Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Directional solidification (DS) of ''powder-cloth'' (PC) processed sapphire-NiAl composites was carried out to examine the influence of fabrication technique on the fiber-matrix interfacial shear strength, measured using a fiber-pushout technique. The DS process replaced the fine, equiaxed NiAl grain structure of the PC composites with an oriented grain structure comprised of large columnar NiAl grains aligned parallel to the fiber axis, with fibers either completely engulfed within the NiAl grains or anchored at one to three grain boundaries. The load-displacement behavior during the pushout test exhibited an initial ''pseudoelastic'' response, followed by an ''inelastic'' response, and finally a ''frictional'' sliding response. The fiber-matrix interfacial shear strength and the fracture behavior during fiber pushout were investigated using an interrupted pushout test and fractography, as functions of specimen thickness (240 to 730 mu m) and fabrication technique. The composites fabricated using the PC and the DS techniques had different matrix and interface structures and appreciably different interfacial shear strengths. In the DS composites, where the fiber-matrix interfaces were identical for all the fibers, the interfacial debond shear stresses were larger for the fibers embedded completely within the NiAl grains and smaller for the fibers anchored at a few grain boundaries. The matrix grain boundaries coincident on sapphire fibers were observed to be the preferred sites for crack formation and propagation. While the frictional sliding stress appeared to be independent of the fabrication technique, the interfacial debond shear stresses were larger for the DS composites compared to the PC composites. The study highlights the potential of the DS technique to grow single-crystal NiAl matrix composites reinforced with sapphire fibers, with fiber-matrix interfacial shear strength appreciably greater than that attainable by the current solid-state fabrication techniques.
Asthana, R.; Bowman, R. R.; and Tewari, Surendra N., "Influence of Fabrication Technique on the Fiber Pushout Behavior in a Sapphire-Reinforced Nial Matrix Composite" (1995). Chemical & Biomedical Engineering Faculty Publications. 25.
Asthana, R., Tewari, S.N., & Bowman, R.R. (1995). Influence of Fabrication Technique on the Fiber Pushout Behavior in a Sapphire-Reinforced Nial Matrix Composite. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 26, 209-223.
Copyright 1995 ASM International. This paper was published in Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, Vol. 26, Issue 1, pp. 209-223 and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.
Available on publisher's site at: http://www.springerlink.com/content/n010853112075397/.