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The permanently chemically cross‐linking solid–solid phase change materials (SSPCMs) were designed to solve the problem of leakage and poor shape stability during the whole process of phase transformation. However, these materials lead to environment pollution and resources waste because of the non‐recyclability. Therefore, a SSPCMs was fabricated using dynamic thermal reversible Diels–Alder bonds. The prepared SSPCMs exhibited excellent shape, heat storage stability, and reliability and reprocessed ability, resulting from dynamic Diels–Alder bonds. Moreover, the Halloysite nanotubes decorated with Fe3O4 nanoparticles (HNTs@Fe3O4) were used to enhance the thermal conductivity of SSPCMs. When the filler content was 0.5 wt%, the best integrated properties (phase change properties and thermal conductivity) of the SSPCMs were obtained, it had the highest melting and freezing phase change enthalpies about 116.8 and 127.2 J/g, and thermal conductivity value, 0.223 W/m K, which was 101% higher than pure SSPCMs. Hence, the prepared SSPCMs can be considered as promising save‐energy, friendly‐environment thermal management materials. [ABSTRACT FROM AUTHOR]

Due to the outstanding properties comprised of thermal, anti-corrosion and excellent processing properties, the polyurethane coating has received attention from many researchers. However, absence of self-healing capacity limited their applications. In the present work, a self-healing polyurethane (PU) was developed for protective coating via Diels–Alder reaction. Moreover, incorporation of Halloysite nanotubes (HNTs) by in situ polymerization method in the PU enhances the mechanical properties. The macro- and micro-mechanical properties of materials were investigated by tensile and nanoindentation measurement, these results show the composites displayed higher tensile strength (34.2 MPa) and hardness (5.13 MPa) in comparison with pure PU (22.9 MPa and 4.24 MPa). The tensile and POM results indicated that the PU and composites have excellent self-healing property. The simulative salt spray tests indicated the coating possessed an excellent corrosion protection property. Therefore, this work is promising for the self-healing ability protective polymer coating. [ABSTRACT FROM AUTHOR]

MoS2–TiL/MoS2–TiH coating (L and H are low and high power of the sputtered Ti target) possesses excellent tribological properties owing to its nano-multilayer structure. In this study, the tribological properties of MoS2–TiL/MoS2–TiH coating were extensively analyzed at different loads. Relative to the MoS2–Ti monolayer coating, the nano-multilayer structure not only improved the wear resistance but also increased the critical load at which the coating began to peel off. The MoS2–Ti coating maintained its lubrication only in the early stage of the test even at a load of 2 N. In contrast, the friction coefficient and wear rate of the multilayer coating were small and stable until the load reached 20 N. The critical load of the optimized MoS2–TiL/MoS2–TiH coating was 10 times that of the MoS2–Ti coating. At excessive loads, the multilayer coating lost its lubrication in the early stage of the test because the coating was completely worn off under such loading. [ABSTRACT FROM AUTHOR]

In the present work, the effect of artificial aging on the Cu-Mg co-clustering and mechanical behavior in a pre-strained Al-Cu-Mg alloy are investigated by tensile and fatigue testing, X-ray diffraction (XRD), transmission electron microscope (TEM) and atom probe tomography (APT). Results show that in the pre-strained samples, sample with artificial aging (170 °C/30 min) possesses unchanged strength and higher elongation in comparison with naturally aged sample. This is due to the greater strengthening effect caused by cluster hardening but the weaker strengthening effect caused by strain hardening in 170 °C/30 min sample. The fatigue crack propagation (FCP) resistance of 170 °C/30 min sample is higher than that of naturally aged sample. APT analysis indicates that artificial aging remarkably increases Cu-Mg co-cluster size, which leads to a greater critical shear stress for dislocation motion. This undoubtedly enhances fatigue crack closure effect and FCP resistance. Meanwhile, artificial aging reduces the dislocation density, which enhances FCP resistance as well. Compared to the sample without pre-strain, the pre-strained samples exhibit a higher FCP rate as a high density dislocation favors a detrimental effect on FCP resistance. [ABSTRACT FROM AUTHOR]

