Abstract: A blended NiCr-Cr2O3-Ag-BaF2/CaF2 feedstock was sprayed using an atmospheric plasma spraying process. Due to the differences in physical and thermophysical properties of each constituent, coating microstructures and resulting coating properties were largely dependent on the interactions between each constituent phase and plasma jet in view of the physics of thermal spraying. Thus, hydrogen gas flow rate was changed to affect the plasma jet characteristics such as gas enthalpy and gas thermal conductivity in this study. According to it, evolutions of chemical composition and microstructures of the as-sprayed coatings were observed. As the hydrogen gas flow rate was increased, Cr2O3 weight fraction was increased with the decrease of Ag and porosity. Vickers microhardness and bond strength of the coatings showed consistent behaviors to the phase composition and microstructures. Friction coefficient and weight loss during a pin-on-disc dry sliding wear test were measured from room temperature to 500°C at the interval of 100°C. Finally, the effects of phase fraction and coating properties on the friction and wear were investigated.
Abstract: TiN coated films were prepared by a reactive ion physical vapor deposition method. In this research, we studied the relationships between textures and friction coefficient, erosion-corrosion resistance and corrosion resistance in textured TiN films. The surface roughness of (115) textured TiN films is lower than that of (111) textured TiN films. The friction coefficient of (115) textured surface is similar with that of (111) textured surface of TiN coated films. The erosion-corrosion and corrosion resistance of (115) textured surface is better than that of (111) textured surface of TiN coated films.
Abstract: In the present study, PIM process has been employed to produce sintered specimens with the various porosities from the initial stage of sintering and to the stage of nearly full density. A series of tensile tests has been conducted on these specimens at room temperature to elucidate the effect of a wide range of porosity. The material used in this study was 17-4 PH stainless steel. Based on the results of tensile tests on PIMed specimens with the various porosity, a new approach to predict the strength and the elongation of sintered materials has been carried out and a new framework combining neck growth model and ideal pore model has been established. By applying this new model to not only the results obtained in this study but also to previously published data, its generality and validity were sufficiently verified.
Abstract: CROMeP (Research Centre on Tools, Materials and Processes) experience in rapid tooling development is related. Focus is placed on two processes, namely the Direct Metal Laser Sintering/DMLSⓇ and STRATOCONCEPTⓇ currently under consideration for the manufacturing of thermoplastic injection moulds. The principle of the two processing routes as well as the benefits attainable by using those processes will be briefly reviewed. Recent results on the microstructure and the mechanical performances of sample tools built up using both processes are presented.
Abstract: In this paper, the effect of electric current on sintering of hydroxyapatite (HAp) in spark plasma sintering (SPS) process was investigated. The carbonate partially substituting hydroxyapatite was sintered up to 900 °C, and CO2 evolved from HAp powder were measured in situ by using mass spectroscopy apparatus in the same time. The same gas analysis was performed in thermal analysis as comparison. In the thermal analysis, CO2 gas was evolved at about 600 °C. On the other hand, in the SPS process, CO2 gas was detected at lower temperature than that of thermal analysis. This result indicates that the surface of hydroxyapatite particles would be heated up locally in SPS process due to electric current.
Abstract: CNTs/metal/Al2O3 nanocomposite powders were fabricated by thermal chemical vapor deposition (CVD) of C2H2 gas over metal/Al2O3 nanocomposite catalysts prepared by the selective reduction of oxide/Al2O3 powders. The yield and diameter of CNTs significantly depended on the kind of metal catalyst and catalyst size. X-ray diffraction (XRD) was used for phase identification. The morphology of CNTs was determined using field emission scanning electron microscopy (FESEM). FT-Raman spectroscopy revealed that the CNTs have single- and multi-walled carbon nanotubes structure. The relationship between the CNT yield/diameter and the characteristics of the composite catalyst was systematically investigated.
Abstract: Magnetic Pulse Compaction (MPC), as a dynamic compaction, can be possible to reach higher relative density of nano metallic compacts owing to sufficiently high pressure and adiabatic heating in very short duration of an order of µsec. The present work is concerned with the magnetic pulsed compaction of the nano-sized aluminum powders, which particle size was a range of 50 ~ 100 nm passivated in air. The compaction pressure was 1.5 GPa for 300 µsec in the temperature range from 20°C to 500°C. The grain size of compacts was maintained less than 50 nm, which was analyzed by X-ray diffraction (XRD) using Scherrer method. From the calculation of adiabatic heat and of pressure induced by thermal expansion, and the observation by transmission electron microscopy (TEM), it was found that Al2O3 could be broken and dispersed with a few nano-meter sizes in the Al matrix and that the ultra fine and uniform bulk structure was maintained up to 400°C of compaction temperature.e
Abstract: Phase relation and mechanical property of Cr2Zr Laves phase alloy systems were investigated in terms of ternary alloying based on geometric concept of atomic sizes of constituent alloying elements. Ternary phase diagrams at 1573 K of Cr-Zr-Nb and Cr-Zr-Hf alloy systems were examined using SEM-EPMA analysis in order to understand the site occupation behavior of ternary elements and the phase stability of Laves phase. In the Cr-Zr-Nb alloy system, Laves phase had a broad off-stoichiometry range in the middle of Cr2Zr-ZrNb2 pseudo-binary line, while a limited and uniform range of Laves phase field was found in the Cr-Zr-Hf alloy system. For both Laves phase alloys, 0.2% offset yield strength decreased with increasing content of allying element, on the other hand compressive ductility increased with increasing content of alloying elements. Details will be discussed in conjunction with microstructure, phase stability and atomic size considerations.
Abstract: Thermal stability and mechanical properties of L12 Al3Hf and (Al+12.5 at.%Zn))3Hf
synthesized by mechanical alloying(MA) and spark plasma sintering(SPS) were investigated. Nanocrystalline L12 phase was produced after MA for 8 and 10 hrs in Al3Hf and (Al+12.5 at.%Zn))3Hf powders, respectively. The grain sizes were reduced to about 10 nm in both systems after MA for 20 hrs. After SPS, L12 phase was maintained only in Zn added system. In (Al+12.5 at.%Zn))3Hf, L12 to D023 phase transformation was started at about 850°C and finished at about 1150°C Microhardness was decreased with increasing the annealing temperature while fracture toughness was increased due to the grain growth. Fracture toughness of (Al+12.5 at.%Zn))3Hf was greater than that of Al3Hf in all annealing temperatures. Fracture toughness of (Al+12.5 at.%Zn))3Hf after annealing at 1200°C was about 5.38 MPam1/2.
Abstract: Alloys of Ti39.4Al10V (at.%) that consisted mainly of ordered β-Ti, γ-TiAl and α2-Ti3Al phases were oxidized at 700, 800, 900, and 1000oC in air. The oxide scales formed consisted largely of an outermost, thin TiO2 layer, an outer, thin Al2O3 layer, and an inner, very thick (TiO2+Al2O3) mixed layer. Vanadium, which was uniformly distributed throughout the oxide scale, harmfully decreased oxidation resistance, and made thick, nonadherent scales owing to the formation of low melting compounds of V-oxides. The oxidation progressed via the outward diffusion of Ti, Al and V ions, and the concurrent inward transport of oxygen.