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Using the magnetron sputtering technique, two typical high-entropy alloy (HEA) films namely CoCrFeNiCu (Al-0) with a face-centered cubic (fcc) structure and CoCrFeNiCuAl 2.5 (Al-2.5) with a body-centered cubic (bcc) structure were prepared by alloy targets. The as-deposited HEA films have a columnar-growth mode and nanocrystalline grains. The creep behaviors of both HEA films were systematically investigated by nanoindentation with a Berkovich indenter. The bcc Al-2.5 exhibited a stronger creep resistance than the fcc Al-0. In addition, with the increase of holding load and/or loading rate, the creep deformation was significantly enhanced in the fcc Al-0. Interestingly, it was almost history-independent in the bcc Al-2.5. The creep characteristics of HEA films could be related to the distinct lattice structures, which apparently affect the kinetics of plastic deformation. The strain rate sensitivity (SRS) and activation volume of the dislocation nucleation were carefully estimated for both HEA films. In view of the large differences of activation volumes between Al-0 and Al-2.5, we present discussions to explain the observed creep characteristics in HEA films.

Phase change materials (PCMs) are gaining increasing attention and becoming popular in the thermal energy storage field. Microcapsules enhance thermal and mechanical performance of PCMs used in thermal energy storage by increasing the heat transfer area and preventing the leakage of melting materials. Nowadays, a large number of studies about PCM microcapsules have been published to elaborate their benefits in energy systems. In this paper, a comprehensive review has been carried out on PCM microcapsules for thermal energy storage. Five aspects have been discussed in this review: classification of PCMs, encapsulation shell materials, microencapsulation techniques, PCM microcapsules’ characterizations, and thermal applications. This review aims to help the researchers from various fields better understand PCM microcapsules and provide critical guidance for utilizing this technology for future thermal energy storage.

a b s t r a c tUsing the magnetron sputtering technique, two metallic glassy films namely Cu 44.3 Zr 45.1 Al 10.6 and Cu 44.2 Zr 43 Al 11.3 Ti 1.5 were prepared by alloy targets. The minor Ti addition effectively induces excess free volume. Upon spherical nanoindentation, the creep behaviors of both films were studied at various peak loads. As the increase of peak load, the creep deformations became more severely in both samples. Interestingly, Cu-Zr-Al-Ti film crept stronger than Cu-Zr-Al at small-load holdings (nominal elastic regimes), whereas it is opposite at high-load holdings (plastic regimes). The creep characteristic could be intrinsically related to the scale variation of the shear transformation zone (STZ) with Ti addition. Statistical analysis was employed to estimate the STZ volume, which increased by 60% with Ti addition in the Cu-Zr-Al film. The finite element modeling indicated that STZs would be activated even at the minimum load we adopted. Higher activation energy of larger STZs in Cu-Zr-Al-Ti enables less flow units, which offsets the creep enhancement by the excess free volume with Ti addition. The deeper the pressed depth of the indenter, the more contribution of the STZ operation on creep deformation. In addition, experimental observation on the creep flow rates implies that STZ could be the dominating mechanism at the steady-state creep. This study reveals that STZ volume could also be important to the time-dependent plastic deformation in metallic glass, besides as a key parameter for instantaneous plasticity.

Friction stir welding (FSW) is a promising welding method for welding dissimilar materials without using welding flux. In the present work, 5A06-H112 and 6061-T651 aluminium alloys were successfully welded by friction stir welding with forced air cooling (FAC) and natural cooling (NC). Nanoindentation tests and microstructure characterisations revealed that forced air cooling, which can accelerate the cooling process and suppress the coarsening of grains and the dissolution of precipitate phases, contributes to strengthening and narrowing the weakest area of the joint. The tensile strength of joints with FAC were commonly improved by 10% compared to those with NC. Scanning electron microscopy (SEM) images of the fracture surface elucidated that FSW with FAC tended to increase the number and reduce the size of the dimples. These results demonstrated the advantages of FSW with FAC in welding heat-sensitive materials and provide fresh insight into welding industries.

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a b s t r a c tThis paper presents a convenient method which is referred to as "Revised Step-Hold" method for determination of shear creep compliance of linear viscoelastic-plastic solids using instrumented indentation. Its main idea is using the revised load-depth curve which does not contain plastic deformation to determine the shear creep compliance instead of using the measured load-depth curve. The revised load-depth curve can be obtained through a three-step procedure. Applications are illustrated on two typical viscoelasticplastic solids, namely PMMA and UPVC. The shear creep compliance of PMMA and UPVC determined by the revised step-hold method has satisfactorily good agreement with the corresponding uniaxial tensile result. Therefore, it demonstrates that the revised step-hold method is a reliable method for determination of shear creep compliance of linear viscoelastic-plastic solids.

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