O. I. Fushchich

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.

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.

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 the Material and Sliding Rate of the Counterface on the Tribotechnical Properties of a CM(Ti–Mo–BN)–Steel Friction Pair

The effect of the material and sliding rate (1, 2, 4, 6, and 15 m/sec) of the counterface on the tribological characteristics of a (composite Ti–Mo–BN)–counterface (steels 45, 65G, ShKh15, 40Kh, and Kh18N9T, nitrided titanium, and BrO10 bronze) friction pairs in dry friction in air under a pressure of 0.8 MPa is investigated. It is established that, under these friction conditions, the composite in pair with BrO10 bronze is ineffective. During friction of the composite in pairs with steels 45, 65G, ShKh15, 40Kh, and Kh18N9T, an increase in the sliding rate from 1 to 6 m/sec results in an increase of the friction coefficient, linear wear of the friction pairs, mass loss of the composite and counterface, whereas the temperature of the friction surface increases. The highest temperature of the friction surface of the composite is reached in pair with steel 45. The temperature, sliding rate, and pressure applied lead to the synthesis of a secondary film (on the surface of the composite) of such a phase composition and structure that provide (in pair with steel 45) higher tribological characteristics of the composite than those in pairs with the other steels. At all sliding rates of the counterface, the tribological properties of the friction pairs depend not only on the properties of the composite material (chemical and phase composition, structure, and mechanical characteristics), but also on the same properties of the counterface material.

Interaction Between Components of the Copper-Based Self-Lubricating Antifriction Composite at 900 and 950°C

It is shown that a self-lubricating antifriction composite with microheterogeneous structure is synthesized during sintering of the Cu–Ni–P–MoS2 powder in hydrogen at 900 and 950°C. The structure of the self-lubricating antifriction composite formed at 900°C represents an α-solid solution of nickel in copper hardened by complex phosphide MoNiP, in which sulfide Cu2Mo3S4 is distributed. Molybdenum disulfide interacts with hydrogen at 950°C to form Cu2S and MoP. The structure of the self-lubricating antifriction composite formed at 950°C differs from the previous one in the amount of α-solid solution of nickel in copper, type (MoP) and content of hardening phase in it, and type (Cu2Mo3S4 and Cu2S) and amount of antifriction structural component.

Tribological Characteristics of the Iron-Based Composite at 500°C

The tribological characteristics of the Fe–W–CaF2 composite antifriction material (CAM) in combination with 1Kh18N9T steel are examined in air at a temperature of 500°C, a pressure of 0.8 to 3.3 MPa, and a sliding velocity of 0.5–2.0 m/sec. It is established that the friction coefficient, mass wear Im, and linear wear Il of the composite decrease, respectively, from 0.3 to 0.26, from 5 to 2 mg/km, and from 30 to <5 μm/km at constant pressure (0.8 MPa) with increase in the sliding velocity from 0.5 to 2 m/sec. At a constant sliding velocity (0.5 m/sec), with increase in pressure on the tribological system from 0.8 to 3.3 MPa, the friction coefficient f decreases from 0.3 to 0.26, whereas its mass wear Im and linear wear Il increase from 5 to 8.4 mg/km and from 30 to 57 μm/km. It is shown that secondary lubricating films form in friction on the working surface of the material. Like the starting material, they have a microheterogeneous structure and determine antifriction properties. The bcc solid solution of tungsten in α-iron hardened by inclusions of iron tungstate is a bearing structural component of the secondary lubricating films, and inclusions of iron oxides and calcium fluoride are antifriction structural components. The presence and content of the phases as well as the percentage of structural (antifriction and bearing) components in the secondary lubricating films depend on friction conditions (P · V). With increasing amount of the bearing structural component in the secondary film, wear of the material decreases. Higher content of the antifriction structural component in the film decreases the friction coefficient of the material.