V. E. Oliker

Effect of Rhenium on Formation of the Structure of Eutectic Alloys Based on β-NiAl + γ-Re

We have studied phase equilibria and plotted the partial phase equilibria diagram for Ni ― Al ― Re in the region of compositions ranging from 0.2 to 14 at.% rhenium. We have established the dependence of the structure and the phase composition of the alloys in the Ni ― Al ― Re system on the rhenium concentration. We have determined the optimal ratio of the components at which the alloys have the maximum melting point. We have shown that the structure of the alloys is a composite consisting of a NiAl-based matrix and γ-Re fibers.

Mechanico-Chemical Synthesis, Structure and Properties of Alloys Based on the System Ti ― Al

The kinetics of structure and phase formation in Ti ― Al and Ti ― Al ― Sc alloy powders in the process of mechano-chemical synthesis from elemental powders was investigated. It was established that the formation of microdimensional x-ray amorphous composite particles with nanodimensional structural components occurs. It was shown that in consolidation of the mechanically alloyed powders by hot isostatic pressing structural heredity is realized, and that the materials produced have unusually high microhardness compared to that of similar cast alloys. This is characteristic of nanostructured materials. In addition to high hardness the materials are characterized by high work of plastic deformation at room temperature. Microalloying the alloy powders with scandium has a complex positive effect on the strength properties of the hot pressed materials, due to the formation of a dispersion hardened microstructure with purified nanodimensional grains.

Structure and Properties of Detonation Coatings Based on γ-TiAl

Investigations of a coating ― substrate composite before and after oxidation in air at 900°C revealed that the main structural features were: formation of an Al2O3 scale on the surface of the TiAlCrSc(γ) coating (as a result of oxidation) and of inner layer at its interface with a 90% titanium substrate (as a result of diffusion in the composite). The observed phenomenon was caused by a Kirkendall effect resulting in the formation of titanium-enriched phases, apparently Ti3Al and α-Ti, which have a broad homogeneity range. The formation of a diffusion zone in the system with displacement of the Kirkendall plane in the direction of the substrate has a positive effect on the adherence of the coating. Furthermore, the filling of vacancies and pores in the coating with additional material supplied by the diffusion of titanium should have a favorable effect on the strength and durability of the coating, particularly its fatigue resistance.

Effect of magnetic treatment on the microstructure and abrasive resistance of WC–Co detonation-sprayed coatings

The effect of magnetic field on the phase composition and mechanical properties of VK-9 and VK-15 hardmetal detonation-sprayed coatings is studied. It is established that the magnetic field induces phase and structural transformations in sprayed coatings, such as reinforcement of the Co matrix due to the dissolution of WC in Co and the formation of WxCoyCz binary carbides. Magnetic treatment reduces residual internal stresses in the coating, decreases the amorphicity of its structure, and increases abrasive wear resistance.

Influence of the Structure and Properties OF WC – Co Alloy Powders on the Structure and Wear-Resistance of Detonation Coatings

We have made comparative investigations of the structure, phase composition and abrasive wear resistance of WC – Co coatings sprayed by the detonation method using powders of identical chemical composition and different particle structure, because the powders are prepared by different technologies. The laws we have found that govern how the structure evolves from the initial powder to a coating allow us to predict the physicotechnical properties of the coating. The more porous the powders, the more they are affected by the gas atmosphere in the spraying process and thus, the more significant changes in the phase composition are observed in the powder – coating system. The use of powders with highly porous particles results in the formation of porous coatings with low wear resistance.

Effect of Scandium and Chromium on the Structure and Heat Resistance of Alloys Based on γ-TiAl

It is established that microalloying of γ-titanium aluminides with scandium provides an increase in heat resistance, structure refinement and modification, and formation of a dispersion-strengthened structure with a coherent bond between the strengthening and matrix phases. Proceeding from this an improvement might be expected in strength characteristics over a wide temperature range. The effect in scandium consists in changing the ratio of Al:Ti thermodynamic activities in the direction of forming aluminum oxide at the alloy surface during oxidation as a result of the deoxidizing effect of scandium and the formation of fine oxide inclusions. As a result of this aluminum does not form oxides within the alloy. The distribution of elements within the microstructure of γ-Ti ― Al with 5%Cr after oxidation at 900°C for 300 h is studied. It is established that the surface scale layer that forms sometimes contains Cr in addition to Al and O. A diffusion mechanism is suggested for realizing the Cr-effect according to which chromium and aluminum ions participate in place of titanium ions in forming Al2O3 ― Cr2O3 scale at the metal ― air atmosphere interface.

Magnetoabrasive Fe-C-W alloy powders

ConclusionsWith a titanium alloy, the shaping of a surface being polished is linked to a large extent with plastic deformation (work hardening). In the polishing of a harder material (steely cutting plays a more important part. This explains why in the polishing of a titanium alloy surface roughness is reduced more effectively by round than by faceted particles. In the polishing of a titanium alloy with the powders investigated a dominant role is played not by their hardness but by their magnetic properties: In our work the best results were obtained with the powder of lowest tungsten content. With steel, probably because of an increasing role of the hardness of the powder particles, the quality of polishing is best at a higher tungsten content. A slight fall in magnetic properties is apparently compensated, compared with a titanium alloy, by the high magnetic permeability of steel. A magnetoabrasive Fe-C-W alloy powder can be successfully used for polishing titanium alloys, polished surfaces having a finish two or three classes higher than that attainable in polishing with Zh15KT material (15 wt. % TiC-Fe cermet).

Microstructure and properties of detonation-sprayed thermal barrier ZrO2 coatings

The formation of detonation-sprayed thermal barrier ZrO2 coatings is studied. The influence of spraying modes on the structure and mechanical properties of the coatings is determined. It is established that the microstructure of the coatings and thus their mechanical properties can be improved by controlling the weight of ZrO2–7%Y2O3 powder sprayed per shot. A quantitative evaluation of the mechanical properties of thermal barrier coatings by indentation method has shown good results.

Effect of magnetic treatment on the microstructure and strength of WC–Co detonation-sprayed coatings

The influence of magnetic treatment on fracture of the WC–Co detonation-sprayed coating–St3 steel substrate system is studied in bending tests. It is established that magnetic treatment leads to the redistribution of elements at the coating–substrate interface. It is shown that magnetic treatment improves the mechanical properties of the coating–substrate system: plastic strain of the system increases from 0.15% to 0.35% when coating starts cracking and stresses developed at fracture increase from 700 to 1300 MPa. The improvement of properties is due to better adhesion at the coating–substrate interface resulting from diffusion-controlled redistribution of elements during magnetic treatment.

Effect of magnetic field on residual stresses in NiAl–Re detonation coatings

The influence of a magnetic field on the internal stresses in NiAl–Re detonation coatings is experimentally confirmed. It is shown that the magnetic field has a substantial effect on the behavior and type of internal stresses. The changes are attributed to the residual stresses in the “substrate– coating” system, which are induced at all stages of preparation and subsequent treatment of the material in the magnetic field.