Effects of pre-strain on Cu-Mg co-clusters and mechanical behavior in a naturally aged Al-Cu-Mg alloy were investigated by tensile and fatigue testing, transmission electron microscope (TEM) and atom probe tomography (APT) in present work. Results show that pre-strain contributes to increasing tension strength, not only by increasing dislocation density as previously recognized, but also through enhancing Cu/Mg ratio of Cu-Mg co-cluster and resultant critical shear stress for dislocation slip. Fatigue crack propagation (FCP) resistance is not degraded by further increasing pre-strain from 5% to 10%, in spite of a FCP resistance degradation when a pre-strain of 5% is initially applied. APT analysis indicates, comparing with 5% pre-strain, 10% pre-strain remarkably enhances Cu-Mg co-cluster size and Cu/Mg ratio during natural aging, which leads to a greater critical shear stress for dislocation slip. This undoubtedly enhances fatigue crack closure effect, and retards FCP resistance degradation when a greater pre-strain of 10% is applied. [ABSTRACT FROM AUTHOR]

The close association between the Ω precipitation and various Ag additions is systematically investigated by quantitative transmission electron microscopy and atom probe tomography analysis. Our results suggest that the precipitation of Ω phase is strongly dependent on Ag variations. Increasing the bulk Ag content favors a denser Ω precipitation and hence leads to a greater age-hardening response of Al-Cu-Mg-Ag alloy. This phenomenon, as proposed by proximity histograms, is directly related to the greater abundance of Ag solutes within Ω precursors. This feature lowers its nucleation barrier and increases the nucleation rate of Ω phase, finally contributes to the enhanced Ω precipitation. Also, it is noted that increasing Ag remarkably restricts the precipitation of θ' phase. [ABSTRACT FROM AUTHOR]

The effect of 2.5% pre-stretching on the solute clustering and subsequent precipitation of an initial aged Al-Cu-Mg-Ag alloy is investigated by quantitative transmission electron microscopy (TEM) and atom probe tomography (APT) technique. In present work, 2.5% pre-stretching is found to restrict the dense precipitation of Ω phase, leading to the slower age-hardening response at 180 °C. The dominant Mg-Ag co-clustering, as revealed in non-stretched alloy, becomes weak by 2.5% pre-stretching prior to aging. This suppressed Mg-Ag co-clustering leads to a steep drop of the number density of Mg-Ag co-clusters by 70% and finally fails to induce the formation of high density Ω plates. High density dislocations introduced by pre-stretching also serve as the heterogeneous nucleation sites of θ′ phase and favor an enhanced precipitation of coarse θ′ needles. In addition, pre-stretching also exhibits a negative effect on initial Cu-Mg co-clustering. [ABSTRACT FROM AUTHOR]

In this work, the Polyurethane/MoS2 composites (PUM) filled with different amount of modified molybdenum disulfide (MoS2) were prepared by solution-blending-casting method. The thermal reversible Diels–Alder (DA) bonds enabled the polymer system recyclable ability. The modified MoS2 were obtained by tannic acid (TA) assistant ultra-sonication exfoliation method were used to improve the gas barrier performance of materials. Compared with the pure PU, about twofold decrease in oxygen gas permeability of PUM composites (from 6719 to 3927 cm3/m2˙d˙Pa) were obtained with 1 wt% MoS2. More important, the samples showed excellent gas barrier and mechanical properties before and after being hygrothermal aged for 100 h. The PUM composites had good gas barrier and recyclability and had great potential application prospects in packing materials. [ABSTRACT FROM AUTHOR]

