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This article uses the self-assessment tool of the European Union's digital competence framework for citizens，to investigate the level of digital competence of 151 university students in China, and examine the relationship between participants' digital competence and their personal factors. The results show that university students have an intermediate level of digital competence, and their competence level has significant differences in the number of digital tools used, but there is no significant difference in gender, age, region, and participation in the competition. The results of the study can be used as a reference for curriculum and teaching reform.

In the era of "Internet+", new generation of information technology such as 5G, Internet of Things, Big Data, and Artificial Intelligence are flourishing, bringing new ideas for expanding and transforming the learning space. Smart learning environments have emerged, which are conducive to cultivating talents with values, mobility, thinking power and creative potential. Therefore, it is urgent to build a smart learning space with the help of various new information technologies and create to meet the innovative smart teaching model. The author tries to build a model of a virtual and real symbiosis learning space that is not limited to time and space, and serves lifelong learning, in order to promote educational reform and enhance learning experience.

Nickel-based alloys have demonstrated significant promise as structural materials for Gen-IV nuclear reactors. However, the understanding of the interaction mechanism between the defects resulting from displacement cascades and solute hydrogen during irradiation remains limited. This study aims to investigate the interaction between irradiation-induced point defects and solute hydrogen on nickel under diverse conditions using molecular dynamics simulations. In particular, the effects of solute hydrogen concentrations, cascade energies, and temperatures are explored. The results show a pronounced correlation between these defects and hydrogen atoms, which form clusters with varying hydrogen concentrations. With increasing the energy of a primary knock-on atom (PKA), the number of surviving self-interstitial atoms (SIAs) also increases. Notably, at low PKA energies, solute hydrogen atoms impede the clustering and formation of SIAs, while at high energies, they promote such clustering. The impact of low simulation temperatures on defects and hydrogen clustering is relatively minor. High temperature has a more obvious effect on the formation of clusters. This atomistic investigation offers valuable insights into the interaction between hydrogen and defects in irradiated environments, thereby informing material design considerations for next-generation nuclear reactors.

In this study, the weldability of single-sided ultrasonic welding of 4-mm-thick carbon fiber/Nylon 66 composite was studied. Extensive welding was performed, and the weld microstructures, fractographies, and appearances of welded joints were examined and analyzed. It was found that the strengths of single-sided ultrasonic welded (SSUWed) joints made with proper welding variables are comparable to that of the ultrasonic welded joints. The solid SSUWed joints with introducing a gap of 1.0 mm can be produced with the use of double-pulse ultrasonic vibration schedule. The robust welding variables include a weld pressure of 0.17 MPa and a weld time of 1.3 s for the first vibration pulse, 5-s cooling, and a weld time of 1.3 s for the second vibration pulse. Microstructure analyses and mechanical testing of the welds revealed that the application of second ultrasonic pulse caused the melting of the materials at periphery of the existing weld, and consequently resulted in an increase in weld area. The use of the second vibration pulse not only improved the strength but also decreased the scatter in strength of the ultrasonic welded 4-mm-thick carbon fiber/Nylon 66 composite. The double-pulse vibration schedule improves the robustness of the SSUW and increases the flexibility of product designs that rely on the ultrasonic welding for assembly.

The ultrasonic welding (UW) technique is a fast-joining process; it is very suitable for the carbon fiber reinforced thermoplastic (CFRTP) composite. For improving the consistency of the welded joint quality, a new pre-pressing ring clamp (PPRC) was designed for ultrasonic welding carbon fiber reinforced nylon composites in this paper. The effects of the PPRC on the weld quality of the ultrasonic welding welded 4.0 mm thick 30% mass short carbon fiber reinforced Nylon 6 composite was investigated and compared with that of normal clamp weld joint. The weld strength, microstructure, and temperature evolution of the joint were analyzed by tensile test, scanning electron microscope, and temperature measurement. The results showed that the PPCR UW joints had larger central weld nugget size (478 mm2 vs. 300 mm2), thicker stable fusion region thickness (1.10 mm vs. 0.96 mm), resulting in a higher joint strength (6.86 kN vs. 6.21 kN) compared with the normal clamp UW joints under the same welding parameters. The real-time monitor curve of the horn displacement and temperature at the faying interface showed that the PPRC increased the heat rating at the faying interface during instable melting stage. The PPRC could improve the contact condition between workpieces and the utilization efficiency of ultrasonic energy, which boosted the melting rate of materials at faying interface and consequently the formation of a sound joint with enough weld size (i.e., 433 mm2) in a shorter welding time (i.e., 1.3 s). Therefore, the flexibility of component assembly would be increased by the use of this sort of clamps.

