Diversity of intergranular corrosion and stress corrosion cracking for 5083 Al alloy with different grain sizes

5083 Al alloy sheets with different grain sizes(8.7-79.2 μm) were obtained by cold rolling and annealing. Their microstructures, intergranular corrosion(IGC), stress corrosion cracking(SCC), and crack propagation behaviors were investigated. The results showed that samples with coarse grains exhibit better IGC resistance with a corrosion depth of 15 μm. The slow strain rate test results revealed that fine-grained samples exhibit better SCC resistance with a susceptibility index(ISSRT) of 11.2%. Furthermore, based on the crack propagation mechanism, grain refinement can improve the SCC resistance by increasing the number of grain boundaries to induce the corrosion crack propagation along a tortuous path. The grains with {011} orientation could hinder crack propagation by orientating it toward the low-angle grain boundary region. The crack in the fine-grained material slowly propagates due to the tortuous path, and low H;and Cl;concentrations.

Enhanced Cu/graphene adhesion by doping with Cr and Ti:A first principles prediction

We presented a density functional theory study on doping effects of transition metals(Cr and Ti)on the Cu/graphene interface adhesion.Various undoped Cu/graphene interface structures were constructed using both the sandwich and the surface models.Energetics calculations showed that the interface binding strength only weakly depends on interface coordination.Both interface models predicted the top-fcc coordination type as the most energy-favored,with a low binding energy value.Segregated Cr prefers to substituting for Cu, while Ti occupies a hollow site at the interface.Although the segregation tendencies are both very weak,once present on the interface,both dopants can greatly increase the interface binding energy and improve the adhesion.

Microstructure evolution and recrystallization behavior of cold-rolled Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy during annealing

The effects of cold-rolling reduction,annealing temperature,and time on recrystallization behavior and kinetics of cold-rolled Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy were investigated using the Vickers hardness test,scanning electronic microscopy(SEM),transmission electron microscopy(TEM)and electron backscatter diffractometry(EBSD).The results show that the rate of the recrystallization increased with increasing annealing temperature and rolling reduction.Recrystallized grains nucleated preferentially at sites with high density dislocation and deformation stored energy and then grew into integral grains.Recrystallization texture changed from-1010-//RD to-1120-//RD.The grain orientation changed from random orientation to the orientation with the maximum misorientation around 30°.Recrystallization kinetics and maps were constructed based on the Johnson-Mehl-Avrami-Kolmogorov(JMAK)equation to derive parameters sensitive to the microstructure.The activation energies for recrystallization of 30%,50%and 70%cold-rolling reductions were determined to be 240,249 and 180 kJ/mol,respectively.

Hot deformation behaviors and dynamic recrystallization mechanism of Ti-35421 alloy inβsingle field

Hot deformation behaviors and microstructure evolution of Ti-3Al-5Mo-4Cr-2Zr-1Fe(Ti-35421)alloy in theβsingle field are investigated by isothermal compression tests on a Gleeble-3500 simulator at temperatures of 820-900°C and strain rates of 0.001-1 s^(-1).The research results show that discontinuous yield phenomenon and rheological softening are affected by the strain rates and deformation temperatures.The critical conditions for dynamic recrystallization and kinetic model of Ti-35421 alloy are determined,and the Arrhenius constitutive model is constructed.The rheological behaviors of Ti-35421 alloys aboveβphase transformation temperature are predicted by the constitutive model accurately.The EBSD analysis proves that the deformation softening is controlled by dynamic recovery and dynamic recrystallization.In addition,continuous dynamic recrystallization is determined during hot deformation,and the calculation model for recrystallization grain sizes is established.Good linear dependency between the experimental and simulated values of recrystallized grain sizes indicates that the present model can be used for the prediction of recrystallized grain size with high accuracy.

Point defect concentrations of L12-Al3X(Sc, Zr, Er)

The point defect concentrations of L12-A13X（Sc, Zr, Er） were systematically investigated using the first- principle calculations with thermodynamics approach. The results show that the constitutional point defects of off- stoichiometric L12-A13X（Sc, Zr, Er） prefer to occur in X sublattice, that is X anti-site in X-rich alloy and X vacancy in Al-rich alloy, respectively. And A1 anti-site also has a high density in Al-rich Llz-A13X（Sc, Er）. It is found that the point defect concentrations of stoichiometric L12-A/3X（Sc, Zr） follow in the sequence as： A1 vacancies （VA0 〉 X vacancies （Vx） 〉 X anti-sites （XA1） 〉 A1 anti- sites （Alx）. The point defect concentration of stoichio- metric A13Er is similar to that of L12-A13X（Sc, Zr）. The result suggests that the A1 vacancy （VA1） is a dominant point defect in L12-A13X（Sc, Zr, Er）. A simple parameter Hvx-HVA1 can be used for a rough estimation of the point defect concentrations in L12-A13X structure. Some rules of point defect concentrations for L12-A13X（Sc, Zr, Er） are also revealed.

Enhanced Wear Resistance of Ni/h-BN Composites with Graphene Addition Produced by Spark Plasma Sintering

Ni-based self-lubricating composites containing a fixed amount of hexagonal boron nitride (h-BN)(5 wt%) and different amounts of graphene (0-1.5 wt%) were prepared by ultrasonic dispersion, high-energy ball milling, and spark plasma sintering. The effects of the graphene content on the physical, mechanical, and wear properties of the Ni/h-BN composites were evaluated. These properties were first enhanced with increasing graphene content, reaching optimal behavior for a graphene content of 1 wt%, and then degraded with further graphene addition. Compared to the pure Ni/h-BN composite, the relative density, hardness, and bending strength of the composite with 1 wt% graphene increased by 2.7%, 7.4%, and 6.3%, respectively, while the friction coefficient decreased by 56% to 0.31, and a reduction in wear rate by a factor of 5-15 was observed. The mechanism for improving the wear properties of the composite with added graphene was due to the formation of a graphene lubricating film on the worn surface, which increased the load bearing capacity of the surface and enhanced lubrication during wear.

