IMPROVING THE SURFACE STRUCTURE OF MASSIVE PARTS BY THE PLASMA METHOD

An increase in the reliability of the operation of large-sized and massive parts by plasma hardening of their surfaces is substantiated. It has been established that the formation of several structural zones of different microhardness is observed in detail along the depth of hardening, indicating the formation of a gradient-layered structure. It has been proved that at ultrafast heating rates, which occur during surface plasma hardening, phase and structural changes move to the high temperature region, changing the kinetics of the appearance and growth of new phase nuclei. In this case, fine-grained austenite is formed, which is transformed into a highly dispersed martensitic structure, which increases the strength and reliability of the surfaces of the parts.

Influence of heat treatment on the phase transition of ZrMo2O8 and photocatalytic activity

ZrMo2O7(OH)2·2H2O was obtained from ZrOCl2·2H2O and Na2MoO4·2H2O by a coprecipitation method. The phase and structural changes occurred during the heat-treatment of ZrMo2O7(OH)2·2H2O were investigated by XRD, IR and XPS analysis. The sequence of phase transformation can be divided into three stages: (1) transformation of ZrMo2O7(OH)2·2H2O to orthorhombic LT-ZrMo2O8 up to 300°C; (2) obtaining of mixture of both polymorphs of ZrMo2O8: cubic and trigonal at 400°C; (3) conversion to single trigonal (α) ZrMo2O8 above 450°C. The microstructure of the obtained trigonal (α) ZrMo2O8 was observed by scanning electron microscopy (SEM). The particle sizes were below 0.5 µm. The specific surface area was measured by modified BET method. The photocatalytic activity of the obtained trigonal (α) ZrMo2O8 powders was investigated by degradation of a model aqueous solution of Malachite Green (MG) upon UV-light irradiation.

Phase, Structural and Microstructural Changes in the TiC1-x – Cr3C2 Materials

The earlier studies showed that addition of different chromium carbides to nonstoichiometric fine titanium carbide improve sintering in the similar way. The phase, structural and microstructural changes for addition of various chromium carbides were also similar. In the present work the composite materials were made of various carbon quantity saturated titanium carbide (as matrix) and commercial chromium carbide Cr3C2 (as additive). The titanium carbide powders with variable content of carbon in structure were synthesized by the SHS method. The chromium carbide in quantity of 7.5 % by volume was added to the initial mixture. The influence of various stoichiometry of titanium carbide on onset temperature of sintering was examined by use of high temperature dilatometer. The phase and structural changes of examined materials during sintering were made using XRD and Rietveld method. The evolution of microstructure, versus of different stoichiometry titanium carbides, was observed by use of scanning electron microscopy.