Advanced Materials Research Vol. 500

Abstract: Oil suspension was made with different concentrations of SiO₂ particles.The effects of SiO₂ with different concentrations on frictional pairs 45# -PTFE under different velocities is investigated on MRH-3 abrasion tester. The worn of PTFE surfaces was investigated by scanning electron microscopy (SEM).The results show that the friction coefficient increases with increasing SiO₂ concentrations. The wear rate increases with the increasing particle concentration and then decreases a bit. Meanwhile the degree of wear increases with increasing particle concentrations. Furthermore, as shown in SEM micrographs, the main machenism of PTFE is furrowing wear.

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: In this paper, a TiB₂/Al₂O₃ composite was hot-pressed. The effect of hot pressing parameters on the TiB₂/Al₂O₃ composite microstructure and mechanical properties was investigated. The flexural strength and fracture toughness were measured by three point bending testing and direct indentation method, respectively. Experimental results show that the flexural strength decreases consistently with an increase in the sintering time, however, the fracture toughness increases consistently with an increase in the sintering time and sintering temperature. The maximum of the flexural strength is 1072 MPa at 1530 sintering temperature and 60 min sintering time. The microstructures were revealed by means of SEM. The results show that the TiB₂ grain size and density increases with the increasing temperature and time during hot pressing sintering, which benefits the fracture toughness and flexural strength.

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: 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: Mg-Zn-Nd master alloys containing spherical quasicrystal phase were prepared under conventional casting conditions. The microstructures and phases of Mg-Zn-Nd ternary alloy have been investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The results show that the microstructure of Mg-Zn-Nd master alloys has been changed significantly with the addition of Nd. When adding 5wt% Nd, it is clear that a lot of spherical I-phase with high roundness and size below 10μm distributed evenly in the matrix. With the increase of Nd, the number of spherical I-phases is reduced and rod-like phases increased. The growth process and the final growth morphology of quasicrystal phase are restricted by the element Nd, thus the growth rates of all quasicrystal growth surfaces tend to be consistent, which contributes to the formation of spherical quasicrystal phase.

Abstract: Carbon nanotube (CNT) reinforced aluminum (Al) composites were synthesized using the powder metallurgy (P/M) technique, combined with hot extrusion and hot rolling. 0-2.0wt.% of CNTs were added as reinforcements. The effect of CNTs on the mechanical properties of Al was investigated and a significant enhancement in tensile strength was obtained compared with the pure matrix. The improved strength was analyzed based on (i) Orowan strengthening, (ii) thermal mismatch between CNTs and matrix, and (iii) load partition effect due to the CNTs.

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: nanohydroxyapatite (nHA) and collagen were utilized to fabricate the bio-inspired organic-inorganic composite coating (OICC) via the Drop-on-Demand (DoD) micro-dispensing technique, which could flexibly construct multi-layer structures with varied materials composition within a layer and /or among layers reliably. This technique has been further investigated on its capability of OICC fabrication with regards to various materials (hydroxyapatite and collagen) as well as its dispensing parameters. A four-layered structure was formed, with the sequence of nHA-collagen-nHA-collagen from bottom to top. The dispensing parameters were also investigated with regards to the characteristics of the OICC fabrication. The coating was then subjected to various characterizations including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and adhesion test. SEM and XRD results revealed that the DoD micro-dispensing technique did not change the morphology and phase of these two coating materials. And the results of EDS further demonstrated the corresponding elemental distributions within the four-layered coating structure which demonstrated the feasibility of the DoD micro-dispensing technique for the fabrication of thin-layered OICC.

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.