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1.
In this work, a reactive synthesis process is proposed to obtain ZrAl3-Al2O3 particulate-reinforced aluminum matrix composites. The process involves the in-situ formation of Al2O3 and ZrAl3 from Al-ZrO2 green compacts. Upon compact heating, it is found that reduction of ZrO2 by molten aluminum occurs at temperatures above 750 °C, leading to the development of ZrAl3 and Al2O3 phases. Thermodynamically, it is found that the reduction of zirconium oxide is driven mainly by the dissolution of Zr in molten aluminum. Because the solubility of Zr in liquid aluminum is extremely small, the formation of ZrAl3 is favored after relatively small Zr dissolutions. The first Zr-Al intermetallics to form at the lowest temperatures seem to be metastable, as infered from the measured atom ratios for Al : Zr of 2.83 : 1. At increasing temperatures, the reaction comes into completion, resulting in the formation of equilibrium intermetallic ZrAl3 phases. The results obtained from differential scanning calorimetry (DSC) indicate that by increasing the scanning rates, both the reaction temperature and the exothermic peak intensity also increase. Alternatively, it is found that by reducing the amount of ZrO2 in the green compact, the in-situ reaction temperatures also shift toward higher values.  相似文献   

2.
Oxidation studies were performed at 1100 °C in dry air and air containing fixed partial pressures of water vapor on a number of alloys and coatings that form α-Al2O3 scales under oxidizing conditions. The alloys investigated included RENé N5, PWA 1484, diffusion aluminide coatings (with and without Pt modification) on RENé N5, and a Ni-8 wt pct Cr-6 wt pct Al model alloy. The water vapor affected the oxidation of the alloys in three important ways: (1) The scales spalled more profusely during cyclic oxidation in wet air than in dry air, particularly for those alloys with alumina scales, which are only moderately adherent under dry conditions. The results were consistent with the mechanism previously proposed (Reference 1), whereby the water molecules decrease the fracture toughness of the alumina/alloy interface. (2) Thicker oxides are formed during oxidation in wet air than dry air. This effect comes primarily from accelerated transient oxidation during exposure in wet air. (3) Spinel was found to form on top of the alumina scales during long-term exposure. This phenomenon occurred in all atmospheres but was much more pronounced for exposures in wet atmospheres. Mechanisms for the preceding observations are proposed.  相似文献   

3.
The distribution ratio of nickel between Ag-Ni alloy and CaO-SiO2-Fe t O slag at high temperatures was measured to clarify the dissolution mechanism of nickel in this melt. Also, the nickel oxide capacity was suggested and was compared to phosphate and sulfide capacities. The dissolution mechanism of nickel into the CaO-SiO2-Fe t O slags could be described by the following equation from the effect of oxygen potential and slag basicity on nickel dissolution behavior:
The nickel oxide capacity increases with increasing CaO/SiO2 ratio at a fixed Fe t O content. When the ratio of X CaO to (C/S) is about 1.1 to 1.3, log increases with increasing Fe t O content up to about 35 mol pct, followed by a nearly constant value of . In the composition of C/S=0.5 to 0.7, log exhibits a maximum value at about 50 mol pct Fe t O. From the iso- trends in ternary phase diagram, nickel oxide capacity dominantly depends on Fe t O content in slags; it exhibits a maximum value of at . The relationship between nickel oxide capacity and phosphate (sulfide) capacities exhibit linear correlations, as expected from theoretical equations.  相似文献   

4.
The stability of the reactive interface during the solid-state displacement reaction, Cu2O+Co1−X Fe X =2Cu+(Co1−X Fe X )O, is studied as a function of Co-Fe alloy composition at 1223 K. For X≤0.03, the reaction zone has a layered structure, and the cation diffusion in (Co, Fe)O is the rate-limiting step. The interface is unstable in the early stages of the reaction; the instability decreases with time as the oxide thickness increases, and the interface becomes planar at long times. The time required for the attainment of interface planarity increases with the value of X. The reaction kinetics are consistent with the available cation-diffusion data in (Co, Fe)O. For X≥0.045, the product zone is a composite of Cu+(Co, Fe)O, and the rate is limited by the oxygen transport in copper. The transition to interface instability occurs when the oxide can support a cation flux that exceeds the maximum possible oxygen flux in copper. During the reaction, composition gradients develop in (Co, Fe)O because of higher diffusion rates for iron than for cobalt.  相似文献   

