Osamu Kamiya

Study on reduction in wear due to magnetization

Abstract Operating the pin-rotor type wear test using the ferromagnetic materials, an Ni pin and steel rotor combination, even a weak magnetization of the pin decreased the wear. In order to probe that phenomenon, the grain size distributions of wear particles have been analysed by means of the computer-aided image analyser. The experimental results indicate the relationship that wear rate reduces with the fining down of the wear particles. It is concluded that magnetization accelerated the oxidation at rubbing surfaces and wear particles. Oxidation prevents the rubbing surfaces from mutual material transfer and the consequent pile up to form larger particles, therefore the wear particles remain fine. The cause of wear reduction was the fining down of wear particles by accelerated oxidation in magnetic effect, and those oxidized fine-wear-particles existed between rubbing surfaces and were attracted by a magnetic force, which acted as a lubricant and reduced the wear. The observation that the magnetization accelerated oxidation was verified by the fact that the oxidation reaction of a magnetized steel piece was more severe than one without magnetization. Moreover, the oxygen density at the surface of ferromagnetic materials in air was a little increased by magnetization, which also contributed to the acceleration of oxidation at a rubbing surface.

Effect of microstructure on impact fracture behaviour of SUS304L SAW joint at low temperature

The dependency of Charpy impact value (Ev) of SUS304L submerged arc weldment on test temperature and the angle (θ) between columnar structure and specimen has been studied. The distribution ofEv in the weldment was also measured. The results were summarized as follows. (1) The impact value scarcely depends on the angleθ. (2)Ev of the weld metal decreases with decreasing the test temperature because the brittle fracture occurred along toδ ferrite. (3)Ev indicated a minimum value at the weld metal and increased drastically at the fusion boundary and reached a high value at the base metal. The variation ofEv corresponds to the distribution of oxide inclusion and the change of morphology ofδ ferrite. (4) At low temperature, globular typeδ ferrite causes fine dimples, a discontinuousδ ferrite network causes large dimples, and continuousδ ferrite easily leads to brittle fracture along toδ.

Microporosity formation in partially melted zone during welding of high nitrogen austenitic stainless steels

Gas tungsten arc welding experiments were conducted using austenitic stainless steel containing 0.51%N and 0.78%N. Microstructure observation and hardness measurement were made to study the loss of nitrogen. It was found that welding resulted in a considerable loss of hardness in the weld metal for the case of 0.78%N steel, but not for 0.51%N steel. We explain this in terms of a higher nitrogen content enabling a significantly smaller critical pore size and hence N2 porosity formation to be energetically more favourable. The major finding was that, for the case of 0.78%N steel, a band of microporosity was observed along and near the complete fusion boundary of the weld. It was identified that these micropores were present in the parent metal, not in the weld metal. Partial melting in the zone next to the complete fusion boundary resulted in a nitrogen content significantly higher than the solubility of nitrogen in the liquid channels or pockets. Nitrogen gas pores then formed and became trapped in that zone. Supporting this forming mechanism of microporosity band was the fact that hardness decreased in that zone due to the loss of nitrogen in γ phase matrix for solute strengthening and that nitride particles disappeared after welding.

Wear behaviour in the presence of magnetic fields for pin-on-disc repeated dry wear tests

Abstract Wear behaviour in a magnetic field is discussed for pin-on-disc repeated dry wear tests. The results showed that the sliding distance corresponding to a severe-mild wear transition decreased with increasing magnetic flux density. Consequently, the degree of wear also decreased in the presence of a magnetic field. These phenomena were observed, remarkably, for the case using a carbon steel pin, which is a material that easily oxidizes. To discuss the above phenomena, the oxidation of steel filings in a magnetic field was investigated at high temperature. As a result, it was certain that the activation energy for oxidation decreased both in ac and dc magnetic fields. EPMA observations also proved that the magnetic field promoted oxidation. It was concluded that the degree of wear decrease was caused by magnetic-field-promoted oxidation of wear particles and these oxidized fine wear particles existed and attached to the wear surface owing to the magnetic forces present.

DIAMOND AND METAL BONDING BY ACTIVE SOLDER FOR MICRO – CUTTING WIRE

A new method of bonding diamond to metal with active solder has been developed. This method was then used for making micro-cutting wire saws capable of cutting composite materials with high hardness. This cutting process is an environmentally friendly process, as diamond grains loss and hence pollution is minimum. The active solder contained titanium hydride (TiH2). Titanium hydride dissociates to atomic Ti and H at high temperatures improving wetting between the solder metal and diamond grains and hence high bonding strength can be obtained. An example of using the new wire for cutting a typical IC chip is given. We believe this environmentally friendly micro-cutting process will be widely used in the future.

