Corrosion and wear properties of micro-arc oxidation treated Ti6Al4V alloy prepared by selective electron beam melting

In order to analyze the effect of voltage during micro-arc oxidation(MAO)on corrosion and wear properties of Ti6Al4V(TC4),the MAO technology was employed to treat TC4 samples fabricated by selective electron beam melting(SEBM)at the voltages of 400,420 and 450 V.The results show that the metastable anatase phase gradually transforms to rutile phase with oxidation time and temperature increasing.The surface morphology of coating contains numerous micropores with uniform size distribution.Cracks and pores over 10μm are found on MAO-TC4 sample with applied voltage of 450 V.The thickness of MAO coating is positively correlated with the voltage.The corrosion resistance and wear resistance are related to phase composition,micropore size distribution on the surface and film thickness.When the voltage is 420 V,the coating shows the smallest corrosion current density(0.960×10^-7 A/cm^2)and the largest resistance(7.17×10^5Ω·cm^2).Under the same load condition,the coating exhibits larger friction coefficient and wear loss than the TC4 substrate.With the increase of voltage,the wear mechanism of the coating changes from abrasive wear to adhesive wear,and the adhesive wear is intensified at applied voltage of 450 V,with a maximum friction coefficient of 0.821.

α″phase-assisted nucleation to obtain ultrafineαprecipitates for designing high-strength near-βtitanium alloys

The diffusion-multiple method was used to determine the composition of Ti−6Al−4V−xMo−yZr alloy(0.45<x<12,0.5<y<14,wt.%),which can obtain an ultrafine α phase.Results show that Ti−6Al−4V−5Mo−7Zr alloy can obtain an ultrafineαphase by using the α″phase assisted nucleation.The bimodal microstructure obtained with the heat-treatment process can confer the alloy with a good balance between the strength and plasticity.The deformation mechanism is the dislocation slip and the{1101}twinning in the primary α phase.The strengthening mechanism is α/β interface strengthening.The interface of(0001)α/(110)β has a platform−step structure,whereas(1120)α/(111)βinterface is flat with no steps.

New high-strength Ti–Al–V–Mo alloy: from high-throughput composition design to mechanical properties

The high-throughput diffusion-multiple technique and thermodynamics databases were used to design new high-strength Ti alloys. The composition–microstructure–property relationships of the Ti64–xMo alloys were obtained. The phase fraction and composition of the α and β phases of the Ti64–xMo alloys were calculated using the Thermo-Calc software. After aging at 600℃, the Ti64–6 Mo alloy precipitated ultrafine α phases. This phenomenon was explained on the basis of the pseudo-spinodal mechanism by calculating the Gibbs energy curves of the α and β phases of the Ti64–xMo alloys at 600℃. Bulk forged Ti64–6 Mo alloy exhibited high strength and moderate plasticity after α/β-phase-field solution treatment plus aging. The tensile properties of the alloy were determined by the size and morphology of the primary and secondary α phases and by the β grain size.

Erratum to: New high-strength Ti–Al–V–Mo alloy: from high-throughput composition design to mechanical properties

Erratum to:International Journal of Minerals, Metallurgy and Materials Volume 26, Number 9, September 2019, Page 1151https://doi.org/10.1007/s12613-019-1854-1The original version of this article unfortunately contained a mistake. The presentation of Fig. 11 was incorrect. The correct version is given below:

Evolution of interfacial heat transfer,contact behavior and microstructure during sub-rapid solidification of molten steel with different hydrogen contents

Typical Q235 low-carbon steel samples with different hydrogen contents(0.0004,0.0008,and 0.0013 wt.%)were prepared by adjusting the environment humidity and moisture.The effects of hydrogen on interfacial heat transfer,contact behavior,and microstructure evolution were investigated using a novel droplet solidification technique.The results revealed that when the hydrogen content increases from 0.0004 to 0.0013 wt.%,the maximum heat flux between the molten steel and cooling substrate decreases from 8.01 to 6.19 MW/m^(2),and the total heat removed in the initial 2 s reduces from 10.30 to 8.27 MJ/m^(2).Moreover,the final contact angle between the molten steel and substrate increases from 103.741°to 113.697°,and the number of pores on the droplet bottom surface increases significantly from 21 to 210 with the increase in hydrogen.The surface roughness of the droplet bottom surface increases from 20.902 to 49.181 pm.In addition,the average grain size of the droplet increases from 14.778 to 33.548 pm with the increase in the hydrogen content.The interfacial contact condition becomes worse due to the escape of hydrogen from the steel matrix during the cooling process,which leads to the reduction in the interfacial heat transfer and the increase in the grain size.

