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Abstract In this study, creep behavior of the face-centered-cubic (FCC) {111} and {100} grains in single-phase Fe 20 Co 20 Ni 20 Cr 20 Mn 20 and dual-phase Fe 18 Co 18 Ni 20 Cr 18 Mn 18 Al 8 high-entropy alloys (HEAs) was evaluated using a nanoindentation method over temperatures range of 300–600 °C. We measured the creep response of the two different grain orientations in the two alloys in order to study the orientation and solid-solution effects. Creep stress exponent (∼3.8–5.0) and activation energy (240–260 kJ/mol) were extracted and analyzed from stain rate-stress and stain rate-temperature data to provide information on the creep mechanism. The results indicated that creep was controlled by dislocation climb in both alloys at both orientations. However, we pointed out that, based upon activation energy value alone, it was difficult to identify which elemental constituent would be the dominant diffusing species responsible for vacancy diffusion during the climb. It was found that creep activation volume for the current two HEAs (140 Å3 or ∼12Ω, where Ω is the atomic volume) at 600 °C is larger than that reported for the Ni-based superalloys (∼50–100 Å3 or less) within a similar temperature range. The significance of this larger activation volume is also discussed. Graphical abstract Image 1 Highlights • Nanoindentation creep responses in high entropy alloys are examined over 300–600 °C. • The extracted activation energy under the constant stress condition is around 260 kJ/mol. • The current high entropy alloys possess relatively large volume about 140 Å3 at 600 °C. [ABSTRACT FROM AUTHOR]

Abstract: The effects of O2 partial pressure during RF magnetron sputtering on the structural and nanomechanical properties of a-plane ZnO thin films were investigated by using X-ray diffraction (XRD) and nanoindentation techniques. The XRD and the transmission electron microscopy (TEM) selected area diffraction results indicate that the epitaxial relationship between ZnO thin films and Al2O3 substrates is ZnO //Al2O3 . The average values of the hardness and Young’s modulus of the a-plane ZnO films were found to decrease with increasing oxygen partial pressure. The cross-sectional TEM revealing the localized plastic deformation of ZnO thin films beneath the Berkovich indenter, indicating the prominent role played by the threading dislocations in the film deformation behavior. At higher indentation loadings, the sapphire substrate exhibits extensive deformation with narrow slip bands appearing on {0001} plane. However, no evidence of pressure-induced phase transformation, as well as cracking and/or delamination phenomena at the film–substrate interface was observed. [Copyright &y& Elsevier]

The influence of orientation and loading rate on the pop-in behavior of Ti 60 (AlCrVNb) 40 medium entropy alloy (MEA) under nanoindentation was investigated. The crystal structure of Ti 60 (AlCrVNb) 40 is a single body centered cubic phase, confirmed by both X-ray diffractometer and transmission electron microscopy. Nanoindentation experiments were carried out on the (100), (110) and (111) orientations and over loading rates of 10–500 μN/s. The incipient plasticity showed a clear orientation and loading rate dependences. Specifically, the (110) data exhibit the lowest pop-in load and pop-in displacement, and the associated loads of all orientations increase with increasing loading rate. In addition, the spread of the load at pop-in for (110) is narrower compared to those for (100) and (111), which is caused by the lower influence from defects on (110). The activation volume was estimated to be ~0.7 b3, which falls between those of conventional metals (~0.3 b3) and high entropy alloys (HEAs) (~1.7 b3), suggesting that dislocation activities in MEAs is more difficult than that in traditional metals but easier than that in HEAs. Such a medium activation volume implies that the onset of yielding is associated with a mixture of two mechanisms: heterogeneous nucleation of dislocation through atomic-sized precursors and/or expansion of dislocation loop by pre-existing dislocation multiplication. The crystalline orientation effects can be rationalized by the different densities and dislocation configurations resulted from the different numbers of activated slip systems and Schmid factors for different loading planes. • The orientation and rate effect on pop-in of BCC medium entropy alloy is investigated. • The orientation effects can be rationalized by the different Schmid factors. • The current BCC medium entropy alloy possesses medium activation volume. [ABSTRACT FROM AUTHOR]