Materials are typically ductile at higher temperatures and become brittle at lower temperatures. In contrast to the typical ductile-to-brittle transition behavior of body-centered cubic (bcc) steels, we observed an inverse temperature dependence of toughness in an ultrahigh-strength bcc steel with an ultrafine elongated ferrite grain structure that was processed by a thermomechanical treatment without the addition of a large amount of an alloying element. The enhanced toughness is attributed to a delamination that was a result of crack branching on the aligned {100} cleavage planes in the bundles of the ultrafine elongated ferrite grains strengthened by nanometer-sized carbides. In the temperature range from 60° to –60°C, the yield strength was greater, leading to the enhancement of the toughness.

The development of efficient, low-cost and highly sensitive chemical sensors that can monitor trace amounts of volatile organic compounds (VOCs) has become indispensable for industrial and biomedical applications. Here, we demonstrate a high-performance and flexible VOC sensor based on a 3D Mxene framework (3D-M). The 3D-M was prepared through an effective electrospinning technique coupled with a self-assembly approach. The resulting 3D-M sensor can perform at room temperature, and displays a high sensitivity to extremely low concentrations of VOCs (ppb level) due to its highly interconnected porous structure, which enable the easy access and diffusion of gas molecules. Furthermore, the sensor also exhibits an ultra-wide sensing range (from 50 ppb up to a saturated vapor), fast response and recovery (less than 2 min), and good reversibility and flexibility (no performance decrease for 1000 bending cycles) for various VOCs (e.g. acetone, methanol and ethanol), demonstrating a great potential for both industrial and biomedical applications.

Layered composite materials have become an increasingly interesting topic in industrial development. Cold roll bonding (CRB), as a solid phase method of bonding same or different metals by rolling at room temperature, has been widely used in manufacturing large layered composite sheets and foils. In this paper, we provide a brief overview of a technology using layered composite materials produced by CRB and discuss the suitability of this technology in the fabrication of layered composite materials. The effects of process parameters on bonding, mainly including process and surface preparation conditions, have been analyzed. Bonding between two sheets can be realized when deformation reduction reaches a threshold value. However, it is essential to remove surface contamination layers to produce a satisfactory bond in CRB. It has been suggested that the degreasing and then scratch brushing of surfaces create a strong bonding between the layers. Bonding mechanisms, in which the film theory is expressed as the major mechanism in CRB, as well as bonding theoretical models, have also been reviewed. It has also been showed that it is easy for bcc structure metals to bond compared with fcc and hcp structure metals. In addition, hardness on bonding same metals plays an important part in CRB. Applications of composites produced by CRB in industrial fields are briefly reviewed and possible developments of CRB in the future are also described.

The effects of grain boundary (GB) character and impurity contamination on the recombination activity of grain boundaries (GBs) in multicrystalline silicon (mc-Si) were systematically studied through an electron-beam-induced current (EBIC) technique. First, clean GBs of various characters were checked at 300 and $100\mathrm{K}$ . The EBIC contrasts of these GBs were in the same range of 0%–2% at $300\mathrm{K}$ and 2%–4% at $100\mathrm{K}$ , suggesting that the recombination activity of clean GBs is weak and the GB character has no significant effect on it. Second, the effect of impurities was studied by comparing the EBIC contrasts of the same type of the GBs in mc-Si with different Fe contamination levels. The recombination activity of GBs became stronger as the contamination level rose. The variation in the recombination activity related to the GB character was also observed in these specimens. The random or high-$\Sigma$ GBs showed a stronger EBIC contrast than the low-$\Sigma$ GBs. Moreover, we found that the EBIC contrast was not uniform along one $\Sigma 3$ GB. In a clean mc-Si, the variation in the EBIC contrast of different parts of the $\Sigma 3$ GB was 1% at $300\mathrm{K}$ , whereas it was more than 10% in the contaminated mc-Si. This indicates that not only the GB character but also the GB plane would affect the recombination activity of GBs. These results suggest that the recombination activity of GBs is principally determined by the gettering ability of GBs. Specifically, that random GBs may have the strongest gettering ability, whereas $\Sigma 3$ {111} has the weakest.