PurposeThe purpose of this paper is to study the grey decision model and distance measuring method of general grey number.Design/methodology/approachFirst, intuitionistic grey number (IGN) set and an IGN are defined by grey number probability function. Second, each interval grey number in general grey number is represented by an IGN and converts the general grey number into an IGN set. Final, the operation of two general grey numbers is defined as the operation between IGN sets, and the distance measure of the general grey number is given.FindingsUp to now, the method of measuring the distance and the grey decision model of general grey number is established. Thus, the difficult problem for set up decision mode of general grey number has been solved to a certain degree.Research limitations/implicationsThe method exposed in this paper can be used to integrate information form a different source. The method that a general grey number converted to a set of IGNs could be extended to the case of grey incidence analysis models, grey prediction models and grey clustering evaluation models, which includes general grey numbers, etc.Originality/valueThe concepts of IGN and IGN set are proposed for the first time in this paper; The operation of two general grey numbers can be defined as the operation between IGN sets. On this basis, the algorithm of IGN, the integration operator of IGN and the distance measure between IGN sets are given.

In this study, ZrMgMo

Ti, Co, Cr, Fe, Ni and graphite powders were used to fabricate TiC reinforced CoCrFeNi composite by mechanical alloying and consequently hot pressing sintering at 1200°C for 1 h. Results indicated ...

In this study, a silane coating, KH560, along with an abrasion pretreatment procedure for carbon fiber reinforced PA 6 composite with 30% mass fiber (Cf/PA6) and AA6061-T4 was developed. Composition and structure of this silane coating and effect of this coating on the strength and water resistance of the adhesive-bonded Cf/PA6 and AA6061 were investigated. Test results revealed that silane pretreatment improved the static strengths of the adhesive-bonded Cf/PA6-Cf/PA6 and Cf/PA6-AA6061 by 23% and 21%, respectively. X-ray photoelectron spectroscopy (XPS) analysis of the adhesive-bonded treated Cf/PA6 indicated that the improvement in strength was primarily attributed to the formation of Si-O-Si and Si-N covalent bonds on the surface of Cf/PA6, which enhanced the bond adhesion between the silane coating, adhesive, and adherends. In addition, abrasion of adherends prior to silane pretreatment further improved the strengths of the adhesive-bonded Cf/PA6-Cf/PA6 by another 20%. While silane and abrasion-silane treatment improved the strength of the adhesive-bonded Cf/PA6-Cf/PA6 and Cf/PA6-AA6061 in ambient conditions, the strength of water immersed silane coated joints with and without abrasion was decreased by about 50% (i.e., immersed in water at 54 °C for one week). All tested bare and treated joints with and without water immersion exposure were fractured in adhesive mode. Analyses of the test results revealed that to improve the failure mode and bond strength it is necessary to form a Si-N functional group in the silane coating by thoroughly cleaning and removing the contaminants and weak layers on the surface of Cf/PA6.

ZrMgMo3O12 ceramics were synthesized via primary sintering at 700–750 °C for 5 h and second sintering at 700 °C for various times. The crystal structure and lattice parameters of ZrMgMo3O12 were confirmed by structural refinement. The microstructure, mechanical and thermal expansion properties of the as-synthesized ZrMgMo3O12 specimens were evaluated via XRD, XPS, SEM, TEM, Vickers hardness and coefficient of thermal expansion (CTE) analyses. The results show that single-phase ZrMgMo3O12 ceramics were synthesized via primary sintering at 700–750 °C for 5 h. Second sintering at 700 °C for various times improved the compactness, density and grain bonding of ZrMgMo3O12. The optimal synthesis process is primary sintering for 5 h at 700 °C and then second sintering for 72 h at 700 °C. Structural refinement revealed that each of the as-synthesized ZrMgMo3O12 ceramics had an orthorhombic crystal structure with a Pna21 space group and lattice parameters of a = 13.1886 A, b = 9.49382 A and c = 9.57818 A. Second sintering increased the mechanical properties and decreased the CTEs of the as-synthesized ZrMgMo3O12 ceramics. The ZrMgMo3O12 ceramics synthesized with the optimal synthesis process had hardness values of 205 HV, elastic moduli of 49.45 GPa and CTEs of 0.038 × 10−6 °C−1. Although the hardness was lower than those of traditional ceramics, the near zero CTE of the ZrMgMo3O12 ceramic demonstrated that it is a potential candidate for high dimensional stability materials.

