Surface nanostructure formation mechanism of 45 steel induced by supersonic fine particles pombarding

By means of supersonic fine particles bombarding （SFPB）,a nanostructured surface layer up to 15 μm was fabricated on a 45 steel plate with ferrite and pearlite phases. To reveal the grain refinement mechanism of SFPB-treated 45 steel,microstructure features of various sections in the treated surface were systematically characterized by X-ray diffraction （XRD）,scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Grain size increases with an increase of depth from the treated surface. Plastic deformation and grain refinement processes are accompanied by an increase in strain. Plastic deformation in the proeutectoid ferrite phases has precedence over the pearlite phases. Grain refinement in the ferrite phases involves： the onset of dislocation lines （Dls）,dislocation tangles （DTs） and dense dislocation walls （DDWs） in the original grains; the formation of fine lamellar and roughly equiaxed cells separated by DDWs; by dislocation annihilation and rearrangement,the transformation of DDWS into subboundaries and boundaries and the formation of submicron grains or subgrains; the successive subdivision of grains to finer and finer scale,resulting in the formation of highly misoriented nano-grains. By contrast,eutectoid cementite phase accommodated strain in a sequence as follows： onset of elongated,bended and shear deformation under deformation stress of ferrites,short and thin cementites with a width of about 20-50 nm and discontinuous length were formed. Shorter and thinner cementites were developed into ultra-fine pieces under the action of high density dislocation and strains. At the top surface,some cementites were decomposed under severe plastic deformation. Experimental evidences and analysis indicate that surface nanocrystallization of 45 steel results from dislocation activities,high strains and high strain rate are necessary for the formation of nanocrystallites.

Comparison of Hypolipidemic Effect of Refined Konjac Meal With Several Common Dietary Fibers and Their Mechanisms of Action

The effects of RKM in comparison with pectin, algin and agar on lipid levels in serum and liver and on liver histopathology in rats were studied. In addition, the effects of all the tested materials on the composition and output of fecal bile acid were observed. All four kinds of dietary fiber were given at a level of 5% of diet to young male rats of Wistar strain fed on a lipid-rich diet contalning 5 % lard, 1% cholesteral and 0. 25 % cholate. All the dietary fibers tested have similar effects on serum lipid composition. In all groups, these substances prevent ed increases in total cholesterol in fasting serum, but the level of triglyceride was tmchangd.The concentrations of totaI cholesterol and triglyceride in the liver were lower in the RKM group than in the control group and the other three groups. Hepatic histopathological exami nation also showed the most significant lipotropic effect in the RKM group. The daily output of fecal bile acids (CDCA+GDCA) was significantly increased in the four experimental groups than in the normal group and the control group. The increase of CDCA was more significant than GDCA, suggesting that the increase of fecal bile acids, especially CDCA, may be one of the mechanisms by which RKM and the other three dietary fibers exerts a hypocholesterolemic effect

Refining Effect of a New Al3Ti1B1RE Master Alloy on Al Sheets Used for Can Manufacture and Behavior of Rare Earths in Master Alloy

The refining effect of Al3Ti1B1RE master alloy on Al sheets used for pressure can manufacture and the behavior of mixed rare earths in master alloy were investigated with XRD, OM, SEM and EDAX. It is found that the refining effect of the refiner on the material has superiority over foreign or domestic Al5Ti1B refiner, and the refiner still retains its refining ability for 6 h after adding it to molten Al, thus improving the strength and plasticity of the material remarkably. The excellent refining effect and stability of AlTiBRE refiner result from that RE can lower the surface energy of molten Al and improve the wetting characteristics of molten Al on refinement nuclei such as TiAl 3, TiB 2, etc., thus giving full play to the effect of heterogeneous nucleation and impeding the congregating tendency of TiB 2 phase in molten Al. At the same time, RE gathering in front of solid/liquid interface are also easy to cause composition supercooling in molten Al, thus impeding the growth of α Al grains and promoting α Al nucleation on refinement nuclei. In addition, RE also play certain role in purification and grain refinement, or modification, especially their effect of purification can improve the metallurgical quality of AlTiBRE master alloy.

