Interactions between toughening mechanisms: Transformation toughening versus plastic deformation
- PDF / 208,734 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 266 Views
Rong-Zhi Chen High Temperature Materials Sec., Materials & Electro-Optics Research Division, Chung-Shan Institute of Science and Technology, Lung-tan, Tao-Yuan 325, Taiwan, Republic of China (Received 10 May 2002; accepted 22 August 2002)
In this study, the interactions between transformation toughening and plastic stretching were investigated experimentally. Zirconia and metals, nickel or silver, were incorporated simultaneously into an alumina matrix. The extent of phase transformation of zirconia particles was enhanced due to the coexistence of soft metals. The ductility of nickel was also enhanced in the Al2O3–Ni–ZrO2 composites. However, the presence of zirconia particles at the alumina/silver interface reduced the ability of silver to deform plastically. Due to the interactions, the ratio of composite toughness to matrix toughness for the Al2O3–Ni–ZrO2 composite was higher than the product of the ratio of the composites containing only nickel and only zirconia.
I. INTRODUCTION
The brittle nature of ceramics hinders their applications as structural components. Two alternatives are adopted to solve the problems.1,2 One alternative refines the processing details to reduce the flaw size in ceramics. The strength is consequently enhanced although the toughness remains low. The other approach targets the toughness improvement through the addition of toughening reinforcement. Ceramic or metallic reinforcement is incorporated into a ceramic matrix. The reinforcement interacts with the pre-existing and/or service-induced cracks to slow down their propagation. The toughness of the brittle matrix is thus improved through such interactions. Although the reinforcement also acts as stressconcentration site, the strength may be sacrificed slightly by adopting this approach. However, the latter approach is attractive because the reliability of ceramics during subsequent usage may be improved significantly. The development of tough ceramic-matrix composites has thus been thoroughly studied since 1982.1 Many ceramic or metallic materials, such as zirconia,3 nickel,4 and silver5 have been used as toughening reinforcements. The presence of these toughening agents enhances the toughness of ceramics through the generation of various toughening mechanisms. These toughening mechanisms may be active either in a process zone around the major crack or in bridging crack surfaces.6 The propagation of cracks is hampered due to the effect of these mechanisms, resulting in an increase in the toughness of ceramics. However, the presence of a single toughening J. Mater. Res., Vol. 17, No. 11, Nov 2002
http://journals.cambridge.org
Downloaded: 12 Apr 2015
agent frequently induces more than one toughening mechanism. For example, the addition of zirconia particles can induce transformation toughening, microcrack toughening, and crack deflection mechanisms.7 The metallic inclusions can either bridge the crack surfaces through their plastic deformation4,5 or deflect the crack.5 These mechanisms operate simultaneously to a different extent wi
Data Loading...
