Oxidation of zirconium between 400° and 800°C

The vacuum microbalance method is used to study the oxidation reaction for two surface preparations over the temperature range of 400° to 800°C. The results fit in well with the authors previous work at temperatures of 200° to 425°C and with the work of other groups at higher temperatures. An analysis of the rate data shows that the cubic rate law fits the experimental data best for the abraded specimens. However, the parabolic rate law can be fitted to the data if an initial deviation is disregarded. With chemically polished specimens, a good fit is obtained with the parabolic rate law. The parabolic rate law constant A gives two straight lines when plotted as log A vs 1/T. For the temperature range of 200° to 525°C an energy of activation of 18,200 cal per mol is calculated while a value of 28,600 cal per mol is calculated for the temperature range of 525° to 750°C. The results of this work bring together the previously determined high-temperature oxidation studies of Cubicciotti with the early low-temperature studies of Gulbransen and Andrew.     

Stability of CaNi5Hx stored at temperatures between 20 and 150°C

The stability of CaNi₅H_x stored at different temperatures was studied as a function of time. In general AB₅ metal hydrides are known to be metastable with a tendency to disproportionate at elevated temperatures. In the present study samples of CaNi₅ were stored in the hydrided state (as CaNi₅H_∼4.7) at temperatures between 20 and 150°C. After different periods of time, up to 120 days, the hydrogen absorption capacity was measured electrochemically. Significant capacity decays were observed at temperatures of 40°C and higher. The capacity decay with storage time tended to stop at a level of 147 mAh/g corresponding to 1.83 hydrogen atoms per calcium atom. X-ray diffraction revealed that the CaCu₅ structure was preserved after the degradation. A mathematical model for the decay is proposed.     

Microhardness changes of inclusions of phosphorus compounds in gray irons between 20 and 300°C

Conclusions An increase of temperature to 300°C results in a substantial decrease of the microhardness of certain phosphorus compound-type inclusions in gray irons. The attendant changes in microhardness of pearlite and ferrite were insignificant. The most pronounced softening was observed in the ternary eutectic Fe (P,C)+Fe₃P+Cr₂₃C₆ and binary eutectic Fe₃P+Fe₃C. The relative difference of the microhardnesses ( H) decreased uniformly. At 300°C it fell to 0 and 0.6, respectively.For the ternary eutectic Fe (P,C)+Fe₃P+Fe₃C and carbide Cr₂₃C₆, the factor H assumed a certain intermediate value.     

Oxidation behavior and mechanism of porous nickel-based alloy between 850 and 1000 °C

The oxidation behavior and mechanism of a porous Ni–Cr–Al–Fe alloy in the temperature range from 850 to 1000 °C were investigated by optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) analyses and X-ray photoelectron spectroscopy (XPS). The results show that the oxidation kinetics at 950 and 1000 °C of this porous alloy is pseudo-parabolic type. Complex layers composed of external Cr₂O₃/NiCr₂O₄ and internal α-Al₂O₃ are formed on the surface of the oxidized porous alloys. γ' phases favor the formation of NiO/Cr₂O₃/NiCr₂O₄ during the initial oxidation. Many fast diffusion paths contribute to the development of the oxide layers. The decrease of the open porosity and the permeability with exposure time extending and temperature increasing can be controlled within a certain range.     

Influence of silicon on the oxidation of titanium between 550 and 700°C

The oxidation behavior of Ti-Si alloys (0.25, 0.5, and 1 Wt. % Si) was investigated between 550 and 700°C; in oxygen by continuous thermogravimetry for a maximum duration of about 500 hr and, in air by daily weighing for durations from a few hundred to several thousand hours. The kinetics results revealed that the presence of silicon leads to a decrease in oxidation rate which is more evident when the temperature is raised and the silicon content is increased. Morphological and structural examinations revealed that silicon modifies the internal architecture of oxide layers when compared with unalloyed titanium; in particular, reduced porosity in the layers is observed. Analysis showed that silicon is uniformly distributed in the oxide layer. However, while part of the silicon is in solid solution in the rutile, some is also precipitated as small crystals ( <1 m at 850°C) of SiO₂, of cristobalite structure. The adherence of oxide layers to the metal substrate was measured after cooling of samples; the addition of silicon has been observed to modify, in a manner dependent on its content, the adherence of oxide layers.     

Oxidation of ZC63 Mg alloys reinforced with SiC particles between 390 °C and 500 °C in air

The ZC63 magnesium alloys reinforced with 10 wt.% of SiC particles with an average particle size of 50 μm were cast. The fabricated SiC_p/ZC63 composite consisted of an α-Mg matrix, unreacted α-SiC particles, and an intergranularly formed CuMgZn compound. It was oxidized at 390 °C to 500 °C up to 5 h in air. The oxide scales were thin and compact below 430 °C, but became porous and loose above 450 °C. They consisted primarily of MgO and a small amount of Mg₃N₂. SiC particles were stable over the temperature range explored.     