Effect of Multiple Forging on Microstructure and Mechanical Properties of Powder Metallurgy FGH4096 Superalloy

FGH4096 is an important damage-tolerance-type powder metallurgy （PM） superalloy, which is also the optimized turbine material for high performance aero-engine. To turbine disc, bore and rim are used in high temperature-low stress condition and low temperature-high stress condition, and dual-microstructure is introduced. Coarse-grained microstructure is suit for rim region and fine-grained is no doubt most suitable for bore region. But fine-grained ingot can not make by PM technique, so that gradient heat treatment can not be developed to coarsen the grain of rim region. Under the confine of PM technique, several treatment processir, g should be taken place to refine the coarse grains of PM alloy. Multiple forging with large accumulate deformation was carried cat on PM FGH4096 superalloy, and fine grains of 3.5 μm were obtained by this treatment processing. Mechanical properties testing were ake carried out on both fine-grained and other statuses alloys, Microstrucmre evolution was observed by optical microscopy, scanning electron microscopy and transmission electron microscopy. As a result of repeated dynamic recrystallizafion, coarse grains could be completely refined into fine grains. And the increase of strength was mainly attributed to refinement effect and improvement of defects such as previous particle boundaries. Successful development of fine-grained treatment processing will promote the research of dual-microstructure turbine disc.

Evolution of secondary phase particles during deformation of Al-5Ti-1B master alloy and their effect on α-Al grain refinement

Addition of Al-5Ti-1B alloy to molten aluminum alloys can refine α-Al grains effectively and thereby improve their strength and toughness. TiAl;and TiB;in Al-5Ti-1B alloy are the main secondary-phase particles for refinement, while the understanding on the effect of their sizes on α-Al grain refinement continues to be fragmented. Therefore, Al-5Ti-1B alloys with various sizes and morphologies of the secondary-phase particles were prepared by equal channel angular pressing（ECAP）. Evolution of the secondary-phase particles during ECAP process and their impact on α-Al grain refinement were studied by X-ray diffraction and scanning electron microscope（SEM）. Results show that during the ECAP process, micro-cracks firstly appeared inside TiAl;particles and then gradually expanded, which resulted in continuous refinement of TiAl;particles. In addition, micro-distribution uniformity of TiB;particles was improved due to the impingement of TiAl;particles to TiB;clusters during deformation. Excessively large sizes of TiAl;particles would reduce the number of effective heterogeneous nucleus and thus resulted in poor grain refinement effectiveness. Moreover, excessively small TiAl;particles would reduce inhibitory factors for grain growth Q and weaken grain refinement effectiveness. Therefore, an optimal size range of 18-22 μm for TiAl;particles was suggested.

Refining mechanism of yttrium on primary α-Al in semi-solid Al alloy

Semi-solid Al7Si0.3Mg alloy slurry, which is grain-refined by yttrium, is manufactured by low temperature pouring. The effects of grain-refined by yttrium on the morphology and the grain size of the primary α-Al in semi-solid Al7Si0.3Mg alloy are researched. The results indicate that semi-solid Al7Si0.3Mg alloy with particle-like and rosette-like primary α-Al can be prepared by low temperature pouring from liquid Al7Si0.3Mg alloy grain-refined by yttrium. The grain size and particle morphology of primary α-Al in Al7Si0.3Mg alloy are markedly improved by 0.5 wt pet Y. The refining mechanism of Y on the morphology and the grain size of the primary α-Al in semi-solid Al7Si0.3Mg alloy are delved.

Novel interface regulation of Sn1.0Ag0.5Cu composite solders reinforced with modified ZrO_(2):Microstructure and mechanical properties

With the trends of miniaturization and high density of electronic packaging,there has been an urgent demand to open up lead-free solders with high strength and ductility.In this study,a ZrO_(2)-reinforced Sn1.0Ag0.5Cu composite solder was designed.First,surface modification on ZrO_(2) was conducted with ball milling-pyrolysis method.Subsequently,NiO modified ZrO_(2)(NiO/ZrO_(2))was added to the solder matrix with ultrasonic stirring.The morphology and interface of NiO/ZrO_(2) were discussed.Moreover,the microstructure,interface and mechanical properties of the composite solders were systematically studied.The results showed that NiO nanoparticles were evenly adhered to the ZrO_(2) surface,and the interface relationship between them was semi-coherent and coherent.Further,an appropriate addition of NiO/ZrO_(2) could refine the microstructure of composite solders.The refinement mechanism was systematically investigated.Besides,a micro-mechanical lock and non-micropored clean interface was formed between NiO/ZrO_(2) and the solder matrix.The Sn/NiO/ZrO_(2) interface system based on mutual solid solution was ingeniously designed.The ultimate tensile strength and elongation were increased synergistically,and the fracture mechanism transformed from a ductile−brittle mixed fracture mode to a ductile fracture mode.Therefore,a lead-free solder with high strength and ductility was obtained.