Effect of Cooling Rate on the Formation and Morphology of (W,V)Cx in VC-doped WC–Co Cemented Carbide

The grain growth retardation mechanism and the effect of cooling rate on VC-doped WC–Co cemented carbides were investigated in this work.WC–30Co and WC–30Co–VC were prepared by powder metallurgy,liquid-phase sintering at 1400 ℃ and followed by water quenching（[150 ℃/s） or furnace cooling（＊0.083 ℃/s）.Based on the results of electron probe microanalysis（EPMA）,we found that WC concentration in the Co binder was independent of VC doping during liquid-phase sintering,hence barely contributing to the retardation of WC grain growth.In contrast,the（W,V）Cx phase formed at the WC/Co interfaces played a major role in retarding WC grain growth during liquid-phase sintering.The effect of cooling rate on the morphology of（W,V）Cxwas revealed by high-resolution transmission electron microscopy（HRTEM） and energy-dispersive spectroscopy（EDS）.In the water-quenched WC–30Co–VC,（W,V）Cxprecipitates were found as thin layers at the WC/Co interfaces.In contrast,both thin layers of similar thickness and nanoparticles of（W,V）Cx were observed in the furnace-cooled counterpart.These observations listed above suggested that thin（W,V）Cxlayers were stable structures effectively suppressing the growth of WC grains and their thickness remained independent of the cooling rate.The（W,V）Cxnanoparticles,however,may be inhibited through rapid cooling,ensuring the VC-doped WC–Co cemented carbides desired toughness.

Recrystallization and mechanical properties of cold-rolled FeCrAl alloy during annealing

The efect of cold rolling and annealing on the microstructure and properties of an Fe-13Cr-4.5Al-2.2Mo-1.1Nb alloy was investigated.The results showed that the recrystallization rate increased with increasing annealing temperature and rolling reduction.Recrystallization kinetics was constructed based on Johnson-Mehl-Avrami-Kolmogorov equation.The apparent activation energies of recrystallization were 161.385,144.770,and 95.362 kJ/mol for the samples with 30%,50%,and 70%cold-rolling reduction,respectively.With the cold-rolling reduction increasing,the textureγfber partly changed to<100>//ND.After annealing,γfber of the alloy with 30%thickness reduction retained,the subgrains disappeared through merging,and the proportion of coincident site lattice grain boundaries increased and became more continuous.30%cold-rolling reduction alloy annealed at 730°C for 120 min not only possessed relatively high yield strength(YS)of^730 MPa and ultimate tensile strength(UTS)of^880 MPa,but also exhibited elongation of^16%at room temperature.After annealing at 730°C for 120 min,70%cold-rolled alloy has fner and more uniform grain,with higher elongation of^22%,YS of^615 MPa and UTS of^774 MPa.The mechanism of mechanical properties diference was explained according to Schmid factor analysis.These results provided an efective way for tuning strength and ductility of FeCrAl alloy.

Effect ofαphase on fatigue crack growth of Ti-6242 alloy

Fatigue crack growth as a function ofαphase volume fraction in Ti-6Al-2Sn-4Zr-2Mo（Ti-6242）alloy was investigated using fatigue testing,optical microscopy,scanning electron microscopy,and transmission electron microscopy.Theα＋βannealing treatments with different solid solution temperatures and cooling rates were conducted in order to tailor microstructure with differentαphase features in the Ti-6242 alloy,and fatigue crack growth mechanism was discussed after detailed microstructure characterization.The results showed that fatigue crack growth rate of Ti-6242 alloy decreased with the decrease in volume fraction of the primaryαphase（αp）.Samples with a large-sizedαgrain microstructure treated at high solid solution temperature and slow cooling rate have lower fatigue crack growth rate.The appearance of secondaryαphase（αs）with the increase of solid solution temperature led to crack deflection.Moreover,a fatigue crack growth transition phenomenon was observed in the Paris regime of Ti-6242 alloy with 29.8% αp（typical bi-modal microstructure）and large-sizedαgrain microstructure,owing to the change of fatigue crack growth mechanism.

Superhydrophobic coating on heat-resistant steel surface fabricated by a facile method

Industrial application of superhydrophobic surfaces is often hindered by complicated process and sophisticated machines. A facile wet etching method （sandblast, HCl and sandblast/HCl） with vapor deposition of PFDS （1H, 1H, 2H, 2H- perfluorodecyltriethoxysilane） was applied to fabricate superhydrophobic surface of heat-resistant steel used for vane. The coating component, surface morphology and surface roughness parameters of sample were observed by attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy. Static water contact angle （WCA） of samples with and without PFDS coating was measured by contact angle goniometer. The results showed that WCA values of polished, sandblast, HCl and sandblast/HCl-etched samples are 98°, 97°, 100° and 101°, respectively, and increase to 112°, 148°, 151 ° and 154v after vapor deposition of PFDS. The sandblast/HCl-etched sample with PFDS coating shows higher superhydrophobicity because of very large surface roughness and lotus protrusionlike structure. The superhydrophobicity of this fabricated surface has no obvious change after 38 cycles of the film adhesion test, indicating excellent durability.