A comparative study of surface characterization and corrosion behavior of micro-arc oxidation treated Ti-6Al-4V alloy prepared by SEBM and SLM

Additively manufactured Ti-6Al-4V(TC4)parts have been successfully employed as artificial implants in dental and orthopedic surgery due to their excellent mechanical properties.However,the suboptimal corrosion resistance limits their applications.The surface characterization and corrosion behavior of micro-arc oxidation(MAO)treated TC4 alloy prepared by selective electron beam melting(SEBM)and selective laser melting(SLM)technologies were compared.The corrosion resistance mechanism of SLM-MAO and SEBM-MAO was clarified through the analysis of the microstructure evolution,surface morphology,and electrochemical experiments.The results show that the anatase-type TiO_(2) is partially transformed into the slankite phase after MAO treatment.The surface roughness of SEBM sample was reduced by MAO coating,while the surface roughness of SLM sample increased after MAO,which is related to the difference between the microstructure of the deposited samples caused by different additive manufacturing technologies.When MAO time was 15 min,SLM-MAO and SEBM-MAO coating displayed the best and the worst corrosion resistance,respectively.

Effect of Ca and Ti contents on characteristics of inclusions in Fe-Si-Cr-Mn-Al-Ti-Ca-O melts

The inclusion characteristics in 55SiCr spring steel with different contents of titanium and calcium were investigated.The chemical compositions of steel samples were detected by inductively coupled plasma optical emission spectrometer,and the inclusion characteristics was determined by field emission scanning electron microscopy(FE-SEM)and energy-dispersive spectroscopy.The results show that the Ti/Al ratio should be kept at less than 1,and the content of calcium should be controlled between 0.0015 and 0.0025 wt.%in Si-Mn-Al deoxidized steel,so that more solid inclusions can be converted to liquid inclusions.Moreover,the high Ti content in melts is the direct cause of the high proportion of Ti_(3)O_(5) in the inclusions,which involves[Ti]to reduce SiO_(2) and A1_(2)O_(3) in inclusions.In addition,calcium treatment can reduce the content of Ti_(3)O_(5) in inclusions,and the degree of reduction is closely related to the content of[O].The thermodynamic calculation of Fe-Si-Mn-Cr-Al-Ti-Ca-O molten steel system during solidification process was performed by FactSage software,taking all types of inclusions into account,such as titanium oxide,calcium oxide,aluminum oxide,silicon oxide,manganese oxide,calcium titanate,mullite,calcium aluminate,and liquid inclusion.The inclusion type of calculation results was in accordance with the experimental results at 1550℃,and TiO_(x) aggregation behavior was consistent with the Ti_(2)O_(3)-containing precipitation phase.

Effect of Mg addition on formation of intragranular acicular ferrite in heat-affected zone of steel plate after high-heat-input welding

The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite （IAF） nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investigated by welding simulation and observation using a scanning electron microscope equipped with an energy dispersive spectrometer and an optical microscope. The IAFs are observed in steel with Mg addition, and the volume fraction of IAF is as high as 55.4% in the steel containing 0.0027 mass% Mg. The MgO-Al2O3-Ti2O3-MnS inclusions with size around 2 μm are effective nucleation sites for IAF, whereas Al2O3-MnS inclusions are impotent to nucleate the acicular ferrite. The prior-austenite grain （PAG） size distribution in low Mg steel is similar to that in steel without Mg addition. The austenite grain with size about 200 μm is favorable for the IAF formation. In the steel with high Mg content of 0.0099%, the growth of PAG is greatly inhibited, and PAG sizes are smaller than 100 μm. Therefore, the nucleation of IAF can hardly be observed.

