JOURNAL OF MATERIALS SCIENCE 40(2005)5443-5450 Design of Si3N4-based ceramic laminates by the residual stresses N. ORLOVSKAYA Drexel University, Philadelphia, PA 19104, USA E-mail: orlovsk @ drexeledu J KUEBLER EMPA, Swiss Federal Laboratories for Materials Testing and Research, CH-8600 Duebendorf switzerland V. SUBBOTIN M. LUGOVY Institute for Problems of materials science, 03142 Kiev Ukraine Ceramic laminates with strong interfaces between layers are considered a very promising material for different engineering applications because of the potential for increasing fracture toughness by designing high residual compressive and low residual tensile in separate layers. In this work, Si3 Na/Si3N4-TiN ceramic laminates with strong interfaces were manufactured by rolling and hot pressing techniques. The investigation of their mechanical properties has shown that the increase in apparent fracture toughness can be achieved for the Si3N4/Si3 N4-20 wt %TiN composite, while further increase of Tin content in the layers with residual tensile stresses lead to a formation of multiple cracks, and as a result, a significant decrease in the mechanical performance of the composites Micro-Raman spectroscopy was used to measure the frequency shift across the Si3Na/Si3N4-20 wt %TiN laminate. These preliminary Raman results can be useful for further analysis of residual stress distribution in the laminate 2005 Springer Science Business Media, Inc 1. Introduction apparent fracture toughness of ceramics by creating a Ceramics have found their use in numerous crosscut- layer with compressive stresses on the surface. In such a ng industrial applications because of excellent hard- way, surface cracks will be arrested and achieve higher ness, wear, corrosion resistance, and ability to with- failure stresses [5]. The variable layer composition,as stand high temperatures. However, ceramics'reliabil- well as the systems geometry, allows the designer to y and ductility compared to metals are not very high. control the magnitude of the residual stresses in such a The best approach to increasing the fracture toughness way that compressive stresses in the outer layers near which enables the structural application of ceramics is the surface increase strength, flaw tolerance, fatigue through the development of ceramic composites. Fiber strength, resistance to oxidation, and stress corrosion reinforced composites demonstrate the highest fracture cracking. In the case of symmetrical laminates, thi oughness and damage tolerance. However, since these can be done by choosing layer compositions such that materials have a very high density of weak interfaces, the coefficient of thermal expansion(CTE) of the odd they are not very strong. In addition, their high cost layers is smaller than the CtE of the even ones. The limits their commercial applications. Particulate com- changes in compressive and tensile stresses depend on posites are less expensive to manufacture, but com- the mismatch of CTE's, Youngs moduli, as well as on pared to monolithic ceramics, their fracture toughness the thickness ratio of layers(even/odd). However, if the increases are insignificant. The several publications on compressive stresses exist only at or near the surface ceramics show that the use of layered materials is the of ceramics and are not placed inside the material, they most promising method for controlling cracks by de- will not effectively hinder internal cracks and flaws flection, microcracking, or internal stresses [1-3]. Lay- [6, 7] ered structures clearly offer the key to greater reliabilit It is clear that control over the mechanical behay at a moderate cost and new applications may result as ior and reliability of laminates can be obtained only more complex structures are tailored to specific appli- through design, control of residual stresses, and redis- cations [4] tribution of stresses during loading in laminate mate The way to achieve the highest possible mechanical rials. The sign and value of residual stresses can be properties is to control the level of residual stresses in established by theoretical prediction. There exists a individual layers. One can increase the strength and theoretical background that allows for the design of 005 Springer Science Business Media, Inc. DOI:10.1007/s10853-005-1918-7 5443JOURNAL OF MATERIALS SCIENCE 4 0 (2 0 0 5 ) 5 4 4 3 –5 4 5 0 Design of Si3N4-based ceramic laminates by the residual stresses N. ORLOVSKAYA Drexel University, Philadelphia, PA 19104, USA E-mail: orlovsk@drexel.edu J. KUEBLER EMPA, Swiss Federal Laboratories for Materials Testing and Research, CH-8600, Duebendorf, Switzerland V. SUBBOTIN, M. LUGOVY Institute for Problems of Materials Science, 03142, Kiev, Ukraine Ceramic laminates with strong interfaces between layers are considered a very promising material for different engineering applications because of the potential for increasing fracture toughness by designing high residual compressive and low residual tensile stresses in separate layers. In this work, Si3N4/Si3N4-TiN ceramic laminates with strong interfaces were manufactured by rolling and hot pressing techniques. The investigation of their mechanical properties has shown that the increase in apparent fracture toughness can be achieved for the Si3N4/Si3N4-20 wt.%TiN composite, while further increase of TiN content in the layers with residual tensile stresses lead to a formation of multiple cracks, and as a result, a significant decrease in the mechanical performance of the composites. Micro-Raman spectroscopy was used to measure the frequency shift across the Si3N4/Si3N4-20 wt.%TiN laminate. These preliminary Raman results can be useful for further analysis of residual stress distribution in the laminate.
C 2005 Springer Science + Business Media, Inc. 1. Introduction Ceramics have found their use in numerous crosscut￾ting industrial applications because of excellent hard￾ness, wear, corrosion resistance, and ability to with￾stand high temperatures. However, ceramics’ reliabil￾ity and ductility compared to metals are not very high. The best approach to increasing the fracture toughness which enables the structural application of ceramics is through the development of ceramic composites. Fiber reinforced composites demonstrate the highest fracture toughness and damage tolerance. However, since these materials have a very high density of weak interfaces, they are not very strong. In addition, their high cost limits their commercial applications. Particulate com￾posites are less expensive to manufacture, but com￾pared to monolithic ceramics, their fracture toughness increases are insignificant. The several publications on ceramics show that the use of layered materials is the most promising method for controlling cracks by de- flection, microcracking, or internal stresses [1–3]. Lay￾ered structures clearly offer the key to greater reliability at a moderate cost and new applications may result as more complex structures are tailored to specific appli￾cations [4]. The way to achieve the highest possible mechanical properties is to control the level of residual stresses in individual layers. One can increase the strength and apparent fracture toughness of ceramics by creating a layer with compressive stresses on the surface. In such a way, surface cracks will be arrested and achieve higher failure stresses [5]. 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 layer compositions such that the coefficient of thermal expansion (CTE) of 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). However, if the compressive stresses exist only at or near the surface of ceramics and are not placed inside the material, they will not effectively hinder internal cracks and flaws [6, 7]. It is clear that control over the mechanical behav￾ior and reliability of laminates can be obtained only through design, control of residual stresses, and redis￾tribution of stresses during loading in laminate mate￾rials. The sign and value of residual stresses can be established by theoretical prediction. There exists a theoretical background that allows for the design of 0022-2461
C 2005 Springer Science + Business Media, Inc. DOI: 10.1007/s10853-005-1918-7 5443