Tadaaki Sugita

Material removal mechanism of silicon nitride during rubbing in water

Abstract The material produced at the friction interface and the material removal mechanism were investigated for the rubbing of silicon nitride in water. The material removal rate estimated by the contact time of the specimen was constant at all rubbing speeds, which suggested that the material removal mechanism was attributable to the chemical reaction at the rubbing interface. The analytical results from the ion microprobe analysis spectra indicated that many ions of silicon with hydrogen and oxygen remained on the polished surface. Also, the rubbing remnants in the water were shown to be an amorphous material and were converted into α-cristobalite (SiO2) by a heat treatment in air at 1170 K for 1 h. These results suggested that the oxidized silicon nitride was changed by friction to an amorphous hydrate SiO2·xH2O during rubbing in water and, after that, the amorphous hydrate was removed from the rubbing interface.

A J-Integral Approach to Material Removal Mechanisms in Microcutting of Ceramics

Abstract An approach to analyzing material removal mechanisms in microcutting of ceramics is described. The approach is based on the j-integral method capable of elastic-plastic fracture mechanics. The j-Integral value around a crack ahead of the cutting edge is determined using che finite element method. Both the brittle and ductile mode material removal mechanisms are analyzed by considering crack propagation and plastic deformation behavior. The brattle-ductile transition is elucidated for selected ceramic materials and the applicability of ductile mode removal is also discussed in terms of the material properties and cutting conditions.

Thermal Behaviour of Cutting Grain in Grinding

Abstract Temperature at the interface between the cutting grain and a workpiece is measured using a two-color pyrometer with a fused fiber coupler. For the cutting grain, a conical tool of translucent alumina is used. The infrared rays radiated from the interface and transmitted through the conical tool are accepted by a fused fiber coupler and led to two infrared detectors of different spectral sensitivity. The temperature increases rapidly and reaches a saturated value after a short time (about 0.1 ms). The saturated temperature measured increases with the increase in the cutting speed up to the melting point of the work material.

Adhesion strength of DLC films on glass with mixing layer prepared by IBAD

Abstract The improvement of the adhesion of diamond-like carbon (DLC) films has been tried by ion beam assisted deposition (IBAD). The adhesion strength must be quantitatively evaluated and determined in order to confirm the improving effect of the adhesion of DLC films by IBAD. In this study, DLC films were prepared on a glass substrate with a mixing layer prepared by IBAD. For the samples, the scratch tests were carried out using a scratch tester with a CCD camera and two AE sensors. The detachment process of the DLC film during a scratch test was observed and the detachment area was measured. On the other hand, AE signals were detected corresponding to the detachment of the DLC film, and the force causing the detachment was determined by analyzing the signals. The adhesion strength of DLC films was calculated from the detachment area and the force. From that result, the adhesion strength of DLC films without a mixing layer was 3.2 MPa. When the mixing layer was formed by IBAD with a condition of Ar-30 kV and 2.1 μA/cm2, the adhesion strength increased to 10.7 MPa. Furthermore, that increased up to 44 MPa in the case of 21.0 μA/cm2. Therefore, it was realized that IBAD improved the adhesion of DLC films and the effects were made clear quantitatively.

Application of Fracture Mechanics in Micro-Cutting of Engineering Ceramics

Summary The subject of this study is to analyze the machining mechanism of engineering ceramics based on the fracture mechanics concept. An algorithm for the application of linear fracture mechanics theory is proposed to determine the material removal mechanism in micro-cutting of engineering ceramics. According to the algorithm, the critical cutting force at which the material removal occurs due to unstable crack propagation is determined for hot-pressed Al 2 O 3 in terms of the fracture toughness, the tool geometry and the tool/work interface frictional property. The critical cutting force for plastic flow type material removal is also determined, and the difference in the removal mechanism between the unstable crack propagation type and the plastic flow type is interpreted in association with the material properties and the cutting conditions.

The roles of brittle microfracture and plastic flow in the wear of MgO single crystals

Abstract The roles of brittle microfracture and plastic flow in the wear of MgO single crystals were investigated using a repeated rubbing apparatus. Wear after a small number of rubbing cycles occurs by brittle microfracture under the severe contact stress associated with the small contact area of the slider, although a plastically flowed layer is formed locally in a small region of the wear surface. Plastic flow occupies a larger region of the wear surface as wear increases, owing to the decrease in contact pressure caused by an increase in the contact area of the slider after many repeated slidings. Wear during this period, in which there is a very low wear rate, is caused by removal of the plastically flowed layer from the surface and corresponds to wear under a steady state process. When the tip of the slider approaches a subsurface parallel crack, a rectangular particle is formed; this particle is surrounded by the subsurface parallel crack, by two normal cracks K 1 , which coincide with chevron cracking, and by two normal cracks K 2 , which reach the subsurface parallel crack by a fatigue process after many repeated rubbing cycles. The rectangular particle is removed from the wear track and the subsurface parallel crack plane is locally exposed. The plastically flowed layer is readily produced after the material freed from the matrix is removed by frictional action although a new subsurface parallel crack below the previous subsurface parallel crack can be formed by further rubbing.