Oxidation of P92 steel weldment between 600 and 800 °C in air

P92 alloy with a composition of Fe-9.1Cr-0.5Mo-1.7W (wt.%) was welded, and its oxidation behavior was studied at 600, 700 and 800 °C for up to 6 months in air. The oxidation resistance decreased in the order of the base metal, weld metal, and the heat affected zone. The morphology and the composition of the scales formed on these samples were similar. The scales were either uniform in thickness or nodular. The scales consisted mainly of Fe₂O₃. As oxidation progressed, thick, nodular oxide scales formed. The alloying elements such as Cr, W, and Mn tended to incorporate in the lower part of the oxide scale.     

Interdiffusion and reaction between Zr and Al alloys from 425° to 625 °C

Zirconium has recently garnered attention for use as a diffusion barrier between U–Mo nuclear fuels and Al cladding alloys. Interdiffusion and reactions between Zr and Al, Al-2 wt.% Si, Al-5 wt.% Si or AA6061 were investigated using solid-to-solid diffusion couples annealed in the temperature range of 425° to 625 °C. In the binary Al and Zr system, the Al₃Zr and Al₂Zr phases were identified, and the activation energy for the growth of the Al₃Zr phase was determined to be 347 kJ/mol. Negligible diffusional interactions were observed for diffusion couples between Zr vs. Al-2 wt.% Si, Al-5 wt.% Si and AA6061 annealed at or below 475 °C. In diffusion couples with the binary Al–Si alloys at 560 °C, a significant variation in the development of the phase constituents was observed including the thick τ₁ (Al₅SiZr₂) with Si content up to 12 at.%, and thin layers of (Si,Al)₂Zr, (Al,Si)₃Zr, Al₃SiZr₂ and Al₂Zr phases. The use of AA6061 as a terminal alloy resulted in the development of both τ₁ (Al₅SiZr₂) and (Al,Si)₃Zr phases with a very thin layer of (Al,Si)₂Zr. At 560 °C, with increasing Si content in the Al–Si alloy, an increase in the overall rate of diffusional interaction was observed; however, the diffusional interaction of Zr in contact with multicomponent AA6061 with 0.4–0.8 wt.% Si was most rapid.     

Relation between Development of Microstructure and Magnetic Properties of Sintered NdDyFeB Magnets

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Properties of CuCr contact materials with low chromium content and fine particles

1　INTRODUCTIONCuCralloyhastakentheplaceofCuBialloyforitsexcellentelectricpropertiesandhasbeenwidelyusedinmediumvoltage ,highcurrentvacuuminter rupter[1,2 ] .CuandCrhaveverylittlesolubilityineachother .Atroomtemperature ,thesolubilityisapproximatelyzero .Infact,Cu Cralloyisapseudo alloywiththemixtureofCuandCrcomponent .Cu CrcontactmaterialsreservetheexcellentpropertiesofCuandCrcomponent,sothecontactmaterialshaveexcellentelectricproperties.TheoptimalcontentofCrinCuCrcontactmate rialh…     

Properties and microstructure of NiO/SDC materials for SOFC anode applications

NiO/SDC composites and Ni/SDC cermets for solid oxide fuel cell （SOFC） anode applications were prepared from nickel oxide （NiO） and samada doped ceria （SDC） powders by the powder metallurgy process. The physical and mechanical properties, as well as the microstructure of the NiO/SDC composites and the Ni/SDC cermets were investigated. It is shown that the sintedng temperature of the NiO/SDC composites and NiO content plays an important role in determining the microstructure and properties of the NiO/SDC composites, which, in turn, influences the microstructure, electrical conductivity, and mechanical properties of the Ni/SDC cermets. The present study demonstrated that composition and tprocess parameters must be appropriately selected to optimize the microstructure and the properties of NiO/SDC materials for solid oxide fuel cell applications.     

Effect of water vapor on oxidation and creep behavior of incoloy 800 at temperatures between 850 and 980°C

The oxidation kinetics and creep behavior of Incoloy 800 were studied in air and in water vapor charged with oxygen. Oxidation kinetics were determined by thermogravimetry. The creep behavior of samples tested in air and in H₂OO₂=11 atmospheres was investigated by electron microscopic techniques. The oxidation rate of samples tested in air was governed by a p-conducting chromia interlayer. Depending upon water vapor pressure, chromia became n-conductive. As a consequence, a continuous rate-governing silica interlayer formed. The oxygen activity in the alloy was established by the dissociative pressure of the respective diffusion-rate-governing oxide scale. The stability of the dispersion-hardening Ti(C, N) particulates within the alloy was affected by the respective oxygen activity. In the samples tested in air, partial oxidation of the particulates due to enhanced oxygen activity caused a loss of coherency with the matrix. As a result, the deformation behavior during creep was changed to planar-slip mode, bringing about loss of creep resistance and ductility.     

