Primary Recrystallization Textures in Dilute Fe-C Alloys

Iron, iron-0.012 pct C, and iron-0.032 pct C alloys subjected to a multistage rolling-annealing sequence display significantly different recrystallization textures after a final decarburizing anneal for 100 hours at 870 °C in dry hydrogen. A (110) [001] texture which developed by primary recrystallization was observed in the 0.012 C alloy. The unalloyed iron and 0.032 C alloy exhibited major components, respectively,(111〈011〉 and 111–211). Control of the alloy carbon level during the entire processing is considered to be critical to the development of the various textures.     

Microstructures and Properties of Al-Zn-Mg-Cu-Zr Alloys with Minor Scandium

The microstructures of Al-Zn-Mg-Cu-Zr al- loys with minor Sc were studied by using optical microscope（OM）, scanning electron microscope （SEM） and transmission electron microscope（TEM）. The tensile mechanical properties and electric conductivity of the studied alloys under different treatment conditions were tested. The results show that adding minor Sc can greatly fines the grain size of the Al-Zn-Mg-Cu-Zr alloy ingots and obviously improves the tensile properties and electric conductivity of the alloys. The strengthening mechanism is considered as fine grain strengthening, sub-structure strengthening and dispersion strengthening by Al3 （Sc, Zr）.     

电阻合金的温度系数(英文)

一组不同电导率的某种同一成分的电阻合金试样,具有α=mσ+α_r的关系。根据这个关系,我们可以发展一个温度系数α的快速测试方法。     

Phase-Field Study of the Cellular Bifurcation in Dilute Binary Alloys

Phase-field simulations in both two and three dimensions are used to investigate the microstructures that form closely above the threshold of the Mullins Sekerka instability in the directional solidi fication of dilute binary alloys. It is found that in this regime of shallow cells the simulation results strongly depend on the thickness of the diffuse interfaces even for model parameters that yield quantitative results for deep cells. For the material parameters of a dilute Sn-Bi alloy, the bifurcation is found to be supercritical, whereas weakly nonlinear amplitude expansions predict a subcritical bifurcation. Furthermore, an oscillatory instability of the cell grooves is found, which leads to the pinch-off of liquid inclusions even for relatively shallow cells. Finally, in three dimensions, three different morphologies are found, in agreement with experiments and previous numerical studies: regular hexagons, elongated cells (“stripes”), and inverted hexagons (“node” or “pox” structure, a hexagonal array of local depressions of the solidification front). Nodes and stripes are stable steadystate solutions only very close to the bifurcation. This article is based on a presentation made in the symposium entitled ”Solidification Modeling and Microstructure Formation: In Honor of Prof. John Hunt,” which occurred March 13-15, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.     

Age Hardening Behavior and Corresponding Microstructure of Dilute Al-Er-Zr Alloys

The age hardening and the microstructure of dilute Al-Er-Zr alloys were investigated by microhardness tests and TEM. The Al-0.04Er alloy shows a conventional age hardening behavior and obtains a maximum hardness of 410 MPa after aging for 2 h at 523 K (250 °C) due to precipitation of Al₃Er. The addition of Zr to Al-Er alloy can slow down the growth of the precipitates and make the age hardening effect remain for a long time in Al-0.04Er-0.04Zr alloy. Addition of Zr retards the decomposition of Al-Er and the Al-0.04Er-0.08Zr alloy can reach higher peak hardness than that of Al-0.04Er after aging for long time at elevated temperature. The precipitation behavior of Al-Er-Zr system is likely to be a new commercial way to developing creep-resistant aluminum alloy.     

Diffusion Research in BCC Ti-Al-Mo Ternary Alloys

Interdiffusion in Ti-Al-Mo β solid solution was investigated at 1523 K (1250 °C) by analyzing diffusion couples. From the concentration profiles analytically represented by error function expansion (ERFEX), the ternary interdiffusion coefficients and impurity diffusivity were extracted by the Whittle–Green and generalized Hall methods. A comparison of the diffusion in five Ti-Al-X (Co, Cr, Fe, Mo, and V) ternaries reveals Ti-Al-Mo is comparably like Ti-Al-(Cr, V) while Ti-Al-(Co, Fe) are predominantly of interstitial nature.     

