Papers by Keyword: Intermetallic Matrix Composite

Abstract: The oxidation resistance of Ni-Si-Ti-C, Ni-Si-C-Nb in-situ reinforcement clad layers has been investigated by cyclic oxidation tests at the temperature 1100°C. The oxidation performance were characterized by Thermo-gravimetric (TG),scanning electron microscopy (SEM) and X-ray diffractometer (XRD),the TG date indicates good oxidation resistant was reached for the clad layers. The kinetic constant Kp and the micrograph of oxidized samples shown that NbC reinforce clad layers which oxide products including NiO, SiO2 and Nb2O5 has better oxidation resistant than TiC reinforce clad layers which oxide products including NiO, some SiO2 and TiO2.

Abstract: In this research, the formation mechanisms of a (NiCr)Al-Al2O3 nanocomposite were investigated. The structural changes of powder particles during mechanical alloying were studied by X-ray difractometry (XRD) and the morphology and cross sectional microstructure of powder particles were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The methodology involved mechanical alloying of NiO, Cr, and Al with molar ratios of 3:3:8. During mechanical alloying, NiO was first quickly reduced by aluminum atoms to produce NiAl nanocrystalline and Al2O3. Subsequently, and when a longer milling time was applied, chromium atoms diffused into the NiAl lattice. The heat treatment of this structure led to the formation of the (NiCr)Al intermetallic compound as well as Al2O3 with crystalline sizes of 23 nm and 58 nm, respectively.

Abstract: SiC fiber reinforced intermetallic is one of the promising candidate material for the next generation space plane, because of its excellent high temperature specific strength and elastic modulus. Oxidation behavior of the fiber-reinforced intermetallic (FRIM) is one of the most important properties for the practical use in the severe environment. Recently fabrication process of CVD-SiC fiber reinforced γ-TiAl matrix composite has been developed. Oxidation behavior of SiC/γ-TiAl and γ-TiAl was studied. Cyclic oxidation experiments were executed at 900°C under the dry airflow for 200 hours. Mass gains of the specimens were measured. The cross sections of specimen were observed by optical microscope. Mass gain of the SiC/γ-TiAl composite material was two times larger than that of γ-TiAl. Surface of the SiC/γ-TiAl composite was covered with a comparatively thick oxide scale. Furthermore, formation of the oxide at the vicinity of interface between SiC fiber and γ-TiAl matrix was observed. Oxidation mechanism of SiC/γ-TiAl composite was discussed.

Abstract: The hardness and indentation fracture toughness of sub micron WC composites based on aluminide and cobalt binders were investigated. Doped Fe60Al40 and Ni3Al alloys with boron levels ranging from 0 to 0.1 wt%, were used as the aluminide binders. The composite materials were processed by uniaxial hot pressing of milled powder samples at 1500 °C under argon atmosphere. The hardness of WC-40vol%(FeAl-B) was found to be higher than that of WC-40vol%(Ni3Al-B), and it approached to the hardness level of the commercial grade of WC-10wt%Co (H10F). The fracture toughness of both WC-40vol%(FeAl-B) and WC-40vol%(Ni3Al-B) cermets was higher than that of WC-40vol%Co and the toughness increased with increasing boron content. It is believed that boron addition to the aluminide binders leads to improvement in the fracture toughness of the intermetallic matrix composites as a result of increase in the ductility and toughness of the aluminides and also due to increase in WC solubility in the aluminide binders in presence of boron.

Abstract: Ni/Ni-aluminide//Ti/Ti-aluminide laminate composite, considered as a functionally gradient material, was manufactured by thin foil hot press technique. Thick intermetallic layers of NiAl and TiAl3 were formed by a self-propagating high-temperature synthesis (SHS) reaction, and thin continuous layers of Ni3Al and TiAl were formed by a solid-state diffusion. Fracture resistance with loading along the crack arrester direction is higher than crack divider direction due to the interruption of crack growth in metal layers. The Ni3Al and NiAl intermetallic layer showed cleavage and intergranular fracture behavior, respectively, while the fracture mode of TiAl3 layer was found to be a intragranular cleavage. The debonding between metal and intermetallic layer and the pores were observed in the Ni/Ni-aluminide layers, resulting in the lower fracture resistance.