The hardness and fracture toughness of high-temperature wear-resistant transition metal aluminum nitride multilayer films depend largely on the constituting layer's structure, compositional ...modulation, morphology, and interface coherency. We present a study on 1-micron thick multilayered films consisting of stacked layers of TiN and Zr0.37Al0.63N1.09, each layer being 10 nm thick. The films were grown using ion-assisted reactive magnetron sputtering on MgO(001) and Si(001) at substrate temperatures ranging from ambient to 900°C. By increasing growth temperature, we found that the ZrAlN layers transition from near amorphous to nanocrystalline wurtzite to decomposed c-ZrN and w-AlN domains. Concurrently, the TiN layers exhibit strong fiber texture, polycrystallinity, and epitaxial growth carried by the ZrN domains. Both hardness and fracture stress, evaluated by nanoindentation and micromechanical tests, increase with temperature from H=24 GPaMgO, 23 GPaSi to 36 GPaMgO, 30 GPaSi, and σFSi= 6.1-7.7 GPa, respectively. An improved fracture toughness of KIC=2.4-2.8 MPa√m is related to different toughening mechanisms for the various microstructures. The difference in hardness between the substrates is related to compressive stress due to the deposition conditions and thermal contraction. The superior fracture stress is attributed to dense multilayers, free from macroscopic defects due to ion-assisted growth. After being deposited at 200°C, the multilayers remained thermally stable when vacuum annealed for 15 hours at 900°C, with no significant change in phase composition or hardness. The improved hardness, toughness, and temperature stability of the otherwise brittle nitrides are promising for industrial applications.
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•The CrCoNi medium-entropy alloy shows a superior strength and ductility synergy, Charpy impact energy (AK), and fracture toughness at cryogenic temperatures as compared to both 316L and 316LN ...stainless steels.•These three alloys all rely heavily on shear transformations upon plastic straining, with deformation twinning dominating in CrCoNi while martensitic transformation involved in stainless steels.
We systematically compared the mechanical properties of CrCoNi, a recently emerged prototypical medium-entropy alloy (MEA) with face-centered-cubic (FCC) structure, with hallmark FCC alloys, in particular, the well-known austenitic 316L and 316LN stainless steels, which are also concentrated single-phase FCC solid solutions and arguably next-of-kin to the MEAs. The tensile and impact properties, across the temperatures range from 373 K to 4.2 K, as well as fracture toughness at 298 K and 77 K, were documented. From room temperature to cryogenic temperature, all three alloys exhibited similarly good mechanical properties; CrCoNi increased its tensile uniform elongation and fracture toughness, which was different from the decreasing trend of the 316L and 316LN. On the other hand, the stainless steels showed higher fracture toughness than CrCoNi at all temperatures. To explain the differences in macroscopic mechanical properties of the three alloys, microstructural hardening mechanisms were surveyed. CrCoNi MEA relied on abundant mechanical twinning on the nanoscale, while martensitic transformation was dominant in 316L at low temperatures. The deformation mechanisms in the plastic zone ahead of the propagating crack in impact and fracture toughness tests were also analyzed and compared for the three alloys.
The fracture behavior was investigated of a bulk nanostructured 316L austenitic stainless steel with embedded nanotwin bundles incorporated by dynamic plastic deformation. The nanotwin bundles were ...demonstrated to be critical to strengthen and toughen the as-deformed samples with mixed microstructures of nano-grains and nano-twins. With increment in strength, the fracture toughness decreases due to the generation of increasingly more nano-grains. Additional controlled thermal annealing that makes the nano-grains recover or recrystallize leads to reduced strengths but more remarkably improved fracture toughness. The enhanced strength−fracture toughness synergy can be attributed to the nanotwin bundles that constrict the damage development in the matrix of either nano-grains or recrystallized grains, and that resist crack propagation via acting as ductile crack bridging ligaments.
