Abstract: A new type of sintered diamond reinforced by diamond-MWCNTs composite fibers which were randomly orientated and even distributed in the diamond matrix was synthesized by using 3(wt)% mullti-walled carbon nanotubes(MWCNTs) as starting additive under high pressure of 5.8GPa at temperature of 1500°C for 1 min. A special polycrystalline diamond structure of direct bonding of both diamond to diamond and diamond to diamond-MWCNTs composite fiber was observed. The testing results show that it possesses not only high hardness (49-52GPa) and Young’s modulus (878GPa) but also high bending strength (1320~1540GPa) and fracture toughness (9.0~9.2MPa•M1/2) as it was theoretically predicted. The high performances of the composite were contributed to the fiber strengthening effect and the special structure which can offer more extensive diamond to diamond bonding.
Abstract: Oxidization of diamond in the sintering process of diamond/borosilicate glass composites would result in low compressive fracture strength (CFS) of the grit and uncontrolled expansion with many irregular pores in the composites, causing low bending strength of the tools. In this paper diamond/borosilicate glass composites were prepared by cold pressing and sintering at 850 C for 120 min in air. An active element Zn was incorporated into the composites in order to resolve the above issues. The effects of Zn contents on the properties of the composites was investigated by the bending strength tests, the volume expansion rate tests, differential scanning calorimeter test (DSC), thermogravimetry (TG), X-ray diffraction analysis (XRD), and scanning electron microscope (SEM). The results showed Zn was oxidized and then converted to ZnAl2O4 and Zn2SiO4 phases during sintering. The bending strength improved and the expansion phenomenon was inhibited for the composites with various Zn additions. The maximum bending strength and minimum volume expansion rate were obtained for the composite GZ8. This Zn content resulted in a decrease of volume expansion rate from 8.57% to -20.53%, and an increase in bending strength from 28.49 MPa to 74.02 MPa compared with the composite GZ0. The CFS results of the diamond grits separated from GZ0 and GZ8 was 21N and 26N, respectively.
Abstract: Diamond with inorganic coating such as silicon coatings was used to promote applications. Different kinds of silicon structures were found in the coatings. In this paper, first principle calculation was used to study the stability of cubic silicon and hexagonal silicon coatings deposited on diamond substrate. The simulation data suggest that the single layer hexagonal silicon coating form easily under low temperature due to the low lattice mismatching and thermodynamic temperature. However, the stronger bonding of Si-C bonds between substrate and coating direct the formation of cubic silicon coatings, as well as Si-Si bonds inner coatings, in agreement with experiments.
Abstract: In SiC whisker reinforced Al matrix composite, the interface reaction significantly influences the property of the composite. Si films have been deposited on SiC whiskers by quasi atomic layer deposition from gaseous SiH4 to protect the whiskers from being eroded by Al matrix. The structure and morphology of the coating were characterized by X-ray diffraction and transmission electron microscope. The coating deposited on SiC whiskers is cubic phase polycrystalline silicon and this ultrathin Si film is even and continuous, completely covering every individual SiC whisker. The effect of the Si coating on improving the whisker/matrix interaction was also studied in this work. The interface layer, Si coating, could effectively protect the SiC whisker from erosion caused by Al matrix during the high temperature manufacturing process and improve the adhesion between the SiC whisker and the Al matrix.
Abstract: During the brazing process, the high brazing temperature, the chemical and physical reaction between diamond and alloy, and the residual stress would result in the thermal damage of diamond. The morphology and mechanism of thermal damage is studied when the brazed diamond grits is brazed using Ni-Cr alloy in this paper. The results show that the manifestations of the thermal damage mainly include surface graphitization, erosion pits, microcrack and breaking. The graphitization only occurs on the surface of diamond grits. And the microcrack of diamond grits appears near interface.
Abstract: Despite the facts that carbon fiber reinforced plastics (CFRP) components are mostly produced near net shape, machining, especially drilling is often required in order to bring the component into dimensional requirements and prepare it for assembly. Rapid drill wear and serious machining defects are the key problems in CFRP drilling, and employing proper drill is an effective way to solve these problems. In this paper, tests of the brazed diamond core drill are presented and the related issues, such as the thrust force, the drilling quality and the drill wear are studied.
Abstract: Multilayer brazed CBN wheel segments based on graphite self-lubricating has been fabricated. The bending strength of wheel segments was measured and the fracture morphology of tested segments was detected. The results show that the bending strength of segments with CBN grains decrease to a small extent from 116MPa to 97MPa with the linear increase of graphite content from 5 wt.% to 15 wt.%. Due to the poor strength and certain stress concentration by the added graphite, the fracture interface transfers from the whole CBN grains to the bonding matrix with the increasing of the graphite. In addition, the pore sizes are decreased obviously.
Abstract: In order to assess the bonding of brazing alloys to diamonds, an investigation was conducted to measure the forces while shearing brazed diamonds. A device was designed to shear diamonds and shearing forces were recorded under different brazing parameters. The morphologies of diamonds were followed before and after shearing. It is found that the shearing force reduces with the increase of grit protrusion height. For specific grit protrusion, shearing forces decrease with the increase of holding time in brazing.
Abstract: Monolayer brazed diamond tools, which are high bonding strength at the interface between brazing alloy and grits, are becoming the active field in which improvements in processing and advanced products can be anticipated. Some researchers proposed brazing diamond methods with Ni-Cr and Ag-Cu-Ti alloy, but there is a shortage of the comparative study of the characteristics of the brazed diamond tools fabricated with the different brazing alloy. In this paper, machining performance experiments have been carried out, including contrast tests about tool life and machining efficiency for thin-walled monolayer brazed diamond core drills fabricated with Ni-Cr and Ag-Cu-Ti alloy. The results show that the Ag-Cu-Ti alloy can improve the machining performance. Wear mechanism of diamond grits was studied in those drilling processes. The results show that the low ratio of grit breakdown of the core drill using Ag-Cu-Ti alloy is the key factor of its longer life. Furthermore, based on the experimental results, the areas of the grits wear flat increase the feed force, and decrease the machining efficiency.