Key Engineering Materials Vols. 359-360

Abstract: Formation, propagation and length of crack and hardness of single silicon wafer were investigated at different temperatures by means of Vickers indentation, using lower temperature testing unit with semiconductor refrigerating chip and higher temperature testing unit with closed electric furnace. The results show that the hardness of single silicon wafer decreases with the increase of temperature, while the length of crack increases with the increase of temperature. Ductile-brittle transition of the single silicon wafer can occur at different temperatures with the increase of load. When the load is smaller and temperature is lower, no cracks can be found.

Abstract: Molecular dynamics (MD) simulations of nanometric scratching with diamond tip are conducted on single crystal copper crystal plane (010), and MD simulations are carried out to investigate the mechanism of material removal and the generation of defects on the surface, subsurface and inner of material. During the process of diamond tip scratching the surface of single crystal copper on conditions of different scratching speeds, depths and widths. We achieved the forming details of the chip. While the generation and moving process of defects, such as dislocation, are recorded. The different times of atomic displacement and interaction force are also shown through MD simulation. The evolvement of the lattice pattern in the abrasive processes are analysed by radial distribution function (RDF) and computing the changes of workpiece’s atomic displaces and forces. At the same time, the lattice reconfiguration and the onset and the evolvement process of defects and are analysed by RDF and atomic perspective method, respectively. The simulation results show that scratching speed play role in the course of the form of removing chips, and that different scratching widths and depths of tool have effect on onset and evolvement of lattice defects of workpiece in abrasive processes. This study can give more fundamental understanding of nanosconstruction from atomistic motions and contribute to the design, manufacture and manipulation of nano-devices

Abstract: The adhesion between diamond grits and the bond strongly influence the properties of diamond tools. Since diamond is covalent crystal, the high interfacial energy leads to the poor interface bonding between diamond grits and the bond. Furthermore, the sintering temperature of traditional vitrified bond is also very high because of the high refractoriness of alkalis containing in the bond, resulting in serious thermal damage to diamond grits. In this paper, a low melting point and high strength vitrified bond has been prepared mainly from borate glass, clay and lead glass. The bond is completely glassy above 850°C and the bending strength of the bond sintered at 850°C for 7 minutes is 125.7MPa with a 6.5:3.5 corundum/bond ratio. Moreover, this bond possesses good wettability with diamond abrasive from 600°C to 850°C.

Abstract: Fe-based metal bond has been widely used in fabricating diamond tools recently since the production cost could be greatly reduced for the low price of iron. However, graphitizing elements such as Fe, Co and Ni in the matrix catalyze the transformation of diamond to graphite during high temperature sintering process, which significantly decreases the tool’s efficiency and lifetime. In this paper, Si and Ti coating were coated on diamond grits by quasi atomic layer deposition (QALD) and vacuum slow vapor deposition (VSVD) separately not only to protect diamond from erosion but also to promote the adhesion between diamond grits and the bond. Three-point bending experiment was taken to measure the bending strength of Fe-Cu-Sn-Ni based metal bond diamond blade. In comparison with uncoated diamond blade, the bending strength of coated diamond blade improves dramatically. The theoretic calculation shows that the interface bonding strength between diamond and the metal bond increases by 181.68MPa owing to the Si coating. The effect of Si and Ti coating on interface bonding between diamond and the bond under different sintering temperatures was also illuminated.

Abstract: A stirring mill, an ultrasonic bath and a high-speed shearing emulsifier were adopted to modify the surface characteristics of nanodiamond (ND) respectively. The ζ-potential, size distribution and Fourier transform infrared spectroscopy (FT-IR) of ND were measured to evaluate its properties. Results show that the ζ-potential of ND modified with SHP (either by Mechano-chemical Modification or Ultrasonic measurement) drops sharply. Results also show that the rotating speed of the emulsifier exerts little influence on the size D5 but great influence on the size D95 of ND.

Abstract: Friction and wear behavior of fine-grained diamond (FGD) films were investigated in the ambient air, deionized water and paraffin oil lubricating environment. The FGD films were deposited on WC substrates using HFCVD method and the tribologcial tests were conducted in a ball-on-plate type reciprocating friction tester where the mating balls were made of ball-bearing steel. Scanning electron microscopy (SEM), surface profilometer and Raman spectrascropy were used to study the characterizations of the deposited FGD films, and after sliding tests, the worn areas on both mating balls and FGD films were investigated and the wear debris layer adhered to the friction area of FGD films were analyzed with EDX. The experiment results suggested that FGD films exhibited steady friction coefficient as about 0.25 in water, lower than that in open air, which is up to 0.40; but the mating ball in water suffered much severer wear lost and its specific wear rate was more than two times higher than that in air, up to 3.6E-4 mm3N-1m-1. As while, a thick and compact layer of wear debris was observed on the worn area of FGD films sliding with water lubrication while only little debris existed in the diamond grain boundaries, which might dominate the friction process and attribute to the lower friction coefficient and higher specific wear rate in water environment. In oil environment, furthermore, both the friction coefficient and specific wear rate reached minimum value as low as 0.1 and 1.1E-4 mm3N-1m-1, no observable wear scar could be measured on the sliding surface of the FGD film.

Abstract: The wear resistance samples of brazed single crystal diamond with Ni-Cr filler alloy were prepared, using high frequency induction brazing and vacuum brazing methods. By wear test of brazed single crystal diamond, the wear performance of the samples with different brazing processes was studied. The test result indicates that the wear performance of the high frequency induction brazed diamond samples is better than that of the vacuum brazed diamond samples. Because of different brazing processes, the wearing pattern of diamond varied; the wear course of the vacuum brazed diamond samples in the initial wear period were abnormal and the failure modes is different.

Abstract: This paper deals with an investigation of the grindability of Titanium alloy Ti–6Al–4V with brazed monolayer CBN grinding wheels, and systematically studies the effect of process parameters on specific energy and grinding temperature. In the investigation, a groove is machined with a brazed monolayer CBN grinding wheel, and the dimension accuracy of groove has been proved to meet the design requirements. There is no microcrack in surface layer of the groove, and the depth of work-hardening is less than 40 μm, which indicates that the grinding affected zone is small. The results show that brazed monolayer CBN grinding wheels have excellent performance during grinding titanium alloy.

Abstract: A new segmented grinding wheel of the brazed monolayer diamond was developed with a defined grains pattern on the wheel surface. Results of grinding zirconia using brazed segmented diamond wheel were presented. The experiment results showed that the grinding forces ratio becomes higher with the increasing of the specific material removal rate and the specific energy falls with the increasing of the maximum undeformed chip thickness during grinding zirconia process. In this investigation, brazed diamond wheels with defined distribution patterns was conditioned by touch-dressing method so that grit tips get micro-conditioned and allow the underlying grits to participate and consequently improve the quality of finish. All the ground surfaces of zirconia were generated by the combined removal modes of brittle and ductile.