Heat Capacity and Thermodynamic Functions of Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> from 14 to 320 K

The heat capacity of Ga₂Se₃ is measured from 14 to 320 K by adiabatic calorimetry. The smoothed heat capacity data are used to evaluate temperature-dependent thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) of gallium selenide. Under standard conditions, the thermodynamic properties of Ga₂Se₃ are C _p ⁰ (298.15 K) = 120.8 ± 0.2 J/(K mol), S⁰(298.15 K) = 180.4 ± 0.4 J/(K mol), H⁰(298.15 K) - H⁰(0) = 25.32 ± 0.05 kJ/mol, and Φ⁰(298.15 K) = 95.52 ± 0.19 J/(K mol). The Debye characteristic temperature of Ga₂Se₃ evaluated from heat capacity data is 340 ± 10 K.     

Surface Modification of Iron Carbon Alloys by Plasma Detonation Treatment

Plasma detonation method (PDM) is based on the use of pulse plasma jets formed by transformation of a detonation wave into a plasma pulse. Energy density in such a jet amounts to 10⁷ W cm_-2, Consumable electrodes used here allow the vapors of various metals to be introduced into the jet. PDM is applied for heat treatment of surfaces, their alloying, as well as for coating deposition. The process of surface modification of carbon steels using various electrodes is investigated. The effect of the treatment conditions and the electrode materials on surface hardening is discussed.     

Electrolyte-plasma hardening of circular saws

Cold circular saws with an external diameter of 600–900 mm and a disk thickness of 5–8 mm are used for cutting measured pieces of bent shapes and pipes in lines of shaping mills. Strict requirements are imposed on the quality of the circular saws, namely, they should possess high wear resistance of the teeth and withstand the loads exerted by the cut bent shapes in the direction perpendicular to the plane of the disk. A method of electrolyte-plasma hardening of circular saws with the use of pulse heating has been developed in order to meet these requirements. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 9–12, January, 1998.     

Tribological and physical-mechanical properties of protective coatings from Ni-Cr-B-Si-Fe/WC-Co-Cr before and after fission with a plasma jet

A new type of coating is developed, which is a mechanical mixture of two different powders, namely, Ni-Cr-B-Si-Fe (PG-19N-01) and WC-Co (hard alloy). After the coatings from this mixture are deposited, their surface layer is fused with a plasma jet using an eroding electrode made of W. The additional treatment of the coatings with the plasma jet yields new phases and causes the redistribution of elements in the layer 45–60 μm deep; the percentage ratio of the phases WC, α-CoCr, Co, and Ni, as well as Cr₃Ni₂ + γ-(Fe, Ni) appearing during coating deposition also changes. The redistribution of elements occurs in the upper coating layer owing to fusion with the plasma jet. These processes yield variations in the physical-mechanical properties of the coatings, such as the hardness and elastic modulus; the coating wear rate decreases severalfold. It is found that with increasing load applied to the Berkovich pyramid the elastic modulus of the coating drops from 240 (at an indentation depth of 50 nm) to 175 GPa (at 150 nm). The elastic modulus of the substrate rises from 25 to 42 GPa. The coating hardness calculated from the loading-unloading curves is 15.3 to 10.6 GPa under increased load applied to the indentor. Specimens covered with the coating fused with the plasma jet in three passes demonstrate the lowest material wear.