非化学计量对铁氧化物还原热力学平衡的影响

铁氧化物是具有非化学计量比的化合物,非化学计量对铁氧化物的还原过程带来一系列影响.本文采用Dieckmann缺陷模型和Weiss的浮氏体理想固溶体模型分别对非化学计量比的磁铁矿和浮氏体进行了热力学计算.同时根据电荷守恒和物质守恒,对铁氧化物固溶体的综合缺陷度δ与还原失重率和亚铁含量的关系进行了分析,以期对实验终产物的判定提供依据.通过理论分析与计算,最终明确了不同化学计量比的磁铁矿和浮氏体在不同温度下的平衡还原势P_CO(H2),即相应的优势区图.在给定还原势的纯赤铁矿等温还原过程(未有金属Fe生成时),当失重率小于6%时,还原产物属于Fe³⁺占优势的磁铁矿区域;当失重率高于6%时,反应进入Fe²⁺占优势的浮氏体区域.     

The effect of nonstoichiometry on the positive temperature dependence of strength of Ni3AI and Ni3Ga

Compression tests have been carried out on the polycrystalline Ni₃Al and Ni₃Ga alloys over the temperature range 77 ~ 1000 K. The flow stress and the temperature dependence of strength are found to be sensitive to small composition change within the phase field. The anomalous strengthening of these compounds with temperature is more significant for Al-and Ga-rich deviations than for Ni-rich deviations from stoichiometry. The change in activation constant of these compounds derived from the flow stress increment appears to be discontinuous at the stoichiometric composition. The influence of deviations from stoichiometry on the temperature dependence of strength could be accounted for by the phase stability concept proposed by the present authors. It is concluded that the phase stability of the Ni₃Al and Ni₃Ga alloys with respect to the D0₂₂ phase as well as the D0₁₉ phase are reduced as the composition of the minority component is increased. This change leads to the relatively reduced {100} antiphase boundary energy which increases the propensity for the cross slip onto cube plane. formerly graduate student, Department of Material Science and Engineering, Tokyo Institute of Technology.