5.
Cast particulate composites, containing in-situ generated reinforcing particles of alumina, have been developed by solidification of slurry obtained by dispersion of externally added manganese dioxide particles (MnO2) in molten aluminum, and alumina is formed by reaction of manganese dioxide with molten aluminum. The chemical reaction also releases manganese into molten aluminum. Magnesium is added to the melt in order to help wetting of alumina particles by molten aluminum and to retain the particles inside the melt. The present work aims to understand the influence of key parameters such as processing temperature, time, and the amount of MnO2 particles added on the microstructure and mechanical properties of the resulting cast in-situ composites. The sequence of addition of MnO2 particles and magnesium has significant influence on the microstructure and mechanical properties. Increasing processing temperature and time increases the extent of reduction of MnO2 particles, generating more alumina particles as well as releasing more manganese to the matrix alloy. Alumina helps to nucleate finer and sometimes blocky MnAl6 in the matrix of the composite and thereby results in relatively higher ductility and increased strength in the composite as compared to the base alloy of similar composition. Even in the presence of relatively higher porosity of 8 to 9 vol pct, one observes a percent elongation not below 7 to 8 pct, which is considerably higher than those observed in cast Al(Mg)-Al2O3 composite synthesized by externally added alumina particles.  相似文献   

6.
Alloys of Co78-x Pt x B10Si12 were produced using the melt-spin process in order to study the crystallization behavior and ensuing magnetic properties of the Co-Pt amorphous alloys as a function of the Pt content. We showed that when x>15, well below its stoichiometric composition, CoPt intermetallic compound crystallized in the amorphous alloy. Below this composition, the main crystallization product was Co with Pt dissolved in its lattice. The nucleation of CoPt greatly altered the crystallized microstructures and magnetic properties of the Co-Pt amorphous alloys during annealing. In spite of the nucleation of CoPt with its high magnetic anisotropy, the highest coercivity was obtained when x was 15, free of the CoPt grains. It was also concluded that the Pt addition, in general, triggered crystallization to occur at a progressively lower temperature.  相似文献   

7.
The effect of platinum addition on the interdiffusion behavior of γ-Ni + γ′-Ni3Al alloys was studied by using diffusion couples comprised of a Ni-Al-Pt alloy mated to a Ni-Al, Ni-Al-Cr, or Ni-based commercial alloy. The commercial alloys studied were CMSX-4 and CMSX-10. Diffusion annealing was at 1150 °C for up to 100 hours. An Al-enriched γ′-layer often formed in the interdiffusion zone of a given couple during diffusion annealing due to the uphill diffusion of Al. This uphill diffusion was ascribed to Pt addition decreasing the chemical activity of aluminum in the γ + γ′ alloys. For a given diffusion couple end member, the thickening kinetics of the γ′ layer that formed increased with increasing Pt content in the Ni-Al-Pt γ + γ′ alloy. The γ′-layer thickening kinetics in diffusion couples with Cr showed less of a dependence on Pt concentration. Inference of a negative effect of Pt and positive effect of Cr on the Al diffusion in this system enabled explanation of the observed interdiffusion behaviors. There was no or minimal formation of detrimental topologically close-packed (TCP) phases in the interdiffusion zone of the couples with CMSX-4 or CMSX-10. An overlay Pt-modified γ + γ′ coating on CMSX-4 showed excellent oxidation resistance when exposed to air for 1000 hours at 1150 °C. Moreover, the Al content in the coating was maintained at a relatively high level due to Al replenishment from the CMSX-4 substrate.  相似文献   

8.
The stability of a lamellar structure consisting of α 2 and γ phases in alloys Ti-48Al, Ti-48Al-2Mo, Ti-48Al-4Nb, and Ti-48Al-1Mo-4Nb has been studied as a function of aging time and temperature. The alloys were solution treated (1400 °C, 30 min, and air-cooled (AC)) and aged at 1000 °C and 1100 °C for 1, 4, and 16 hours, respectively. The results indicate that the kinetics of lamellae to equiaxed transformation depends on alloy chemistry, aging time, and temperature. The Nb decreases and Mo increases the kinetics of transformation. The combined effect of Nb and Mo results in the highest volume fraction of equiaxed microstructure at a given aging time and temperature. The results have been discussed in relation to microstructural features and have been compared with those reported in other α 2+γ alloys.  相似文献   

