High-temperature Deformation Kinetics of Gold at 473K to 773K
- PDF / 262,014 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 378 Views
1137-EE04-10
High-temperature Deformation Kinetics of Gold at 473K to 773K Vineet Bhakhri, and Robert J. Klassen Mechanical & Materials Engineering, The University of Western Ontario, London, N6A 5B9,Canada ABSTRACT: High-temperature constant-force indentation creep tests of 200 seconds duration were performed on an annealed gold specimen at 473K to 773K, to investigate the dependence of the micro-/nano-indentation deformation kinetics upon indentation stress, temperature and time. The indent stress displayed a clear indentation size effect at 473 K. An analysis of the measured indentation creep rate, and its dependence upon temperature and stress, indicate that the strength of the deformation rate limiting obstacles increases with temperature. This is consistent with the expected temperature dependent evolution of the dislocation cell structure whose boundaries become the primary obstacles to dislocation glide.
INTRODUCTION: Instrumented indentation is a well established technique for the characterization of mechanical properties of a material at the nano- and micro-scales [1]. Its use has been prevalent at ambient test temperature however high-temperature indentation testing presents several practical challenges such as increased rates of electronic and thermal drift arising from the extreme thermal sensitivity of the sensing and actuating devices in an instrumented indentation tester [2]. While most indentation studies report mechanical properties, such as the hardness and the elastic modulus, of materials, few report on the extraction of kinetic parameters that describe the dependence of the rate of plastic deformation upon indentation stress and time [3,4]. The use of nano- and/or micro-indentation experiments to study the timedependent deformation of materials is generally performed with sharp-tip pyramidal indenter probes subjected to constant force over a prescribed length of time. During such Constant Force (CF) pyramidal indentation creep tests the indenter applies a high local stress state, represented by the average indentation stress σ ind , and the indented sample creeps which causes σ ind and the local indentation strain rate ε&ind to decrease continuously with time. The average indentation stress σ ind and local indentation strain rate ε&ind can be expressed, for a Berkovich indenter, as a function of the indentation depth h and the indentation velocity h& as
σ ind =
h& F and ε&ind = αA(h) h
(1)
Where A(h) is the area function of the indenter probe and α is an empirical factor accounting for the material sink-in or pile-up around the indenter. The σ ind and the ε&ind can be represented by an equivalent average indentation shear stress, τ ind and an equivalent average indentation shear strain rate γ&ind as
τ ind =
σ ind 3 3
and γ&ind = 3ε&ind =
3h& h
(2)
Since the local stress around the indentation is very large, the underlying deformation mechanism, in most ductile metals, is one involving obstacle-limited dislocation glide. The relationship between γ&ind and τ ind for this deformation
Data Loading...
