Sintering Prealloyed Powders Fe-Ni-Cu-Mo Modified by Boron Base on Thermodynamic Investigations

One of the methods to reduce porosity and increase mechanical properties of Fe‐Ni‐Cu‐Mo powder type is applying activated sintering with the boron powder. In the experiments, a diffusion bonded prealloyed powder type Distaloy SA (Fe‐1.75%, Ni‐1.5%, Cu‐0.5%, Mo) was used alloyed by 0.2, 0.4, and 0.6 mas.% elemental boron powder with the addition of 0.8 mas.% of zinc stearate lubricant. Powders were 15 min blended, compacted and then sintered. The sintering process was elaborated in detail based on microstructure investigations and thermodynamic analysis, which showed that the liquid phase has to be formed as a result of eutectic reaction between matrix elements (Fe, Mo, Ni) and mixed boride (Fe, Mo, Ni)2B. In alloys with boron excess, the liquid phase may occur already a 1176°C in conformity with the reaction: L ↔ γ‐Fe + Fe2B. Its quantity is increased with liquid solution formed in the eutectic reaction running between boron and copper at 1027°C. If the system tends to be in equilibrium, the chemical composition of the liquid solution should be shifted toward higher Fe levels

The Influence of Ag2Te Addition on Thermoelectric Properties of Bismuth Telluride

The resistivity, Seebeck coefficient and thermal diffusivity were determined for BiTe3 + Ag2Te composite mixtures. Subsequent measurements were carried out in the temperature range from 20 to 270°C, and for compositions from pure Bi2Te3 to xAg2Te = 0.65 selected along the pseudo-binary section of Ag-Bi-Te ternary system. It was found that conductivity vs. temperature dependence shows visible jump between 140 and 150°C in samples with highest Ag2Te content, which is due to monoclinic => cubic Ag2Te phase transformation. Measured Seebeck coefficient is negative for all samples indicating they are n-type semiconductors. Evaluated power factor is of the order 1.52·10-3 and it decreases with increasing Ag2Te content (at. %). Recalculated thermal conductivity is of the order of unity in W/(m K), and is decreasing with Ag2Te addition. Finally, evaluated Figure of Merit is 0.43 at 100°C and decreases with temperature rise