Wear damage of MgO single crystals

Mechanisms of surface and sub-surface wear damage in MgO single crystals were investigated by scratching with two sintered alumina sliders, having tip radii of 60 and 120μm, using a simple scratching apparatus in a controlled atmosphere. The degree of surface and sub-surface cracking is dependent on the shape of the slider and the normal contact load, which are related to the penetration into the crystal. The chevron crack on the (001) plane in the [100] sliding direction consists of cracks intersecting at an angle of 90°, and with a spread angle of about 120°, and the normal crack. The nature of the sub-surface damage is investigated; a parallel crack develops in front of the slider and an oblique crack propagates towards the front of the slider. Then an internal normal crack is formed between the oblique crack and the parallel crack. In the [110] direction, the oblique crack initiates from the top of the normal crack under the surface, and the parallel crack continues from the oblique crack. This wear damage is explained by the dislocation interactions occurring due to the distribution of resolved shear stresses during sliding. The wear caused by the chevron crack is a factor of 10 higher than that with plastic flow. Internal cracks do not have a direct influence on the increase of wear.

Wear characteristics of magnesium oxide single crystals on steel

Abstract Wear characteristics of MgO single crystals sliding in the [100] direction on the (001) cleavage plane on a low carbon steel disk were investigated. There were two different wear behaviours. At slow sliding velocities, wear of the MgO was severe and was initially caused by micro brittle fracture due to the contact stress at the true point of contact. This resulted in chevronshaped surface damage and abrasion by wear fragments embedded in the steel disk, which was followed by a slower steady state of wear after oxidation of the steel wear track had occurred. At higher sliding velocities, solid state diffusion between MgO and iron oxide in the wear interface resulted in a reduced volume of wear. The wear process at all sliding velocities indicated a discontinuous or stepwise removal of material, which suggested that the wear of MgO could be associated with fatigue fracture. Iron oxide which acted as a solid lubricant was produced on the wear surface of the steel after a certain sliding distance because of the high frictional heat at the true point of contact. Oxidation depended on the sliding velocity; it was present immediately at 50 m s −1 but only after about 1 km of sliding at 10 m s −1 . Electron microprobe X-ray analysis indicated that the iron oxide was FeO and that, especially at high sliding velocities, a chemical reaction occurred to form a solid solution between FeO and MgO in the wear interface.

Friction and wear of MgO single crystals on sintered Al2O3 in vacuum

Abstract Experiments were carried out on the wear of MgO single crystals on sintered Al 2 O 3 using a pin-on-disk type machine in a vacuum chamber. Minimum values of friction and wear with a smooth wear surface were found in the range 10 −2 –10 0 Torr; these were shifted to higher values and/or to poor vacuum with increasing sliding velocities. High wear rates in a high vacuum were due to repeated micro brittle fractures because of adhering wear fragments. Low wear rates in a poorer vacuum were caused by the tearing off of the laminated surface film by plastic flow.

Characteristics of magnesium oxide single crystals polished with vibrational sliding in water

Abstract The finished surface of magnesium oxide single crystals polished with vibrational sliding in water was studied. The specimen was rubbed on a rotating disk of sintered magnesium oxide while being moved spirally and vibrated perpendicular to the sliding direction. Two distinct types of finished surface were observed: a rough surface with. R max = 1–3 μm and a smooth surface with R max = 0.01 μm . Surface characteristics were examined using optical microscopy, X-ray diffraction and ion microprobe mass analysis in order to understand the formation mechanisms of the finished surface. The rough surface was mainly formed by cleavage planes, caused by the brittle fracture which occurred irregularly around the surface. The hydration of the magnesium oxide played a dominant role in the formation of the smooth surface. The finishing of the surface on the {100} plane was markedly dependent on the mechanical contact conditions and the presence of water and independent of the main direction of sliding. A critical set of contact conditions for the formation of the smoothed surface was determined in terms of the contact load, the amplitude and frequency of vibrational sliding and the rotational speed of the disk. The volume removed was increased by vibrational sliding because of the increase in sliding distance and the equivalent increase in contact load caused by the moment of inertia of the apparatus.