Key Engineering Materials Vol. 642

Abstract: The effects of surface forces (SF) on pure squeeze elastohydrodynamic lubrication (EHL) motion of circular contacts with coated layer are explored under constant load condition by using the finite element method (FEM) and the Gauss-Seidel iteration method. The difference between SFEHL model and EHL model is apparent as the film thickness is thinner than 5 nm. The oscillation phenomena in pressure and film thickness come mainly from the action of solvation forces. The effects of surface forces become significant as the film thickness becomes thinner.

Abstract: This paper presents a combined diamond disk that is designed and manufactured to markedly improve the leveling of diamond tips, thereby reducing the amount of diamond grit. First, a small brazed diamond disk was manufactured. Second, 12-or 24-disk brazed diamond disks were mounted onto a substrate with a diameter of 108 mm for completing the combined diamond disk. Four types of disks were fabricated, and their performances were compared with that of a conventional diamond disk. The experimental results showed that the combined diamond disk has more complete diamond crystal shapes and distribution with better leveling, which increases the effectiveness of the working diamond grits. Compared to a conventional diamond disk, the combined diamond disk achieved a higher wafer removal rate and better uniformity while consuming less pad material. The number of diamond grits required was significantly lower. Roughly, 7,600 and 12,000 diamond grits were used for the 24-and 12-disk brazed diamond disks, respectively, in the new disk, whereas 20,000 diamond grits were used in a conventional diamond disk. In the case of the conventional diamond disk, the diamond tips are leveled to more than 50 μm. However, in the case of the combined diamond disk, the diamond tips can be leveled to less than 30 μm because the diamond tips are already leveled. These results contribute to the understanding of conditioning techniques and further improvement of the chemical mechanical polishing process.

Abstract: In this study, apparent ferro-viscosity on applied directional field, through the evaluation of mean piping flow velocity, is examined. Here viscosity in magnetized ferro-flow is found to be closely dependent on the field intensity as well as direction, which is quite different from the constant thermal property usually used in traditional fluid dynamics problem. To predict ferro-magnetization and ferro-viscosity induced under horizontal and vertical field imposed , an auxiliary electromagnetic mechanism is then designed and set up ,As a result, the apparent viscosity ,for ferro-concentration ψ0.4 and 0.04 exposed to field in different direction, will initiate a faster growth within field strength of 6~12 mT where the quick magnetization of ferro-particles starts working, and magnetic field along with flow direction is found to have more potential to induce viscous drag. While compared with theoretic results on Brownian relaxation theory in Langevin function, experimental vortex viscosity behave a good agreement within the working magnetic intensity 0~36 mT and their maximum relative errors will be less than 10% and 50% for ferro-concentration ψ0.4 and 0.04 at working temperature at 25 ^o c.

Abstract: Polishing process is a primary technique for planarization of material surface in manufacture fabrication. The pad structure and its material properties are important to determine the polish rate and planarity that can be achieved by the polishing process. Besides, the pad conditioning is used to regenerate the surface of the polishing pad surface by breaking up the glazed areas. Because the polishing and pad conditioning mechanism is inadequately understood and because higher levels of pad polishing performance are desired, the investigation of experiment becomes more important.In this paper, a high precision polishing machine has established. With an improved design, a test rig can be easily used to simulate the polishing, pad conditioning process and acquire the signals of temperature. The temperature of test pads (i.e. Rodel IC1000A, Rodel IC 1000B and Opetech SB 660) is measured during polishing and pad conditioning process. For the self-design test rig, its surface temperature is measured by T-type thermocouples screwed behind the polishing (or conditioning) interface of the carrier. The experimental results provide a temperature index to end-point-detection and contribute to understanding of the mechanism on polishing pads.

Abstract: To research the friction and wear of silicon nitride ceramic with bovine serum albumin lubricant, the tribological properties of silicon nitride ceramic against stainless steel were investigated on CETR UMT-2 under lubrication of bovine serum albumin, deionized water, physiological saline and physiological saline mixed with bovine serum albumin. The worn surfaces of silicon nitride ceramic ball and stainless steel pin were examined with a digital microscope (VHX-2000). The friction coefficients of steady state are 0.26, 0.35, 0.69 and 0.8 under bovine serum albumin, physiological saline mixed with bovine serum albumin, physiological saline and deionized water. The lowest friction coefficient of steady state is 0.26 which is under lubrication of bovine serum albumin. The highest friction coefficient is 0.8 under the lubrication of deionized water. The measured worn areas of silicon nitride ceramic balls are 1282.3μm², 1898.6μm², 2753.9μm² and 3645.7μm² under bovine serum albumin, physiological saline mixed with bovine serum albumin, physiological saline and deionized water. The smallest worn area of silicon nitride ceramic ball is 1282.3μm² which is measured under the lubrication of bovine serum albumin. The highest worn area of silicon nitride ceramic ball is 3645.7μm² which was measured under the lubrication of deionized water. The same wear mechanism of silicon nitride ceramic ball had been found under the lubrication of bovine serum albumin, deionized water, physiological saline and physiological saline mixed with bovine serum albumin. The depth of scratches of worn surface of silicon nitride ceramic ball lubricated with BSA is 3μm which are the shallowest.

