Tailored Residual Stresses in High Reliability Alumina‐Mullite Ceramic Laminates

Abstract

A design and processing approach to fabricate ceramic laminates with high mechanical reliability, i.e., high failure resistance, limited strength scatter, and increased damage tolerance is presented in this paper. Different ceramic layers are stacked together to develop a specific residual stress profile after sintering. By changing the composition of the laminae and the composite architecture it is possible to produce a material with predefined failure stress which can be evaluated from the fracture toughness curve correlated to the residual stresses. In addition, by tailoring the fracture toughness curve, surface defects can be forced to grow in a stable way before reaching the critical condition, thus obtaining a unique-value strength ceramic material. Laminates composed of alumina/mullite composite layers are designed and created in this work by the implementation of the proposed approach. The material obtained shows a ''constant'' strength of 456 MPa (standard deviation o7%) even when large surface damage is produced by Vickers indentation.

Loading configuration effects on the strength reliability of alumina–zirconia multilayered ceramics

“…Although it is welldocumented that multilayered ceramics exhibit an enhanced fracture behaviour , independent of the specific loading configuration under consideration, i.e. with loading axis either parallel (transverse flexure) [11] or perpendicular (longitudinal flexure) [17,23,24] to the layer plane, studies where the mechanical strength of such multilayered systems are directly compared as a function of loading orientation are quite scarce. In this regard, a recent work from R.J.…”

“…As an extension of this lamina r ceramic/fibre-reinforced concept, multilayered architectural designs have also been attempted in many ways aiming to improve both the resistance to crack propagation and the mechanical reliability of ceramic components [11,[14][15][16][17] . This approach has demonstrated to be less cost effective than the one based on fibre structures and more accurate in terms of tailoring mechanical 3 requirements.…”

Processing and characterisation of cermet/hardmetal laminates with strong interfaces

“…They have been proposed as an alternative for the design of structural ceramics with improved fracture toughness, strength and mechanical reliability [13][14][15][16][17][18][19][20][21][22][23][24][25]. Good results have also been obtained in metal-ceramic [26] and metal-intermetallic laminates [27,28].…”

“…In the former case, the effect of the compressive residual stresses results in a higher, but single-value, apparent fracture toughness together with enhanced strength (the main goal) and some improved reliability [13,14,32]. In the latter case, the internal compressive layers are designed to act rather as a stopper to any potential crack growing from processing and/or machining flaws, at or near the surface layers such that failure tends to take place under conditions of maximum crack growth resistance [15,17,18,21].…”

Modelling of edge crack formation and propagation in ceramic laminates using the stress–energy coupled criterion

“…In an attempt to reduce the level of uncertainty in mechanical strength and to overcome the lack of toughness of structural and functional ceramics, newer approaches have been developed in which knowledge about the energy release mechanisms has resulted in the creation of "flaw tolerant" materials (i.e. reducing strength variability), with improved fracture toughness [9,10,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27].…”