Tribotechnical characteristics of polymer composites reinforced with fibrous structures

Studies have been made on the effects of the nature, textile structure, and strength characteristics of fibrous reinforcement and on hybrid reinforcement, nature of the polymer matrix, and the addition of ultrafine diamond powder on the coefficient of friction and wear of a polymer composite containing a thermoreactive matrix. The tests were performed in air without lubricant with an insert-shaft pair scheme with counterbody composed of chromed cast iron and with a ceramic counterbody (boron carbide, silicon carbide and nitride) at sliding speeds of 5, 10, and 15 m/sec and pressure 0.5 MPa. Glass plastics show more wear than carbon plastics on reinforcements with woven or knitted structures. The carbon plastics have tribotechnical properties at the level of the best ones. The ultrafine diamond powder substantially reduced the wear. The best tribotechnical properties occurred with the friction pair carbon-glass plastic against silicon nitride.     

Tribotechnical characteristics of titanium diboride electrospark coatings

Conclusions The tribotechnical characteristics of an alloyed layer obtained by electroerosion hardening of 45 steel with TiB₂-Mo sintered materials were studied. It was established that at increased temperature the maximum wear resistance is possessed by a hardened layer in alloying with a material containing the optimum quantity of hard and plastic phases. A higher content of hard phase leads to brittle failure of the hardened layer and an increased content of plastic phase to seizing of the contacting pairs.Translated from Poroshkovaya Metallurgiya, No. 5(269), pp. 86–88, May, 1985.     

Evaluation of characteristics of the porous structures of fibrous framework of composite electrocontact materials

Translated from Poroshkovaya Metallurgiya, No. 5(341), pp. 56–60, May, 1991.     

Tribotechnical characteristics of powder composite materials based on copper in high-speed friction

Conclusions Copper and the composite materials based on copper (with mullite, glass ceramic, and also sulfur and molybdenum sulfide) have a high friction coefficient (0.23–0.46), a medium temperature of the friction surface (130–270°C), and are susceptible to bonding with the contacting surface (07Khl6N6 steel).The materials containing 10% graphite, sulfur, and molybdenum disulfide have a low friction coefficient (0.09–0.15), do not bond to 07Khl6N6 steel, and can be recommended for service in high-speed friction units.Translated from Poroshkovaya Metallurgiya, No. 7(283), pp. 52–56, July, 1986.     

Microscopic characteristics of fatigue crack propagation in aluminum alloy based particulate reinforced metal matrix composites

Microscopic characteristics of fatigue crack propagation in two aluminum alloy (A356 and 6061) based particulate reinforced metal matrix composites (MMCs) were investigated by carrying out three point bending fatigue tests. The impedance offered by the reinforcing particles against fatigue crack propagation has been studied by plotting the nominal and actual crack lengths vs number of cycles. Surface observation shows that fatigue cracks tend to develop along the particle-matrix interface. In the case of Al (A356) MMCs, stronger interaction of fatigue crack with Si particles, as compared to SiC particles, was evident. In both MMC materials, particle debonding was more prominent as compared to particle cracking. The attempted application of Davidson's model to calculate ΔK_th indicated that for cast MMCs the matrix grain including the surrounding reinforcing particles has to be considered as a large “hard particle”, and the grain boundary particles themselves behave like an hard “egg-shell” to strengthen the material.     

Melt-Processed Ni3Al matrix composites reinforced with TiC particles

TiC-reinforced Ni₃Al metal matrix composites have been investigated. The composites were prepared by in situ precipitation of either 0.01, 0.05, or 0.1 vol fraction TiC in molten Ni3Al. These precipitates are thermodynamically stable in the Ni₃Al at 1000 °C up to 50 hours. Although almost ideal precipitate distribution was achieved at low volume fraction of TiC, at higher volume fraction, there was a tendency toward agglomeration. Room and hightemperature mechanical testing showed significant improvement in modulus, yield strength, and ultimate tensile strength, while still maintaining a 2.5 pct elongation at 0.1 vol. fraction TiC and 500 °C. The density of precipitates (number/m³) is strongly dependent on the fraction of TiC, on temperature, and on the holding time at that temperature. The critical nucleation temperature for these precipitates was determined to be at 1475 °C. Experimentally evaluated growth rate constants indicate a diffusion-controlled coarsening mechanism along with coalescence and multiparticle interaction at higher volume fractions of TiC. This is in accordance with either the Lifshitz Slyozov Encounter Modified (LSEM) model or with the Voorhees and Glicksman (VG) model.     

Thermal cycling-induced deformation of fibrous composites with particular reference to the tungsten-copper system

Dimensional stability of fibrous composites under conditions of elevated temperature cycling has been examined with reference to the familiar model system, tungsten wirereinforced copper. Preferential growth of the matrix in the direction parallel to the reinforcing fibers, the amount of which increased with the number of cycles, was observed in specimens subjected to hundreds of repctitive thermal cycles in the temperature range between 0.35 and 0.8 of the matrix homologous temperature. The amount of growth per unit length after a given number of cycles was found to increase with increasing the holding time at the upper cycling temperature; it was also dependent on such composite variables as the fiber length, fiber diameter, and fiber volume fraction. This observation strongly suggests that interface sliding plays an important role in elevated temperature deformation of this class of material. On the basis of a model which assumes a viscous nature of the phase boundaries, the phenomenon observed is theoretically explained in terms of interfacial sliding-induced relaxation of the internal stress built up in the composite due to differential thermal expansion of the composite constituents. Formerly Graduate Student.