Investigations have been carried out to determine ways of tailoring ceramic materials in order that one or more toughening mechanisms are activated in service. Microstructural manipulations, as well as composite formulations involving metallic, intermetallics, and ceramic phases have been used with ceramic matrices. Macrostructurally, laminated structures and functional gradient materials (FGMs) have also been formulated to enhance mechanical properties. Although significant improvements in material properties have been reported, ceramics are still below their projected positions on the materials map. This article presents a review of research activities pursuant to improving fracture toughness of alumina matrix systems and the enhancements achieved.

Fracture Toughness Enhancement for Alumina Systems: A Review

A new process has been developed to produce sintered α-Al2O3 reinforced with sub-micron Ni particles. The process is based on the infiltration of ceramic preforms with liquid salts, which are reduced during pressureless sintering to form metal particles. The reduction occurs within the open pores of the ceramic preform, after evaporation of the metal salts into the gas phase. By controlling the partial pressure of oxygen during the sintering process, a reaction between the Ni particles and the alumina matrix can be invoked to form Ni-spinel (NiAl2O4) particles. Three-point bending experiments show an increase in strength for the nickel-reinforced alumina and a significant increase for the spinel-reinforced alumina.

Processing and properties of Al2O3 nanocomposites reinforced with sub-micron Ni and NiAl2O4

A resin-soluble thermoplastic polymer veil toughening element for a curable composition wherein the polymer element is a non-woven veil in solid phase adapted to undergo at least partial phase transition to fluid phase on contact with a component of the curable resin matrix composition in which it is soluble at a temperature which is less than the temperature for substantial onset of gelling and/or curing of the curable composition and which temperature is less than the polymer elements melt temperature; a method for the preparation thereof, a preform support structure for a curable composition comprising the at least one thermoplastic veil element together with structural reinforcement fibers, methods for preparation thereof, a curable composition comprising the at least one thermoplastic veil element or the support structure and a curable resin matrix composition, a method for preparation and curing thereof, and a cured composite or resin body obtained thereby, and known and novel uses thereof.

Resin-soluble thermoplastic veil for composite materials

Effect of grain size on thermal shock resistance of Al2O3–TiC ceramics

Many layered ternary ceramics displayed unusual thermal shock behavior, i.e., the retained strengths of as-quenched samples increased with increasing quench temperature above a critical quench temperature. However, the causation was not clear even though this phenomenon has been observed for 10 years. In this study, the thermal shock behavior of Ti3SiC2 and Ti3AlC2, two representative members of layered ternary ceramics, was investigated. The results indicated that the formation of surface oxides was responsible for this abnormal phenomenon. These results might contribute to the understanding of this unusual behavior of other layered ternary ceramics.

Abnormal thermal shock behavior of Ti3SiC2 and Ti3AlC2

Over recent years, it has been established that the incorporation of metallic particles into a ceramic matrix can lead to enhanced fracture properties. Relatively few attempts, however, have been made to establish whether or not the improved fracture toughness typically observed in such composite systems can offer improved performance in demanding environments. The current study is concerned with the thermal shock behaviour of a ceramic matrix composite consisting of an alumina matrix containing 20 vol% of discrete iron particles. The composite material has been produced by both hot pressing and conventional sintering techniques. The hot pressed composite shows a greater resistance to thermal shock than the monolithic matrix, both in terms of the critical temperature differential and retained strength, whereas the sintered material has been found to behave as a typical low strength refractory ceramic. The calculation of thermal shock resistance parameters for the composites and the monolith has indicated possible explanations for the differences in thermal shock behaviour.

The thermal shock behaviour of ductile particle toughened alumina composites

A stabilizable preform precursor for composites is provided. The preform precursor has at least one layer of a structural fabric comprised of reinforcing fibers wherein at least one of the layer(s) of structural fabric has integrated therein one or more stabilizing fiber(s) that dissolves at a dissolution temperature in a resin for infusing into the structural fabric to make the composite. The stabilizing fiber stabilizes the stabilizable preform precursor when the stabilizable preform precursor is subjected to an elevated temperature.

Matt Aldridge

Papers

The thermal shock behaviour of ductile particle toughened alumina composites

Stabilizable preform precursors and stabilized preforms for composite materials and processes for stabilizing and debulking preforms