9.
Density measurements of a low-silica CaO-SiO2-Al2O3 system were carried out using the Archimedes principle. A Pt 30 pct Rh bob and wire arrangement was used for this purpose. The results obtained were in good agreement with those obtained from the model developed in the current group as well as with other results reported earlier. The density for the CaO-SiO2 and the CaO-Al2O3 binary slag systems also was estimated from the ternary values. The extrapolation of density values for high-silica systems also showed good agreement with previous works. An estimation for the density value of CaO was made from the current experimental data. The density decrease at high temperatures was interpreted based on the silicate structure. As the mole percent of SiO2 was below the 33 pct required for the orthosilicate composition, discrete \textSiO44 - {\text{SiO}}_{4}^{4 - } tetrahedral units in the silicate melt would exist along with O2– ions. The change in melt expansivity may be attributed to the ionic expansions in the order of
\textAl 3+ - \textO 2- < \textCa 2+ - \textO 2- < \textCa 2+ - \textO - {\text{Al}}^{ 3+ } - {\text{O}}^{ 2- } < {\text{Ca}}^{ 2+ } - {\text{O}}^{ 2- } < {\text{Ca}}^{ 2+ } - {\text{O}}^{ - }  相似文献   

10.
Magnesium alloy-based hybrid composites with carbon-fiber, SiC p , and in-situ Mg2Si reinforcements have been prepared by the squeeze-infiltration technique. The results of the studies done on the measurement of the coefficient of thermal expansion after thermal cycling of these composites show that the thermal cycling initially leads to rapid linear expansion of the composite. However, the expansion becomes stabilized after a few cycles, pointing toward formation of the stable interfaces due to the formation of stable precipitates. The model for the growth kinetics of these precipitates at the interface shows a rapid initial growth of the precipitates with the number of thermal cycles, which becomes staturated after a few thermal cycles. The thermal treatment of the composite lowers the coefficient of linear thermal expansion, which can be explained on the basis of further stabilization of the interfaces after the thermal treatment.  相似文献   

11.
From the viewpoint of thermodynamics, using the Wilson equation and an extended Miedema model, the effect of the alloying element on the stability of the precipitated phases during the fabrication of in-situ reinforced TiB2/Al composites was evaluated. The result shows that additions of alloying elements, such as Mg, Cu, Zr, Ni, Fe, V, and La, can promote the formation of Al3Ti and TiB2 phases. Particularly, Zr has the most pronounced effect among these alloying elements. In addition, alloying elements can hinder the formation of AlB2 to a small extent. The calculation results also show that it is easier for magnesium to react with the salts to form TiB2 than aluminum during the fabrication of in-situ reinforced TiB2/Al using the flux-assisted synthesis (FAS) technology.  相似文献   

12.
13.
The mechanical performance of A357 cast ingot aluminum alloy specimens subjected to 25 different artificial aging heat treatments has been experimentally investigated. For the quality evaluation of the artificially aged alloys, the quality index Q D , proposed by the authors, has been involved. The index Q D interprets quality as the potential of an alloy to offer combinations of tensile strength, ductility, and toughness at certain levels of values. The evaluation of the alloy quality using Q D relies on the availability of the materials tensile flow curve. To facilitate the exploitation of Q D for quality assessment, approximations of Q D are developed. In the proposed approximations, Q D is formulated as a function of ultimate tensile strength, yield strength, and elongation to fracture, or alternatively, as a function of Rockwell hardness E and Charpy impact energy values. Accurate estimations of the quality index Q D are compared against Q D values obtained by using the proposed approximations.  相似文献   

14.
A nonisothermal Johnson-Mehl-Avarami (JMA) equation with optimized JMA parameters is proposed to represent the kinetics of transformation of α-ferrite to γ-austenite during heating of 1005 steel. The procedure used to estimate the JMA parameters involved a combination of numerical heat-transfer and fluid-flow calculations, the JMA equation for nucleation and growth for nonisothermal systems, and a genetic algorithm (GA) based optimization tool that used a limited volume of experimental kinetic data. The experimental data used in the calculations consisted of phase fraction of γ-austenite measured at several different monitoring locations in the heat-affected zone (HAZ) of a gas tungsten arc (GTA) weld in 1005 steel. These data were obtained by an in-situ spatially resolved X-ray diffraction (SRXRD) technique using synchrotron radiation during welding. The thermal cycles necessary for the calculations were determined for each monitoring location from a well-tested three-dimensional heat-transfer and fluid-flow model. A parent centric recombination (PCX) based generalized generation gap (G3) GA was used to obtain the optimized values of the JMA parameters, i.e., the activation energy, pre-exponential factor, and exponent in the nonisothermal JMA equation. The GA based determination of all three JMA equation parameters resulted in better agreement between the calculated and the experimentally determined austenite phase fractions than was previously achieved.  相似文献   

