Some recent results on magnetism in alloys

The effect of local atomic environment on the atomic moment of Fe in Fe?Al alloys and of V in Au?V alloys is reevaluated, using improved methods of analysis and new magnetic data. Magnetic clusters with giant moments occur in many alloys in which one of the components has no magnetic moment. This is true for FeAl in spite of the presence of well-developed atomic long range order, although the concentration of magnetic clusters does decrease with increasing long range order. The phenomena of mictomagnetism are reviewed. Mictomagnetism occurs in many alloys having no long range atomic order, and it is characterized by the freezing of the spin orientations at low temperatures but, in contrast to ferromagnetism and to antiferromagnetism, without long range magnetic order.     

Mn含量对Cu-Mn合金结构与性能的影响

基于Cu-Mn中间层可改善Cu与CuCrZr合金的连接性能,采用高能球磨法制备Cu-Mn合金粉末,研究烧结温度为650~850℃、Mn含量(质量分数)为10%~50%的Cu-Mn合金的烧结性能。结果表明:随Mn含量增加,Cu-Mn合金的相对密度和抗拉强度先增大后减小,但Mn含量过高时生成较多的Mn O,导致合金性能下降;随烧结温度升高,合金的相对密度和抗拉强度增大。850℃下烧结的67Cu-33Mn合金孔隙较小、组织均匀,其相对密度和抗拉强度均达到最大值,分别为91.62%和610.91 MPa,表明67Cu-33Mn合金具有最佳的烧结活性,宜作为Cu与CuCrZr合金连接的中间层。     

Atomic ordering and magnetism in L10 ordered FePd alloys

Intermetallic compounds due to their promising corrosion resistance and high-temperature mechanical strength give hope for their application as high-temperature structural materials. Inter-metallics of L1₀ type structure in recent years in addition have attracted great interest as potential recording media. These alloys are ferromagnetic and display marked mechanical and magnetic anisotropy with the tetragonal c-axis of the ordered domains as the “easy axis” of magnetization High-density magnetic recording may be achieved by a preferential domain orientation with the c-axis perpendicular to the surface, if these materials can be stabilized as low-dimensional magnetic structures. Knowledge of kinetic parameters, that determine alloy stability is essential for alloy design. technical application, and performance of materials. We used FePd as a model system for this class of L1₀-ordered intermetallics and have studied the changes of long-range order during heat treatments in the bulk and in thin films produced by different techniques. Results of X-ray diffraction (XRD). resistivity measurement. Mößbauer spectroscopy, and measurement of magnetization in both geometries are compared.     

Intrinsic diffusion and vacancy flow effects in vanadium-titanium alloys

Intrinsic diffusion coefficients and vacancy flow parameters have been determined in the vanadium-titanium system from 900 to 1500°C. The experimental results reflect a greater influence of the vacancy flow phenomenon on the intrinsic flux of each species than that predicted on the basis of the random alloy model. The principal assumptions of the random alloy model are that a single vacancy mechanism is the operative diffusion mechanism and that all diffusing species find themselves in random environments with the absence of preferred sites for either atoms or vacancies. Solvent diffusivity enhancement calculations have been performed, however, and suggest that existence of two compcting, vacancy mechanisms in this system. The observed discrepancies between theoretical and experimental values are examined in light of the occurrence of a combined monovacancy-divacancy mechanism. In addition, other nonrandom effects are discussed which result in violations of the random alloy model assumptions and which lead to differences between theoretical and experimental quantities.     

Intrinsic diffusion and vacancy wind effects in Ag-Cd alloys

Diffusion in the Ag-Cd system was investigated at 600°C with vapor-solid and solid-solid diffusion couples in the α-phase for the determination of intrinsic diffusion coefficients, atomic mobilities and interdiffus ion coefficients. Intrinsic diffusion coefficients, D_Cd and D_Ag, determined experimentally, were compared with those predicted from the models of Darken, Manning, and Dayananda with the aid of tracer diffusion and thermodynamic data. The experimental coefficients for various alpha alloys were found to be higher than those evaluated from each of the three models. On the other hand, the experimental values of the ratio, D_Cd/D_Ag were found to be in good agreement with the models of Manning and Dayananda where the vacancy wind effects on intrinsic diffusion are taken into account. Darken’s relations are considered inadequate to interrelate tracer and intrinsic diffusion coefficients in the Ag-Cd system, since vacancy wind effects are found to be appreciable in this system.     

Thermodynamics of Mn in Cu-Mn Melts

The present work aimed to measure the thermodynamic data of manganese in Cu-Mn melts over a broad manganese concentration range, using the equilibrium among the liquid copper/MnO_(s)/CO-CO₂ gas mixture in the temperature range from 1673 K to 1873 K (1400 °C to 1600 °C). Darken’s quadratic formalism was introduced to correlate the activity coefficient of manganese in copper to composition, and the excess molar Gibbs energy change of mixing of Cu-Mn melts was described satisfactorily by Redlich–Kister type polynomial.