In this study, the effects of lithium(Li) content (1.0, 1.5, 2.0, and 2.5 wt%) on the microstructure, micro-yield strength (MYS) and coefficient of thermal expansion (CTE) of Al–Cu–Mg–Li–Sc–Ag alloys were investigated. The results showed that increased Li content promoted the formation of primary T1 phases and secondary T1 precipitates. While the primary T1 phases decreased the MYS of the Al–Cu–Mg–Li–Sc–Ag alloys due to large residual stress and stress concentration, secondary T1 precipitates increased the MYS due to their excellent pinning and impeding effect on mobile dislocations. In addition, the increase in Li content caused the CTETT (i.e., CTE transition temperature) first increased and then decreased, while the CTEH (CTETT to 300 °C) of alloys to first decrease and then increase. The CTEH and CTETT values were influenced by the MYS rather than by the macro-yield strength of alloys, arising from the differences in the amounts of the T1 precipitates among the four tested alloys; this was due to the superior thermal stability of the T1 precipitates.

To minimize the structure distortion and potential de-bonding in adhesive bonding of dissimilar materials (e.g., metals and polymeric composites), a two-component (2 K) low temperature cure modified adhesive consisting of 93.5 wt% commercial Henkel 5089 adhesive, 2.5 wt% N-(2-Hydroxyethyl) ethylenediamine (AEEA) and 4.0 wt% 2-ethyl-4-methylimidazole (2,4-EMI) was formulated. Experimental results showed that the use of the modified adhesive lowered the curing temperature from recommended 177 °C (for 20 min) for Henkel 5089 to 100 °C (for 20 min) or 120 °C (for 10 min) for AA6061-AA6061 joint, and 120 °C (for 20 min) or 130 °C (for 10 min) for AA6061-Cf/PA6 (Nylon 6) and Cf/PA6-Cf/PA6 joints, respectively, due to the faster curing reaction caused by the combined addition of AEEA and 2,4-EMI. It took 5, 3, and 2 days to cure the adhesive-bonded AA6061-AA6061, AA6061-Cf/PA6, and Cf/PA6-Cf/PA6 joints made with the modified adhesive and cured at ambient temperature, respectively. In addition, the modified adhesive had sound working life (5 h) at ambient temperature. The static strengths of all adhesive-bonded AA6061-AA6061, AA6061-Cf/PA6, and Cf/PA6-Cf/PA6 joints with the modified adhesive were hardly affected by thermal exposure cycle (i.e., exposure to 82 °C for 30 min). These results indicated that the modified adhesive possesses the promising characteristics for joining of similar and dissimilar materials.

In this study, Al-Cu-Li alloys were pre-strained to various plastic strains before ageing. The T1 (Al2CuLi) precipitates and dislocation density in various pre-strained Al-Cu-Li alloys were analyzed with transmission electron microscopy (TEM) and X-ray diffraction (XRD) technology respectively. The micro-yield strength (Micro-YS) of tested alloys was measured and the strengthening mechanism was discussed. It is found that the pre-strain increases the dislocation density, promotes the precipitation and inhibits the growth of T1 precipitates. The precipitation strengthening of T1 precipitates is higher than strain strghening of dislocations and it first increase then decrease whearas the strain strenthening continuously increase with pre-strain. The improvement in strength of Al-Cu-Li alloy caused by pre-straining is mainly due to strain strengthening rather than precipitation strengthening. Therefore, although pre-strain improves the macro-yield strength (Macro-YS) as well as the Micro-YS, excessive pre-strains are not conducive to the improvement of the Micro-YS. The pre-strain of 2% is a promising method to simultaneously improve the Micro-YS and Macro-YS of Al-Cu-Li alloys due to its synergistic improvement effect on precipitation strengthening and strain strengthening. Macro-YS and Micro-YS of pre-strained Al-Cu-Li alloys can be estimated with a simple strength mode. However, the larger error between the estimated and measured Micro-YS suggests that the accurate estimation of Micro-YS requires further to consider the adverse effect of mobile dislocations caused by pre-strain on the Micro-YS.