15.
The chemical diffusion coefficient of sulfur in the ternary slag of composition 51.5 pct CaO-9.6 pct SiO2-38.9 pct Al2O3 slag was measured at 1680 K, 1700 K, and 1723 K (1403 °C, 1427 °C, and 1450 °C) using the experimental method proposed earlier by the authors. The P\textS2 P_{{{\text{S}}_{2} }} and P\textO2 P_{{{\text{O}}_{2} }} pressures were calculated from the Gibbs energy of the equilibrium reaction between CaO in the slag and solid CaS. The density of the slag was obtained from earlier experiments. Initially, the order of magnitude for the diffusion coefficient was taken from the works of Saito and Kawai but later was modified so that the concentration curve for sulfur obtained from the program was in good fit with the experimental results. The diffusion coefficient of sulfur in 51.5 pct CaO-9.6 pct SiO2-38.9 pct Al2O3 slag was estimated to be in the range 3.98 to 4.14 × 10−6 cm2/s for the temperature range 1680 K to 1723 K (1403 °C to 1450 °C), which is in good agreement with the results available in literature  相似文献   

16.
A concept for calciothermic direct reduction of titanium dioxide in molten CaCl2 is proposed and experimentally tested. This production process consists of a single cell, where both the thermochemical reaction of the calciothermic reduction and the electrochemical reaction for recovery of the reducing agent, Ca, coexist in the same molten CaCl2 bath. A few molar percentages of Ca dissolve in the melt, which gives the media a strong reducing power. Using a carbon anode and a Ti basket-type cathode in which anatase-type TiO2 powder was filled, a metallic titanium sponge containing 2000 ppm oxygen was produced after 10.8 ks at 1173 K in the CaCl2 bath. The optimum concentration of CaO in the molten CaCl2 was 0.5 to 1 mol pct, to shorten the operating time and to achieve a lower oxygen content in Ti.  相似文献   

17.
Rare earth CeO2 was investigated as an additive for in-situ preparation of TiC/Al composites using XD (exothermal dispersion) + casting technology. Experiment results showed that an optimum CeO2 addition of 0.5 wt pct promotes the generation and refinement of TiC particles, prevents the formation of Al3Ti, increases the wettability between the TiC ceramic particles and the Al matrix, and improves the mechanical properties of composite. A corresponding thermodynamic model was proposed for the mechanism.  相似文献   

18.
A mathematical model developed previously is used to obtain equations for the calculation of the standard enthalpies of formation of some stoichiometric oxides and complex oxides of a variable composition in the Fe-O-Ti system. These entropies have been determined.  相似文献   

19.
The interdiffusion coefficients in bcc (α) and fcc (γ) Fe-Ni alloys below their Curie temperatures have been calculated based on the magnetic contribution to the free energy for interdiffusion. The free energy for interdiffusion due to magnetic ordering in bcc Fe-Ni alloys is positive. The calculated interdiffusion coefficients in bcc Fe-Ni alloys fit the experimental data quite well. In fcc Fe-Ni alloys, the magnetic contribution to interdiffusion depends on both temperature and composition and is abnormal for Ni compositions in the Invar region. The free energy of vacancy formation is positive and the free energy of vacancy migration is negative, due to the effect of magnetic ordering. The interdiffusion coefficient in the ferromagnetic phase is lower than that extrapolated from the paramagnetic phase for Ni compositions of 50 at. pct and greater and is higher than that extrapolated from the paramagnetic phase for Ni compositions of 40 at. pct and lower.  相似文献   

20.
In-situ Al2O3/TiAl3 intermetallic matrix composites were fabricated via squeeze casting of TiO2/A356 composites heated in the temperature range from 700 °C to 780 °C for 2 hours. The phase transformation in TiO2/A356 composites employing various heat-treatment temperatures (700 °C to 780 °C) was studied by means of differential thermal analysis (DTA), microhardness, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). From DTA, two exothermic peaks from 600 °C to 750 °C were found in the TiO2/A356 composites. The XRD showed that Al2O3 and TiAl3 were the primary products after heat treatment of the TiO2/A356 composite. The fabrication of in-situ Al2O3/TiAl3 composites required 33 vol pct TiO2 in Al and heat treatment in the range from 750 °C to 780 °C. The hardness (HV) of the in-situ Al2O3/TiAl3 composites (1000 HV) was superior to that of nonreacted TiO2/A356 composites (200 HV). However, the bending strength decreased from 685 MPa for TiO2/A356 composites to 250 MPa for Al2O3/TiAl3 composites. It decreased rapidly because pores occurred during the formation of Al2O3 and TiAl3. The activation energy of the formation of Al2O3 and TiAl3 from TiO2 and A356 was determined to be about 286 kJ/mole.  相似文献   

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