A. G. Kostornov

Effect of dry friction parameters on the tribosynthesis of secondary structures on composite antifriction iron-based material

The paper examines the tribological characteristics of a Fe–W–CaF2 composite antifriction material (CAM) in combination with 65G steel during dry friction in air at a high sliding velocity (15 m/sec) and insignificant (0.64–1.28 MPa) pressures. It is established that with twofold increase in pressure (from 0.64 to 1.28 MPa), CAM friction coefficient decreases from 0.25 to 0.20 (by 20%) and wear increases from 0.0158 to 0.03085 mg/km (by 49%) but remains insignificant. The factors acting in the friction process lead to the formation of secondary lubricating films. They prevent mechanical contact between the rubbing surfaces and provide necessary antifriction and operating properties. It is shown that the secondary lubricating films as thin layers with inclusions of solid lubricants differ from the starting material in chemical and phase composition, structural state, and better mechanical characteristics.

Composite Ceramic Materials and Coatings for Tribological Use

The tribological properties over a broad range of sliding velocities and loads under dry friction in air of promising composite materials and coatings based on titanium carbide and carbonitride were studied. The dominating effect of secondary structures arising in the process of tribooxidation was investigated. Isomorphous oxide phases which form solid solutions and are strongly adherent to the surface of the material or coating promote the development of a continuous and dense screening film.

High-porosity permeable materials from metal fibers I. Effect of sintering on size variation phenomena and the quality of interparticle contacts in fiber materials

ConclusionsIt has been established that in materials forming, during the specimen shaping stage, sufficiently strong interfiber contacts the residual stress relaxation effect is less pronounced. During sintering at 0.9Tm high-porosity materials from thin metal fibers experience only negligible dimensional changes; after sintering such materials exhibit optimum conductivity.

Sintering of Cu–Sn–P–MoS2 Powder Samples at 780°C

The influence of initial porosity and MoS2 content of pressed Cu + 9Sn + 1.5P + (5, 10, 15%) MoS2 powder samples on their growth during sintering in hydrogen at 780°C is studied. The growth of samples with the same MoS2 content decreases with higher initial porosity and the growth of samples of the same size and same porosity after pressing increases with greater MoS2 content. Water vapors generated during the hydrogen reduction of oxides present on the starting tin powder and phosphorous-copper alloy powder cause swelling of the samples. Moreover, phase transformations in the material during sintering can increase the samples as new phases are formed (copper sulfide Cu2S) with a larger crystal lattice that that of the matrix and molybdenum disulfide.

Some characteristic features of the production of extruded nickel fibers

ConclusionsThe catalytic action of nickel on the process of carbon removal during the heat treatment of viscose filaments filled with nickel powder enables virtually nonporous metal fibers to be obtained. In the sintering of nickel-containing viscose fibers the fiber preoxidation operation can be dispensed with, which simplifies the process of production of such fibers.

Prospects of Improving the Tribotechnical Characteristics of Titanium Composites

Titanium-based composites containing MoS2, MoSe2, CaF2, and BN solid lubricants are synthesized. Their tribological characteristics are investigated without lubrication at different sliding velocities (0.5, 1, 2, 4, 6, and 15 m/sec) and low pressures (0.27, 0.54, 0.8, 1.1, 1.35, 1.47, and 2.7 MPa) in air. In view of the high friction coefficient and large wear, the composite materials cannot be proposed as antifriction ones for operation at small sliding velocities and low pressures. The titanium-based composites are promising as antifriction materials at an increased sliding velocity (15 m/sec) and low pressures when their friction coefficients range from 0.3 to 0.36 and wear ranges from 1.91 to 68.3 mg/km. In dry friction at a high sliding velocity in air, the temperature of their working surface increases resulting from the formation of titanium oxides and then a dense secondary lubricating microheterogeneous film. The composition and structure of the secondary films differ from those of the starting materials and determine their antifriction properties and friction performance.

EFFECT OF OXIDE CONTENT ON THE TRIBOLOGICAL AND PHYSICOMECHANICAL PROPERTIES OF FILLED POLYTETRAFLUOROETHYLENE

The effect of the nature and the amount of oxide fillers on antifriction properties of polytetrafluoroethylene under dry friction conditions with different loads and slow sliding rates is studied. It is established that oxides with a high hardness increase the friction coefficient and reduce the wear resistance of filled polytetrafluoroethylene, but oxides with a low hardness do not give rise to an increase in friction coefficient for polytetrafluoroethylene with a marked increase in its wear resistance, and this is connected with formation of a separating layer at the surface of the friction pair.

Particle contacts in a porous fibrous copper material at early sintering stages

Electrical conductivity measurements have been used in quantitative state evaluation for particle contacts in fibrous copper pressings at early stages of sintering under vacuum. The results agree with ultrasonic data and stretching tests. Contact formation in such a material begins after the specimen has been heated to 600–800°C, i.e., after the complete relaxation of the residual stresses accumulated in the pressure working.

Microplasticity behavior of porous nickel

We have used a physical and structural approach to study the mechanical behavior of monoporous И=5–45%) and biporous (И=45–70%) nickel powder at room temperature within the strain range 10−5 to 5·10−3. We have shown that for both low porosity and high porosity materials, the true microyield curves depend on the hardening provided by grain boundaries or interparticle boundaries. We found effects connected with the geometrical structure of the materials under investigation. The increase in the deforming stresses in the base metal material when the porosity is greater than 25% can be explained by the peculiarities of the stress states in the interparticle connections. The softening effect, which depends mainly on the porosity of the powder subsystem, is related to initiation of cracks in the initial phases of microyield.

Elastic modulus of highly porous nickel-based materials

The results of experimental and theoretical investigations of the structural sensitivity of the elastic modulus of powders biporous nickel are reported. The previously proposed theoretical dependence of the elastic modulus of a biporous system on structural parameters has been verified. It is shown that the elastic characteristics of biporous materials can be varied over a wide range if the parameters θmicr θmacr and λ (the particle size ratio of the pore-forming agent and the powder) are varied. The values of those parameters to some degree also affect the mechanical behavior of biporous nickel near the porosity limit θc. If λ and θmacr/θmicr increase while the integrated porosity remains constant the elastic modulus and the porosity limit rise.