Review of non-reactive CaO-Al2O3-based mold fluxes for casting high-aluminum steel

Advanced high-strength steels (AHSSs) have been gradually applied to modern auto industry, as they have the advantages of improving the steel strength and lightening the car weight, which not only ensures the safety but also saves the energy. However, the high-aluminum (Al) content in AHSSs may react with SiO2 in conventional CaO-SiO2-based mold flux during the process of continuous casting, which leads to the deterioration of the mold flux properties and a poor slab quality. Then, the non-reactive CaO-Al2O3-based mold flux was proposed and has been developing for the casting process of high-Al steels, but there are some problems of low consumption and insufficient lubrication that need to be solved. Thus, previous researches on the effect of each component on the properties of CaO-Al2O3-based mold flux were systematically summarized, and the situation of plant trials on CaO-Al2O3-based mold flux was evaluated. The results indicated that the proposed CaO-Al2O3-based mold fluxes could avoid the slag-metal reaction problems;however, the problems of lubri-cation, crystallization and heat transfer issues still exist. Therefore, tremendous works still need to be conducted for the development of new generation of CaO-Al2O3-based mold flux system. The review was performed aiming to provide a technical guidance for designing and optimizing CaO-Al2O3-based mold flux system that meets the demand of the continuous casting process of high-Al steels.

A comparison study on viscosity and heat transfer property of fluorinebearing and fluorine-free mold flux for casting silicon steel

A comparison study was conducted on viscosity and heat transfer property of the traditional fluorine-bearing(F-bearing)mold flux and the newly designed fluorine-free(F-free)mold flux for casting silicon steel.The results showed that the viscosity of F-free mold flux is lower than that of F-bearing mold flux,as the apparent activation energy of F-free mold flux is also lower than that of F-bearing mold flux confirmed by the kinetics results for viscous flow,which meant that the energy barrier of F-free mold flux that the migration of ion clusters needs to overcome is smaller,and thus leads to a lower viscosity of F-free mold flux.Besides,the research results of the heat transfer suggested that the comprehensive heat transfer coefficient of F-free mold flux is lower than that of F-bearing mold flux in all directions.One reason is that the true density of F-free mold flux increases from glassy state to crystalline state,while that of F-bearing mold flux is opposite.Another reason is that the air gap gets increased due to the volume shrinkage of F-free mold flux from glassy state to crystalline state and the solidification of the molten steel.These introduce a larger thermal resistance of F-free mold flux than that of F-bearing mold flux.Through the comparison,the designed F-free mold flux shows a better lubrication and capacity to control the heat transfer than the traditional F-bearing mold flux.

Subgrain microstructures and tensile properties of 316L stainless steel manufactured by selective laser melting

316L stainless steel samples were manufactured by selective laser melting(SLM).The microstructure of SLM-made 316L stainless steel and the room temperature tensile properties both perpendicular and along the building direction were studied and characterized.The static temperature field during the molten pool formation was simulated by finite element simulation.It indicates that the nonlinear asymmetrical inclined temperature gradient in SLM process produces a large surface tension gradient.The melt forms a Marangoni flow with different convection modes under the action of surface tension as well as a micro-molten pool morphology with subgrain structures such as strip,hexagonal and elongated cellular structures.In addition,there are also epitaxially grown columnar grains.The growth of columnar crystals is not affected by the boundary of the molten pool.Subgrain structures and low-angle grain boundaries make the tensile strength and the elongation of SLM-made 316L sample higher as compared to those of the cast and wrought samples.The room temperature tensile strength of the sample perpendicular to the building direction is higher than that of the sample along the building direction,while the elongation is lower than that of the sample along the building direction.

