New ultra-high temperature nanoindentation system for operating at up to 1100 °C

Self Cite

Body-centered cubic metals like molybdenum and tungsten are interesting structural materials for high-temperature applications. These metals, are however, brittle at low homologous temperature, caused by the limited mobility of screw dislocations. In this study, the thermally activated deformation mechanisms in bcc Mo have been investigated using strain rate jump nanoindentation and compression tests as well as Charpy V-notch impact testing. The material shows a significant softening with increasing temperature and a maximum in strain rate sensitivity is found at the critical temperature, before decreasing again in the ductile regime. The activation volume, however, showed a distinct increase from about 5 b3 at the onset of the brittle to ductile transition temperature. Here we propose to use temperature-dependent nanoindentation strain rate jump testing and the activation volume as a complementary approach to provide some indication of the brittle to ductile transition temperature of bcc metals. Graphic Abstract

Section: Discussionmentioning

confidence: 99%

Thermally activated dislocation mechanism in Mo studied by indentation, compression and impact testing

Minnert

Rehman

Durst

2021

Self Cite

“…Over the last decade, substantial advances in the nanoindentation (also known as instrumented or depth-sensing indentation) systems and new test protocols have opened new directions to study the small-scale mechanical properties [63][64][65]. For example, fast time constant (10's of µs) and high data acquisition rates (close to MHz) [66] allow to capture various events (e.g., slip transmission across the GB [67][68][69][70], phase transformation [71,72], cracking [73][74][75][76], etc.)…”

Section: Introductionmentioning

confidence: 99%

Dislocation–grain boundary interactions: recent advances on the underlying mechanisms studied via nanoindentation testing

Javaid

Pouriayevali

2021

Self Cite

To comprehend the mechanical behavior of a polycrystalline material, an in-depth analysis of individual grain boundary (GB) and dislocation interactions is of prime importance. In the past decade, nanoindentation emerged as a powerful tool to study the local mechanical response in the vicinity of the GB. The improved instrumentation and test protocols allow to capture various GB–dislocation interactions during the nanoindentation in the form of strain bursts on the load–displacement curve. Moreover, the interaction of the plastic zone with the GB provides important insight into the dislocation transmission effects of distinct grain boundaries. Of great importance for the analysis and interpretation of the observed effects are microstructural investigations and computational approaches. This review paper focused on recent advances in the dislocation–GB interactions and underlying mechanisms studied via nanoindentation, which includes GB pop-in phenomenon, localized grain movement under ambient conditions, and an analysis of the slip transfer mechanism using theoretical treatments and simulations. Graphical abstract

“…As the modulus is directly proportional to the contact stiffness [33], any uncertainty in load frame stiffness directly impacts the modulus determination. Hence, caution needs to be exercised in applying the often-used constant modulus assumption [34], wherein the contact stiffness and a known value of modulus are used to eliminate the need to know the displacement or area function to determine hardness. Any error in stiffness due to plasticity will lead to errors in hardness determination in such cases, and hence it is preferable to use the new method wherein the plasticity error is minimized and constant with depth.…”

Section: Experimental Assessment Of the New Methodologymentioning

confidence: 99%

Measurement of hardness and elastic modulus by load and depth sensing indentation: Improvements to the technique based on continuous stiffness measurement

Phani

Oliver²,

Pharr

2021

The method to measure hardness and elastic modulus of small volumes of material by instrumented indentation was developed in the early works of Oliver and Pharr (1992, 2004). This helped to establish the field of small scale nanomechanical testing. Since then, several advances in measurement electronics have enabled testing over a wider range of test conditions (speeds) using methodologies that were developed earlier. Here, we present an updated overview of the various factors that affect the precision and accuracy of the nanoindentation test results at different test conditions with specific focus on the continuous stiffness measurement technique (CSM). A step-by-step procedure for performing a CSM based indentation test is presented. In addition, calibration procedures that yield the best possible precision and accuracy at the chosen test conditions are also presented. Finally, we present an assessment and comparison of the different testing procedures.