Investigation of Viscoelastic Properties of Amorphous Selenium near Glass Transition Using Depth‐Sensing Indentation

Abstract

New procedures involving depth-sensing indentation are used to measure the submicron scale elastic modulus, hardness, viscosity, and activation energy and volume for creep of amorphous selenium below glass transition. The accurate measurement of Young's modulus in a highly viscoelastic situation using depth-sensing indentation remains a challenge, and a creep correction procedure is employed here to measure the modulus. The measured Young's modulus exhibits a strong decreasing trend from 10 GPa to 4.4 GPa as temperature increases from 302 K to 309 K, in reasonably good agreement with bulk behavior. Two new procedures are also proposed here to measure the viscosity. The measured shear viscosity decreases from 1 Â 10 12 Pa-s to 2 Â 10 10 Pa-s when the temperature increases over the same range, and the variation with temperature is found to obey an Arrehnius rate equation. The activation energy for the viscous creep process is found to be 463 kJ/mol. Both the viscosity and the activation energy are lower than the bulk values, and this is thought to be due to the much higher stress levels of over 200 MPa involved in the nanoindentation 125 experiments here. The apparent activation volume exhibits a rising trend from 1.04 Â 10 231 to 2.35 Â 10 230 m 3 over the same temperature range.

Continuous Strain Bursts in Crystalline and Amorphous Metals During Plastic Deformation by Nanoindentation

“…The deformation of amorphous selenium was found to be smooth with no unambiguous bursts. This is not surprising, as room temperature is already a very high homologous temperature compared to the glass transition temperature of about 35-40°C, 15 and so deformation at this temperature is likely to occur by bulk viscous flow, which should be very smooth with little discrete internal obstacles. On the other hand, serrated flow is a wellknown phenomenon in metallic glass at room temperature, and is thought to be due to the operation of shear bands in the amorphous structure.…”

The use of nanoindentation for characterizing the properties of mineralized hard tissues: State‐of‐the art review

“…Thus, corrections for viscoelasticity are needed to avoid errors in the computed values of the nanomechanical properties. Tang et al 8,9 have presented a method for correcting for viscoelastic effects when bone tissue specimens are tested. The method involves assuming a Maxwell law-type viscoelastic model to derive the real elastic contact stiffness, S e , and substituting S e for S u in Eq.…”

An improved method for the measurement of mechanical properties of bone by nanoindentation

“…The basic assumption involved in this method is that the sample behaves purely elastically during unloading, but biological tissues such as bone are well-known to be viscoelastic in both the macroscopic level [16] as well as the microstructural level [5,9,10,12]. Material viscoelastic effects during unloading are well-known to lead to erroneous results in the estimation of contact stiffness and area using the Oliver-Pharr method [17][18][19][20][21][22][23][24], and in the past, increasing the holding time before unloading and increasing the unloading rate have been suggested as effective procedures to reduce viscoelastic effects during unloading [12,14,15]. As applied to very soft materials including most biological tissues, since the severity of the viscoelasticity depends on a complicated convolution of the peak load, the holding duration before unloading and the unloading rate [18], it is seldom known whether a subjective choice of the pre-unloading holding duration and unloading rate can in fact be effective in suppressing viscoelastic effects.…”