Instrumented nanoindentation investigation into the mechanical behavior of ceramics at moderately elevated temperatures
- PDF / 486,413 Bytes
- 12 Pages / 584.957 x 782.986 pts Page_size
- 58 Downloads / 239 Views
Jianye Wang, Naeem Ur-rehman, and Constantin Ciurea Centre for Advanced Structural Ceramics, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom; and Department of Materials, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
Finn Giuliani Centre for Advanced Structural Ceramics, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom; and Department of Materials, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom; and Department of Mechanical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
Luc J. Vandeperre Centre for Advanced Structural Ceramics, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom; and Department of Materials, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom (Received 5 May 2011; accepted 19 July 2011)
An analysis of indentation hardness data from three ceramic materials, zirconium diboride, silicon carbide, and titanium nitride, is presented to extract the fundamental deformation parameters at 295 to 623 K. The measured activation volume was of the order of 1 b3 to 4 b3 (b is the Burgers vector). The calculated activation energies were in the range of 0.75 to 1.61 eV and are typical of lattice-controlled dislocation glide mechanism. Using finite difference simulations, it was demonstrated that there is a significant difference between the plastic strain rate and the total strain rate for materials showing substantial elastic deformation (i.e., large hardness/elastic modulus ratio). Therefore, the measured total strain rates must be converted into plastic strain rates, which require a reduction during loading and an increase during the dwell at maximum load. Additionally, importance of quantification of instrumental thermal drift was discussed and use of either short duration indentation tests or high loads was emphasized.
I. INTRODUCTION
Ceramics in either bulk or thin film form have found considerable use where high temperatures and stresses are encountered, e.g., coatings for cutting tools or ceramic bearings. Furthermore, it has been observed that the hardness of these materials drops rapidly with temperature and more importantly that the room temperature hardness is not always a reliable indicator of the high temperature properties, see Fig. 1.1–7 Given the considerable work done by Tabor,8–10 Marsh,11 Johnson,12 and many others, see e.g., Refs. 13–25, a clear link between the measured hardness and the uniaxial yield stress has now been established, provided other deformation mechanisms such as compaction,26–28 phase transformations,29–32
dc ¼ qm b v ; dt
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.246 J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
http://journals.cambridge.org
and cracking33 are suppressed. Thus, it is reasonable to assume that the rapid change in hardness with temperature must be related
Data Loading...
