Katsuzo Okada

Investigation of micro-adhesion by atomic force microscopy

Abstract Atomic force microscopy (AFM) was used to investigate the micro-adhesive interactions between solid interfaces. By operating the force calibration mode of AFM at different ambient (in air, in water and charge eliminated in air), the main factors of micro-adhesion (van der Waals force, capillary force and electrostatic force) of a sample were separated, measured and compared in a single measurement for lamellar materials, such as graphite, MoS 2 and mica. It is found that on an average, the capillary force, which is determined by environmental humidity, has the largest contribution to the adhesive interactions at the present conditions of 50% humidity. The van der Waals, which is defined by material properties, has the smallest impact for graphite. For dielectric materials, the electrostatic effect is a little weaker than capillary force, but much stronger than van der Waals effect. The results infer that at micro-dimensions or nano-dimensions, it is the environmental conditions, not the material properties that play the most important role on adhesive interactions between solids.

Nano-ball bearing effect of ultra-fine particles of cluster diamond

Abstract It was supposed that cluster diamond on account of its special structure could manifest rolling friction under a sliding frictional process. Friction tests and surface analysis by scanning probe microscopy were carried out to testify the rolling effect. The results strongly suggested the possibility of the rotation of ultra-fine particles of cluster diamond.

Contact voltage drop and wear of self-lubricating Ag-Pd alloy base composite materials

Wrought self-lubricating Ag-Pd alloy base composite materials containing graphite are described and the contact voltage drop, wear, and friction of self-lubricating brushes and the novel metal-alloy slip rings are studied. The study indicates that: (1) wrought composites with evenly dispersed graphite in Ag/Pd alloy can be produced; (2) hardness of the wrought composites is less than that for sintered ones; (3) the graphite content that produces the minimum contact voltage drop and wear with a low friction coefficient was determined; and (4) in the case of the contact between the Ag-10% Pd-5%C wrought brush and the Cu-10%Ag slip ring, the contact drop, wear, and friction are significantly small. >

Clean surfaces of metals prepared by scribing with a diamond tip

Abstract Atomically clean surfaces of various metals prepared by scribing with a diamond tip are studied, using quantitative Auger analysis. For metals immiscible with carbon, atomically clean surfaces are prepared easily and quickly, and surface compositions are in good agreement with the bulks. For metals miscible with carbon, carbide-like layers are observed at the top of the surfaces prepared by scribing without heating. Atomically clean surfaces, however, are prepared by scribing at room temperature just after heating.

Friction properties of PTFE, h-BN and Al-4%Cu alloy in a vacuum at super low temperature

Abstract Friction with ploughing components at super low temperature ina vacuum was studied on the soft plates of PTFE, h-BN and Al-4%Cu alloy sliding with the hard pins of 18-8 stainless steel with a pin-on-plate friction tester. The chief finding was that the friction was affected by low temperature ; for all the same load, friction forces of both of PTFE and h-BN were 16K > 300K, that of Al-4%Cu alloy was 16K

New self-lubricating aluminum alloy base composites for vacuum technology

Abstract New self-lubricating Al-4wt%Cu alloy base composites containing MoS 2 have been developed by applied power metallurgy and evaluated with respect to their friction and wear properties in a vacuum. For Al-4wt%Cu–50wt%MoS 2 , the friction coefficient is ⩽0.1 at of 5 × 10 −4 Pa, the specific wear rate is also very small and the PV limit is about 800 kg cm −2 · m min −1 .

Effect of Friction on Mass Transfer in a Bismuth Alloy Liquid Metal.

In order to obtain fundamental data on die castings, the mass transfer from high-Mn aluminum bronze to carbon steel in a bismuth alloy liquid metal under sliding friction has been examined. Friction tests in the molten bismuth were carried out using a pin-on-plate friction tester at temperatures of 105-205°C, at an applied load of 0.1N and a speed of 20 cm/s. Carbon steel pins with a radius of 3 mm and high-Mn aluminum bronze plates were used as samples. The main results obtained are as follows : (1) Frictional contact increases mass transfer as compared to the static contact. (2) The friction coefficient increases with increasing temperature of the molten alloy. (3) Adhesion particles on the pin and plate consist of elements from both the plate and the molten alloy. (4) Hardness of the friction surface layer of the plates gradually decreases from the interior to the surface, as a results of selective diffusion of matrix elements.

Friction and wear of graphite-dispersed tin-base composite materials.

The aim of this paper is to develop new graphite-dispersed tin-base composite materials made by melting for dry bearing and to investigate the friction and wear on the sliding contact between new bearings and steels. The main results are as follows : (1) Hardness of new graphite-dispersed tin-base composite materials is larger than that of solid-state sintered ones. (2) Coefficient of friction and specific wear rate of the former composites are smaller than those of the latter ones.