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The deformation behavior of semi-crystalline polymers is strongly dependent on the morphology formed during processing. In this study, in-situ synchrotron X-ray was firstly used to identify the morphological distributions of injection-molded isotactic polypropylene (iPP) with different concentrations of β-nucleating agent. It was found that under relatively high concentration of β-nucleating agent (i.e., ≥0.03 wt.%), the outer region (skin and shear region) of the iPP was dominated by mainly highly oriented α-phase as well as certain amount γ-phase, while the core region was rich in β-crystals with little if any orientation. The addition of the β-nucleating agent was beneficial for the formation of lamellae with large lamellar stacking distance in the shear layer. Then the synchrotron X-ray was applied to study the structure variation of those morphology-identified samples under tensile deformation. It was found that voids and cavities along the stretching direction existed in the deformed iPP samples and their volume increased with increasing concentration of β-nucleating agent. The increased volume of void and cavity was associated with the β to α phase transition, which mainly occurred at the core region. In addition, upon stretching crystalline fragmentation and rearrangement took place following the formation of thinner lamellae. [ABSTRACT FROM AUTHOR]

Building nanocrystalline/amorphous biphase nanostructure has recently emerged as a new strengthening-toughening route that can combine the strengthening benefits of nanocrystallinity and amorphization. Therefore, it is required exploring on the strain rate-dependent deformation behavior with above different nanostructure in certain system. Herein, three typical nanostructures: polycrystalline, uniform nanocrystalline/amorphous core-shell nanostructure and amorphous matrix with nanoclusters, have been achieved in the sputtered Ti 2 AlNb films by individually regulating the sputtering bias voltage (U bias). Note that a high U bias can promote formation of Nb–rich amorphous tissues via Al preferential resputtering and Nb segregation. Moreover, microstructural evolution and strain rate-dependent hardness and deformation behavior were further explored. Firstly, at a low U bias (−40 V), Ti 2 AlNb film exhibited polycrystalline character; it yielded a relatively low hardness (~10.0 GPa) but a high strain sensitivity coefficient of 0.1505. Subsequently, the novel nanocrystalline/amorphous core-shell nanostructure consisting of Ti 2 AlNb nanocrystalline cores uniformly encapsulated by thin amorphous shells was achieved at a higher U bias (−120 V); this nanostructure provided a remarkable hardness enhancement (~15.2 GPa) without sacrificing its ductility and intermediate strain sensitivity coefficient of 0.1382. Finally, a transition to amorphous matrix with nanoclusters occurred with further increasing U bias to −200 V, thus yielding slight decrease in hardness (~12.5 GPa) and a minimum strain sensitivity coefficient of 0.0915 when shear-band deformation was activated. • High V b can induce Nb segregation to grain boundaries for triggering amorphization in the Ti 2 AlNb films. • The uniform nanocrystalline-amorphous dual-phase structure achieved at V b = −120 V • Vb induced microstructural evolution and strain rate-dependent hardness (H) and deformation behavior were further explored. [ABSTRACT FROM AUTHOR]

Abstract In this work, laminated Al/Ti composites were fabricated by hot rolling at three different temperatures (400 °C, 450 °C and 500 °C). The deformation behavior and fracture mechanism of composites were studied by the in-situ tensile test. The results indicated that the ductile shear fracture (for 400 °C and 450 °C rolled specimens) and ductile delamination fracture (for 500 °C rolled specimen) were the main fracture failure modes of Al/Ti multilayers. Results shown that the tensile load and displacement of the 500 °C prepared Al/Ti were better than other samples due to the higher rolling temperature. The changes of slip lines and plastic bands were the main plastic deformation characteristics for the Al layer and Ti layer metals, respectively. The investigation found that the major crack nucleation type in Ti layer was fold belt cracking. The slip bands cracking, cross-slip cracking, particle interface cracking and grain boundary slide cracking were the primary crack nucleation patterns for the Al layer. Highlights • The width variable and width strain expressions were put forward. • The different plastic deformation characteristics of Al and Ti layer were analyzed. • The crack nucleation mechanism was discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: Cavitation and superstructure evolution of polymers during stretching play crucial roles to influence the mechanical properties of materials. In this study, we investigated deformation-mediated superstructures and cavitation of poly (l-lactide) (PLA) as well as their dependence on stretching temperatures by in-situ small-angle X-ray (SAXS) analysis coupled with mechanical testing. It is found that the cavitation and crystalline deformation are strongly influenced by stretching stress during deformation, which significantly depends on the stretching temperature. At lower stretching temperature (70 °C), the cavitation is initiated before the yielding and then stimulates the crystallite shearing. At higher stretching temperature (90 °C), however, the crystallites shear firstly and then crystalline deformation promotes the formation of cavities orientated along the stretching direction. High stretching temperature benefits the formation of relatively perfect crystals with high orientation. The results provide the basic knowledge of how to adjust the mechanical properties of polymer materials by controlling their superstructure in the deformation process. [Copyright &y& Elsevier]

Abstract: The present work explored the structure-property correlations for the biopolymer poly(l-lactic acid) (PLA) by studying deformation-mediated molecular orientation and crystallization. The structural and morphological variations of amorphous PLA under different strain rates were investigated. The result showed that strain rate significantly influences its strain-hardening behavior. The crystallinity and orientation as well as cavitation of deformed PLA increase with the increase of strain rates. The structure evolution has been divided into three potential stages: (i) at small strains (<100%), the crystallinity of PLA increases by orientation-induced crystallization; (ii) at intermediate strains (100%–160%), the crystallinity of deformed PLA slightly decreases due to the breakage of existing crystals under stress accompanying with newly formed voids and cavities; (iii) at high strains (>160%), the increasing number of oriented chains in the amorphous regions promotes the crystallization of PLA. Our study suggests that strain rate and stretching strain play important roles on modulating the crystallization and orientation of amorphous PLA. [Copyright &y& Elsevier]