Yu. N. Podrezov

Production of Titanium Powder Sheets by Asymmetric Rolling

The influence of symmetric and asymmetric rolling on the formation and properties of titanium powder rolled sheets is studied. It is established that the asymmetric rolling of powder metal produces sheets with higher density and much better mechanical properties than symmetric rolling does. The effect of the titanium powder rolling conditions on the structure of the material before and after sintering is studied. The rolled metal obtained by asymmetric rolling has best mechanical properties at a sintering temperature lower by 200°C than that of symmetric rolling. The technological feasibility of asymmetric rolling of titanium powder is demonstrated.

Gradient Structure Formation by Severe Plastic Deformation

Severe plastic deformation (SPD) techniques are the best for producing of massive nanostructured materials. The methods of equal channel angular pressure (ECAP) and twist extrusion (TE) are realized by simple shear uniform deformation without change of cross-section sizes of sample. In the case of roll forming (RF) the shear strain is localized in the near-surface layer of metal. Intensity of shear strain in the near-surface layer depends on variation of parameters of deformation and conditions of friction in a contact. Steel 65G (0.65C, 0.3Si, 0.6Mn, 0.3Cr, and 0.3Ni) was deformed by roll forming. Transmission electron microscopy (TEM) of “cross-section” samples was used for studying of gradient structure of deformed material. TEM investigation shown that cell substructure in a near-surface layer have been formed. The depth of deformed layer is approximately 40 micrometers. Average cell size in cross-section direction is about 100 - 200 nm. Thin nanostructure layer with cell size about 20-30 nm was detected. In our opinion such substructure formed due to effect of “good” impurities.

Process Approaches for Producing Complex Composite Inoculants by Rolling of Powder Mixtures. I. Inoculant Powder Mixtures. Composition, Structure, and Properties

This series of papers are devoted to the development of process approaches for producing complex composite inoculants to manufacture agricultural machines from spheroidal graphite cast iron. Complex composite inoculants as strips and their fragments can be produced by rolling of powder mixtures. The first paper justifies the choice of inoculants and characterizes the starting powders they consist of. Weight and volume correlations between the brittle and ductile components for different compositions of inoculants are calculated. It is established that all powder compositions belong to critical systems that have approximately 50 vol.% of both brittle and ductile components. Such systems require special process approaches to make high-quality products. Process characteristics of the powders that influence the quality of the rolling strips are determined. These are apparent density of the starting powders and their mixtures, friction index (Hausner ratio), and shear angle and its tangent.

Mechanical properties and structure of tungsten-rhenium powder metallurgy deformed alloys

The properties of tungsten-rhenium alloys, obtained by compact sintering of dispersed powders which formed a tungsten-rhenium solid solution at relatively low temperatures, were investigated. Three systems were compared: a tungsten alloy with 2% rhenium, an alloy with dispersed additions of yttrium and hafnium oxides, and commercially pure tungsten. The properties included ductile-to-brittle transition temperature, bend strength, yield strength, and crack resistance. Structures were determined by scanning electron microscopy. Tungsten alloyed with small additions of rhenium possessed higher plasticity and in other mechanical properties was similar to cast and deformed alloys of the same composition.

Influence of Heat Treatment on High-Temperature Mechanical Properties of Ti-5Dy-5Si-Sn Alloys

By the methods of X-ray diffraction, metallography, TEM, SEM and mechanical testing for compression, the influence of heat-treatment condition on the structure and properties of Ti-bL)y-5Si-Sn alloys was studied. High dispersity and stability of the microstructure were observed, predetermining a high level of mechanical properties. Annealing by the regime 1350°C, 31.5 h + 1250°C, 32 h + 1200°C, 32 h + 1100°C, 32 h was shown to provide optimum combination of high-temperature strength and roomtemperature plasticity.

Strain hardening of porous iron under uniaxial compression

A series of experiments was carried out with powder iron of 1–40% porosity including deformation by compression to various degree of deformation, and strain hardening curves were calculated. It was established that change in the loading sign relative to uniaxial tension had practically no effect on the strain hardening laws of the solid phase, although it basically changed the porosity contribution to the loading curve formation.

Effect of porosity on the ductility and ductile failure mechanism of powder iron

ConclusionsFormation of the ductility characteristics of the powder materials based on iron is associated with the transformation of the porous structure during deformation. The model proposed by Gerland [1] for materials with particles describes accurately the behavior of the material containing pores and links the true strain to fracture with porosity.The experimental dependence er=F(O) explains satisfactorily the formation of certain important processing characteristics of the material, such as cracking resistance and impact toughness. Since the yield stress of the material produced from various powders differs only slightly in a wide range of porosity, the main contribution to formation of cracking resistance and impact thoughness comes from the true strain to fracture (er).The difference in the content of the second phase particles in the iron powders of variousggrades leads to differences in the er values for the dense states; er decreases with increasing porosity. Thus, the high values of the impact toughness for the materials produced from WPL-200 and O Cher MK powders are explained by the low content of the second phase particles (1–2%) in comparison with the other materials, where the volume fraction of the particles was 3–5%.

Effect of the scale factor on the results of determinations of the mechanical properties of iron-base P/M materials

ConclusionsAn investigation was carried out into the effect of the scale factor on results of determinations of the resistance to cracking, σb, and σt of iron-base P/M materials. An optimum specimen cross-sectional area (60 mm2 or more) has been established for obtaining reliable data on these properties. The results of this investigation will be utilized in the development of new and modification of existing standards covering methods of control of materials produced by powder metallurgy techniques.

The Effect of Compacting Rolling on the Properties of Titanium Powder Mill Products

The effect of deformation stress on the consolidating of titanium powder strips obtained by symmetrical and asymmetrical rolling is analyzed. It is determined, that the strength of green strips after asymmetrical rolling is substantially higher than that of conventional strips: for low and medium deformation stress (by a factor of 3–5) and for high deformation stress (by a factor of >10). The repeated rolling improves the mechanical properties of sintered strips. Titanium powder strips produced through optimal asymmetrical rolling possess better mechanical properties than conventional titanium strips.

Process Approaches for Producing Complex Composite Inoculants by Rolling of Powder Mixtures. II. Compacting Conditions, Structure, and Properties of Two-Component Model Systems Fe–FeSi and Al–FeSi

The optimization of compacting processes for two-component model systems consisting of brittle and plastic components is discussed. Fe–FeSi and Al–FeSi compositions with different volume content of the plastic component are tested. The compaction is conducted by pressing with different compacting force. Mechanical properties of cylindrical compacts are determined by axial compression test and the Brazilian test. It is established that the content of brittle component must be ≤ 60% and the compaction force must be ≥ 400 MPa. With increasing compaction force, the strength of the compacts increases significantly. It is established that the application of both iron and aluminum as binder is acceptable. However, iron and aluminum compositions are the best for low and high content of the brittle component, respectively.