The modulus hardening capability of various co-clusters in a low Cu/Mg ratio Al-Cu-Mg-Ag alloy aged at 165 °C is investigated by quantitative atom probe tomography analysis. Prolonged aging from 5 min to 2 h leads to the simultaneous increase in the critical shear stress of both Mg-Ag and Cu-Mg co-clusters. Regardless of the higher shear modulus of Cu-Mg co-clusters, calculation results show that Mg-Ag co-clusters possess a greater modulus hardening capability than Cu-Mg co-clusters, suggesting its primary contribution to the rapid hardening at the early aging stage. As aging extends from 30 min to 2 h, the increment in the critical shear stress of Mg-Ag co-clusters is lower than that of Cu-Mg co-clusters due to the precipitation of high density Ω phase. In addition, the shear modulus of Mg-Ag co-clusters is generally independent on its size at each investigated condition. [ABSTRACT FROM AUTHOR]

It is well known that deformation prior to artificial aging considerably decreases the strength properties of Al-Cu-Mg-Ag alloys by suppressing the formation of the main strengthening Ω precipitates. This negative effect is the as-yet unresolved obstacle for the wide applications of Al-Cu-Mg-Ag alloys. In this work, preaging prior to deformation is conducted to evaluate its possible influence on improving the typical microstructure and strength of deformed Al-Cu-Mg-Ag alloy. Quantitative transmission electron microscopy (TEM) and atom probe tomography (APT) analysis of the initial solute clustering and subsequent Ω precipitation of the deformed alloy with and without preaging indicate that preaging ensures strong Mg-Ag co-clustering and hence benefits the dense precipitation of Ω phase in deformed Al-Cu-Mg-Ag alloy. Naturally, the strength of 1% stretched Al-Cu-Mg-Ag alloy is obviously enhanced by preaging. [ABSTRACT FROM AUTHOR]

Quantitative and qualitative analyses on the dissolution behavior of various size Cu-Mg co-clusters near a fatigue crack tip of underaged Al-Cu-Mg alloy during cyclic loading were performed by means of transmission electron microscopy (TEM) and atom probe tomography (APT). Results showed that the driving force for dissolution of Cu-Mg co-clusters was increased with the increase of the co-clusters size. Therefore, Cu–Mg co-clusters in smaller sizes were easier to dissolve. The number density of small Cu–Mg co-clusters (20–50 atoms) increased and that of Cu–Mg co-clusters (50–200 atoms) reduced in the fatigue crack tip region during cyclic deformation. This was because that the large cluster could be repeated cut by moving dislocations to two or more parts of smaller clusters. Besides, the small clusters containing 20–100 atoms also might re-form after fatigue crack propagation (FCP) test in the fatigue crack tip region. The average equivalent radius of large Cu–Mg co-clusters (100–200 atoms) decreased from 1.38 nm to 1.31 nm during fatigue deformation in 170 °C/1 h sample. But there was no obvious difference of that in 170 °C/8 h sample. This result indicated that the dissolution of the large co-clusters in 170 °C/1 h sample was more violent than 170 °C/8 h sample. [ABSTRACT FROM AUTHOR]

The effect of intensifying Goss texture and refining Goss grains on the enhancement of fatigue crack propagation (FCP) resistance in an Al-Cu-Mg alloy was systematically investigated. The way to improve fatigue performance mainly includes two steps: intensifying Goss texture component and then refining these Goss grains. Hot rolling at elevated temperature and pre-solution treatment are capable of Goss texture formation. Then large cold rolling reduction can refine grains and obtain more these Goss grains, which increases the twist angle boundary components with their adjacent grains to enhance fatigue crack deflection and FCP resistance. By contrast, refining Brass etc. rolling-oriented grains can increase the tilt angle boundary components and promote fatigue crack growth. And the reason why grain refinement cannot always improve fatigue properties in alloys with micrometer grains can depend mainly on grain orientations and the relative boundary components in this Al-Cu-Mg alloy. Besides, coarse Fe-, Si- and Mn-rich inclusions are detrimental to fatigue properties, but the fine, globular and homogeneous distribution of these particles can improve fatigue properties to some extent. [ABSTRACT FROM AUTHOR]

