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Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science


The influence of microstructure of the fiber-matrix interface on the interfacial shear strength, measured using a fiber-pushout technique, has been examined in a sapphire-fiber-reinforced NiAl(Yb) matrix composite under the following conditions: (1) as-fabricated powder metallurgy (PM) composites, (2) PM composites after solid-state heat treatment (HT), and (3) PM composites after directional solidification (DS). The fiber-pushout stress-displacement behavior consisted of an initial ''pseudoelastic'' region, wherein the stress increased linearly with displacement, followed by an ''inelastic'' region, where the slope of the stress-displacement plot decreased until a maximum stress was reached, and the subsequent gradual stress decreased to a ''frictional'' stress. Energy-dispersive spectroscopy (EDS) and X-ray analyses showed that the interfacial region in the PM NiAl(Yb) composites was comprised of Yb2O3, O-rich NiAl and some spinel oxide (Yb3Al5O12), whereas the interfacial region in the HT and DS composites was comprised mainly of Yb3Al5O12. A reaction mechanism has been proposed to explain the presence of interfacial species observed in the sapphire-NiAl(Yb) composite. The extent of inter facial chemical reactions and severity of fiber surface degradation increased progressively in this order: PM < HT < DS. Chemical interactions between the fiber and the NiAl(Yb) matrix resulted in chemical bonding and higher interfacial shear strength compared to sapphire-NiAl composites without Yb. Unlike the sapphire-NiAl system, the frictional shear stress in the sapphire-NiAl(Yb) composites was strongly dependent on the processing conditions.

Original Citation

Tewari, S.N., Asthana, R., Tiwari, R., Bowman, R.R., & Smith, J. (1995). Influence of Interfacial Reactions on the Fiber-Matrix Interfacial Shear-Strength in Sapphire Fiber-Reinforced Nial(Yb) Composites. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 26, 477-491.








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