Effect of AI_(2)O_(3)and MgO on crystallization and structure of Ca0-Si0_(2)-B_(2)0_(3)-based fluorine-free mold flux

The crytallization behavior and melt structure of the CaO-Si0^(2-)B20_(3)-based fluorine-free mold fux were investigated.The results show that the crytallization of the mold fux was first inhibited and then promoted with the increase in Al_(2)0_(3) content from 4 to 12 wt.%.However,it was enhanced by MgO in the range of 2-10 wt.%.The results of Fourier transform infrared spectroscopy and Raman spectroscopy showed that Al_(2)0_(3) worked as a network former in the mold flux melt when its content was in the range of 4-8 wt.%,whereas it worked as the network breaker to provide 0^(2-)when its content was in the range of 8-12 wt.%.In addition,the combined efects from the charge compensation by Mg^(2+)and the network broken by 0^(2-)led to the increase in some typicalT-O-T(AI-O-A1,B-O-B,etc.,)and simpler structural units(Q^(2)(Si),B_^(O-)in the[B0_(2)0^(-)],.etc.)when the MgO content was in the range of 2-6 wt.%.The continuous increase in 0^(2-)provided by the addition of MgO from 6 to 10 wt.%further depolymerized the network of the melt and fnally caused fast crystallizationo.

Effect of Al2O3/SiO2 and CaO/Al2O3 ratios on wettability and structure of CaO-SiO2-Al2O3-based mold flux system

The effect of Al2O3/SiO2 and CaO/Al2O3 ratios on the molten structure of CaO-SiO2-Al2O3-based mold flux system was analyzed by Fourier transform infrared spectroscopy,Raman spectroscopy,and X-ray photoelectron spectroscopy.Also,the variation in the wettability between the mold flux system and an interstitial free(IF)steel substrate was investigated using the sessile drop method.The results indicate that the contact angle and interfacial tension between the molten slag and solid steel increase slightly with the increase in the Al2O3/SiO2 ratio,while they decrease with the increase in the CaO/Al2O3 ratio.The network structure for the designed mold flux system changes gradually from silicate to aluminosilicate and aluminate with the increase in the Al2O3/SiO2 ratio,and the network is simplified with the increase in the CaO/Al2O3 ratio.Besides,combining the results of sessile drop method and melt structure analyses,it suggests that the variation in interfacial properties of mold flux/IF steel substrate is mainly caused by the change in melt structure,especially the variation in free oxygen ions(O^2-)and non-bridged oxygen(O^-)at the interface.

Research methods and influencing factors of interfacial heat transfer during sub-rapid solidification process of strip casting

Interfacial heat transfer behavior between the molten steel and twin-rolls is a key issue in the strip casting process,and it has already attracted wide attention from industrial and academic communities of steel.The research methods and influencing factors on the interfacial heat transfer were summarized.Numerical simulation models,semi-industrial scale,and laboratory equipment have been developed in this field,and these methods were also improved by worldwide researchers based on the development of computer,automatic,and visual technologies.Coating properties,naturally deposited film,and casting parameters are the main factors which affect the heat transfer significantly.Although lots of research has been carried out,the internal relations among these influencing factors,interfacial heat transfer,and the quality of the strip are still worth to be further explored.Keywords Strip casting Interfacial heat transfer Simulation method Coating property Naturally deposited film Casting parameter.

Preface

Continuous casting is one of the most important innovations in the steel industry due to its high yield,high product quality,energy savings,less pollution,lower cost,as well as better working conditions.Over 96% of crude steel in the world was cast by continuous caster.As a very important functional material,mold flux works as several roles in the continuous casting process.It protects liquid steel from oxidation,insulates it from freezing,and absorbs inclusions,when floating on the top of liquid steel;whereas it lubricates the shell and moderates the heat transfer in the mold,when it infiltrates into the mold/shell channel.Therefore,the quality of final cast product is greatly determined by the performance of mold flux.Improper properties may lead to defects in the bloom,slab or billet,such as severe oscillation marks,cracks,inclusions and slag entrapment,improper solidification structure distribution,and even breakout.