Effect of Ag additions on the mechanical properties and microstructures of the peak-aged Al-Cu-Mg alloys during prolonged thermal exposure at 150 °C, was investigated by tensile testing, conventional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The results showed that after exposure for 500 h, > 85% of the peak strength remained. Microstructure observations indicated that increasing the Ag content from 0.14 to 0.57% promoted the precipitation of a fine and uniform Ω phase and suppressed the formation of the θ′ phase, leading to a notable improvement of the strength properties and thermal stability of the studied alloys. Quantitative TEM analysis showed that the coarsening of Ω phase was predominated by plate lengthening rather than thickening, while its lengthening rate was independent of various Ag additions during exposure at 150 °C. In addition, an increase of Ag also facilitated the formation of a cubic σ phase, which was further supported by STEM results. [ABSTRACT FROM AUTHOR]

The texture evolution of AA2524 cold-rolled sheet during annealing process and texture effect on fatigue crack propagation (FCP) behavior were investigated. Results showed the sample annealed at 400 °C for 45 min and solid solution-treated at 490 °C for 20 min had the strongest Goss and P textures, and possessed the lowest FCP rates. EBSD examination indicated Goss, P, Q, Cube, R and S grains induced great crack deflection to retard crack growth, when having large twist and tilt angle component boundary or pure twist boundary with neighboring grains. In the case of small angle boundary or relatively large angle tilt boundary with adjacent grains, Cube, Copper and R grains induced little crack deflection. Additionally, SEM results showed, in the presence of large twist angle component boundary or pure twist boundary, more severely plastic deformation presenting numerous slip bands occurred in Cube, R and S grains than that in Goss, P and Q grains during crack propagation. In contrast, no evident slip bands formed in Cube, Copper and R grains when having small angle boundaries or relatively large tilt angle boundary. [ABSTRACT FROM AUTHOR]

The effect of Cu–Mg cluster size and number density on the fatigue fracture behavior of Al–Cu–Mg alloy with various aging conditions was investigated by means of transmission electron microscopy (TEM), atom probe tomography (APT), scanning electron microscopy (SEM) and fatigue testing. Results showed that the fatigue crack propagation (FCP) resistances of 170 °C/1 h and 170 °C/8 h samples were higher than that of 170 °C/0.5 h sample due to increased number density of great size Cu–Mg co-clusters (>50 atoms). These large clusters were harder to dissolve during cycle deformation, thus reduced the cyclic softening effect and enhanced the FCP resistance. Moreover, as aging prolonged, the critical shear stress ( τ m ) of co-clusters by modulus hardening increased from 10.2 (MPa) in 170 °C/0.5 h sample to 12.4 in 170 °C/1 h sample and 12.1 in 170 °C/8 h sample. Thus the force required for the movement of dislocations impeded by co-clusters, as well as the resistance of FCP caused by co-clusters, in 170 °C/1 h and 170 °C/8 h sample was higher than that in 170 °C/0.5 h sample. The 170 °C/8 h sample possessed the lower FCP resistance than 170 °C/1 h sample because of the existence of S′ phase. S′ phase was a kind of semi-coherent unshearable precipitate and hence reduced the planar-reversible slip. [ABSTRACT FROM AUTHOR]