Host Atom Diffusion in Ternary Fe-Cr-Al Alloys

In the Fe-rich corner of the Fe-Cr-Al ternary phase diagram, both interdiffusion experiments [1048 K to 1573 K (775 °C to 1300 °C)] and ⁵⁸Fe tracer diffusion experiments [873 K to 1123 K (600 °C to 850 °C)] were performed along the Fe₅₀Cr₅₀-Fe₅₀Al₅₀ section. For the evaluation of the interdiffusion data, a theoretical model was used which directly yields the individual self-diffusion coefficients of the three constituents and the shift of the original interface of the diffusion couple through inverse modeling. The driving chemical potential gradients were derived using a phenomenological Gibbs energy function which was based on thoroughly assessed thermodynamic data. From the comparison of the individual self-diffusivities of Fe as obtained from interdiffusion profiles and independent ⁵⁸Fe tracer diffusivities, the influence of the B2-A2 order–disorder transition becomes obvious, resulting in a slightly higher activation enthalpy for the bcc-B2 phase and a significantly lower activation entropy for this phase.     

Eutectic Morphology of Al-7Si-0.3Mg Alloys with Scandium Additions

The mechanisms of Al-Si eutectic refinement due to scandium (Sc) additions have been studied in an Al-7Si-0.3Mg foundry alloy. The evolution of eutectic microstructure is studied by thermal analysis and interrupted solidification, and the distribution of Sc is studied by synchrotron micro-XRF mapping. Sc is shown to cause significant refinement of the eutectic silicon. The results show that Sc additions strongly suppress the nucleation of eutectic silicon due to the formation of ScP instead of AlP. Sc additions change the macroscopic eutectic growth mode to the propagation of a defined eutectic front from the mold walls opposite to the heat flux direction similar to past work with Na, Ca, and Y additions. It is found that Sc segregates to the eutectic aluminum and AlSi₂Sc₂ phases and not to eutectic silicon, suggesting that impurity-induced twinning does not operate. The results suggest that Sc refinement is mostly caused by the significantly reduced silicon nucleation frequency and the resulting increase in mean interface growth rate.     

Intrinsic diffusion coefficients and the vacancy flow factor in Dilute Cu-Zn Alloys

Interdiffusion coefficients in copper-rich copper-zinc solid solutions containing up to 8 at. pct of Zn at 1168 K have been determined by Matano's analysis using semi-infinite diffusion couples consisting of pure copper and Cu-Zn alloys with Kirkendall markers. From the marker shift and Darken's relation, intrinsic diffusion coefficients, D_Zn and D_Cu, in the alloys containing 3.2 and 4.7 at. pct of Zn have been determined. Further, using thin plate couples, D_Zn and D_Cu in Cu alloys containing 0.9, 2.3, 3.5, and 4.6 at. pct of Zn at 1168 K have been determined by Heumann's method. The ratio of the intrinsic diffusion coefficients, D_Zn/D_Cu, has been found to be about two for all the compositions examined. Using the values of the intrinsic diffusion coefficient of copper at infinite dilution of zinc obtained by extrapolating the concentration dependence of D_Cu, and the self- and impurity diffusion coefficients in pure copper, the vacancy flow factor has been estimated to be - 0.22_-0.15 ^+0.06 at 1168 K. By combining this value of the vacancy flow factor with the solute enhancement factor of solvent diffusion determined by Peterson and Rothman, the correlation factor for impurity diffusion of Zn in Cu at 1168 K has been evaluated to be 0.5, which is in good agreement with the value of 0.47 determined by Peterson and Rothman based on the isotope effect measurement. KAZUTOMO HOSHINO, formerly Graduate Student, Tohoku University is now with Materials Science Division, Argonne National Laboratory, Argonne, IL 60439. YOSHIAKI IIJIMA, Instructor, and KENICHI HIRANO, Professor, are both with the Department of Materials Science, Faculty of Engineering, Tohoku University, Sendai 980, Japan.     

高导紫铜及微合金化高铜的熔铸加工技术

高导紫铜及微合金化高铜是美国铜加工产品标准中最重要的产品系列,简要介绍该类材料的成分、用途,重点阐述该类材料的熔炼铸造技术、设备结构、生产工艺流程等.     

