High Toughness Ceramic Laminates by Design of Residual Stresses
- PDF / 3,673,341 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 0 Downloads / 211 Views
High Toughness Ceramic Laminates by Design of Residual Stresses Nina A. Orlovskaya, Jakob Kuebler1, Vladimir I. Subotin2, Mykola Lugovy3 Department of Materials Engineering, Drexel University, Philadelphia, PA, 19104, U.S.A. 1 Department of High Performance Ceramics, EMPA, Duebendorf, CH-8600, Switzerland 2 Institute for Problems of Materials Science, Kiev, 03142, Ukraine 3 Université Catholique de Louvain-la-Neuve, Louvain-la-Neuve, 1348, Belgium
ABSTRACT
Multilayered ceramic composites are very promising materials for different engineering applications. Laminates with strong interfaces can provide high apparent fracture toughness and damage tolerance along with the high strength and reliability. The control over the mechanical behavior of laminates can be obtained through design of residual stresses in separate layers. Here we report a development of tough silicon nitride based layered ceramics with controlled compressive and tensile stresses in separate layers. We design laminates in a way to achieve high compressive residual stresses in thin (100-150 micron) Si3N4 layers and low tensile residual stresses in thick (600-700 micron) Si3N4-TiN layers. The residual stresses are controlled by the amount of TiN in layers with residual tensile stresses and the layers thickness. The fracture toughness of pure Si3N4(5wt%Y2O3+2wt%Al2O3) ceramics was measured to be of 5 MPa m1/2, while the apparent fracture toughness of Si3N4/Si3N4-TiN laminates was in the range of 7-8 MPa m1/2 depending on the composition and thickness of the layers.
INTRODUCTION
Layered ceramics with a strong interface is a very promising material for crosscutting industrial applications since it has high fracture toughness, strength, damage tolerance and improved reliability [1]. The way to achieve the highest possible mechanical properties is to control the level of residual stresses in separate layers. There is a possibility to increase the fracture toughness of ceramics by creating a layer with compressive stresses on the surface and in such a way, arrest the surface cracks and achieve higher failure stresses. The variable layer composition, as well as the system's geometry, allows the designer to control the magnitude of the residual stresses in such a way that compressive stresses in the outer layers near the surface increase strength, flaw tolerance, fatigue strength, resistance to oxidation and stress corrosion cracking. In the case of symmetrical laminates, this can be done by choosing the layer compositions such that the coefficient of thermal expansion (CTE) in the odd layers is smaller than the CTE of the even ones. The changes in compressive and tensile stresses depend on the mismatch of CTE's, Young's moduli, as well as on the thickness ratio of layers (even/odd). U8.7.1
Silicon nitride is the most promising and well-developed ceramics for structural application because of its outstanding mechanical properties as well as its superior wear resistance. The addition of TiN to Si3N4 leads to an increase of Young's modulus, electrical condu
Data Loading...