A novel annealing method to uniformly refine deformed mixed grain microstructure of a solution-treated Ni-based superalloy

Increasing static recrystallization(SRX)nucleation rate and decreasing grain growth rate are the main ways to obtain uniform and fine grain microstructure by annealing treatment.However,it is contradictory to raise the SRX nucleation rate and reduce grain growth rate during isothermal annealing treatment.This is because the increase of the SRX nucleation rate needs to raise annealing temperature,while the decline of grain growth rate needs to reduce the annealing temperature.To solve the contradiction,a novel method named cooling recrystallization annealing treatment(CRT)is designed and verified.For the CRT,the relatively high annealing temperature in the primary stage can promote SRX nucleation,and the gradually decreased annealing temperature can reduce the growth rate of SRX grains.Besides,an aged treatment is first carried out to precipitate high content of theδphase before the CRT.Enoughδphases not only provide large numbers of sites for SRX nucleation but also limit the grain growth due to the pinning effect,especially in the primary high-temperature stage.The results show that the novel method can refine deformed mixed grain microstructure well when the suitable cooling rate,start and final recrystallization annealing temperatures are employed.The deformed mixed grain can be uniformly refined to an average size of 8.26μm with the route of 900℃×12 h+1020℃→970℃×20 min.

Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy

Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction（XRD）,EPMA,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）.The results showed that the dendrites sizes of α phase were decreased by the Nd addition.When the amount of addition Nd was 1.6 wt.%,the alloy with the smallest α phase was obtained.The refining mechanism mainly owed to the increasing constitutional supercooling at the solidification front.Furthermore,the compound Al 2 Nd generated by the reaction of Al and Nd,which distributed at the phase boundary and inside β phase,could also restrain the growth of α phase.Nd could improve the tensile strength and elongation of Mg-8Li-3Al alloy,however,excessive Al 2 Nd might also become crack source and decrease the elongation.

Inclusion evolution in 50CrVA spring steel by optimization of refining slag

In order to control the CaO-Al;O;-SiO;-MgO system inclusions in 50 CrVA spring steel in a lower melting temperature region,high temperature equilibrium experiments between steel and slag were performed in the laboratory,under the conditions of the initial slag basicity within 3-7and the content of Al;O;between 18-35mass%,to investigate the formation and evolution of this type of inclusion.The results indicate that the total oxygen content in the steel decreases with the increase of slag basicity and the decrease of Al;O;content in slags,and CaO-Al;O;-SiO2-MgO inclusions tend to deviate from the low melting point region with the increase of Al;O;content in slags.The most favorable composition for the refining slag is composed of 51-56mass% CaO,9-13mass% SiO;,20-25mass% Al;O;and 6mass% MgO.In this case,the inclusions in 50 CrVA spring steel are mostly in the low melting point regions,in which their plasticities are expected to improve during steel rolling.The MgO-based inclusions were observed in the steel matrix and the formation mechanism was theoretically and schematically revealed.It is also found that adding around 11mass% of MgO into the refining slags is beneficial to reducing the refractory corrosion.Further work should be carried out focusing on the evolution rates of MgO-based inclusions.

Combination of ultrasonication/mechanical refining with alkali treatment to improve the accessibility and porosity of bamboo cellulose fibers for the preparation of magnetic bionanocomposite cellulose beads

Ultrasonication and mechanical refining pretreatments were carried out to enhance alkali swelling of bamboo fibers to improve accessibility and porosity.Cellulose-based magnetic beads were synthesized with the alkali swollen bamboo fibers and Fe3O4 nanoparticles.Compared to the fibers treated with alkali alone,the water retention value(WRV)increased by 33.87%for the fibers treated by sonication and alkali,and by 94.58%for those treated by mechanical refining and alkali.The increased WRV was attributed to disruption of the crystalline region of fibers in the combined treatments which resulted in decreased crystallinity and degree of polymerization of cellulose.Furthermore,compared with the control sample which was treated by alkali alone,the specific surface area and pore volume of the samples treated by the combined processes increased markedly,which favored the adsorption of Fe3O4 nanoparticles in the synthesis of functional magnetic cellulose beads for the applications of protein immobilization,drug carrier and wastewater treatment.

Grain Refining Efficiency of SHS Al-Ti-B-C Master Alloy for Pure Aluminum and Its Effect on Mechanical Properties

A new Al-5Ti-0.75B-0.2C master alloy was successfully prepared by self-propagating high-temperature（SHS）reaction from an Al-Ti-B_4C system with molten Al.Microstructure and phase characterization of the prepared Al-5Ti-0.75B-0.2C master alloy show that the nearly spherical TiC particles,hexagonal or rectangular TiB_2 particles,and blocklike TiAl_3 particles distribute uniformly in the aluminum matrix.Grain refining test on commercial pure aluminum indicates that Al-5Ti-0.75B-0.2C master alloy exhibits a better grain refining performance than Al-5Ti-lB master alloy.By addition of 0.2 wt%Al-5Ti-0.75B-0.2C master alloy,the average grain size of a-Al can be effectively refined to160 ± 5 μm from about 3000 μm,and the tensile strength and elongation are increased by about 20%and 14.1%due to the grain refinement.