Effect of Strain Ratio on Fatigue Model of Ultra-fine Grained Pure Titanium

The ultra-fine grained(UFG)pure titanium was prepared by equal channel angular pressing(ECAP)and rotary swaging(RS).The strain controlled low cycle fatigue(LCF)test was carried out at room temperature.The fatigue life prediction model and mean stress relaxation model under asymmetrical stress load were discussed.The results show that the strain ratio has a significant effect on the low cycle fatigue performance of the UFG pure titanium,and the traditional Manson-coffin model can not accurately predict the fatigue life under asymmetric stress load.Therefore,the SWT mean stress correction model and three-parameter power curve model are proposed,and the test results are verified.The final research shows that the threeparameter power surface model has better representation.By studying the mean stress relaxation phenomenon under the condition of R≠-1,it is revealed that the stress ratio and the strain amplitude are the factors that significantly afiect the mean stress relaxation rate,and the mean stress relaxation model with the two variables is calculated to describe the mean stress relaxation phenomenon of the UFG pure titanium under different strain ratios.The fracture morphology of the samples was observed by SEM,and it was concluded that the final fracture zone of the fatigue fracture of the UFG pure titanium was a mixture of ductile fracture and quasi cleavage fracture.The toughness of the material increases with the increase of strain ratio at the same strain amplitude.

Gradient Ultra-fine Grained Surface Layer in 6063 Aluminum Alloy Obtained by Means of Rotational Accelerated Shot Peening

Gradient ultra-fine grained surface layer in 6063 aluminum alloy was obtained by means of a novel surface self-nanocrystallization technique,namely rotational accelerated shot peening(RASP)treatment.The average grain sizes along the vertical section vary from hundreds of nanometers in the top surface to micrometers in the matrix.By using orthogonal experimental design to compare roughness values and hardness values,we synthesized the processing parameters to obtain sample of smaller roughness values and higher hardness.

Microstructures of ultra-fine grained FeCoV alloys processed by ECAP plus cold rolling and their evolutions during tempering

A new processing method,equal channel angular pressing(ECAP)plus cold rolling(CR),was applied to producing ultra-fine grained FeCoV alloy.The microstructures of ultra-fine grained FeCoV alloy after ECAP,ECAP plus CR,and the effect of tempering treatment on the microstructure of FeCoV alloy produced by ECAP plus CR were investigated.The results show that an elongated substructure with a width of about 0.3μm is obtained after four-pass ECAP using Route A.Cold rolling after ECAP cannot change the morphologies of elongated substructure,and it results in higher fraction of high-angle boundaries and higher dislocation density compared with the identical ECAP without rolling.Subsequent tempering for 30 min at 853 K brings about many nano-phases precipitating at subgrain boundaries and insides the grains,and the size of precipitated phase is measured to be about 10 nm.Nano-phases grow up with increasing tempering temperature and equiaxed structure forms at 883 K.

Microstructural Evolution and Thermal Stability of Ultra-fine Grained Al-4Mg Alloy by Equal Channel Angular Pressing

Experiments were conducted to evaluate the grain refinement and thermal stability of ultra-fine grained Al-4Mgalloy introduced by equal-channel angular pressing (ECAP) at 473 K. The results show that the intensities of X-ray(111/222) and (200/400) peaks for the alloy processed by ECAP decrease significantly and the peak widths of halfheight become broadening compared with the corresponding value in the annealed alloy. The microstructure of 2passes ECAPed alloy consists of both elongated and equiaxed subgrains. The residual strain in the alloy increaseswith increasing passes numbers, that appears as increasing dislocation density and lattice constant of matrix. Anequiaxed ultra-fine grained structure of～0.2μm is obtained in the present alloy after 8 passes. The ultra-fine grainsare stable below 523 K, because the alloy retains extremely fine grain size of～1μm after static annealing at 523 Kfor 1 h.

Surface Cracking Behaviors of Ultra-Fine Grained Tungsten Under Edge Plasma Loading in the HT-7 Tokamak

Tests of the candidate plasma facing materials（PFMs） used in experimental fusion devices are essential due to the direct influence of in-situ plasma loading.A type of ultrafine grained（UFG） tungsten sintered by resistance sintering under ultra-high pressure（RSUHP） method has been exposed in the edge plasma of the HT-7 tokamak to investigate its performance under plasma loading.Under cychc edge plasma loading,the UFG tungsten develops both macro and micro cracks.The macro cracks are attributed to the low temperature brittleness of the tungsten material itself,while the micro cracks are generated from local intense power flux deposition.

