Effect ofαphase morphology on fatigue crack growth behavior of Ti−5Al−5Mo−5V−1Cr−1Fe alloy

Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case,the fatigue crack growth sensitivity and fracture features with various tailoredαphase morphologies were thoroughly investigated using fatigue crack growth rate(FCGR)test,optical microscopy(OM)and scanning electron microscopy(SEM).The tailored microstructures by heat treatments include the fine and coarse secondaryαphase,as well as the widmanstatten and basket weave features.The sample with coarse secondaryαphase exhibits better comprehensive properties of good crack propagation resistance(with long Paris regime ranging from 15 to 60 MPa·m1/2),high yield strength(1113 MPa)and ultimate strength(1150 MPa),and good elongation(11.6%).The good crack propagation resistance can be attributed to crack deflection,long secondary crack,and tortuous crack path induced by coarse secondaryαphase.

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.

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.

Hot deformation behavior and microstructure features of FeCrAl-ODS alloy

The hot deformation behavior of FeCrAl-ODS alloys at temperatures of 1050-1200℃ and strain rates of 0.001-1 s^(-1),investigated.The peak stress of FeCrAl-ODS alloy during hot deformation decreased with increasing temperature and decreasing strain rate.In addition,the stress-strain curves show a dynamic softening phenomenon according to the shape of the flow curves.Based on the Arrhenius-type model,a constitutive equation and processing map of FeCrAl-ODS alloy were established.Thereafter,we proposed optimum processing parameters of 1200℃ and 0.001 s^(-1)based on the processing map.Compared with FeCrAl alloys,there was no significant phenomenon of grain coarsening during hot deformation in FeCrAl-ODS alloy.In the electron backscattered diffraction images,both recrystallized and recovered grains were observed in the matrix under dfferent deformation conditions.The fraction of dynamically recrystallized grains in the matrix under the deformation of 1100 C/0.001 s^(-1)(42.5%)was significantly higher than that at 1200℃/0.001 s^(-1)(10.6%),which was consistent with the stress-strain curves.

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.