Materials Science Forum Vols. 534-536

Abstract: Metal-bonded diamond impregnated tools are being increasingly used in the processing of natural stone, sawing and drilling concrete and brickwork, road repair, petroleum exploration, production of ceramics, cutting frozen foods, etc. Although the main tool wear mechanisms seem to be well identified, the scientific background is still inadequate and extensive fundamental research has to be carried out to better understand how the tool performs in actual applications. This work attempts to address the complex issues of modelling the abrasive wear of the metallic matrix under laboratory conditions. In view of the generated wear data, it becomes evident that a comprehensive characterisation of the matrix’s susceptibility to wear by 2-body and 3-body abrasion can be reliably assessed in a quick and inexpensive manner; whereas tests carried out on diamond impregnated specimens may assist in the prediction of the tool life in abrasive applications.

Abstract: The kinetics of sintering of Co-Fe materials was studied. The main objective of the work was to establish the effects of iron content and sintering parameters on the microstructure and phase composition of the as-sintered materials. Specimens containing from 3 to 25 wt.% iron were sintered in a dilatometer for one hour at 900, 1000 and 1150OC in either hydrogen or nitrogen atmosphere. The length of specimens during the heating, hold at the temperature and cooling steps were monitored to establish the sample’s shrinkage. Microstructural observations were carried out on polished and etched transverse sections which were also subjected to the X-ray phase analysis.

Abstract: Kinik Company pioneered diamond pad conditioners protected by DLC barrier (DiaShield® Coating) back in 1999 (Sung & Lin, US Patent 6,368,198) and there has been no follower since then. Kinik's offered two varieties of DiaShield® Coatings: ultrahard tetrahedral amorphous carbon and superhard hydrogenated DLC. Kink also evaluated Cermet Composite Coating (CCC or C3, patent pending). C3 is unique that the coating composition grades from a metallic (e.g. stainless steel) under layer to a ceramic (e.g. Al2O3 or SiC) exterior. The metallic under layer can form metallurgical bond with metallic matrix on the diamond pad conditioner. The ceramic exterior is both wear and corrosion resistant. The gradational design of C3 coating will assure its strong adherence to the substrate because there is no weak boundary between coating and substrate. By dipping diamond pad conditioners of various designs in acidic solution (e.g. copper cleaning solution) for extended periods of time (e.g. 50 hours) the chemical inertness of various matrix materials are determined with the decreasing ranking as: hydrogenated DLC > C3 coating > tetrahedral amorphous carbon > sintered nichrome > brazed alloy > electroplated nickel.

Abstract: Diamond grits in tools are typically held in a sintered matrix of metal powder (e.g. Co). The bonding between diamond and the matrix is essentially mechanical. As a result, most diamond grits are easily knocked out from the tool during cutting. The diamond industry has designed various metal coatings (e.g. Ti, Cr, Si) to improve the adherence of diamond grits in the matrix, but the improvements have been modest (e.g. up to 50% increase of tool life). A revolutionary “Active Braze Coated Diamond” (ABCD) is now being developed. The coating of ABCD is much thicker (e.g. 20 microns) than conventional ones (about 1 micron). The molten braze is wetted and reacted with diamond to form strong chemical bond at the interface so that the diamond does not become knocked out of tools. ABCD is coated with a nickel alloy that can form metallurgical diffusion bonds readily with the metal matrix of the tool. In essence, ABCD turns diamond into a metal grain so that the diamond tools can be made by conventional powder metallurgical process without being concerned about the poor bonding between matrix metal powder and the diamond as before.

Abstract: Diamond grits synthesized under ultrahigh pressure have been commercially manufactured since 1957. Most of the diamond grits are for sawing rocks (granite, marble) and concrete. In 2004, more than 4 billion carats (800 tons) of diamond saw grits were produced worldwide. About 3/4 of total production was made in China, but the Chinese diamond grits tend to be smaller in size (<40 mesh) and with inferior quality, so their total value accounts for only 1/4 of the world sales (about $600 millions). The ultrahigh pressure process for synthesizing diamond grits is due to make a quantum leap: the raw materials will incorporate diamond seeds with a predetermined pattern. The result is doubling the diamond yield with a narrower size distribution. Moreover, the shape of diamond crystals can be precisely tuned. For example, diamond octahedra or diamond cubes, that are not available today, can be mass-produced. The new technology is now being implemented worldwide so the future diamond grits will have improved quality at reduced prices.