Influence of the Surface Topography on the Micromechanical Properties and Performance of a CMP Finished AlN Component for Silicon Plasma Etching

A microtibological study of the effect of the CMP machining surface damages (SD) on the micromechanical properties of AlN electro-static chuck (ESC) for silicon plasma etching is presented. AFM and SEM examinations of the AlN ESC, which were CMP finished to a surface roughness, Ra = 20 nm, have revealed machining geometry errors and chemical mechanical SD caused by the CMP slurry. The elastic modulus (E) and hardness (H) of AlN and those of yttrium (Y) particles were discretely clarified using localized nanoindentation technique. The results showed that the CMP machining SD fatally affected the AlN/Y boundary strength and resulted to errors in the first contact points between the indenter and the sample. In addition to SD, the micro scale viscoelasticity phenomena of AlN in indentation caused peculiarities at peak loads in the load vs. depth plots. Under these circumstances, the values of E and H measured using Oliver and Pharrs method are in fact underestimated; E = 400 GPa and H = 20 GPa for AlN particles, 300 GPa and 17 GPa for Y particles and 500 GPa and 16 GPa for AlN/Y interface, respectively.

Effects of magnetization on wear

The repeated wear tests between a ferromagnetic pin and a paramagnetic rotor indicate that the abrasive action of the wear particles attracted to the pin by magnetic force increases the wear amount of the rotor when the difference in micro-Vickers hardness between the wear particles and the rubbing surface of rotor exceeds 100. Furthermore, the pin magnetized by AC current for a virgin surface increases wear. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

Comparison of Welding Behaviour of SUS316L Steel by Gas Tungsten and Gas Metal Arc Processes in High Pressure Nitrogen Atmosphere

Austenitic stainless steels of SUS316L were welded by GTA and GMA methods in high pressure nitrogen atmosphere and have investigated the welding condition, nitrogen absorption and microstructure. In the case of GTA welding could not be started are over 2.1MPa of nitrogen atmosphere, because the tungsten electrode was remarkably consumed in high-pressure nitrogen. However, in case of GMA welding, welding could be performed up to 6.1MPa of nitrogen atmosphere at constant welding current of 200A and the are length of 7mm. Are voltage increased with increase in pressure of nitrogen atmosphere. Nitrogen content of GMA solidified metal increased from 0.2 to 0.65 mass % with increase in pressure from 0.1 to 6.1 MPa. Bending test indicated formation of a few micro cracks in solidified metal that included more than 0.5% nitrogen content.

Low Cycle Fatigue Behavior and Surface Feature by Image Processing of Sn-0.7Cu Lead-Free Solder

The low-cycle fatigue behavior on Sn-0.7Cu lead-free solder as-cast and Sn-Pb eutectic solder as-cast were investigated at a strain rate 0.1%/s under various temperatures of 25, 80 and 120oC. In addition, the relationships between the surface feature in the low-cycle fatigue test and low-cycle fatigue life of those solders at 25oC were investigated by image processing. The low-cycle fatigue life of Sn-0.7Cu decreased when the temperature increased. And the fatigue life of Sn-0.7Cu was better than that of the Sn-Pb eutectic solder at the temperatures of 25 and 80oC. The low-cycle fatigue behavior on the solders investigated followed Coffin-Manson equation. The fatigue ductility coefficient of Sn-0.7Cu was found to be affected by the temperature. The surface deformation as fine meshes in the low-cycle fatigue test of Sn-0.7Cu did not appear until 10% of the fatigue life. Although it was over 10% of the fatigue life, the surface deformation that was caused by micro cracks and coalesces occurred with the increasing number of cycles. The relationships between the surface feature in the low-cycle fatigue test and the low-cycle fatigue life on Sn-0.7Cu and Sn-37Pb solders were discussed.

An Evaluation of Low-Cycle Fatigue Property for Sn-3.5Ag and Sn-0.7Cu Lead-Free Solders Using Surface Deformation

The low-cycle fatigue behavior and the relationship between the surface features in the low-cycle fatigue testing and the fatigue life of Sn-3.5Ag and Sn-0.7Cu lead-free solders were investigated at strain rate of 0.1%/s at room temperature, 80 and 120oC. In addition, the fatigue life was estimated by using the surface deformation of the solders, and image processing. And also, it was compared with Coffin-Manson type of fatigue behavior. The fatigue life of Sn-3.5Ag solder was superior to that of Sn-0.7Cu solder at temperatures, 80 and 120oC. The fatigue life determined by surface deformation indicated a close behavior to Coffin-Manson type fatigue behavior in those solders. Therefore the low-cycle fatigue life of solders could be estimated by the surface deformation.