The association between Mg variations and the precipitation of Ω phase in Al–Cu–Mg–Ag alloys were investigated by transmission electron microscopy and quantitative atom probe tomography analysis. After aging at 165 °C for 2 h, the highest number density of Ω phase was revealed in 0.81Mg alloy, leading to the highest strength properties. The lowest strength properties of 0.39Mg alloy was related to the lowest precipitation kinetics of Ω phase. The parabolic change in the plate number density with increasing Mg highlighted the existence of a critical Mg content that contributed to the strongest precipitation kinetics of Ω phase. The number density of Mg–Ag co-clusters was not the sole factor in controlling the Ω precipitation. It was found that the precipitation of Ω phase was not only determined by initial Mg–Ag co-clustering but also related to the effective competition for solutes. In addition, the cluster-dominated microstructure facilitated the dense precipitation of Ω phase. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the bulk Ag content ranging from 0.14 to 0.57wt% on the aging hardening response and microstructures of Al–Cu–Mg alloys was investigated in the present study. The strong dependence of the hardening response on the bulk Ag content was obtained as the hardening response at 165°C was accelerated by increasing Ag content. The highest hardening response was observed in the alloy containing 0.57wt% Ag, whereas the least one was obtained in the alloy containing 0.14wt% Ag. The tensile testing at various temperatures also revealed a similar trend. Based on the TEM study on peak aging conditions at 165°C, it was found that the competitive precipitation kinetics between Ω and θ′ phases was sensitive to the variation of Ag content. The dense precipitation of the Ω plates promoted by increasing Ag content was responsible for the increasing hardening response. Meanwhile, the formation of θ′ phase was greatly suppressed. Subsequent long term aging at 200°C for 500h following the peak aging treatment further suggested that the thermal stability of the Ω plates was enhanced with increasing Ag as the presence of the Ω plates could be clearly confirmed in 0.57wt% Ag alloy but was hard to distinguish in the alloy containing 0.14wt% Ag. [Copyright &y& Elsevier]

Ti(C,N)-based cermets were prepared by vacuum hot-pressing sintering enhanced by the second phase of ZrO 2 whiskers via sulfate flux. The effects of ZrO 2 whiskers on the material properties of Ti(C,N)-based cermets at high temperature are discussed, including the room temperature microstructure, high-temperature oxidation resistance, and microstructure and mechanical properties at high temperature. The experimental result indicated that the addition of ZrO 2 whiskers improves the bending strength, fracture toughness, and oxidation resistance of Ti(C,N)-based cermets at high temperature. At a temperature of 1000 °C, the hardness, flexural strength, fracture toughness and elasticity modulus of the cermets with 7.5 wt% ZrO 2 whiskers were 9.32 GPa, 1032 MPa, 6.71 MPa m1/2 and 193.5 GPa, respectively. The high-temperature strength and toughness of Ti(C,N)-based cermets with ZrO 2 whiskers were weakened by the softening of grain boundaries, the decrease in elastic modulus, and oxidation. Conversely, the high-temperature strength and toughness of Ti(C,N)-based cermets were increased by maintaining the rod crystal shape of ZrO 2 whiskers at a high temperature, enhanced the elastic modulus of cermets through the whiskers, and improved oxidation resistance. • Properties of cermets with ZrO 2 whiskers at a high temperature were investigated for the first time. • Adding 7.5 wt% of ZrO 2 whiskers can effectively enhance the high-temperature properties. • Discussed the evolution mechanism of the microstructure and mechanical properties at high temperatures. [ABSTRACT FROM AUTHOR]

The realization of recyclable materials is an urgent problem to be solved for extending practical applications in industry. Herein, a simple method was proposed to prepared the recyclable materials thorough dynamic reversible chemistry. In this work, we design the recyclable and self-healing polyurethane based on the thermoreversible dynamic Diels-Alder reaction. In addition, the Halloysite nanotubes (HNTs) were introduced into the system to improve the thermal properties, mechanical properties of polyurethane nanocomposites (PUDM/HNTs). The tensile tests showed that the HNTs can significantly improved the mechanical properties of nanocomposites. The healing efficiency above 90% on average was achieved which was determined by the recovery of breaking strength. Besides, the composites exhibited outstanding reprocessability via thermally induced. Therefore, Such excellent recyclable performance and self-healing ability give the polyurethane materials an opportunity to have great potential in the fields of save-energy, friendly-environment materials. Image 1 • The Polyurethane/HNTs nanocomposites show enhanced mechanical and thermal properties. • The polyurethane materials have very high healing efficiency. • The Polyurethane had good thermal self-healing and reprocessability behavior. [ABSTRACT FROM AUTHOR]