Influence of interfacial reactions on the fiber-matrix interfacial shear strength in sapphire fiber-reinforced Nial(Yb) composites

Abstract

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 NiAI(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 NiAI(Yb) composites was comprised of Yb203, O-rich NiAI and some spinel oxide (Yb3A15Ol2), whereas the interfacial region in the HT and DS composites was comprised mainly of Yb3A15Ot2. A reaction mechanism has been proposed to explain the presence of interracial species observed in the sapphire-NiAl(Yb) composite. The extent of interfacial chemical reactions and severity of fiber surface degradation increased progressively in this order: PM < HT < DS. Chemical interactions between the fiber and the NiAI(Yb) matrix resulted in chemical bonding and higher interracial shear strength compared to sapphire-NiA1 composites without Yb. Unlike the sapphire-NiA1 system, the frictional shear stress in the sapphire-NiAl(Yb) composites was strongly dependent on the processing conditions.

Interface response to solidification in sapphire-reinforced Ni-base composites

“…Figure 6 shows the various interfacial reaction product phases that formed in the PC and DS NiAl(Yb) specimens. The Ni and Al contents of the NiAl(Yb) matrix did not change during processing, but a near 50% reduction in the amount of Yb occurred after DS (Table 1) [14,16] of fiber clumping, deformed casting, and incomplete infiltration. On the other hand, the top-fill infiltration yielded sound castings with good metal penetration of interfiber spaces even at lower infiltration pressures.…”

“…The oxide of Yb (Yb 2 O 3 ) is stabler than Al 2 O 3 , and a reaction between the sapphire and ytterbium is expected from the thermodynamic considerations (the free energies of formation of Yb 2 O 3 and Al 2 O 3 are −1727.5 kJ mol −1 and −1583.1 kJ mol −1 , respectively). The reaction products identified using the phase analysis were Yb 2 O 3 and Yb 3 Al 5 O 12 [14,16]. Figure 6 shows the various interfacial reaction product phases that formed in the PC and DS NiAl(Yb) specimens.…”

“…Additionally, substantial mechanical damage to the fibers could be caused during the solid-state consolidation. Liquid-phase composite fabrication techniques such as vacuum-and pressure casting [9][10][11][12], and directional solidification [13][14][15][16][17][18][19][20] have been employed to synthesize intermetallic-matrix composites such as NiAl, Ni 3 Al, TiAl and FeAl reinforced with a variety of alumina fibers (DuPont's fibers FP and PRD166, Saphikon's single crystal sapphire, and others). Likewise, high-temperature superalloys also have been reinforced with both metals (tungsten fiber [21]) and ceramics (Al 2 O 3 fiber [22]).…”

Investigations on NiAl composites fabricated by matrix coated single crystalline Al2O3-fibers with and without hBN interlayer

“…A promising way to overcome these deficiencies is to reinforce NiAl by means of continuous ceramic fibers. In the past two decades intensive investigations were carried out in order to explore the possibility of NiAl composites as structural components for load bearing applications at high temperatures [1][2][3][4][5][6][7][8][9]. Due to the good chemical compatibility between NiAl and Al 2 O 3 -fiber at elevated temperatures, some polycrystalline fibers (e.g.…”

Microstructure and mechanical properties of continuous Al2O3fibre reinforced Ni45Al45Cr7.5Ta2.5alloy (IP75) matrix composites

“…The intermetallic alloy NiAl has been extensively investigated with respect to its high temperature mechanical properties because it is considered a candidate material for structural applications owing to its high melting point, low density, good thermal conductivity and outstanding oxidation resistance [1,2]. However, NiAl suffers from its low strength at high temperature and poor toughness at room temperature.…”