W. H. Rhee

Pressure casting of a zirconia-toughened alumina fiber-reinforced NiAl composite

A pressure-cast NiAl composite reinforced with polycrystalline alumina (PRD-166) fibers containing 0.2 weight fraction of partially stabilized zirconia was examined by optical and transmission electron microscopy (TEM). Fibers in the preform used for casting were forced into contact, and fiber bonding occurred in a number of instances. Fiber volume fraction was increased from an initial value of 0.4 to 0.6 as a consequence of the applied pressure. An explanation is offered for the interaction of applied pressure, wetting angle, and the rigidity of the fiber preform on the final volume fraction of the fibers in the composite. At the fiber/matrix interface, the alumina was free of zirconia particles. It is proposed that alumina grain growth forced the zirconia into the molten NiAl, where it dissolved. As solidification took place, the concentration of zirconium in the molten NiAl increased to a point where zirconium reacted with alumina to form zirconia again.

Microstructural characterization of a zirconia-toughened alumina fiber reinforced niobium aluminide composite

Abstract An NbAl3 + Nb2Al composite reinforced with continuous zirconia-toughened alumina, PRD-166 fibers, was produced by pressure casting and was examined by optical and transmission electron microscopy and energy dispersive spectroscopy. Exposure of the fiber to the molten metal resulted in ZrO2 and Al2O3 grain growth, formation of a thin layer of an amorphous phase on the grain boundaries of Al2O3 and transformation of ZrO2. Preferential Al2O3 grain growth near the surface of the fiber led to the rejection of ZrO2 from this region into the molten metal. In NbAl3 slip occurred by the glide of a superdislocations and tolesser extent by the glide of a pair of 1 + 11 ] dislocations on the (112) planes and a /2 superpartial dislocations on the (001) plane. The operating slip system in Nb2Al was identified as {010) a dislocations were dissocaited into a x partial dislocations joined together by a stacking fault.

Fiber strength and fiber/matrix bond strength in single crystal Al2O3 fiber reinforced Ni3Al based composites

AbstractA series of single-crystal A12O3 fiber (Saphikon), reinforced Ni3Al-based composites were fabricated by a liquid metal infiltration technique, pressure casting. Tensile testing and indentation techniques have been employed to measure fiber strength and fiber/matrix interfacial debond shear stress. The Weibull mean strength of the fiber has been observed to decrease drastically upon handling, exposure to high temperature, and casting. Alloying of Ni3Al with Ti has resulted in a further decrease in fiber strength. Thermal expansion mismatch between the fiber and matrix led to the formation of compressive twins in the fiber. These twins, forming on % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrpepeei0xd9vqVe0x% b9q8qqqrpe0db9pwe9Q8fs0-yqaqVepee9pg0Firpepe0de9vr0-vr% 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiaacUhaceaIXa% GbaebacaaIXaGaaGimaiaaikdacaGG9baaaa!3BD5!

Mechanical behavior of a fiber reinforced Ni3Al matrix composite

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Oxidation behavior of single-crystal Al2O3-fiber-reinforced Ni3Al-based composites

planes, produced cracks at their intersections, which were parallel to the fiber axis,c-axis. Twin-induced fiber cracking was observed in all cases, but most predominantly when Cr was present. While addition of Cr at the 1 at. pct level had no appreciable effect on the interfacial debond shear stress, addition of 0.5 at. pct Cr resulted in an approximately threefold increase in debond stress, from 19 MPa to about 54.5 MPa. Alloying of Ni3Al with Cr has also resulted in partial dissolution of the A12O3 fiber. Addition of Ti had a moderate effect on increasing the fiber/matrix bond strength.

