Effect of surface damage induced by cavitation erosion on pitting and passive behaviors of 304L stainless steel

The corrosion behavior of 304L stainless steel(SS)in 3.5wt%NaCl solution after different cavitation erosion(CE)times was mainly evaluated using electrochemical noise and potentiostatic polarization techniques.It was found that the antagonism effect resulting in the passivation and depassivation of 304L SS had significant distinctions at different CE periods.The passive behavior was predominant during the incubation period of CE where the metastable pitting initiated at the surface of 304L SS.Over the rising period of CE,the 304L SS experienced a transition from passivation to depassivation,leading to the massive growth of metastable pitting and stable pitting.The depassivation of304L SS was found to be dominant at the stable period of CE where serious localized corrosion occurred.

Additive manufacturing of magnesium and its alloys: process-formabilitymicrostructure-performance relationship and underlying mechanism

Magnesium and its alloys,as a promising class of materials,is popular in lightweight application and biomedical implants due to their low density and good biocompatibility.Additive manufacturing(AM)of Mg and its alloys is of growing interest in academia and industry.The domain-by-domain localized forming characteristics of AM leads to unique microstructures and performances of AM-process Mg and its alloys,which are different from those of traditionally manufactured counterparts.However,the intrinsic mechanisms still remain unclear and need to be in-depth explored.Therefore,this work aims to discuss and analyze the possible underlying mechanisms regarding defect appearance and elimination,microstructure formation and evolution,and performance improvement,based on presenting a comprehensive and systematic review on the relationship between process parameters,forming quality,microstructure characteristics and resultant performances.Lastly,some key perspectives requiring focus for further progression are highlighted to promote development of AM-processed Mg and its alloys and accelerate their industrialization.

Impact of Cooling Rate on the Results of Vibration Treatment of the Aluminum Casting

The effect of vibration(50 Hz)on the formation of aluminum castings of 99.5%purity at various cooling rates was studied.It was found that the presence of vibration leads to an increase in the cooling rate of the castings.It was found that the higher the speed without vibration,the stronger the effect of increasing the speed when vibration was applied.Apparently,this effect is associated with additional mixing of the melt by free-floating crystals.

Anomalous{1012}tensile twinning and subsequent detwinning in a friction stir processed carbon fiber-reinforced Mg composite

1.Main text Owing to their low density and high specific strength,magnesium alloys and magnesium-based composites have great potential as structure metal materials in applications where lightweight matters[1–4].Deformation twins[5],especially the{1012}tension twins(also called tensile or extension twins)with a low critical resolved shear stress(CRSS)[6],are commonly observed in Mg alloys.They can provide the much-needed deformation along the c-axis in their hcp structure resulting from the very few easily activated slip systems in this crystal structure[7].The tensile twinning activation usually follows the macroscopic Schmid factor law[2],i.e.,the twin variant with the highest Schmid factor occurs,and it only appears when its Schmid factor is positive.

Microstructural characteristics and properties in centrifugal casting of SiC_p/Zl104 composite

The microstructural characteristics and Brinell hardness of a cylinder produced by centrifugal casting were investigated using 20%(volume fraction)SiCp/Zl104 composites.Macrostructure and XRD analysis show that most of SiC particles segregate to the external circumference of the cylinder,the other SiC particles maintain in the inner circumference of the cylinder,and a free particle zone is left in the middle circumference of the cylinder.Microstructural characteristics and quantitative assessment of SiC particles show that most of congregated SiC particles in 20%SiCp/Zl104 composites are dispersed by centrifugal force,and the other congregated SiC particles and most of alumina oxide are segregated to the inner circumference of the cylinder.The SiC particles in aluminum melt can promote the refinement of primaryα(Al)during solidification,and fine primaryα(Al)grains can also promote the uniform distribution of SiC particles.Brinell hardness of SiCp/Zl104 composites is connected with not only the volume fraction of SiC particles,but also the distribution of SiC particles in matrix alloy.

