Dry sliding wear behaviour of sub-zero processed Cr–V ledeburitic steel Vanadis 6 against three counterpart types

The effect of sub-zero treatments on dry sliding wear performance of Vanadis 6 tool steel was investigated by pin-ondisc tests against three counterpart types: alumina, 100Cr6 ball bearing steel, and CuSn6 bronze. The microstructure of the examined steel consists of tempered martensitic matrix with very small amounts of retained austenite, and three carbide types. Sub-zero treatments increase the carbides count. The hardness of the steel increases with increasing the austenitizing temperature but slightly decreases with the application of sub-zero treatments. Sub-zero treatments affect the wear performance of the Vanadis 6 steel when tempered at the secondary hardening peak as follows: almost no effect of this kind of treatment was detected when alumina was used as a counterpart but moderate amelioration was recorded when either 100Cr6 steel or CuSn6 bronze was used in the sliding couple. This behaviour is attributed to the combined effect of hardness variations and changes in population density of carbides, due to application of sub-zero treatment.

Evaluation of tribological properties of lubricants based on Hersey’s–Stribeck’s characteristics

The content of the paper presents the results of investigations of selected lubricants. The study led to obtaining Hersey’s-Stribeck’s curves and to comparison of the lubricating properties of lubricants belonging to different groups such as hydrocarbon oils, perfluoropolyether oils (PFPE), and ionic liquids. The following liquids were evaluated for tribological properties: PAO-6 polyalphaolefin oil base, CJ 006 ionic liquid (3-methyl-1-propylpyridinium bis(trifluoromethylsulphonyl)-imide) and Fomblin Y 04 synthetic perfluoropolyether oil. The research was carried out using the universal nano/micro tribotester (UNMT-CETR, CA, USA) at the Department of Tribology, Surface Engineering and Service Fluids Logistics, Faculty of Mechanical Engineering, Military University of Technology. The study consisted of friction of a ball bearing steel (100 Cr 6) with a round specimen of a certain roughness (ball-on-disc). Friction occurred in rotational motion of the specimen, at different rotational speeds at constant radius and at constant load (0.25 N; 5 N; 50 N). The friction node was lubricated with the tested liquid. Keywords: tribology, friction factor, Hersey’s−Stribeck’s characteristics.

OPTIMIZATION OF GRANULOMETRIC COMPOSITION OF POWDERS MADE BY ELECTROEROSION DISPERSION OF BALL BEARING STEEL WASTE

As practice shows, most of the methods to obtain powder materials have several disadvantages: high power consumption, environmental problems (waste water, emissions), high cost of technological equipment. Currently, one of the most promising methods for producing powder materials from the conductive waste is the method of electroerosion dispersion (EED). EED method has a relatively low energy consumption and environmental cleanliness of the process. The development of technology of making powder materials from ball bearing steel waste, and assessment of their use effectiveness requires comprehensive theoretical and experimental studies. The iImplementation of the planned measures will allow us to solve the problems of obtaining powder materials including iron based nanopowder, elimination of ball bearing steel waste and their further use and, thereby, reduce the production cost of the final product. The aim of the present paper is to optimize the granulometric composition of powders made by electroerosion dispersion of waste-bearing steel waste. Our study has experimentally determined inversely proportional relationship between average particle size of powder material and the capacity of energy discharge capacitors and the voltage on the electrodes in the reactor. It has also stated inversely proportional dependence of the average particle size of powder material on pulse repetition frequency of EED installation in the range up to 90 Hz. Further increase of energy discharge capacitors capacity leads to an increase in the average particle size of powder material. By making factorial experiment there have been determined the optimal settings for the process of powder materials production by the method of electricerosion dispersing in distilled water: the capacity of energy discharge capacitors is 58 ufd, voltage on the electrodes is 140 W, pulse repetition frequency is 140 Hz.

Bimodal Particle Reinforcement for Wear Resistant Powder Metallurgy Steels

Reinforcement of powder metallurgy steels with fused tungsten carbide (FTC) has been shown to improve the wear resistance under certain loading conditions. A weakness is however the low hardness of the matrix, which results in selective wearing of the matrix between the carbide particles, i.e. “washing-out” effects. In the present study, in a first round fine metallic or carbidic particles were added to the iron-graphite powder mix, and the blends were die compacted and sintered in protective atmosphere. The specimens were then tested under different wear loads. It showed that also metallic powders added were transformed into carbides during sintering, thus resulting in reinforcement by fine carbides. Since Mo alloying proved to be most effective with regard to hardness and strength, specimens Fe-3%Mo-0.8%C reinforced with 20% coarse FTC (all in mass%) were sintered and tested according to ASTM G65, Continuous Impact Abrasion and dry sliding against ball bearing steel. It showed that Mo addition had quite pronounced positive effect on the G65 erosion resistance and, somewhat less, on dry sliding, while wear resistance in CIAT was less affected; the basic wear mechanisms however remained unchanged.

Comparative Study on the Tribological Performance of HFCVD Diamond and DLC Films under Water Lubricating Condition

The tribological performance of conventional microcrystalline diamond (MCD) film and diamond-like carbon (DLC) film is investigated comparatively under water lubricating condition. The MCD and DLC film are deposited on cobalt cemented tungsten carbide (WC-Co) substrate using the hot filament chemical vapor deposition (HFCVD) method and the vacuum arc discharge with a graphite cathode respectively. Scanning electron microscopy (SEM), white light interferometer, and Raman spectra are employed to characterize as-deposited MCD and DLC samples. The friction tests are carried out on a ball-on-plate reciprocating friction tester, where the sliding process is conducted under water lubricating condition. Silicon nitride, tungsten carbide, ball-bearing steel and copper are used as counterpart materials. The results indicate that DLC film always exhibits lower friction coefficient than MCD film under water lubricating condition, except the case of sliding against the silicon nitride, in which DLC film is worn out very rapidly and thus leads to the high friction coefficient. The wear resistance of DLC film under water lubricating condition is significantly poorer than that of MCD film. While sliding against silicon nitride, tungsten carbide, ball-bearing steel and copper, its wear rate is calculated as 3.67´10-7mm3N-1m-1, 9.31´10-9mm3N-1m-1, 3.54´10-7mm3N-1m-1, and 4.97´10-8mm3N-1m-1respectively. Comparatively, no measurable wear track can be found on the worn surface of MCD films.