Effect of Scandium and Zirconium on Mechanical and Exfoliation Corrosion Properties of Al-Mg-Mn Alloys

To quest for the best combination of mechanical properties and exfoliation corrosion resisting property of Al-Mg-Mn base alloys, and to seek after the effect of Sc and Zr on mechanical and exfoliation corrosion properties of Al-Mg-Mn alloys, comparative research technique was used, the mechanical properties of Al-Mg-Mn alloys with and without minor Sc and Zr treated by different annealing were measured, the degrees of exfoliation corrosion for these alloys through accelerated exfoliation corrosion test were evaluated, and polarization curves of these alloys were measured, too. The micro-morphologies of corrosion specimens were observed by SEM and the corrosion product was analyzed using EDS. Optical microscope and TEM were used, the relationship between their microstruc-tures and mechanical properties, exfoliation corrosion resisting property was investigated, and the results show that the addition of minor Sc and Zr can enhance the strength greatly and also improve the combination of strength and plasticity. Moreover, the addition of minor Sc, Zr does not cause appreciable decrease of exfoliation corrosion resisting property, the Al-Mg-Mn-Sc-Zr alloy annealed at 350 ℃ for 1 h has excellent combination of mechanical properties and exfoliation corrosion resisting property, the satisfied combination of mechanical properties nad exfoliation corrosion resisting property can be obtained by means of adding minor Sc and Zr, decreasing the content of Mn, and adopting reasonable annealing practice.     

碳原子在钴粘结相中的扩散系数研究

对硬质合金渗碳时碳原子在钴粘结相中的扩散行为进行了研究,所导出的扩散系数方程式适用于非金属扩散原子在液态金属中的扩散系数计算,所得到的结果与实际具有较好的符合性。     

Effect of Rare Earths on Diffusion Coefficient and Transfer Coefficient of Carbon during Carburizing

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Mapping of Diffusion and Nanohardness Properties of Fcc Co-Al-V Alloys Using Ternary Diffusion Couples

Ternary diffusion behavior in Co-Al-V ternary alloys was investigated at 1373 K and 1473 K (1100 °C and 1200 °C) by the solid-state diffusion-couple technique. The extraction and interpolation of diffusion data allows the diffusion properties of Fcc Co-Al-V alloys to be mapped in the composition arrays of Al and V. A full picture of the diffusion properties was then constructed by interpolating all accessible interdiffusivities and impurity diffusivities of Co-Al binary and Co-Al-V ternary with a Redlich–Kister polynomial, in a graphic manner depicting a rapid increase of Al diffusion with increasing Al and a weak decrease with the V addition alone. Further incorporation of a nanoindentation technique enables the nanohardness property of the Co-Al-V fcc alloys to be screened in the Al and V arrays. The hardenability in the Co-Al-V alloy system has been evidenced; specifically, the alloy arrays containing higher contents of V, being solution-and-quenching processed, exhibit more effective strengthening than those with the addition of Al. The discovery of Co-Al-V alloys with comparable nanohardness but differing alloy compositions could facilitate the strengthening design of next generation Co-based alloys.

     

Interdiffusion and Diffusion Mobility for fcc Ni-Co-Al Alloys

Ternary fcc Ni-Co-Al diffusion couples annealed at 1173 K (900 °C), 1373 K (1100 °C), and 1573 K (1300 °C) have been studied by using electron probe microanalysis. The interdiffusion coefficients were extracted using the Sauer–Freise and Whittle–Green methods from the measured concentration profiles of binary and ternary diffusion couples, respectively. Based on the diffusion coefficients reported in the literature and those determined in the present work, the diffusion mobilities for fcc Ni-Co-Al alloys were assessed. In general, reasonable agreements were reached and the resulted mobility database can be used to study the diffusion behavior of the ternary fcc Ni-Co-Al alloys in a wide composition range.     

Application of the square root Diffusivity to Diffusion in Ni-Cr-Al-Mo Alloys

The square root diffusivity matrix [r] and diffusivity matrix [D] have been measured for a Ni-4.0 at. pct Cr-6.3 at. pct Al-3.5 at. pct Mo quaternary alloy at 1100 °C. Using a constant diffusivity analysis, the diffusivities were obtained from three diffusion couples having small initial concentration differences of 5 at. pct or less. When elements of [r] were substituted into the error function solution of the diffusion equation, it was found that the predicted concentration profiles were accurate to within ±0.1 at. pct of measured values. Also, it was found that Mo tends to reduce the diffusion kinetics of Cr and Al in Ni-base alloys. These results suggest that these methods of analyzing diffusion data and predicting interdiffusion data can be applied to alloys containing more than four components.