Microstructure and wear behavior of laser cladding Ni-based alloy composite coating reinforced by Ti(C,N) particulates

In this paper, Ni-based alloy composite coating reinforced by Ti （C, N） particles was fabricated on the mild steel through laser cladding technology. The microstrncture of laser cladding layer was analyzed by means of optical microscopy （OM）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The wear resistance test of the coating was evaluated using an M-2000 tester. The results showed that the Ni-based composite coating had an ability of rapid solidification to form dendritic crystals microstructure consisting of Ti （ C, N） particulates uniformly distributed in the matrix. It was found that some Ti（ C,N） particles are similar to be round in shape, and the others are irregular. Laser cladding layer reinforced by Ti（ C, N） particulates was found to possess good wear resistance property.

Microstructural characteristics of intermetallic phases in spray-deposition Al-8.5Fe-1.3V-1.7Si alloy

Analysis electron microtechnique (AEM) and high resolution electron microtechnique (HREM) studies were conducted on a spray deposition Al 8.5Fe 1.3V 1.7Si(mass fraction, %) alloy to determine the characteristics of the intermetallic phases. The results show that the striking characteristics of the microstructures in as deposited and as extruded alloys indicate the presence of a large amounts of homogeneously distributed fine particles and a few coarse particles, while small amount of eutectics consisted of α (Al) and α AlFeSi are found in local zone in as deposited alloy. The fine particle is identified to be bcc α AlFeSi phase, and the coarse particles are monoclinic α Al 13 Fe 4 equilibrium phase, bcc α AlFeSi phase and newly found hexagonal h AlFeSi metastable phase. In α Al 13 Fe 4 , stacking faults on (100) and (001) plane and microtwin on (100) twinning plane are frequently observed. The extra reflection spots in α AlFeSi reflection pattern can be induced by α AlFeSi superstructure. The hexagonal metastable phase transforms to bcc phase, and the compositions of two phases are very similar. A close crystallographic orientation relationship between hexagonal and bcc phases are determined, and HREM image shows that the interface between them is coherent. [

Isothermal oxidation behavior of Ti_3Al-based alloy at 700-1000 ℃ in air

The isothermal oxidation behavior of a Ti3Al-based alloy (Ti-24Al-14Nb-3V-0.5Mo-0.3Si, molar fraction, %) at 700-1 000 ℃ in air was investigated. The oxidation kinetics of tested alloy approximately obeys the parabolic law, which shows that the oxidation process is dominated by the diffusion of ions. The oxidation diffusion activity energy is 241.32 kJ/mol. The tested alloy exhibits good oxidation resistance at 700 ℃. However, when the temperature is higher than 900 ℃, the oxidation resistance becomes poor. The XRD results reveal that the oxide product consists of a mixture of TiO2 and Al2O3. Serious crack and spallation of oxide scale occur during cooling procedure after being exposed at 1 000 ℃ in air for 16 h. According to the analysis of SEM/EDS and XRD, it is concluded that the Al2O3 oxide forms at the initially transient oxidation stage and most of it keeps in the outer oxide layer during the subsequent oxidation procedure.

Microstructure, Mechanical Properties and Wear Behaviourof Deep-Cryogenic-Treated HSS

In this paper we compare the wear behaviour of a vacuum-heat-treated ESR AISI M2 high-speed steel and the same steel that was vacuum heat treated in conjunction with a deep-cryogenic treatment at -196 °C. Four different tempering temperatures for the specimens austenized at the same austenitizing temperature were carefully selected to obtain various in-advance-determined combinations of the microstructures, the fracture toughness, KIc and the Rockwell-C hardness. Each of the eight specimens was therefore characterised by these microstructures and resulting material properties. The wear study was performed using a reciprocating sliding device under well-controlled contact conditions. Relatively high loads were used to provide enough wear for a comparison of the selected samples. A much harder and dissimilar model counter-material, i.e. silicon nitride ceramic, was used in order to avoid excessive wear of the counter samples and adhesion, which could occur in contacts with similar materials (metals/steels) under such high loads and in non-lubricated conditions. The wear behaviours were then compared and discussed in terms of these microstructures and the related properties. The differences in the wear resistance obtained in our investigation were as high as an order of magnitude. However, the beneficial effects are not a direct result of the type of the treatment, but relate to a proper combination of the resulting fracture toughness and the hardness. The more uniform and moderate values, which, however, tend to be obtained with a deep-cryogenic treatment, are beneficial to the high wear resistance of the selected high-speed steel.

