Papers by Author: Chuan Zhen Huang

Abstract: Three kinds of Al2O3 ceramics matrix composites, such as Al2O3-TiB2, Al2O3-SiC and Al2O3-TiC, were prepared by two steps, which were synthesis of the composites by thermal explosion under a pressure of 20MPa and hot pressing of the composites at 1700°C under a pressure of 32MPa respectively. The preparation process, the composition and the microstructure of the composites were investigated in detail. The Gibbs free energy and the adiabatic temperature (Tad) of three exothermic synthesis reactions were calculated. Disc-shaped and elongated TiB2 grains were synthesized in the Al2O3-TiB2 composite. Some whiskers and platelet grains were synthesized in the Al2O3-SiC composite. Nano-particles were synthesized in the Al2O3-TiC composite and distributed both within the Al2O3 matrix grains and along the grain boundaries.

Abstract: The titanium diboride reinforced titanium nitride-based ceramic cutting tool composite materials were fabricated by a new technology namely in situ synthesis followed by hot-pressed sintering. The experimental results showed that the highest density and the best mechanical properties of the composite material were obtained when the content of Ni was 5wt%. X-ray diffraction (XRD) was used to identify the phases of the composite. Microstructures of the composite were observed by means of scanning electron microscope (SEM). It is concluded that the sintered material was pure, no harmful reaction products was found; with the increase of Ni content, the proportion of short rod-like TiB₂ increased, fracture toughness of the composite materials were improved because lots of TiB₂ were pulled out; bridging phenomenon of short rod-like particles and metal particles were observed in the crack propagating process. The main toughening mechanisms of the composites were deflection and bridging of the crack as well as grains pulling out.

Abstract: Ti (C,N)-TiB₂-WC composite ceramic tool materials with sintering aids such as Ni and Mo were fabricated at a temperature of 1550 °C for 1h sintering duration time in vacuum by a hot-press technique. The microstructure and mechanical properties were investigated. The composite ceramic tool materials were analyzed by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). The main phases were composed of Ti (C, N), TiB_2, WC and MoC, which indicated that no severe chemical reactions occurred in the composite. The flexural strength, fracture toughness and hardness of Ti (C,N)- 20 wt.%TiB₂-WC ceramic material were 795.7 MPa, 6.4 MPa·m^1/2 and 19.2 GPa respectively.

Abstract: Cobalt additive was added into the Al₂O₃-TiC composite to improve the mechanical properties. The microstructure and fracture mode of composite tool materials Al₂O₃-TiC and Al₂O₃-TiC-Co were investigated, emphasizing on the difference of thermal residual stress distribution with added cobalt. The interfacial thermal stress and the stress distribution in each phase were worked out according to thermoelasticity theory. The results demonstrated that cobalt could strengthen the interfacial bonding strength of ceramic grains and influence the residual stress distribution in Al₂O₃ matrix, which change the fracture mode and lead to the flexural and irregular crack propagation path.

Abstract: TiB₂-Ti (C_0.5N_0.5)-WC composite tool materials were fabricated by the hot-pressing technique. The effects of sintering process on microstructure and mechanical properties of TiB₂ -Ti (C_0.5N_0.5) -WC composite tool materials were studied. The flexural strength was measured by three point bending test, and Vickers hardness and the fracture toughness were measured on polished surfaces by Vickers indentation. The microstructure of TiB₂-Ti (C_0.5N_0.5)-WC composite ceramic was analyzed by XRD and SEM observations. The results show that the mechanical properties can be improved in a proper heating mode. When the direct heating-up mode was conducted, the flexural strength, fracture toughness and hardness reached 854MPa, 7.2MPa·m^1/2 and 19.7GPa, respectively.

Abstract: Toughening mechanisms and flank wear behavior of a TiC whisker toughening Al₂O₃-based ceramic cutting tool composite were investigated. The results showed that the wear behavior of the tool composite was greatly influenced by the whisker toughening mechanisms, of which the toughening effects on the composite can increase with increasing cutting temperature. As a result, the tool composite could still possess enough high fracture toughness and flexure strength at high cutting temperature, which resulted in an interesting phenomenon that the wear resistance of the tool composite at higher cutting speed was higher than that of itself at lower cutting speed.

Abstract: Al₂O₃-TiN-TiC ceramic materials with different MgO content were fabricated by hot-pressing technique. The MgO volume percent was varied from 0vol% to 5vol%. The mechanical properties such as flexural strength, Vickers hardness and fracture toughness were tested. The phase composition of the sintered body was analyzed by XRD while the microstures of the sintering body were observed by OM (Optical Microscope) and SEM. The effects of MgO content on the mechanical properties and microstructures of Al₂O₃-TiN-TiC were investigated. The results shows that the addition of MgO can change the phase composition of the sintered ceramic materials which displayed with diverse solid solutions and intermetallic compounds. Meanwhile the new sintering products changed the the microstructure morphology which made the crack path complex and affected the mechanical properties.

Abstract: A Monte Carlo Potts model for the sintering process of two-phase nanocomposite ceramic tool materials is proposed. The grain growth, pore diffusion and vacancy annihilation at grain boundaries are simulated in the model. Simulation results are presented and discussed. It is found that pore and nanophase can pin the ceramic matrix and decrease the growth rate of matrix grain during the microstructure evolution. The addition of nanoparticles is not only beneficial to the refinement of ceramic matrix grain and the formation of intra/intergranular-type microstructure but also advantageous to the densification of ceramic materials.

Abstract: The profile of a single-pass milling can be assumed as a cosine curve. Therefore, the maximal depth model for single-pass milling is established which indicates the quantitative relationship between the AWJ single-pass milling depth and the milling parameters. The depth model of milled surface, which shows the effect of water pressure, standoff distance, lateral spacing, abrasive flow rate and the properties of the material on the AWJ milling depth, is established based on the maximal depth model for single-pass milling. The derived model is assessed by AWJ milling experiments. The results show that the milling depth increases with an increase in water pressure and standoff distance, and decreases with an increase in lateral spacing and traverse speed. The theoretical milling depth predicted by the mathematical model is good agreement with the experimental result.

Abstract: Tool wear was investigated at the different cutting conditions in rough ball-end milling of Cr12MoV die steel using an indexable cutter with asymmetric inserts. The wear patterns on rake face and flank face of major insert and minor insert, and chip patterns were observed by VHX-600E large depth-of-view 3-D scanner. The relationships of tool wear and cutting conditions, and their mechanisms were discussed. The tool life was determined by the flank wear at No. 1 cutting condition. At Nos. 2-8 cutting conditions, the life of major inset and minor insert were determined by the wear of their rake faces and flank faces respectively. At No. 8 cutting condition, the tool wear was dominated by boundary wear, adhesion and diffusion wear, and the slight chipping. Both type and color of chips identified the cutting stability at the different cutting conditions.