In this study, 5 wt.% nanodiamond (ND) reinforced 2024Al matrix composites (ND/2024Al) were fabricated with various ball milling processes. The microstructure, compressive yield strength (σyc) and coefficient of thermal expansion (CTE) of ND/2024Al composites were investigated. It is found that the addition of 5 wt.% NDs significantly increases the σyc and decreases the CTE of 2024Al. High energy ball milling further increases σyc and decreases CTEs of ND/2024Al composite due to it enhances the fine grain strengthening of α-Al matrix and the dispersion strengthening of NDs, decreases the thermal mismatch stress at the ND/α-Al matrix interface, and increases the constraint of NDs on α-Al. The composites fabricated by the combinations of ball milling speeds and times of (5−7) h×(200−250)rpm and 9 h×300 rpm have the highest σyc and the lowest CTE respectively. Considering the different influence of ball milling parameters on σyc and CTEs, a evaluation coefficient α = σ ycC ⋅ e k c C σ y c M ⋅ e k c M ⋅ C T E M C T E C is proposed to evaluate the synergistic influence of mechanical properties and CTEs on the dimensional stability of ND/2024Al composites. Large value of α may lead to high dimensional stability of material, hence the α can be used to determine the ball milling parameters.The ball milling process of 250−300 rpm ball milling speeds and 5−7 h ball milling times are recommended based on α, which causes a 95–100 % increase in σyc and a 30–35 % decrease in CTE compared with 2024Al alloy, respectively.

Ultrasonic welding (UW) of polymeric composites is significant in automobile industry; however, maintaining the perfect contact condition between workpieces is a great concern. In this study, effect of preloading and welding pressure on strengths of UWed 2.3-mm-thick short carbon fiber reinforced nylon6 (Cf/PA6) joints with poor contact between workpieces was investigated through stress simulation and energy dissipation at the faying interface. Results showed the application of preloading can increase the strength of normal joint by 18.7% under optimal welding parameters. Gaps between upper and lower workpieces decreased the joint strength significantly, especially for gaps greater than 1.5 mm. Preloading improved the strengths of the joints with gaps remarkably, where the strength of joints with 1.5 mm gap recovered to 95.5% of that the normal joint. When combining the weld nugget evolution, stress-deformation simulation during UW, and ultrasonic vibration transmission analysis, the improvement mechanism of the joint under preloading was mainly because the preloading compacted the contact between workpieces, which favored the energy transmission at faying interface.

Lightweight Al

The microstructure, phase, alloying behavior, and oxidation behavior of the Co

Ultrasonic welding of thermoplastics is widely applied in automobile and aerospace industries. Increasing the weld area and avoiding thermal decomposition are contradictory factors in improving strength of ultrasonically welded polymers. In this study, relations among the loss modulus of carbon-fiber-reinforced polyamide 66 composite (CF/PA 66), time for obtaining stable weld area, and time for CF/PA 66 decomposition are investigated systematically. Then, a double-pulse ultrasonic welding process (DPUW) is proposed, and the temperature evolutions, morphologies and structures of fractured surfaces, and tensile and fatigue properties of the DPUWed joints are measured and assessed. Experimental results show the optimal welding parameters for DPUW include a weld time of 2.1 s for the first pulse, a cooling time of 12 s, and a weld time of 1.5 s for the second pulse. The DPUW process enlarged the weld area while avoided decomposition of CF/PA 66 under appropriate welding parameters. Compared to the single-pulse welded joint, the peak load, weld area, and endurance limit of the DPUWed joint increased by about 15%, 23% and 59%, respectively. DPUW also decreases the variance in strengths of the joints.