Abstract: A series of W-Al nanolayer coatings were deposited with varying content of aluminum from 0 at.% to 65 at.% by a unbalanced magnetron (UBM) sputtering system. The as-deposited coatings were investigated first. Then, the coatings were oxidized aiming to study their oxidation behavior. SEM, TEM, XRD, GDOS and nanohardness tester were used. The results showed that the Al content had a significant effect on the performance of W-Al coatings. The hardness of as-deposited and oxidized coatings decreased with increasing Al content. The pure W coating was heavily oxidized. As the Al content increased, the oxidation decreased fast and then remained stable as the Al content was higher than 45at.%. The effects of formed oxides on hardness were discussed.

Abstract: The a-C:H coatings were deposited on AISI M2 steel disks using an unbalanced magnetron sputtering technique with a single titanium metal target, three graphite targets and mixed methane/ acetylene reactive gas. The various currents (9A-17A) were applied to the tungsten filament to enhance ionization rate of reactive gas. Tribological properties of a-C:H coatings were conducted used reciprocating friction tester. The results show that the tungsten filament current has a significant effect on the deposition rate, hardness and tribological properties of the coatings. With the increase of the tungsten filament current, the deposition rate and hardness of the coating increases, respectively. In sliding against an AISI 52100 steel ball for 24 minutes, all of coatings reduce the wear depth by a factor of at least 11 compared to that observed on an uncoated substrate. The 17A coating yields the best tribological properties that are the minimum wear depth, the lowest friction coefficient and the maximum lifetime when sliding against an AISI 52100 steel ball.

Abstract: The contact behavior between indenter and single crystal copper substrate is performed to investigate based on EAM and Morse potentials and Verlet algorithm. Effects of different velocities on the contact behavior and substrate deformation are compared and analyzed. The results show that the single crystal copper material’s resist deformation level is limited by low velocity, and more dislocated atoms were accumulated under the direction of indenter moving in higher indenting velocity. During sliding process, lager chip volume is produced in front of the indenter as the sliding speed or sliding distance increases. The dislocated band in basis lies at the angle of 45 degrees with the direction of indenter moving in indenting and sliding process. Furthermore, the contact force, friction force and normal force increase with the rising of speed. On the contrary, the friction coefficient decrease gradually with higher sliding speed.

Abstract: This project investigated the tribological properties and nanomechanics of Cu-benzotriazole (BTA) composite nanooils. Cu-BTA nanoparticles were synthesized by a thermal decomposition process. Cu-BTA nanoparticles were added into paraffin oil to form the nanooils. Cu-BTA explores the nanomechanics of sphere geometry functions as a rolling medium for friction lower. BTA nanoparticles functions as a protector from oxidation of the Cu nanoparticles in various test circumstances. Tribological experiments were conducted using a pin-on-disk (ASTM G99) test for the wear scar diameter, friction coefficient, and morphology of worn surfaces. The experiment results revealed the dispersion capability of the benzotriazole-capped Cu nanoparticles and indicated the dispersing stability in liquid paraffin oil for the BTA-capped surface of Cu nanoparticles. The testing results show that the Cu-BTA nanoparticle used as an additive in paraffin oil at an appropriate concentration exhibits better tribological properties than those of pure paraffin oil. Cu-BTA functioning as an additives have different anti-wear abilities due to its small size effect and a high absolute viscosity given high Herser number, corresponds to relatively thick lubricant film and an larged elastohydrodynamic lubrication area. A thin film or powder consisting of spherical Cu-BTA nanoparticles on pin-on-disk (ASTM G99) test iron surface protests against damage from relative rolling movement, which reduces friction and wear.

Abstract: A finite element model is developed to study the transient thermo-mechanical contact between a rough body and a flat body. The model consideres the heat flux coupling, the interaction among adjacent contact asperities and elasto-plastic deformation of the rough body. It is observed that the temperature / contact pressure / stress are coupled and fluctuate obviously when the interaction of contact asperities enhances. The fluctuation of the VonMises equivalent stress makes the equivalent plastic strain of the frictional surface layer accumulate continually which might cause fatigue wear and plastic deformation wear of the material when the frictional rotating process repeated.