Cyclic oxidation of AISI 316L stainless steel – influence of water vapour between 800 and 1000°C

At 800 and 900°C, 10 vol.-%H₂O in air has little effect on the AISI 316L stainless steel oxidation under isothermal and cyclic conditions. The oxide scale is composed of Cr₂O₃ with a small amount of Mn_1·5Cr_1·5O₄ at the external interface. Results show that water molecules or protons can modify the diffusion process in the scale and lower the oxidation rate. At 1000°C, a deleterious effect of water vapour on the scale structure is observed. In situ X-ray diffraction was used to analyse the oxide formation on AISI 316L specimens during isothermal oxidation at 1000°C in moist air. Results show that the breakaway oxidation is due to the iron oxidation starting after 31 h oxidation. This leads to an external Fe₂O₃ scale growth and an internal multilayered FeCr₂O₄ scale formation. In wet air, thermal cycling conditions lead to continuous weight losses at 1000°C, whereas the scale remains adherent in dry air.     

The influence of sulphur content upon the dissolution of nickel in 10N HCl between 45 and 75°C

The influence of the sulphur content of nickel on its dissolution in 10N HCl has been investigated between 45 and 75°C. The rate of dissolution increases with both increasing temperature and sulphur content. The activation energies for commercial and electrodeposited nickel having sulphur contents of 0·006–1·345 were between 11·0 and 16·7 kcal g at^?1. The results are in agreement with the conclusion of Schorr and Yahalom that the activation energies for metal dissolution in acids should be below 25 kcal g at^?1. A brief discussion of the results is given.     

Chloridation-oxidation of Fe-Cr and Ni-Cr alloys at 800°C

The chloridation-oxidation behavior of Fe-Cr (0–25 wt. %Cr) and Ni-Cr (0–20 wt.%Cr) alloys was studied at 800°C in three different H₂-HCl-H₂O() environments. In a low-HCI and low-H₂O() environment, where Cr₂O₃ is thermodynamically stable, the corrosion resistance of the Fe-Cr alloys increased with increasing Cr content in the alloys. In a high-HCl and high-H₂O() environment, where FeCr₂O₄ is stable and CrCl₂ is metastable, the corrosion resistance of the Fe-Cr alloys depended similarly on the Cr content. Low-Cr-Fe-Cr alloys exhibited large weight losses, while Fe-Cr alloys with higher than 19 wt. %Cr showed good corrosion resistance. In an environment of high-HCl in the absence of H₂O(), the evaporative corrosion rate was fast and limited by gas phase diffusion, and independent of the Cr content in the Fe-Cr alloys. Ni and Ni-Cr alloys generally showed good corrosion resistance in the environments of high H₂O() because of the low NiCl₂ vapor pressure and formation of a protective Cr₂O₃ scale. However, in the environment of high HCl in the absence of H₂O(), selective formation and evaporation of CrCl₂ occur, which results in Cr depletion and networks of voids for even a high-Cr Ni-Cr alloy.     

Oxidation of orthorhombic titanium aluminide Tl-22AL-25NB in air between 650 and 1000 °C

The oxidation behavior of orthorhombic titanium aluminide alloy Ti-22Al-25Nb was studied in air between 650 and 1000 °C by isothermal thermogravimetry and postoxidation scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction. Microhardness measurements were performed after exposure to gage hardening due to nitrogen and oxygen ingress. The parabolic rate constant of Ti-22Al-25Nb was of the same order as conventional titanium alloys and Ti₃Al-based titanium aluminides at and below 750 °C. Between 800 and 1000 °C, the oxidation resistance of Ti-22Al-25Nb was as good as that of γ-TiAl based aluminides; however, the growth rate changed from parabolic to linear after several tens of hours at 900 and 1000 °C. The mixed oxide scale consisted of TiO₂, AlNbO₄, and Al₂O₃, with TiO₂ being the dominant oxide phase. Underneath the oxide scale, a nitride-containing layer formed in the temperature range investigated, and at 1000 °C, internal oxidation was observed below this layer. In all cases, oxygen diffused deeply into the subsurface zone and caused severe embrittlement. Microhardness measurements revealed that Ti-22Al-25Nb was hardened in a zone as far as 300 μm below the oxide scale when exposed to air at 900 °C for 500 h. The peak hardness depended on exposure time and reached five times the average hardness of the bulk material under the above conditions.     

Metallography of fatigue crack initiation in coarse-grained Astroloy at 20°C

Fatigue crack initiation in coarse-grained Astroloy was studied by initiating cracks under bending loads. The specimen was not replicated in order to preserve any debris or extrusions associated with the cracks. Cracks were found to have initiated at pores and along slip lines. Debris and tonguelike extrusions were found coming from some cracks, but not all of them. Illustrations are given of the five different crack extrusion-related phenomena that were observed. It is concluded that the extrusion of material in the form of tonguelike or other debris may accompany the initiation of fatigue cracks, but that it is not a requisite part of the processes causing the crack.     

Relationship between elongation and porosity for high porosity metal materials

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