CoxCrCuFeMnNi (x = 0.5, 1.0, 1.5, 2.0 mol) high-entropy alloy (HEA) powders were synthesized by mechanical alloying (MA). The effects of milling time, Co content, and vacuum annealing on the structural evolution, thermostability, and magnetic properties were investigated. After 50 h of milling, the Co0.5CrCuFeMnNi HEA powder consisted of a major face-centered cubic (FCC) phase and minor body-centered cubic (BCC) phase, whereas the other three HEA powders were composed of single FCC phase. The Co0.5CrCuFeMnNi HEA powder was composed of FCC1, FCC2, and minor ρ phases when annealed at 700 and 800 °C and then completely transformed into FCC1 and FCC2 phases at 900 °C. For the other three HEA powders, the single FCC phase transformed into the FCC1 and FCC2 phases during annealing at 700–900 °C. Both increasing Co content or prolonging balling time can improve the soft magnetic properties of HEA powders. Therefore, the Co2.0CrCuFeMnNi HEA powder with a maximum saturated magnetization of 52 emu/g and a minimum coercivity of 14 Oe exhibited the best soft-magnetic properties among the four HEA powders.

A 2024Al metal matrix composite with 10 vol% negative expansion ceramic ZrMgMo3O12 was fabricated by vacuum hot pressing, and the influence of sintering temperature on the microstructure and thermal expansion coefficient (CTE) of alloys was investigated. Experimental results showed that all ZrMgMo3O12p/2024Al composites sintered at 500–530 °C had a similar reticular structure and exhibited different linear expansion coefficients at 40–150 °C and 150–300 °C. The addition of 10 vol% ZrMgMo3O12 decreased the CTEs of 2024Al by ~ 16% at 40–150 °C and by ~ 7% at 150–300 °C. This addition also increased the hardness of 2024Al by ~ 23%. The density of the composites and the content of Al2Cu in ZrMgMo3O12p/2024Al increased as the sintering temperature increased. The CTEs of the composites decreased, whereas hardness increased. Thermal cycling from 40 °C to 300 °C caused the CTEs of the composites to decrease gradually and reach a stable value after seven cycles. The lowest CTEs of 15.4 × 10−6 °C−1 at 40–150 °C and 20.1 × 10−6 °C−1 at 150–300 °C were obtained after 10 thermal cycles and were reduced by ~ 32% and ~ 17%, respectively, compared with the CTE of the 2024Al. Among the current reinforcements, ZrMgMo3O12 negative expansion ceramics showed the highest efficiency to decrease the CTE of Al matrix composites.

Many techniques have been applied for quality inspection but none is currently suitable for on-line bond quality inspection of uncured adhesive joined polymeric composites. A newly nondestructive e...

Two enhanced solution treatments (ESTs) were applied to an Al–Cu–Li–Sc alloy. Results showed that the ESTs reduced the amount and size of the soluble phases, and promoted the recrystallisation of t...

To minimize the part distortion and investment in the E-coat oven in adhesive bonding of metals for automotive applications, lowering the curing temperature of adhesive without apparent loss of the joint strength is desirable. The key to lower the curing temperature of adhesive bonding of lightweight materials is to accelerate the curing process of structural adhesives. In this study, curing agent (i.e., aliphatic polyamine) and curing accelerator (i.e., acetylacetone salt) were added into commercial Henkel 5089 adhesive and the effect of these curing additives on the curing temperature of Henkel 5089 in adhesive bonding of aluminum AA6061-T4 was studied. The test results showed that the addition of a curing agent and accelerator in Henkel 5089 lowered the curing temperature from 177°C to 130°C without sacrificing the strength of the adhesive-bonded aluminum AA6061-T4.

Ultrasonic welding of 4 mm thick carbon fiber/polyamide 66 (C f /PA 66) composite samples in a lap configuration was completed to characterize the effect of weld energy on weld strength. In general, it was seen that weld strength was proportional to weld energy; however, with excessive energy, the weld strength decreased. Weld indentation had little influence on joint strength, whereas thermal decomposition of C f /PA 66 composite was the main reason for the low joint strength. Higher weld energy caused thermal decomposition of C f /PA 66 composite and degradation of tensile strength of welded workpieces. A decomposition index of the joint was proposed and calculated to predict weld quality. When the decomposition index was small, joint strength increased with the weld area while high decomposition index of polyamide 66 (i.e. >30.5%) led to the decrease in joint strength based on the experimental data. The optimal decomposition index was found in the range of 12–30.5% depending on joint strength.