An in vivo Evaluation of Ultra-fine Grained Titanium Implants

The present work focuses mainly on an in vivo evaluation of ultra fine grained titanium （UFG-Ti） obtained by severe plastic deformation （SPD）. The SPD on commercially produced Grade 2 titanium （Cp-Ti） resulted in the refinement of the grain size by several orders of magnitude. Polished surfaces having similar roughness from both UFG-Ti and Cp-Ti were prepared. In vitro test revealed the presence of fibronectin, which was involved in the attachment of the cells to the substrate. Phase contrast micrographs showed the highest signal of fibronectin in UFG-Ti, indicating that it is more cytocompatible than Cp-Ti. In vivo tests, by subcutaneous implantation of the metals in the rats showed the better biocompatibility of UFG-Ti over Cp-Ti. The improved biocompatibility of UFG-Ti was attributed to the presence of surface discontinuities （in the form of nano-defects）, surface energy, higher wettability, surface stress and stable TiO2 films, which increased the protein adsorption on the surface.

Corrosion behavior of ultra-fine grained industrial pure Al fabricated by ECAP

Corrosion behavior of ultra-fine grained(UFG) industrial Al fabricated by equal channel angular pressing(ECAP) for 16 pass times was investigated by potentiodynamic polarization test,potentiostatic polarization test,electrochemical impedance spectroscopy(EIS) measurement,immersion test and surface analyses (OM and SEM). The microstructures including grain size,grain boundaries and dislocations were also observed by TEM. The results show that the UFG industrial pure Al has more positive pitting potential,less corrosion current density and five times larger passive film resistance compared with the coarse grained(CG) one. It was found that the increased pitting resistance is profited from the more stable passive film kept in the Cl-aggressive solution due to more grain boundaries,larger fraction of non-equilibrium grain boundaries and residual stress of the UFG industrial pure Al.

Superplasticity of fine-grained Mg-10Li alloy prepared by severe plastic deformation and understanding its deformation mechanisms

The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy(LAZ1011)with a grain size of 3.2μm,primarily composed of the BCCβphase and a small amount of the HCPαphase,were examined in a temperature range of 473 K to 623 K.The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling.The best superplasticity was achieved at 523 K and at strain rates of 10^(-4)-5×10^(-4)s^(-1),where tensile elongations of 550±600%were obtained.During the heating and holding stage of the tensile samples prior to tensile loading,a significant increase in grain size was observed at temperatures above 573 K.Therefore,it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms.In the investigated strain rate range,the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding,while at high strain rates,lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism.It was concluded that solute drag creep is unlikely to occur.During the late stages of deformation at 523 K,it was observed that grain boundary sliding led to the agglomeration of theαphase,resulting in significant strain hardening.Deformation mechanism maps were constructed forβ-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate,stress,temperature,and grain size,using the constitutive equations for various deformation mechanisms derived based on the data of the current tests.

Application of novel constrained friction processing method to produce fine grained biomedical Mg-Zn-Ca alloy

In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced.Compared to the previous as-cast microstructure,the grain size was reduced from more than 1 mm to around 4μm within 3 s by a single process cycle.The compressive yield strength was increased by 350%while the ultimate compressive strength by 53%.According to the established material flow behaviors by“tracer material”,the plastic material was transported by shear deformation.From the base material to the rod,the material experienced three stages,i.e.deformation by the tool,upward flow with additional tilt,followed by upward transportation.The microstructural evolution was revealed by“stop-action”technique.The microstructural development at regions adjacent to the rod is mainly controlled by twinning,dynamic recrystallization(DRX)as well as particle stimulated nucleation,while that within the rod is related to DRX combined with grain growth.

Microstructure and mechanical properties of ultra-fine grained MoNbTaTiV refractory high-entropy alloy fabricated by spark plasma sintering

The MoNbTaTiV refractory high-entropy alloy(RHEA)with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying(MA)and spark plasma sintering(SPS).The microstructural evolutions,mechanical properties and strengthening mechanisms of the alloys were systematically investigated.The nanocrystalline mechanically alloyed powders with simple bodycentered cubic(BCC)phase were obtained after 40 h MA process.Afterward,the powders were sintered using SPS in the temperature range from 1500℃to 1700℃.The bulk alloys were consisted of submicron scale BCC matrix and face-centered cubic(FCC)precipitation phases.The bulk alloy sintered at 1600℃had an average grain size of 0.58μm and an FCC precipitation phase of 0.18μm,exhibiting outstanding micro-hardness of 542 HV,compressive yield strength of 2208 MPa,fracture strength of 3238 MPa and acceptable plastic strain of 24.9%at room temperature.The enhanced mechanical properties of the MoNbTaTiV RHEA fabricated by MA and SPS were mainly attributed to the grain boundary strengthening and the interstitial solid solution strengthening.It is expectable that the MA and SPS processes are the promising methods to synthesize ultra-fine grains and homogenous microstructural RHEA with excellent mechanical properties.

