Papers by Author: Chuan Zhen Huang

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: 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: Ti(C,N)-TiB₂-WC composite ceramic cutting tool materials with nano-scale additives Ni and Mo, and micro-scale additives Ni and Mo as sintering aids were sintered respectively at a temperature of 1550 °C for holding time of 1hour in vacuum by a hot-press technique. The effects of nano-scale additives Ni and Mo, and micro-scale additives Ni and Mo on microstructure and mechanical properties of composites were compared and investigated. It is concluded that the wettability of nano-scale Ni and Mo to the composites is better than that of micro-scale Ni and Mo. The nano-scale whiskers were found in the composite ceramic tool materials with nano-scale additives. The addition of nano-scale Ni and Mo instead of micro-scale Ni and Mo could make the flexural strength and fracture toughness of Ti(C, N)-TiB₂ –WC composites have a promotion, but could not make the hardness of the composites increase in this study.

Abstract: A study on the radial-mode abrasive waterjet turning (AWJT) process is presented and discussed. An experimental investigation is carried out to explore the influence of process parameters on the depth of turning and material removal rate (MRR) when turning 96% alumina ceramics. The experiment is designed by the multifactor orthogonal experiment methods. The effect of feed speed, water pressure, abrasive mass flow rate, nozzle tilted angle and surface speed are investigated by the range analysis and variance analysis. The results show that the feed speed is the most significant variables affecting the depth of turning. Based on the test conditions, it is found that the most efficient conditions to maximize depth of turning are at a jet angle of 105 degree, a water pressure of 310MPa, an abrasive mass flow rate of 11.5 g/s, a surface speed of 5.5m/s and a feed speed of 0.05mm/s. At last, the effect mechanism of process variables on the depth of turning is analyzed qualitatively.

Abstract: Abrasive waterjet (AWJ) turning is an emerging technology, which plays an important role in machining cylindrical parts with the distinct advantages of negligible thermal effects and extremely low cutting force. This paper presents an experimental study of abrasive waterjet turning (AWJT) of Al₂O₃ ceramics. The machining process and performance in terms of the depth of penetration (DOP), surface roughness (Ra) and actual impact angle (β) are discussed to understand the effect of standoff distance (SOD) on the processing performance at two different turning modes. Based on the results of these investigations, there is a significant change of DOP and Ra at different SOD in radial mode turning and the optimal SOD of gaining maximum DOP and the minimum Ra is about 5.5mm.However, the DOP is nearly independent on the SOD in offset mode turning. Smaller Ra and DOP can be obtained in offset mode. Furthermore, the results indicate that the roundness error of cylinder parts is probably improved with the proper SOD interval in radial mode turning and it is suitable for machining cylinder part with considerably different radial size. The offset mode turning as the next operation after radial mode turning is recommended to process workpiece with excellent roundness. In this way, by understanding the effect of SOD on processing alumina ceramics, the paper establishes a good basis for developing strategies for optimizing processing parameters in order to generate the desired part geometry and achieve better surface quality.

Abstract: Abrasive water jet (AWJ) technology, due to its potential advantages, is a promising machining method for precision machining brittle materials. In this research, the AlN ceramics was polished using an AWJ machining system. A considerable processing quality has been achieved and a reduction up to 62% of the surface roughness has been obtained. Effects of different process parameters on the surface roughness of the polished workpiece were analyzed. Under the current conditions of the experiments, using a lower impact angle, smaller abrasives and a lower nozzle traverse speed may be appropriate for polishing AlN ceramics.

Abstract: Three kinds of in-situ growth TaC whiskers toughening Al₂O₃ matrix ceramic cutting tool materials were prepared by two steps, which were in-situ synthesis of TaC whiskers in Al₂O₃ matrix powder by carbothermal reduction process and hot pressing of the composites respectively. The preparation process, microstructure, mechanical properties and toughening mechanisms of the composites were investigated. The in-situ synthesized TaC whiskers had a diameter of 0.1-0.5μm and an aspect ratio of 10-30. The composite containing 20vol.% TaC had the optimal comprehensive mechanical properties with flexural strength of 638MPa, fracture toughness of 6.5MPa·m^1/2 and hardness of 17.4GPa. The improvement of the mechanical properties was attributed to the TaC particles and whiskers which induced the toughening and strengthening effects such as crack deflection, crack branching, grain and whisker fracture, interface debonding and whisker pullout. The fracture mode of the composites was the combination of intergranular and transgranular fracture which also improved the mechanical properties of the composites.

Abstract: Ultrasonic vibration-assisted machining (UVAM) is an effective and promising technology for processing hard and brittle materials, it has been explored in many experimental and theoretical investigations. In this paper, a study on the erosion performance of monocrystalline silicon with UVAM is presented and discussed. In the erosion experiments, monocrystalline silicon wafers were eroded by the abrasive water jet machine assisted with an ultrasonic vibration system. A contrast experiment was carried out firstly to study the influence of the ultrasonic vibration, and then an orthogonal experiment investigation was carried out to understand the effect of process variables (the abrasive particle diameter, jet impact angle, standoff distance, abrasive mass flow rate and ultrasonic vibration power) on the depth of erosion and material removal rate (MRR). The experimental results revealed that ultrasonic vibration-assisted abrasive water jet erosion (UVA-AWJE) can obviously improve the depth of the erosion and MRR compared with those in traditional AWJE and the variation trends of the effect of the abrasive particle diameter, jet impact angle, standoff distance and abrasive mass flow rate on the erosion performance in UVA-AWJE are very similar to those effect in the traditional AWJ machining.

Abstract: A Monte Carlo Potts model coupled with sintering pressure for the sintering process of nanocomposite ceramic tool materials is proposed, the relation between grain growth and sintering pressure is presented. The grain growth process at different sintering pressure is investigated in this model, and the effect of sintering pressure on microstructure evolution is discussed, it is found that the mean grain size increases with the increase of sintering pressure during simulation. The results from this simulation are shown to correlate well with the experimental observations.

Abstract: Monte Carlo simulation method of microstructure evolution in nanocomposite ceramic tool materials is set up. Two-phased material systems with the same area fractions but various sizes of nanoparticles are designed, and the processes of microstructure evolution are simulated. The influences of nanoparticle size on microstructure and grain growth are observed and discussed quantitatively. It is found that the mean size of matrix grains increases with the increase of nanophase size during simulation, and intragranular-type microstructure is more difficult to form. The material Al₂O₃/nanoSiC is developed and the simulated results are verified.