Electrochemical performance and production cost are the main concerns of electrode materials for the practical supercapacitor applications. Here we use a simple and universally applicable two-step hydrothermal treatment process to prepare the flower-like CuCo2S4 nanosheet arrays directly grown on Ni foam and employ it as binder-free and conductive-agent-free electrode for pseudocapacitors. The electrode at a current density of 5 mA cm−2 exhibits an ultrahigh capacitance of 908.9 F g−1 and at 30 mA cm−2 delivers an outstanding cycling stability with retaining 91.1% after 2000 cycles compared with its initial capacity. Furthermore, the assembled flower-like nanostructured CuCo2S4//active carbon asymmetric supercapacitor displays a specific capacitance of 93.5 F g−1 at 1 mA cm−2, an energy density of 29.2 Wh kg−1 at 127 W kg−1, as well as 126.39% capacitance retention through 2000 cycles at the high current density of 25 mA cm−2, suggesting the flower-like CuCo2S4 nanosheet arrays hold promise for practical application of high-performance supercapacitors.

Lightweight Al2NbTi3V2Zrx (x = 1.0, 0.8, 0.6, 0.4, 0.2, 0) high entropy alloys are produced by mechanical milling and vacuum hot pressing. The microstructure, phase evolution and mechanical properties of the alloys are analyzed. The microstructure of the alloys with x = 1.0, 0.8, 0.6 consists of BCC solid solution matrix and two intermetallics (i.e., α and β), and then β phase disappears in Al2NbTi3V2Zr0.4 alloy. Further decreasing Zr content to below 0.2, α phase vanishes and γ and δ intermetallics emerge in Al2NbTi3V2Zr0.2 and Al2NbTi3V2 alloys. The Al2NbTi3V2Zrx alloys cannot obtain a single phase structure by decreasing Zr content with current fabrication process, which is likely because that the mixing entropy of the HEA system is not large enough to prohibit the formation of the secondary phases at hot pressing temperature of 1250 °C. All the bulks possess low density ranging from 4.93 to 5.21 g/cm3. Hardness of the Al2NbTi3V2Zrx alloys decreases from 781 HV to 697 HV and then increases to 814 HV with the decrease of Zr from x = 1 to 0. This varying tendency is closely related with the content of secondary intermetallic phases. The compressive test shows the Al2NbTi3V2Zr0.4 alloy has a yield strength of 1742 MPa, fracture strength of 2420 MPa, compressive strain of 38.2 %, which is probably related to its simplest microstructure. The comprehensive mechanical property of Al2NbTi3V2Zr0.4 alloy is superior to the majority of other HEAs and Ti64 alloy.

The effects of external stress on the precipitation of T1 precipitates and mechanical properties of creep-aged Al-Cu-Li-Ag alloys are investigated. Promotion mechanisms of external stress to the precipitation of T1 precipitates are discussed. It is found that external stress significantly promotes the precipitation and improves the distribution of the T1 precipitates in the creep-aged alloys. There is a threshold stress, close to the yield stress, that has only a limited promotion effect on the precipitation of T1 precipitates. The external stress below and above the threshold stress promotes the precipitation of T1 precipitates by two different mechanisms. One is the promotion mechanism of lattice distortion produced by the elastic stress. Another is the promotion mechanism of multiplication of dislocations produced by the plastic stress. Both elastic and plastic external stress can synergistically improve the strength and ductility. Especially, the plastic external stress resulted in the best improvement to ductility of creep-aged alloys. Hence, the creep ageing with plastic external stress is an alternative method to synergistically improve the strength and ductility of Al-Cu-Li-Ag alloys. However, it is necessary to avoid using excessive plastic stress for the creep ageing because it may cause creep damage and degrade its mechanical properties.

