ABSTRACT
The effectiveness of the nanoindentation technique in understanding the mechanical properties of a fiber-reinforced composite at the local microstructural length scale has been established with ample credence in Chapter 23. Now we shall be discussing the nanoindentation study on the multilayer ceramics matrix composites (MLCC), mainly developed by the tape casting method. The MLCC materials are capable of sustaining enhanced strain to failure, i.e., they show damage tolerance [1-4]. In such composites, the sequential failure of each layer is usually accompanied by a load drop, i.e., stress decrement [1-3]. The crack propagation can take place along the interfacial layer, which should be a low-failure-energy material called the weak interface. This interface could be weak with a low-strength, low-toughness material such as graphite; porous materials; or a low-strength but more damage-tolerant plastic material such as glass-fiber-reinforced polymer (GFRP) or carbon-fiberreinforced polymer (CFRP) [1-4]. The interface can also contain a soft, easily deformable phase like MoSi2. Lanthanum phosphate (LP) is reported to form a weak interface with alumina, zirconia, as well as zirconia-toughened alumina (ZTA) [1, 2]. Crack deflection is then expected to take place at the weak interface, leading to an increase in crack path and, hence, an enhancement in the failure energy. Our point of interest here is on the nanoindentation responses of the individual component layers of the tape-cast, sintered alumina/lanthanum phosphate/alumina (A/LP/A) MLCC architecture, which had shown a damage-tolerant characteristic [1-3]. A typical photomicrograph of the MLCC shows an interfacial crack growth during a high-load Vickers microindentation (Figure 24.1). In fact, the particulate A/LP composites have been developed to achieve machinable ceramics [4-7]. However, we have found [1, 2] that nanoindentation studies of the individual elements of tape-cast A/LP/A MLCC are yet to be explored.