Microstructure of AI2O3 fiber-reinforced superalloy (INCONEL 718) composites

A Ni3Al composite reinforced with zirconia-toughened alumina fiber, PRD-166 fiber, was produced by pressure casting. The thermochemical stability of the composite at 1100 °C in vacuum and air was investigated by optical and transmission electron microscopy and energy- dispersive spectroscopy (EDS). Vacuum annealing resulted in precipitation of needle-shaped ZrB and cuboid-shaped Cr-rich, tentatively identified as Cr7C3, particles. Annealing in air led to the precipitation of large ZrO2 particles at the fiber/matrix interface and fine ZrO2 platelets in the matrix. A thin layer of A12O3 was observed to cover the fiber/matrix interface and to envelop the ZrO2 platelets. Diffusion of Ni through the A12O3 layer and its oxidation and sub- sequent reaction with A12O3 resulted in the formation of NiAl2O4 spinel around the ZrO2 particles at the fiber/matrix interface. Further annealing resulted in the formation of a thin layer of Cr2O3 on the A12O3 layer and precipitation of A12O3 and Cr2O3 particles within the matrix. These particles subsequently reacted with NiO to form Ni(AlxCr1-x)2O4grains. Diffusion of oxygen through the fiber is believed to be responsible for the rapid oxidation of the composite.

Microstructure of Al{sub 2}O{sub 3} fiber-reinforced superalloy (INCONEL 718) composites

Abstract Pressure casting has been used to reinforce a Ni 3 Al-based alloy, IC218, with continuous Al 2 O 3 -based fibers, DuPonts 20 μm diameter PRD-166 TM fibers. The mechanical properties of the cast composites and the unreinforced IC218 were evaluated at room temperature and 1000°C, in air. Optical, transmission and scanning electron microscopy were employed to characterize the microstructure and fracture of the composites. Reinforcing IC218 with PRD-166 fibers resulted in an increase in elastic modulus and a reduction in strength. A high degree of fiber-fiber bonding is believed to be responsible for the observed reduction in strenth. Residual stresses which resulted from the thermal expansion mismatch between the fiber and matrix were not sufficient to deform the matrix during cool-down from the processing temperatures.

Oxidation behavior of single-crystal Al 2 O 3 -fiber-reinforced Ni 3 Al-b

AbstractA composite of NiAl reinforced with continuous zirconia-toughened alumina (PRD-166) fibers was fabricated by pressure casting. The chemical stability of the composite at 1100 °C in vacuum and air was investigated by optical and transmission electron microscopy and energy-dispersive spectroscopy (EDS). Exposure of the fiber to the molten metal caused ZrO2 particles in the fiber to move to the surface, thus permitting dissolution of ZrO2 into the molten metal. The dissolved Zr reacted with A12O3 of the fiber and formed ZrO2 particles in some regions at the fiber/matrix interface. Vacuum annealing did not result in any noticeable change in the microstructure. Air annealing led to the precipitation of ZrO2 within the matrix near the fiber/matrix interface. A thin layer of A12O3 was observed to envelop the ZrO2 particles and cover the fiber. During air annealing, Al oxidized preferentially, thereby continually reducing the Al content of the β-NiAl. This caused a progressive change in the microstructure of the matrix from β-NiAl to premartensitic microstructure, to martensitic structure, followed by nucleation and growth of Ni3Al, to the development of a two-phase microstructure consisting of Ni3Al cuboids dispersed in a disordered α-Ni(Al) and, subsequently, the formation of single-phase α-Ni(Al). The orientation relationship between Ni3Al and NiAl was % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrpepeei0xd9vqVe0x% b9q8qqqrpe0db9pwe9Q8fs0-yqaqVepee9pg0Firpepe0de9vr0-vr% 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiabgMYiHlaaig% daceaIXaGbaebacaaIXaGaeyOkJe-aaSbaaSqaaiaab6eacaqGPbGa% aeyqaiaabYgaaeqaaOGaai4laiaac+cacqGHPms4caaIWaGabGymay% aaraGaaGymaiabgQYiXpaaBaaaleaacaqGobGaaeyAamaaBaaameaa% caqGZaaabeaaliaabgeacaqGSbaabeaaaaa!4BFE!