The microstructure, phase, alloying behavior, and oxidation behavior of the CoxCrCuFeMnNi (x = 0, 0.5, 1.0, 1.5, 2.0, named as Co0, Co0.5, Co1.0, Co1.5, and Co0.5, respectively) high entropy alloy powders (HEAPs) prepared by mechanical alloying were studied. The results indicated that the HEAPs began to be alloyed after ball milling for 5 h, and the particle size is about 40∼60 μm. After 50 h of milling, the Co0 and Co0.5 HEAPs are composed of metastable FCC and minor BCC solid solution phases, while the other HEAPs consist of single metastable FCC solid solution phase. After vacuum annealing or atmospheric oxidation at 700 °C, the metastable FCC and BCC phases decompose into FCC1 and FCC2 and ρ phases, respectively. The oxidation mass gain of CoxCrCuFeMnNi HEAPs shows a parabolic upward trend. With the increase of Co content, the oxidation rate constant decreases, indicating that the oxidation resistance of the HEAPs decreases with the increase of Co content.

The effects of carbon nanotube aspect ratio (R) on mechanical properties of CNT/Al composites containing 0–2.0 wt% CNTs are studied. The optimum carbon nanotube (CNT) reinforced aluminum (Al) composites are fabricated at 580 °C for 1 h under 60 MPa, and subsequently hot extruded at 480 °C. CNT addition within 0.5 wt% can increase the strength significantly without plasticity loss, which overcomes the dilemma of strength and toughness. Strength and hardness increase significantly due to the uniformly distributed CNTs in Al matrix within a content of 1.0 wt%. Quantitatively fitting results also show that the main strengthening mechanism of CNT/Al composites should be dispersion strengthening rather than load transfer. The R, which is very crucial for load transfer theory, has only small effects on the mechanical properties of CNT/Al composites. The calculated CNTs diameters are close to the experimental used ones.

Lightweight Al2NbTi3V2Zr alloy was fabricated through mechanical milling and vacuum hot pressing. The effects of milling on the microstructure, phase evolution, and hardness of the fabricated alloy were investigated. High-energy (HE) milling decreased the size of crystalline grains and activated the powders for subsequent sintering. HE-annealed powders at above 900 °C and all sintered bulks consisted of body-centered cubic (BCC) and intermetallics α and β. Low-energy (LE) milling only provided homogeneity to the powders. LE bulks exhibited a microstructure similar to that of HE bulks at 1450 °C–1550 °C. The hardness of the HE bulk was higher than that of the LE bulk and exhibited a peak value of 781 HV at 1250 °C. All Al2NbTi3V2Zr bulks possessed low density ranging from 5.05 g/cm3 to 5.25 g/cm3. Two empirical equations for hardness of the bulks were proposed for the BCC matrix bulks and simple cubic matrix bulks respectively and the estimated results are consistent with the experimental measurements. Keywords: Al2NbTi3V2Zr alloy, High-energy balling, Vacuum hot pressing, Microstructure, Hardness

A method of applying ultrasonic welding to repair adhesive-bonded 2.3 mm thick injection molded short carbon fiber reinforced Nylon 6 (Cf/PA6) composite with 30 wt% fiber was developed. The method included positioning the ultrasonic horn and anvil proximate the region on the workpieces having the partially adhesive-bonds and applying an ultrasonic oscillation at the workpieces where insufficient adhesive was dispensed at the faying surfaces. The effects of horn force, oscillation time, and inadequate adhesive on the quasi-static strengths of the nominal, partially adhesive-bonded and repaired joints were investigated. It was found out that the strengths of the partially adhesive-bonded joints with 0%, 25%,50% and 75% adhesive coverages were restored and achieved over 90% of the nominal joint strength (i.e., full adhesive coverage). Microstructure analyses of the repaired joints demonstrated that the second ultrasonic pulse produced viscoelastic heating and frictional heating, and consequently fused carbon fiber composites at the faying surfaces of the workpieces. The strengths of the repaired (i.e., weld-bonded) lap-shear joints were primarily from the combined contribution of adhesive-bond and ultrasonic weld at the faying surfaces, which were virtually unchanged regardless the amount of adhesive missing. Therefore, for the substrate and joint configuration and dimensions studied here, application of ultrasonic welding virtually restored the quasi-static strengths of partially adhesive-bonded lap-shear Cf/PA6 composites with 30 wt% fiber. Consequently, by the application of this repair method the scrap of the component assembly would be reduced.

