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Effects of humidity on friction and wear of Al-Si alloy impregnated graphite composite

100%

Goto H. , Omori S. , Uchijo K.

tom Vol. 4, no spec.

139-145

Pin-on-disk type sliding friction and wear experiments for an Al-Si alloy impregnated graphite composite (pin) in contact with a bearing steel (disk) were conducted at two loads in air to investigate the effects of relative humidity (RH) on the tribological characteristics of the composite. The friction and wear behavior and the pin-lifting phenomena due to the entrance of wear particles into the contacting surfaces were continuously measured during the experiments. SEM observations, together with EPMA, were also conducted to examine the material transfer on the sliding surfaces of the pin and disk. At 100 N, the friction coefficient is high at low RH levels, decreases with increasing RH to a minimum between 50 and 70 % RH and increases a little at high RH levels. The wear rate is very high in a severe wear regime at low RH levels, decreases with increasing RH to a minimum in a mild wear regime between 30 and 60 % RH and increases a little at high RH levels. From the EPMA results, at the RH levels where the friction and wear exhibit the minimum, the wide, compacted films consisting of the mixtures of graphite powder and wear particles of the Al-Si alloy are generated on the disk sliding surface. The films, preventing metal-to-metal contact with a release in adhesion, lead to a decrease in friction and wear.

Application of ion bombardment to modification tribological properties of rubber

72%

Bieliński D. M. , Jagielski J.

tom Vol. 34, nr 6

639--642

The paper presents effects of surface modification of various elastomers upon bombardment with beams of H+, He+, F+ or Ar+ ions. Changes to composition and structure of rubber macromolecules, subjected to ion beam treatment, are discussed from the point of view of its influence on the modification of surface layer of the elastomers studied. Hydrogen release induced graphitization together with post treatment oxidation of rubber macromolecules increase surface wettability of the materials, facilitating lowering of “wet” friction. Free radicals being created due to interactions between energetic ions and macromolecules produce additional crosslinking, which manifests itself by increased hardness of the elastomers. Modification of mechanical properties of the surface layer changes mechanism of elastomer friction from the bulk (hysteretical) to the surface (adhesional) one, what results in significant reduction of friction. Despite crosslinking induced shrinkage of the surface layer, which results in its microcracking, ion beam treated elastomers showed to be wear resistant due to the lack of delamination under stress.

Artykuł przedstawia wpływ modyfikacji powierzchni różnych elastomerów za pomocą bombardowania wiązką jonów H+, He+, F+ lub Ar+. Zmiany składu i budowy makrocząsteczek spowodowane obróbką jonową zostały omówione z punktu widzenia jej wpływu na modyfikację warstwy wierzchniej badanych elastomerów. Grafityzacja spowodowana uwalnianiem się wodoru wraz z wtórnym utlenianiem makrocząsteczek kauczuku powoduje wzrost zwilżalności powierzchni materiałów, sprzyjając obniżeniu tarcia „na mokro”. Wolne rodniki powstające w następstwie oddziaływań jonów o dużej energii z makrocząsteczkami powodują wzrost usieciowania, przejawiający się we wzroście twardości elastomerów. Modyfikacja właściwości mechanicznych warstwy wierzchniej zmienia mechanizm tarcia elastomerów z objętościowego (histerezyjnego) na powierzchniowy (adhezyjny), powodując znaczące zmniejszenie oporów tarcia. Pomimo skurczu warstwy wierzchniej spowodowanego jej dosieciowaniem i prowadzącego do powstania mikropęknięć na powierzchni materiału, bombardowanie jonowe elastomerów prowadzi do wzrostu ich odporności na zużycie dzięki braku zjawiska delaminacji pod obciążeniem.

Study on Friction and Wear Characteristics of Aluminum Alloy Hydraulic Valve Body and Its Antiwear Mechanism

72%

Rong L. , Lunjun C. , Ming S. , Qi Z. , Yong L.

tom Vol. 17, iss. 1

207--215

In order for the working status of the aluminum alloyed hydraulic valve body to be controlled in actual conditions, a new friction and wear design device was designed for the cast iron and aluminum alloyed valve bodies comparison under the same conditions. The results displayed that: (1) The oil leakage of the aluminum alloyed hydraulic valve body was higher than the corresponding oil leakage of the iron body during the initial running stage. Besides during a later running stage, the oil leakage of the aluminum alloyed body was lower than corresponding oil leakage of the iron body; (2) The actual oil leakage of different materials consisted of two parts: the foundation leakage that was the leakage of the valve without wear and wear leakage that was caused by the worn valve body; (3) The aluminum alloyed valve could rely on the dust filling furrow and melting mechanism that led the body surface to retain dynamic balance, resulting in the valve leakage preservation at a low level. The aluminum alloy modified valve body can meet the requirements of hydraulic leakage under pressure, possibly constituting this alloy suitable for hydraulic valve body manufacturing.