Abstract: Due to their better mechanical and physical properties diamond tools have largely replaced cemented carbide tools for machining of mineral materials like concrete and rocks. The decomposition tendency of diamond has to be taken into consideration during the manufacturing process as well as during their employment in machining tools. By using water cooling the diamond decomposition is reduced, but the contamination of occupied buildings by concrete/rock-watermixture and the need of water supply units on building sites are unfavourable. However, absence of water cooling lead to an increased tribological and thermal wear of conventional diamond tools. Due to the heat development the diamonds in direct contact with mineral materials as well as the diamonds in deeper layers are deteriorated. The Institute of Materials Engineering pursues a novel thermal protection shield concept, in which thermal insulating materials such as Al2O3, ZrO2 or glass in diamond impregnated composite structures act as heat shield, which protects diamonds in deeper layers against high temperature and graphitisation. Before the effectiveness of this concept could be investigated suitable composites have to be manufactured. In this paper the powder metallurgical production processes of diamondalumina- cobalt-composites with varying alumina and cobalt particle sizes, their microstructures and porosities are described. In comparison to composites with larger alumina particle sizes it could be observed that the distribution of alumina particles with particle sizes below 70 ,m in the cobalt matrix is uniform and the porosity of the composite decrease.

Abstract: The dry-milling technique was used for mixing and crushing oxides and graphite powder to get homogeneous mixed powders. The weight ratio of ball-to-powder was 30:1 and argon gas was filled in jar. The carbon content was more 10~ 20wt% than the stoichiometric amount. The drymilling was carried for 20 hours. After milling, the mixed powders were reduced and carburized at 900~980°C for 3 hours flowing Ar gas in tube furnace. The dry-milled powders showed wide diffraction patterns of X-ray. The reactions of reduction and carburization were completed in 3 hours at 980°C. After the reactions, the mean size of WC particles was about 200 nm. The content of free carbon in WC/Co mixed powders decreased as the reaction temperature increased.

Abstract: In this paper, we show some experimental results of binder-free WC sintered by Pulsed Electric Current Sintering (PECS) also known as Field Assisted Sintering Technology (FAST). These binder-free WC have extremely high hardness and stiffness. However, these mechanical properties are dependent on the sintering condition, e.g., maximum temperature, applied pressure, etc. We show some relationship between mechanical properties and sintering condition to improve to sinter the binder-free WC.

Abstract: Injection molding of corrosive super engineering plastics and engineering plastics with various fillers is conducted under severe conditions and causes corrosion and wear problems. Hence, in orde to apply Mo2NiB2 boride base cermets into plastic molding machine parts, the effects of V substitution for Cr on the mechanical properties, corrosion resistance and microstructure of Ni- 5.0B-51.0Mo-(17.5-X)Cr-XV (mass%) model cermets were investigatied. Both transverse rupture strength (TRS) and hardness increased monotonically with increasing V content and reached 2.94GPa and 87.2RA at 10.0%V, respectively. The improvements of TRS and hardness were attributed to microstructural refinement. The excellent corrosion resistance for a molten fluorocarbon resin was obtained up to 5.0%V.

Abstract: Particulate TiC reinforced 465 maraging stainless steel matrix Cermets were processed by conventional P/M. The binder phase was added in the form of elemental powders and master alloy powders. The microstructures, binder phase variation with TiC content and mechanical properties were evaluated. The addition of a type of binder phase largely effects the microstructure and mechanical properties. When a master alloy binder phase was used the microstructure showed interphase debondings, microcracks and large growths of TiC particles. Where as, elemental powders in the composition of binder phases showed defect free microstructure of steel bonded cermets. The binder phase variation from starting composition was observed with increase in wt% TiC content and this variation was higher when the master alloy powders were used as a binder. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was attributed to the aging reaction in maraging stainless steel. The response to heat treatment was decreased with an increase in TiC content due to the shift of binder phase from the starting composition.