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To explore mechanical properties of multilayer TiAlSiN coatings deposited on turning tools and their cutting performance against Inconel 718, TiAlSiN coatings with five different multilayer ...configurations, including single layer TiAlSiN-A (with higher adhesion strength), single layer TiAlSiN-B (with higher hardness), bilayer, four-layer, and eight-layer, were deposited using high power impulse magnetron sputtering (HiPIMS). The microstructure, chemical composition, hardness, adhesion, toughness and surface roughness of those coatings are measured and the cutting performance against Inconel 718 is analyzed. It is demonstrated that the multilayer structure results in an increase of both toughness and compressive stress of TiAlSiN coatings, and the one with eight-layer configuration shows the highest toughness among the five coatings. The results of the cutting experiment showed that eight layer coatings have maximum life while the TiAlSiN-A has minimum. This improvement of multilayer structure is believed to be due to the increasing toughness, which alleviates the damage caused by the frequent impact of Inconel 718 hard particles during cutting. This study also shows there is a negative correlation between spalling area of flank surface and adhesion of coatings.
•The multilayer structure results in an increase of both toughness and compressive stress of TiAlSiN coatings.•The toughness shows the most direct positive correlation with cutting life during the cutting process of Inconel 718.•It is more effective to improve coating toughness to extend tool life rather than merely increasing coating hardness during cutting the Inconel 718.
PC/PBT alloy is flammable resulting in fire safety hazards in practical applications and the existing flame retardants have a great influence on the mechanical properties, which limits its ...application range. Therefore, it is an urgent problem to improve the flame retardancy of PC/PBT alloy while taking its mechanical properties into account. Herein, a novel flame retardant and reactive compatibilizer was synthesized by grafting 9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide (DOPO) onto ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA), named as DOPO-EG, to improve the flame retardancy and mechanical properties of PC/PBT alloy simultaneously. Additionally, based on the effective synergistic effect of enhancing the charring and flame retardancy between silicon and phosphorus, the organosilicon flame retardant (RMSi) is introduced and compounded with DOPO-EG to prepare excellent flame retardancy PC/PBT/DOPO-EG/RMSi composites. The results showed that the PC/PBT/DOPO-EG/RMSi composites with 10 wt% DOPO-EG and 8 wt% RMSi (CBE10P10Si8) reached UL-94 V-0 rating and the peak of heat release rate (PHRR) and total heat release rate (THR) of CBE10P10Si8 decreased by 42% and 16% respectively. This is due to the fact that DOPO is cracked into phosphorus radicals to capture and eliminate the active H and OH radicals, inhibiting the chain free radical reaction, and RMSi is enriched on the surface of CBE10P10Si8 to form an inorganic oxygen insulation protective layer during combustion. The impact strength of CBE10P10Si8 increased from 5.8 kJ/m2 to 11.9 kJ/m2. The improvement of impact strength is owing to the existence of DOPO-EG which promotes the formation of the interface layer between PC and PBT phases, resulting in the transfer of stress between the two phases. This work provides a new method for the preparation of PC/PBT alloy with excellent flame retardancy and mechanical properties, and also provides a certain reference value for the research of flame retardancy and toughening modification of polymer composites.
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•The organosilicon flame retardant (RMSi) is introduced into DOPO-EG to prepare flame retardant masterbatch.•The impact strength of PC/PBT/DOPO-EG/RMSi composites increased from 5.8 kJ/m2 to 11.9 kJ/m2.•With the addition of DOPO-EG and RMSi the PC/PBT composites reached UL-94 V-0 rating.
The fracture toughness was measured by the Vickers indentation method and by chevron notch for a series of xCaO‐xAl2O3‐(100 − 2x)SiO2 glasses. As the silica content was increased, the fixed ξ value ...Vickers indentation fracture toughness (IFT) values increased, while the chevron notch values decreased. Glasses with higher silica contents deform with more densification and less shear when indented with a Vickers tip, thus resulting in reduced residual stress in the region surrounding the indent. The reduction in residual stress for high silica glasses results in less median/radial crack extension and unreasonably high Vickers IFT values. This indicates that a fixed ξ value of 0.016 is not appropriate for the glasses in this series. By repeating the IFT method with a sharper 110° four‐sided pyramidal diamond indenter, it is demonstrated that indentation toughness and chevron notch toughness values now trend in the same direction and are in good agreement with a fixed ξ value of 0.0297. With the sharper indenter tip, the densification component to the deformation is substantially reduced for all glass types such that it no longer has such a prominent influence on the residual stress field. This result suggests that a fixed ξ value IFT method may be appropriate for all glass types if a sharper indenter tip is substituted in the place of the Vickers tip.