Effect of Al_(2)O_(3)/Na_(2)O ratio and MnO on high-temperature properties of mold flux for casting peritectic steel

The influences of Al_(2)O_(3)/Na_(2)O ratio and MnO content on high-temperature properties,such as melting,crystallization,heat transfer,and viscosity of mold flux for casting peritectic steel,have been investigated.The results show that the melting temperatures of mold flux decrease,whereas the ratio of crystalline layers increases with the decrease in Al_(2)O_(3)/Na_(2)O ratio and increase in MnO content.The average response temperatures of the three mold fluxes decrease from 566,525,to 512℃,respectively,which indicates that the heat transfer controlling ability of mold flux is promoted due to the increase in crystallization ability and addition of transition metal oxide MnO.Furthermore,the viscosity-temperature curves suggest that the viscosity at 1300℃ decreases,but the break temperature increases with the reduction in Al_(2)O_(3)/Na_(2)O and addition of MnO.

A comparison study on interfacial properties of fluorine-bearing and fluorine-free mold flux for casting advanced high-strength steels

A comparison study on interfacial properties of a traditional fluorine-bearing(F-bearing)mold flux and a newly designed fluorine-free(F-free)mold flux to produce advanced high-strength steels(AHSSs)by compact strip production technology was conducted.The results showed that these two kinds of mold fluxes gradually spread out on the typical AHSS substrate when slags began to melt with the increase in heating temperature,and they had a good interfacial ability between the two mold fluxes and the AHSS substrate,and there was no other interfacial reaction except the oxidization of steel substrate by the mold fluxes.In comparison,the wettability of the designed F-free mold flux with the AHSS substrate was better than that of the F-bearing mold flux.The reason could be explained as the addition of B_(2)O_(3) would increase the complexity and polymerization degree of the melt structure and weaken the attractive force between the ions and ionic groups,then leading to a better wettability.Besides,B_(2)O_(3) is an effective flux,which can reduce the melting temperature obviously,and the surface tension of the liquid F-free mold flux would get reduced with the addition of B_(2)O_(3).

Effect of electropulsing treatment on solidification behavior of spring steels in a continuous casting mold simulator

An electropulsing-assisted mold simulator technique was developed to investigate the effects of a pulsed electric voltage on the quality of spring steels during continuous casting by analyzing the mold flux film,shell surface profile,shell micro-structure and inclusion distributions.The results revealed significantly increased crystallization fraction of the mold flux film from 61.2%to 75.3%and finer crystalline phase morphology in the case of electropulsing treatment.The surface of the initially solidified shell could be effectively healed,resulting in smoother shell surface profiles with higher pulsed voltage from 0 to 30V.Furthermore,an increase in the pulsed voltage from 0 to 30V resulted in finer dendritic structures during solidification with decreasing secondary dendrite arm spacing from the values of 17.6-32.2 to 9.7-15.0μm in the direction of shell side toward melt side.In addition,an area scan analysis of inclusions in the as-cast spring steel samples showed that the number of MnS inclusions in the size range of 2.0-4.0μm gradually decreased from 836 to 114 and the number of Al2O3 inclusions in the same size range decreased from 144 to 39,as the voltage increased from 0 to 30V.

Understanding thermal compression and deformation behavior of 3.15 wt.%Si non-oriented electrical steels prepared by sub-rapid solidification

Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels.However,research on the hot deformation behavior of sub-rapid solidified non-oriented electrical steel,particularly at varying strain rates,has yet to be fully understood.The effect of thermal compression on the microstructure and mechanical properties of 3.15 wt.%Si non-oriented electrical steel strips produced through a strip casting simulator was systematically investigated.The findings reveal that increasing the deformation temperature enhances grain recrystallization,while the peak stress decreases with higher temperature.Furthermore,a lower strain rate favors dynamic recrystallization and reduces thermal stress.It can be seen that sub-rapid solidification can effectively reduce the thermal activation energy of non-oriented electrical steel,and the thermal activation energy is calculated to be 204.411 kJ/mol.In addition,the kinetic models for the dynamic recrystallization volume fraction of the studied 3.15 wt.%Si non-oriented electrical steel were established.