Key Engineering Materials Vols. 589-590

Abstract: Al2O3-MgO, Al2O3-Y2O3 and Al2O3-MgO-Y2O3 composite ceramics were fabricated respectively by hot-press sintering technique. With the analysis of the mechanical properties and microstructure, it was found that single additive MgO could be more favorable to the grains’ refinement and densification than Y2O3; the composite additive including both MgO and Y2O3 was better than single additive MgO or Y2O3, because their interactions could improve the mechanical properties of the Al2O3 ceramics; The sintering temperature could be reduced by adding the suitable amount of composite additives.

Abstract: Ti(C,N)-based cermets were fabricated by the vacuum hot-processing technique. The effect of sintering process, initial powder size and binder content on mechanical properties of Ti(C,N)-based cermets were investigated. The composite was analyzed by the observation of scanning electron microscope (SEM) and energy dispersive spectrometry (EDS). The results showed that a lower sintering temperature led to insufficient liquid-phase sintering process, which reduced the density of the composite. However, higher temperature and longer holding time resulted in abnormal grain growth, which was not good for improving the mechanical properties of the composite. With the refinement of the initial powder size of the Ti(C,N), the fracture toughness reduced slightly, the flexural strength and Vickers hardness increased. The better mechanical properties were obtained when the binder content of the cermets was designed based on the eutectic composition of Mo-Ni binary alloy phase diagram.

Abstract: In this study, titanium carbonitride (Ti(C,N)) based cermets were prepared by submicron particles, sintered in a vacuum and hot-pressing furnace. And the effect of different ball-milling time (36 h, 48 h, 60 h and 72 h, respectively, mostly aimed for mixing) on the mechanical properties of Ti(C,N)-based cermets, including transverse rupture strength (TRS), Vickers hardness (HV20), fracture toughness (K_IC) and microstructure were investigated. The results showed that the TRS, hardness and fracture toughness were all improved with an increase in ball-milling time (not more than 60 h). Scanning electron microscopy (SEM) investigations on the microstructure of cermets with different ball-milling time revealed that the compound powders were not very well-distributed as a whole and there were coarse hard phase grains, but the microstructure was very homogeneous in parts, and the microstructure of cermets with a ball-milling time of 60 h is relatively more homogeneous. So a refinement to Ti(C,N) raw particles is needed in later studies.

Abstract: In order to investigate the effects of TiN content on Al₂O₃/TiN ceramic material (ATN), the ATN ceramic materials were prepared of TiN content in 30%, 40%, 50%, 60% in the condition of hot press sintering. The sintering temperature is 1700°C, the sintering press is 32MPa, and the holding time are 5min, 10min, 15min. The effects of TiN content on mechanical properties and microstructure of ATN ceramic materials were investigated by analyzing the bending strength, hardness, fracture toughness. The results show that ATN50 has the best mechanical property, its bending strength is 659.41MPa, vickers hardness is 13.79GPa, fracture toughness is 7.06MPa·m^1/2. It is indicated that the TiN content has important effect on microstructure and mechanical properties of ATN ceramic materials.

Abstract: In the present study, Ti (C,N)/Al₂O₃ nanocomposite ceramic die material was fabricated through adding nanosize Ti (C,N) powders into micrometer Al₂O₃ matrix by vacuum hot-pressing technology. Effects of the hot press sintering process on mechanical property and microstructure of the nanocomposite ceramic die material were investigated. The optimum hot-pressing technology with the sintering temperature of 1650°C, time duration of 15min and pressure of 30MPa was achieved. The microstructural morphology of the material was also analyzed. It reveals that the intergranular/intragranular microstructure and the resulted intergranular/transgranular fracture mode are the main causes for strengthening and toughening in the nanocomposite ceramic die material.

Abstract: Tool wear condition monitoring technology is one of the main parts of advanced manufacturing technology and is a hot research direction in recent years. A method based on the characteristics of acoustic emission signal and the advantages of wavelet packets decomposition theory in the non-stationary signal feature extraction is proposed for tool wear state monitoring with monitor the change of acoustic emission signal feature vector. In this paper, through the method, firstly, acoustic emission signal were decomposed into 4 layers with wavelet packet analysis, secondly, the frequency band energy of the have been decomposed signal were extracted, thirdly, the frequency band energy that are sensitive to tool wear were selected as feature vector, and then the corresponding relation between feature vector and tool wear was established , finally, the state of the tool wear can be distinguished according to the change of feature vector. The results show that this method can be feasibility used to monitor tool wear state in high speed milling.

Abstract: The normal circular arc bevel gears are used in industrial areas of high speed, high bearing and high strength widely. A mathematical simulation model is built and it can analyze transmission error and contact zone of normal circular arc bevel gears. In this model, the instantaneous engaging points of gear pair are transformed into the least-values of rotary angles of corresponding points between two gears along the final motion, so this method is very simple and effective. Under the condition of existing helix angle error, transmission error and contact zone of a pair of normal circular arc bevel gears are simulating analyzed. At last, the operation test of contact zone of gears indicates gears transmission is stable and the gears contact zones are largely in line with the simulation results.

Abstract: Inside the indirect heating chamber, raw material itself is not being electrified nor giving out heat. Instead, heat is offered by some heater outside and transferred inside to heat the raw material indirectly. Gradient of pressure parallels to as well as matches with that of temperature, which solves the mismatch between these two elements inside the high-pressure chamber. Meanwhile, both electrical resistance and temperature remain unchanged when raw material reacts. What described above realizes uniformity and stability of pressure and temperature. During the process of synthesizing diamond, we employ the technology of two-parameter dynamic matching of pressure and temperature. In this way, attached load increases gradually while attached power decreases little by little to keep pressure and temperature in the rich diamond crystal growth area and allow them to move in a restricted area in direction of identical quality line. As a result, pressure and temperature can match dynamically and diamond crystal can grow steadily and continuously in a long time period to produce high-quality product, per unit output reaches as much as 580cts, 60% of which are of high grade.

Abstract: This study explores the feasibility of using a novel process, micro planing with multi-cutter, to fabricate graphite composite bipolar plates of proton exchange membrane fuel cells (PEMFCs). Through the use of multi-cutter, this study succeeds in machining micro flow channels with dimensions of 0.2 mm×0.23 mm×0.4 mm (channel width × rib width × depth size) on graphite composite bipolar plate (21 mm × 80 mm × 1.5 mm), in a reaction area of 10 mm × 60 mm. The graphite composite plates fabricated by multi-cutter are tested for cell performance under varying back-pressures. Results show that the cell performance increase with the rising back-pressures and can be promoted apparently by decreasing the size of flow channels.

Abstract: Si-doped diamond films are deposited on cobalt cemented tungsten carbide (WC-Co) welding dies using hot filament chemical vapor deposition (HFCVD) method, where tetraethoxysilane (C8H20O4Si) is introduced in the reactive chamber as silicon source by bubbling method. Filed emission scanning electron microscope (FESEM) and Raman spectroscopy are used to characterize the as-deposited diamond films. The results show that silicon doping can reduce the diamond crystal size and residual stress of diamond films, and also increase the FWHM of first order diamond Raman line. The polishing time of diamond coated welding dies also can be shortened by silicon doping. Si-doped diamond coated welding dies possesses comparable practical application performance with conventional diamond coated welding dies. Compared with the nylon and WC-Co welding dies, the working lifetime of diamond coated welding dies increases 200 and 10 times, respectively.