-Mn alloy, AM50, at 34 kinds of creep conditions in the temperature range between 423 and 498 K. The creep curve is characterized by a minimum in the creep rate followed by an extended accelerating stage. The minimum creep rate (ε̇m) and the creep rupture life (trup) follow the phenomenological Monkman-Grant relationship
trup = C0/ε̇ mm. It is found for the die-cast AM50 alloy that the exponent m is unity and the constant C0 is 0.13, independent of creep testing temperature. The values of m and C0 are compared with those for other die-cast magnesium alloys. © 2008 The Japan Institute of Metals.

DOI： 10.2320/matertrans.MBW200701

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DOI： 10.2320/matertrans.MBW200701

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Language：English   Publisher：JAPAN INST METALS  

Tensile creep tests were conducted to determine the creep parameters for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) in a temperature range from 423 to 498 K. The stress exponent of the minimum creep rate, n, increases at the yield stress of the alloy, and it lowers at higher temperatures. The activation energy for creep, Q(c), decreases with increasing applied stress typically below the yield stress. The change in the creep parameters, n and Q(c), is associated with the decreased creep strength caused by the collapse of the eutectic intermetallic phase covering the primary alpha-Mg grains during creep. The thermally activated component of Q(c) is evaluated to be 143 kJ/mol below the yield stress, which is very close to the activation energy for the lattice self-diffusion of magnesium. It is deduced that the creep for the alloy is controlled by the high-temperature climb of dislocations.

DOI： 10.2320/matertrins.MAW200701

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Language：English   Publisher：JAPAN INST METALS  

The internal stress during high temperature creep was investigated for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) at 473 K through the strain-transient dip test technique. The microstructure of the alloy is characterized by the eutectic intermetallic phase covering the primary alpha-Mg grains. The eutectic intermetallic phase plays dual roles in enhancing the creep strength front the viewpoint of the internal stress. First, the eutectic intermetallic phase sustains the stress-independent component of the internal stress with the magnitude of 15 MPa, resulting in the decrease in the effective stress. And second. it lowers the creep rate by two orders of magnitude at a given effective stress by reducing the mobile dislocation density and/or glide velocity of dislocations.

DOI： 10.2320/matertrans.48.97

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DOI： 10.2320/matertrans.48.97

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DOI： 10.1007/s11661-006-0169-9

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DOI： 10.1007/s11661-006-0169-9

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：JAPAN INST METALS  

Thermal conductivity is one of the key parameters required for high-temperature structural applications of metallic materials. In this overview, the thermal conductivity of intermetallic compounds are extensively described based mainly on our past works, since there had been less works in this research field. Emphasis is placed on the B2 and the L1(2) compounds with metallic bonding such as NiAl, Ni3Al, etc., which have been attracting attention for engineering applications at higher temperatures. The thermal conductivity data have been accumulated for the intermetallic compounds, and the phenomenological aspects are reviewed in detail as a function of alloy composition, constituent and temperature. The Wiedemann-Franz law is applicable to the intermetallic compounds, indicating that the carrier of thermal conduction is an electron rather than a phonon. The thermal conductivity of an intermetallic compound with the ordered crystal structure is characterized as an enhancement due to ordering with reference to the basic contribution of solid solution with the disordered crystal structure. It is demonstrated that the thermal conductivity of intermetallic compounds is reduced by the addition of a third element, and this subject is also covered.

DOI： 10.2320/matertrans.43.3167

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