In this study, weldability of ultrasonic welding of 4-mm-thick fiber carbon/nylon 66 composite in lap configuration was investigated. Ultrasonic welding tests were performed, and the weld appearance, microstructure, and fractography of the welded joints were examined using optical and scanning electron microscope. The transient temperatures near the faying surfaces and horn-workpiece interfaces were recorded to understand the weld growth mechanism. It was found that it is feasible to join 4-mm-thick lapped carbon fiber reinforced nylon 66 composite with ultrasonic welding. Under the ultrasonic vibration, the weld initiated and grew at the faying surfaces, while the weld indentation developed at the horn-workpiece interface. The pores observed in the regions between the heat-affected-zone (HAZ) and the fusion zone (FZ), and the severe weld indentation on the surface of upper workpieces decreased the loading capacity of the ultrasonic welded (UW) joints and caused the welded carbon/nylon 66 composite fractured prematurely. The strengths of the ultrasonic welds were determined by the balance of positive effect of the weld area and negative effects of the weld indentation and porosity near the FZ. To ensure the joint strength, it is necessary to apply the proper weld schedules (i.e., welding time and horn pressure) in ultrasonic welding of 4-mm-thick carbon fiber reinforced nylon 66 composite, which were developed based on the joint strength criterion.

A novel lightweight high-entropy alloy Al2NbTi3V2Zr was fabricated by vacuum hot pressing. The effects of sintering temperature (1200–1550°C) on the microstructure, hardness and corrosion resistance of the alloy were investigated. Results showed that Al2NbTi3V2Zr mainly consisted of simple cubic matrix and (Zr, Al)-based intermetallic phase (α-phase) at sintering temperatures of 1200–1350°C. Moreover, the matrix phase transformed from simple cubic to body-centred cubic phase, and (Ti, Zr, Al)-based intermetallic precipitated from the matrix at temperature of 1450°C. The fabricated Al2NbTi3V2Zr alloy had low density of 5.05–5.23 g cm–3, high hardness of 510–728 HV and excellent corrosion resistance in 10 wt-% HNO3 solution.

Firstly, aiming at the characteristics of accuracy and complexity of uncertain information representation. the interval grey number extended the general grey number. Then, the concept of extended general grey number is put forward based on grey number theory, which is used to represent complex uncertain information. Secondly, according to the essence of the kernel and degree of greyness of general grey number, the basic method of reducing general grey number to interval grey number is given. Thirdly, the measurement method of general grey number distance is given based on the essential characteristics of kernel and grey degree and Euclidean metric. Finally, from perspective of expectation and variance, the concept of kernel expectation and kernel variance of general grey number is put forward, and the ranking method of general grey number is given.

A kind of joining method for magnesium alloys, rotation friction pressing riveting (RFPR), is proposed in this paper. In RFPR operation, a rivet with a plug rotating at high speed is brought to contact with the riveted sheets, generating frictional heat between the rivet and riveted sheets, which softens the sheet materials and enables the rivet to be drilled into the sheets under reduced force. When fully inserted, the rivet is stopped rotating, and the plug is immediately pressed into the shank of the rivet by a punch. The expansive deformation of the rivet shank occurs under the action of the plug, thereby forming a mechanical interlock between the rivet and the sheets to fasten the sheets together. The studies show that RFPR of AZ31 magnesium alloy sheet can be carried out at ambient temperature, and provides the joints with superior shear strength and fatigue property when compared with self-piercing riveting (SPR). The effects of the operating parameters of RFPR process on the quality of the joints were investigated in the study. The results shows that while the rivet rotation speed little affects the shear strength of RFPR joints, the punch pressure has a significant influence on the mechanical properties of the RFPR joints. A numerical analysis was also performed to understand the effect of the punch pressure on the interlock between the rivet and the sheets, and the stress and strain distribution inside the sheet materials around the rivet. The results show that the interlock increased with the punch pressure and there is residual compressive stress inside the sheet materials, which seems to explain the good fatigue property of RFPR joints observed.