Mechanical and Microstructural Properties of Ultra-fine Grained AZ91Magnesium Alloy Tubes Processed via Multi Pass Tubular Channel Angular Pressing(TCAP)

Ultra-fine grained （UFG） cylindrical tubes were produced via recently developed tubular channel angular pressing （TCAP） process through different passes from as-cast AZ91 magnesium alloy. The microstructure and mechanical properties of processed tube through one to four passes of TCAP process at 200℃ were investigated. Microhardness of the processed tube was increased to 98.5 HV after one pass from an initial value of 67 Hr. An increase in the number of passes from one to higher number of passes has no more effect on the microhardness. Yield and ultimate strengths were increased by 4.3 and 1.4 times compared to those in as-cast condition. Notable increase in the strength was achieved after one pass of TCAP while higher number of passes has no more effect. Microstructural investigation shows notable decrease in the grain size to around 500 nm from the primary value of - 150 μm. Dissolution and distribution of hard MglTAI12 phase in the grain boundaries of dynamically recrystallized UFG AZ91 with a mean grain size of - 500 nm was an interesting issue of TCAP processing at 200 ℃ compared to other severe plastic deformation processes.

Isothermal Growth Kinetics of Ultra-fine Austenite Grains in a Nb-V-Ti Microalloyed Steel

Ultra-fine austenite grains with size of i-3 μm were prepared in a Nb-V-Ti steel through repetitive treatment of rapid heating and quenching. A model for the growth kinetics of these ultra-fine austenite grains was successfully created through successive 2 processes, and the activation energy Q for growth was estimated to be about 693.2 kJ/mol, which directly shows the inhibition effect of microalloy elements on the growth of ultra-fine austenite grains.

Effect of upsetting force on microstructure of welds in resistance spot welding of 400 MPa ultra-fine grain steel

The ultra-fine grain （UFG） steel is welded by using resistance spot welding technique with or without requirement of upsetting force. Metallographic inspection shows that the grain size of weld nugget is larger than that of the base metal and the microstructure is altered significantly. In addition, contracting defects such as air holes can be found in the nugget center. The experiments show that the defects can be effectively avoided by the technique of adding upsetting force during the nugget cooling and crystallizing processes. In tensile shear tests, the welding joint starts to crack from the inner edge of the corona bond. The results of micro-hardness tests show that the newly born martensite structure dramatically improves the hardness of the joint. Under the interactions between residual stresses and regenerated fine grains, the micro-hardness of the heat-affected zone （ HAZ ） is lower than that of the nugget, but evidently higher than that of the base metal.

Effect of welding heat input on HAZ character in ultra-fine grain steel welding

In this essay, we studied how heat input affected the microstructure, hardness, grain size and heat-affected zone(HAZ) dimension of WCX355 ultra-fine grain steel which was welded respectively by the ultra narrow-gap welding (UNGW) process and the overlaying process with CO 2 as protective atmosphere and laser welding process. The experimental results show when the heat input changed from 1.65 kJ/cm to 5.93 kJ/cm, the width of its HAZ ranged from 0.6 mm to 2.1 mm.The average grain size grew up from 2～5 μm of base metal to 20～70 μm and found no obvious soften phenomenon in overheated zone. The width of normalized zone was generally wide as 2/3 as that of the whole HAZ, and the grain size in this zone is smaller than that in base metal. Under the circumstance of equal heat input, the HAZ width of UNGW is narrower than that of the laser welding.

Grain yield and N uptake of maize in response to increased plant density under reduced water and nitrogen supply conditions