•Toughness of fiber-reinforced concrete under four test conditions is analyzed.•Compressive strength, bending strength and splitting tensile strength are studied.•Influence of different fiber mixing ...ratios on the toughness of concrete is discussed.•Optimum ratio of steel and polypropylene fibers for enhancing toughness is obtained.
The toughening effect of a hybrid combination of steel and polypropylene fibers on high-strength concrete (HSC) is investigated using bending, quasi-static, and dynamic splitting tensile tests. The bending strength and quasi-static splitting tensile strength of polypropylene-fiber-reinforced HSC improves only when the volume fraction of polypropylene fiber reaches 0.22%. The bending strength of steel-fiber-reinforced HSC is higher still, while its quasi-static splitting tensile strength is slightly lower when the steel fiber volume is higher than 2.0%. When an appropriate amount of steel and polypropylene fibers are employed together in HSC, the bending strength and quasi-static splitting tensile strength increases further. By analyzing the toughness ratio, toughness index, and energy dissipation, it is found that the toughness of HSC can be greatly increased by the introduction of steel fiber, but it is only slightly affected by polypropylene fiber. The toughness of HSC can be further improved by introducing an optimal hybrid combination of steel and polypropylene fibers. Hybrid-fiber- reinforced HSC with 0.12% polypropylene fiber has better bending toughness when the volume fraction of steel fiber reaches 2.0%~3.0%. When 2.5% steel fiber and 0.12% polypropylene fiber are mixed in HSC, the dynamic and quasi-static splitting tensile toughness of hybrid-fiber-reinforced HSC reaches the best.
Mental toughness (MT) is an umbrella term that entails positive psychological resources, which are crucial across a wide range of achievement contexts and in the domain of mental health. We ...systematically review empirical studies that explored the associations between the concept of MT and individual differences in learning, educational and work performance, psychological well-being, personality, and other psychological attributes. Studies that explored the genetic and environmental contributions to individual differences in MT are also reviewed. The findings suggest that MT is associated with various positive psychological traits, more efficient coping strategies and positive outcomes in education and mental health. Approximately 50% of the variation in MT can be accounted for by genetic factors. Furthermore, the associations between MT and psychological traits can be explained mainly by either common genetic or non-shared environmental factors. Taken together, our findings suggest a 'mental toughness advantage' with possible implications for developing interventions to facilitate achievement in a variety of settings.
•Presenting the relationship between fracture toughness and the number of freeze–thaw cycles.•Presenting the relationship between fracture toughness and freezing temperature.•Analysis of X-ray CT to ...investigate the damage caused by the freeze–thaw cycles.
The freeze–thaw process is one of the natural phenomena significantly affecting the characteristics of rocks and their properties. This study aimed at investigating the effects of freeze–thaw cycles and freezing temperature on mode I and mode II fracture toughness of Lushan sandstone. To this end, specimens were exposed to 0, 5, 10, 20 and 30 freeze–thaw cycles, and mode I and mode II fracture toughness were evaluated in different cycles. The effect of freezing temperature in a freeze–thaw cycle on mode I and mode II fracture toughness was also investigated. X-ray computerized tomography (CT) was used to determine specimen damages caused by freeze–thaw cycles. According to the results, mode I and mode II fracture toughness nonlinearly decreased with increasing the number of freeze–thaw cycles. The CT photographs showed an increase in the damage factor caused by freeze–thaw cycles. The mode I and mode II fracture toughness of Lushan sandstone nonlinearly decreased with increasing the freezing temperature in the freeze–thaw process.
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