Structure and properties of composites synthesized in situ using solid state displacement reactions

Abstract

1111 _, UU]_ [[[ll _ lUll-_ ulu-_ q I J AbstractSolid state displacement reactions can produce in situ intermetallic and ceramic matrix composites in a process where an intermetallic or ceramic phase(s) and a potential reinforcing phase(s) are grown together during a solid state reaction. Interpenetrating and dispersed microstructures, important for desirable composite properties, have been produced by means of displacement reaction processing techniques. Two such composites have been synthesized which exhibit two distinct microstructures: MoSi2 reinforced with SiC particles, which exhibits a dispersed-phase structure, and NiA1/Ni3A1 reinforced with A1203, which exhibits an interpenetrating-phase structure. Strength in bending and chevron-notch fracture toughness have been determined as a function of temperature, and measured properties compare favorably with composites produced by other means.The measured properties are discussed with regard to the observed microstructures. The potential for displacement reaction processing is assessed, and it appears to be a cost-effective synthesis method compared to others.

Reactive Processing in Ceramic‐Based Systems

“…If the reaction products, MoSi 2 and SiC in this example, are the thermodynamically compatible phases for the overall composition of 25.0 at.% Mo, 12.5 at.% C, and 62.5 at.% Si, then the choice of precursors should not affect the final composition. The MoSi 2 –SiC system was studied by Henager, who used a ternary Mo–Si–C phase diagram to understand the formation of a metastable intermediate phase (Mo 5 Si 3 C) when Mo 2 C and Si were reacted 44 . According to the phase diagram, MoSi 2 and SiC are thermodynamically compatible.…”

“…Compared with the methods summarized in Table I, RHP has the advantage of increased compositional flexibility 44–53 . Single‐ or multi‐phase materials containing oxide ceramics, nonoxide ceramics, intermetallics, and/or metals can be formed by RHP 44,50,54,55 . Often, RHP results in the formation of favorable two‐phase, interpenetrating microstructures 56 .…”

“…One limitation of RHP is that only thermodynamically compatible phases can be produced. Several research groups have produced a variety of composites by RHP including Al 2 O 3 –Ni, Al 2 O 3 –Nb, Al 2 O 3 –MoSi 2 , ZrB 2 –SiC, and SiC–Nb 2 Si 44–53 . Often, the temperature required to produce a composite reactively is much lower than for non‐RHP of the same composition.…”

“…[44][45][46][47][48][49][50][51][52][53] Single-or multiphase materials containing oxide ceramics, nonoxide ceramics, intermetallics, and/or metals can be formed by RHP. 44,50,54,55 Often, RHP results in the formation of favorable two-phase, interpenetrating microstructures. 56 RHP relies on the selection of thermodynamically favorable reactions to produce the desired phases.…”

“…Several research groups have produced a variety of composites by RHP including Al 2 O 3 -Ni, Al 2 O 3 -Nb, Al 2 O 3 -MoSi 2 , ZrB 2 -SiC, and SiC-Nb 2 Si. [44][45][46][47][48][49][50][51][52][53] Often, the temperature required to produce a composite reactively is much lower than for non-RHP of the same composition. For example, dense Al 2 O 3 -MoSi 2 composites can be produced by RHP at 14501C, 51 compared with 17001C for non-RHP.…”