Static and cyclic creep behavior of in situ TiB 2 particulate reinforced aluminum composite
- PDF / 381,751 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 15 Downloads / 191 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Static and cyclic creep behavior of in situ TiB2 particulate reinforced aluminum composite Z.Y. Ma and S.C. Tjonga) Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong
S.X. Li State Key Laboratory for Fatigue and Fracture of Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, People’s Republic of China (Received 20 April 1999; accepted 2 September 1999)
Static and cyclic creep tests of Al–15 vol% TiB2 in situ composite were carried out at 573–623 K. The values of apparent stress exponent and activation energy for cyclic creep of the composite were much higher than that for static creep. Furthermore, the cyclic creep rate tended to decrease with increasing percentage of unloading amount but was independent of the loading frequencies under the frequency ranges investigated. Finally, the true stress exponent of the composite was equal to 8, and the true activation energy was close to the value for the lattice self-diffusion of aluminum by incorporating a threshold stress for the analysis.
I. INTRODUCTION
Discontinuously reinforced aluminum matrix composites (DRAMCs) exhibit several favorable characteristics, such as low rate material costs, near-isotropic properties, and ease of fabrication into complicated shapes. The potential applications of the DRAMCs at high-temperature environments have prompted many researchers to investigate their creep behavior. One common feature of the creep characteristics of DRAMCs is that they exhibit both very high values of the apparent stress exponent and apparent activation energy for steady-state creep.1–19 These values cannot be interpreted by the existing theoretical or phenomenological models for dislocation creep. To rationalize the high stress exponent and activation energy, the concept of the effective stress, i.e., the applied stress minus a threshold stress, is adopted. Such a stress is introduced to explain the creep of oxide dispersion strengthened (ODS) alloys.20 Furthermore, the strong stress and temperature dependence of the creep rate for the DRAMCs5–10,14–21 can be explained satisfactorily in terms of the threshold stress. In general, the characteristics, origin, and physical meaning of the threshold stress still remain controversial.7–10,12,14–19 It is widely accepted that the threshold stress obtained by the extrapolation technique is a function of temperature. For example, Gonzalez-Doncel and Sherby14 showed that the threshold stress compensated
a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 12, Dec 1999
http://journals.cambridge.org
Downloaded: 15 Mar 2015
by the modulus of Al–SiC composites exhibits a linear dependence on temperature. In this case, the threshold stress compensated by modulus is not thermally activated. However, Mohamed et al.9 reported that the threshold stress compensated by modulus of 6061Al– 30 vol% SiCp composite has an exponential depende
Data Loading...