Revealing effect of aluminum alloying on work hardening and impact behaviors of low-density Fe-18Mn-1.3C-2Cr-(4,11)Al casting steel

The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4,11)Al(wt.%)low-density steels.Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum(Al)alloying control.Meanwhile,microstructure evolution and fracture morphology were investigated by X-ray diffraction(XRD),a scanning electron microscope(SEM)equipped with electron backscatter diffraction(EBSD),a transmission electron microscope(TEM),and a stereo-optical microscope(OM).It is found that the Al addition obviously promotes the dislocation planar slipping,resulting in cleavage and brittle impact fracture in 11wt.%Al steel.Besides,the microband-induced plasticity(MBIP)mechanism is found in 4wt.%Al containing steel,introducing considerable work hardening capacity and impact toughness of 156.8±17.4 J.The present study provides a direct illustration of the relationship between work hardening and impact toughness behaviors of these two low-density steels for potential application as impact-resistant components.

Influence of α Phase on Shape Memory Effect and Superelasticity of CuZnAI Alloy

The influence of a small amount of α phase in β′ matrix on shape memory effect and superelasticity of CuZnAl shape memory alloy has been studied systematically.It has been found that transformation temperature can be adjusted in a large scale by controlling the amount of α phase, meanwhile,shape memory effect and superelasticity do not decrease obviously when there exists a small amount of α phase.Based on the optical and trans- mission electron microscopy observation,the influ- ence of α phase on shape memory effect and superelasticity has been discussed.

Effect of Sample Configuration on Droplet-Particles of TiN Films Deposited by Pulse Biased Arc Ion Plating

Orthogonal experiments are used to design the pulsed bias related parameters, including bias magnitude, duty cycle and pulse frequency, during arc ion deposition of TiN films on stainless steel substrates in the case of samples placing normal to the plasma flux. The effect of these parameters on the amount and the size distribution of droplet-particles are investigated, and the results have provided sufficient evidence for the physical model, in which particles reduction is due to the case that the particles are negatively charged and repulsed from negative pulse electric field. The effect of sample configuration on amount and size distribution of the particles are analyzed. The results of the amount and size distribution of the particles are compared to those in the case of samples placing parallel to the plasma flux.

Design of Zr-based AB_2 type hydrogen storage alloys

The influences of the ratio of the radius of atom A（rA） to radius of atom B（rB）, electronegativity and electron number were discussed on the Laves phase formation and the characteristics of Zr-based AB2 type hydrogen storage alloy. An enthalpy model of Zr-based AB2 alloy was obtained from known data and twelve Zr-based alloys were designed to test the model. The results show that the predicted values are in good agreement with the experimental values. The model can be used for predicting enthalpy values of Zr-based hydrogen storage alloys and settles a foundation for experiments.

Thermodynamic Aspects of the Graphene/Graphane/Hydrogen Systems: Relevance to the Hydrogen On-Board Storage Problem

The present analytical review is devoted to the current problem of thermodynamic stability and related thermodynamic characteristics of the following graphene layers systems: 1) double-side hydrogenated graphene of composition CH (theoretical graphane) (Sofo et al. 2007) and experimental graphane (Elias et al. 2009);2) theoretical single-side hydrogenated graphene of composition CH;3) theoretical single-side hydrogenated graphene of composition C2H (graphone);4) experimental hydrogenated epitaxial graphene, bilayer graphene and a few layers of graphene on SiO2 or other substrates;5) experimental and theoretical single-external side hydrogenated single-walled carbon nanotubes, and experimental hydrofullerene C60H36;6) experimental single-internal side hydrogenated (up to C2H or CH composition) graphene nanoblisters with intercalated high pressure H2 gas inside them, formed on a surface of highly oriented pyrolytic graphite or epitaxial graphene under the atomic hydrogen treatment;and 7) experimental hydrogenated graphite nanofibers-multigraphene with intercalated solid H2 nano-regions of high density inside them, relevant to solving the problem of hydrogen on-board storage (Nechaev 2011-2012).

