Thermally Activated Deformation Behavior of ufg-Au: Environmental Issues During Long-Term and High-Temperature Nanoindentation Testing

Abstract

For testing time-dependent material properties by nanoindentation, in particular for long-term creep or relaxation experiments, thermal drift influences on the displacement signal are of prime concern. To address this at room and elevated temperatures, we tested fused quartz at various contact depths at room temperature and ultra-fine grained (ufg) Au at various temperatures. We found that the raw data for fused quartz are strongly affected by thermal drift, but corrected by use of dynamic stiffness measurements all the datasets collapse. The situation for the ufg Au shows again that the data are only useful with drift correction, but with this applied it turns out that there is a significant change of elastic and plastic properties when exceeding 200°C, which is also reflected by an increasing strain rate sensitivity.

Advanced Nanoindentation Testing for Studying Strain-Rate Sensitivity and Activation Volume

“…Applying this dynamic correction protocol to several data sets shows extensively that the mentioned differences in displacement signal just collapse to one reproducible curve, as demonstrated in Ref. 34 .…”

“…To investigate the environmental influences during nanoindentation creep testing at room temperature, Maier et al 34 performed two individual constant load indentations for 2 h at four different indentation depths on the reference material fused quartz. They found that the displacement signal for all indentations showed some significant scatter that obviously could not be explained with actual mechanical properties.…”

“… 10 But also for indentation systems with an independently heated tip and sample, a reduction of thermal drift issues especially during the indentation times was demonstrated for ufg-Au. 34 …”

“…Since nanoindentation testing is a common tool to probe mechanical properties and is not limited anymore to ambient conditions, several methods and protocols can also be used for high-temperature testing. Results of both nanoindentation strain-rate jump tests 8 , 17 , 35 , 68 as well as nanoindentation creep tests 26 – 28 , 34 are reported over a wide range of temperatures and strain-rates, shedding more light on local thermally activated deformation processes. High temperature testing, however, leads to further challenges regarding thermal stability and testing procedures.…”

“…Besides the successful determination of positive SRS, few studies report experiments and results of negative SRS. 31 , 32 Moreover, many other investigations dealing with various materials systems, such as glasses 32 – 34 or intermetallic phases, 35 can also be found.…”