热压制备Mo-Nb-Si系新型高温金属硅化物合金

以Mo粉、Nb粉和Si粉为原料,采用机械活化/热压工艺制备(Mo1-xNbx)5Si3(x=0,0.4,0.6,1.0)型高温金属硅化物.通过XRD、SEM和EDS等分析手段对合金试样进行物相分析、显微组织观察、微区成分分析及力学性能测试.结果表明:合金试样的主要物相为Mo5Si3、α-Nb5Si3、γ-Nb5Si3及其(Mo,Nb)5Si3和β-(Nb,Mo)5Si3固溶体相,Mo有助于高温相β-Nb5Si3的相稳定;随着Nb含量的增加,硬度值呈上升趋势,合金硬度较高,达1 311.5～1 397.5HV;试样的压痕断裂韧度和抗压强度呈先增加后降低的趋势,当x=0.6时断裂韧度和抗压强度达到最大,分别为4.71 MPa·m1/2和1 637 MPa,Nb5Si3和Nbss(Nb基固溶体)有助于合金断裂韧度的提高.     

Improving the calculation of interdiffusion coefficients

Least-squares spline interpolation techniques are reviewed and presented as a mathematical tool for noise reduction and interpolation of diffusion profiles. Numerically simulated diffusion profiles were interpolated using a sixth-order spline. The spline fit data were successfully used in conjunction with the Boltzmann-Matano treatment to compute the interdiffusion coefficient, demonstrating the usefulness of splines as a numerical tool for such calculations. Simulations conducted on noisy data indicate that the technique can extract the correct diffusivity data given compositional data that contain only three digits of information and are contaminated with a noise level of 0.001. Splines offer a reproducible and reliable alternative to graphical evaluation of the slope of a diffusion profile, which is used in the Boltzmann-Matano treatment. Hence, use of splines reduces the numerical errors associated with calculation of interdiffusion coefficients from raw diffusion profile data.     

Thermodynamic properties of condensed silicides

An approximate generalized equation is obtained for the temperature dependence of the change in Gibbs energy in the atomization of condensed silicides; this equation takes account of the number of atoms present in the silicides and their calculated boiling points. For the 16 silicides considered, the discrepancy between the maximum calculated value and the mean is no more than 10%. On that basis, the proposed method may be used to verify data from other sources and also for approximate prediction of the thermodynamic properties of silicides that have not yet been studied.     

Thermodynamic properties of chromium silicides

Conclusions The method of measuring the emf's of high-temperature galvanic cells was employed for determining the isobaric-isothermal potentials, entropies, and heats of formation of the chromium silicides CrSi₂, CrSi, Cr₅Si₃, and Cr₃Si in the temperature range 700–850°C. Using literature data upon the enthalpies and entropies of the chromium silicides and pure chromium and silicon, the standard heats and entropies of formation of these silicides were calculated.Translated from Poroshkovaya Metallurgiya, No. 7 (115), pp. 61–65, July, 1972.     

Thermodynamic properties of manganese silicides

Summary The free energies, heats, and entropies of formation of the manganese suicides between 950 and 1100°K were measured by means of the emf method.     

The electron structure of silicides

Summary The physical properties of disilicides of transition metals are studied, and conclusions are drawn as to the nature of filling of the energy states during the formation of these compounds. The role of silicon atoms in the formation of chemical bonds is shown.     

Modelling the influences of solid-state interdiffusion and dissolution on transient liquid phase sintering kinetics in a binary isomorphous system

A simple model was developed to predict the impact that solid-state interdiffusion and dissolution have on liquid formation and its duration during transient liquid phase sintering (TLPS). The model predicts that solid-state interdiffusion can dramatically reduce the amount of liquid initially formed during heating. This reduction is dependent on the heating rate and initial base metal particle size. In cases of sintering above the additive phase melting point, the model predicts that base metal dissolution increases liquid phase formation and that this additional melting reduces the base metal particle size. The model predicts that longer times are required to solidify isothermally the greater amounts of liquid formed at higher temperatures (because of dissolution). This agreed qualitatively with experimental results for a Ni-65 wt pct Cu TLPS mixture sintered at 1090 °C and 1140 °C. Quantitative comparisons between the model and experiment were good at 1140 °C; however, the rate of isothermal solidification was underestimated by the model for intermediate sintering times at 1085 °C.     

High-temperature evaporation of lanthanum and praseodymium silicides

Mass spectrometry is used to study the evaporation of silicides LaSi, LaSi₂, PrSi_1.8 and PrSi_1.8 at 1800–2000 K. Their standard enthalpies of atomization and formation are determined.