Showing papers on "Tribometer published in 1989"

Relationship between mechanical properties and wear resistance of alumina-zirconia ceramic composites

Abstract: Mechanical behavior of Al2O3-based ceramics can be improved by dispersion of pure or partially stabilized ZrO2 particles. The effective toughening or strengthening effect, which is operating in these composite materials, is determined by microstructural characteristics (composition, processing conditions) and environmental conditions (temperature, loading rate,…). The objective of this work has been to make a correlation between mechanical properties and wear resistance of alumina-zirconia composites. Wear tests were conducted employing a bloc-on-ring tribometer which consists of a steel ring rotating against plane ceramic specimens. Different environmental conditions were investigated: ambient air, and water. The wear volume is determined as a function of sliding distance. The dispersion of ZrO2 particles in Al2O3 matrix improves the fracture behavior but reduces the wear resistance. However, the addition of ZrO2 limits the water corrosion effect observed in Al2O3 materials. Wear seems to be controlled b...

Examination of wear, hardness and friction of nitrogen-, boron-, carbon-, silver-, lead- and tin-implanted steels with different chromium contents

Abstract: Implantations of nitrogen, boron, carbon, silver, lead and tin in four different steels with chromium contents of 1.5%–18% were performed. The doses applied were between 1017 and 5 × 1017 cm−2, the ion energy was 50–100 keV. Wear and friction of the implanted layers were tested using a pin-on-disc oscillating tribometer. Hardness was investigated using a microhardness tester allowing loads down to 0.05 × 10−2 N. It was found that nitrogen is very effective in hardening steels with a high chromium content (around 18%) and in decreasing the wear rate of up to three orders of magnitude. Microscopic observations of the abraded surfaces show a strong effect of fatigue after tribological stress in the case of unimplanted steels. Implanted surfaces have a smooth abrasive path even after a long period of testing. Boron reduces the wear of hardened X90CrMoV18 by two orders of magnitude. Carbon is very effective in hardening and reducing wear in the low-chromium tool steel 100Cr6 which cannot be hardened by nitrogen implantation. All results strongly depend on atmosphere, load and the ball material in use for friction tests. The implantation of silver, tin and lead does not change the hardness of the steels investigated. However, a reduction of friction was found, thus also reducing the wear rate.

Tribological properties of alumina-boria-silicate fabric from 25 C to 850 C

Abstract: Demanding tribological properties are required of the materials used for the sliding seal between the sidewalls and the lower wall of the variable area hypersonic engine. Temperatures range from room temperature and below to operating temperatures of 1000 C in an environment of air, hydrogen, and water vapor. Candidate sealing materials for this application are an alumina-boria-silicate, ceramic, fabric rope sliding against the engine walls which may be made from copper- or nickel-based alloys. Using a pin-on-disk tribometer, the friction and wear properties of some of these potential materials and possible lubrication methods are evaluated. The ceramic fabric rope displayed unacceptably high friction coefficients (0.6 to 1.3) and, thus, requires lubrication. Sputtered thin films of gold, silver, and CaF2 reduced the friction by a factor of two. Sprayed coatings of boride nitride did not effectively lubricate the fabric. Static heat treatment tests at 950 C indicate that the fabric is chemically attacked by large quantities of silver, CaF2, and boron nitride. Sputtered films or powder impregnation of the fabric with gold may provide adequate lubrication up to 1000 C without showing any chemical attack.

Formation and characterization of carbon layers deposited during ion bombardment of silicon

Abstract: Monocrystalline silicon substrates have been implanted with 70 keV N+ and C+ ions. During implantation, thin layers of carbon films, containing about 10% of silicon, have been deposited by controlled vacuum carburization. RBS and AES techniques were used for surface analyses. Friction studies were carried out by a ball on disc tribometer. Drastic reduction of the friction coefficient was observed for the surface treated samples. It was found that the vacuum carburized layer acts as a solid lubricant. Diamond scratch tests also showed a reduced tendency for crack formation on the implanted/vacuum carburized surfaces.

Laser melting of an NiCr alloy precoated with carbon: high-temperature oxidation and wear resistance

Abstract: Laser melting tests were performed on an Ni 70 Cr 30 substrate precoated with carbon. The microstructure of such a cemented material was accurately characterized: the surface alloy is constituted of submicrometre cellular eutectic structures (chromium carbides and γ solid solution). This structure offers a correct thermal stability. The wear tests, conducted with a pin-on-disk tribometer, showed an excellent tribologic behaviour for this material, as good as that obtained by carbide powder injection in superalloys. The high-temperature oxidation resistance was tested at 800°C in pure oxygen, and it was shown that the surface alloy develops, as the substrate Ni 70 Cr 30 , a Cr 2 O 3 oxide scale which acts as an efficient barrier against the hot gas aggression. The wear behaviour of cemented then oxidized materials was characterized and compared with that of the substrate.

Dry wear behaviour of boron- and nitrogen-implanted steels

Abstract: The wear behaviour of steels implanted with boron or nitrogen ions was investigated using a ball-on-disk tribometer. The wear rate of the nitrogen-implanted steels was strongly dependent on the steel composition and on the temperature during implantation or during subsequent annealing. Considerable wear improvement (wear rate three orders of magnitude lower) was obtained only for steels with a high chromium content which had been treated at a temperature of at least 250 °C. Boron implantation resulted in a decrease of the wear rate for steels with high and low chromium content; a heat treatment up to 300 °C had no influence. The improvement of the wear behaviour was correlated with an increase in microhardness. The wear behaviour was dominated by an oxidative wear mode. The benefit of ion implantation was observed only in ambient atmospheres allowing oxidation during the wear process.

Friction and wear studies of oxidized titanium surfaces bombarded with ions in the 100 keV region

Abstract: Titanium and its alloys have found a number of industrial applications. However, the surface has often to be treated in order to avoid oxidation and wear. In the present paper a conventional oscillatory ball tribometer has been computerized, so that accurate time-dependent friction measurements can be performed. In the wear process of a titanium surface, oxidation plays a very important role, so therefore time-dependent friction measurements of anodized titanium are useful in tribological studies of this metal. Direct implantation of nitrogen ions in the 100 keV range has been used to initiate nitride formation in the alloy surface, oxidized film and in the underlying substrate. Varying the oxide film thickness and the ion energy, friction coefficients have been measured and the wear tracks have been studied with a profilometer. The perspectives in formation of oxynitride and nitride layers in titanium are discussed as an alternative to conventional procedures for protection of titanium surfaces such as plasma discharge techniques.