The development of modern agriculture requires the reduction of water and chemical N fertilizer inputs.Increasing the planting density can maintain higher yields,but also consumes more of these restrictive resources.However,whether an increased maize density can compensate for the negative effects of reduced water and N supply on grain yield and N uptake in the arid irrigated areas remains unknown.This study is part of a long-term positioning trial that started in 2016.A split-split plot field experiment of maize was implemented in the arid irrigated area of northwestern China in 2020 to 2021.The treatments included two irrigation levels:local conventional irrigation reduced by 20%(W1,3,240 m^(3)ha^(-1))and local conventional irrigation(W2,4,050 m^(3)ha^(-1));two N application rates:local conventional N reduced by 25%(N1,270 kg ha^(-1))and local conventional N(360 kg ha^(-1));and three planting densities:local conventional density(D1,75,000 plants ha^(-1)),density increased by 30%(D2,97,500 plants ha-1),and density increased by 60%(D3,120,000 plants ha^(-1)).Our results showed that the grain yield and aboveground N accumulation of maize were lower under the reduced water and N inputs,but increasing the maize density by 30% can compensate for the reductions of grain yield and aboveground N accumulation caused by the reduced water and N supply.When water was reduced while the N application rate remained unchanged,increasing the planting density by 30% enhanced grain yield by 13.9% and aboveground N accumulation by 15.3%.Under reduced water and N inputs,increasing the maize density by 30% enhanced N uptake efficiency and N partial factor productivity,and it also compensated for the N harvest index and N metabolic related enzyme activities.Compared with W2N2D1,the N uptake efficiency and N partial factor productivity increased by 28.6 and 17.6%under W1N1D2.W1N2D2 had 8.4% higher N uptake efficiency and 13.9% higher N partial factor productivity than W2N2D1.W1N2D2 improved urease activity and nitrate reductase activity by 5.4% at the R2(blister)stage and 19.6% at the V6(6th leaf)stage,and increased net income and the benefit:cost ratio by 22.1 and 16.7%,respectively.W1N1D2 and W1N2D2 reduced the nitrate nitrogen and ammoniacal nitrogen contents at the R6 stage in the 40-100 cm soil layer,compared with W2N2D1.In summary,increasing the planting density by 30% can compensate for the loss of grain yield and aboveground N accumulation under reduced water and N inputs.Meanwhile,increasing the maize density by 30% improved grain yield and aboveground N accumulation when water was reduced by 20% while the N application rate remained constant in arid irrigation areas.

Ultra-fine ferrite grains obtained in the TSDR process

By careful design of rolling schedule,ultra-fine （～2μm） ferrite grains in a low carbon high niobium （0.09wt%Nb） microalloying steel with average austenite grain sizes above 800 μm can be achieved in the simulated thin slab direct rolling process. The 5-pass deformation was divided into two stages： the refinement of austenite through complete recrystallization and the refinement of ferrite through dynamic strain-induced transformation. The effects of Nb in solution and strain-induced NbCN precipitates on the ferrite transformation were also extensively discussed.

Fine Grained Feature Extraction Model of Riot-related Images Based on YOLOv5

With the rapid development of Internet technology,the type of information in the Internet is extremely complex,and a large number of riot contents containing bloody,violent and riotous components have appeared.These contents pose a great threat to the network ecology and national security.As a result,the importance of monitoring riotous Internet activity cannot be overstated.Convolutional Neural Network(CNN-based)target detection algorithm has great potential in identifying rioters,so this paper focused on the use of improved backbone and optimization function of You Only Look Once v5(YOLOv5),and further optimization of hyperparameters using genetic algorithm to achieve fine-grained recognition of riot image content.First,the fine-grained features of riot-related images were identified,and then the dataset was constructed by manual annotation.Second,the training and testing work was carried out on the constructed dedicated dataset by supervised deep learning training.The research results have shown that the improved YOLOv5 network significantly improved the fine-grained feature extraction capability of riot-related images compared with the original YOLOv5 network structure,and the mean average precision(mAP)value was improved to 0.6128.Thus,it provided strong support for combating riot-related organizations and maintaining the online ecological environment.

Effects of irradiation on superconducting properties of small-grained MgB_(2) thin films

We investigate the effect of ion irradiation on MgB_(2) thin films with small grains of approximately 122 nm and 140 nm.The flux pinning by grain boundaries is insignificant in the pristine MgB_(2) films due to good inter-grain connectivity,but is significantly improved after 120-keV Mn-ion irradiation.The scaling behavior of the flux pinning force density for the ion-irradiated MgB_(2) thin films with nanoscale grains demonstrates the predominance of pinning by grain boundaries,in contrast to the single-crystalline MgB_(2) films where normal point pinning was dominant after low-energy ion irradiation.These results suggest that irradiation-induced defects can accumulate near the grain boundaries in metallic MgB_(2) superconductors.

Investigation on fracture behavior of the welded joint HAZ of ultra-fine grain steel SS400

The critical crack dimensions of both base-metal specimen and HAZ specimen are measured via wide-plate tensile tests. Based on the “fitness for purpose” principle, the fracture behavior of the ultra-fine grain steel SS400 welded joint HAZ is assessed. The test results indicate that overmatching is benefit for the whole capability’s improvement of ultra-fine grain steel SS400. The test results are confirmed by using finite element method (FEM).