Comparing of Hydrogen On-Board Storage by the Largest Car Companies, Relevance to Prospects for More Efficient Technologies

It presented a comparative consideration of General Motors long-term activities on the current subject of fuel-cell-powered electric vehicles vs Toyota Mirai recent results, relevant to prospects on more efficient and safe technologies of the hydrogen on-board storage. It also presented a call on the project International cooperation. The main aim of this paper is to attract attention of General Motors, Toyota and/or other large car companies to a real possibility of developing and using, in the nearest future, of the break-through hydrogen on-board storage technology based on the solid H2 intercalation into graphite nanostructures.

Oxygen and Nitrogen Effects on MC Carbide in K465 Nickel-Base Superalloy

Effects of oxygen and nitrogen on MC carbide in nickel-base superalloy K465 were investigated, because neither of the two gas elements was found to decide MC carbide morphology monotonically. The morphology of MC carbide under alloy solidified in conventional investment casting condition was observed to transform from script-type to block-type with the total oxygen and nitrogen content (gas content) in samples rising up from 1.2×10-6 mol/g to 2.6×10-6 mol/g. The area fraction and composition of the MC carbide also varied with increase of gas content. However, the morphology of MC carbide kept to be script-type even when gas content was up to 3.4×10-6 mol/g in samples solidified with a much higher cooling rate. These results indicate that effects of gas content on formation of MC carbide can be observed in specimens solidified with low cooling rate, but such changes in MC carbide cannot be found when the cooling rate is high.

Getters: From Classification to Materials Design

The demand for getters with high sorption efficiency has generated a need for resources to assist in qualification of getter materials for their practical use. This paper discusses innovative steps which should provide a dramatic improvement in the selection and application of getter technologies used in various processes. The first step was to build a natural classification of chemisorbents, from which we obtain a corresponding order of suitability related to known getter products. The classification system suggested by the authors is based on criteria which are directly connected with the sorption behavior of the material. This has lead to the challenge of developing of a computing algorithm for characterization of sorption properties of getter materials and for solving the inverse problem—the problem of designing a chemisorbent based on the requirements of a fully realized application. The employment of the new methodology is demonstrated in the example of the calculations supporting the selection of getter films for MEMS.

pH value in simulated occluded corrosion cell for magnesium alloys

Corrosion of magnesium alloys is an important issue for their applications in automobile and aerospace industry. pH values as a function of time in two types of simulated occluded corrosion cells(OCC) for magnesium alloys AZ80 and AM60 were measured. The influence of mass ratio of solution to material or liquid to solid ratio(L/S ratio),initial pH value and chemical compositions of solutions on pH value in OCC was discussed. The experimental results show that pH value for magnesium alloys increases gradually or rapidly in Occ,depending on L/S ratio,initial pH value of solution and chloride ions concentration etc,and then reaches up to 10.5-10.6 and finally stabilizes at the level. The onset in the pH value time curve corresponds to the precipitate of magnesium hydroxide according to the theoretical calculation.

The Newest Getter Technologies: Materials, Processes, Equipment

The efficiency of sorption purification of gases, as measured by an improvement in product quality and/or lowering of its cost, can be significantly increased via simple solutions: the substitution of current getter technology with reactive getters;and stimulation of the material in the sorption process using mechanochemical methods instead of heating or cooling. These ideas were embodied by the authors in new sorption apparatuses and devices such as mechanochemical sorption apparatuses for production of ultra pure gases, improved gas purifiers with reactive sorbent for production of pure and high purity gases and, finally, fluidized bed columns for mass production of pure and high purity gases.