Surface Layer Of Alloy Research Articles

Effects of Ultrasonic Surface Rolling Processing and Subsequent Recovery Treatment on the Wear Resistance of AZ91D Mg Alloy.

AZ91D Mg alloy was treated by ultrasonic surface rolling processing (USRP) and subsequent recovery treatment at different temperatures. The dry sliding friction test was performed to investigate the effects of USRP and subsequent recovery treatment on the wear resistance of AZ91D Mg alloy by a ball-on-plate tribometer. The microstructure, properties of plastic deformation layer and worn morphology were observed by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) analysis and microhardness tester. Results illustrate that the grains of AZ91D Mg alloy surface layer are refined to nanocrystallines. The maximum microhardness of the top surface of the USRP sample reaches 102.3 HV. When USRP samples are treated by recovery treatment at 150 °C, 200 °C and 250 °C, the microhardness of the top surface decreases to 90.68 HV, 79.29 HV and 75.06 HV, respectively. The friction coefficient (FC) and wear volume loss of the USRP-R-150 sample are the lowest among all the samples. The worn surface morphology of the USRP-R-150 sample is smoother than that of other samples, indicating that the wear resistance of AZ91D Mg alloy treated by USRP and recovery treatment at 150 °C is improved significantly.

Структурно-фазові перетворення у поверхневих шарах стопів на основі Кобальту з карбідом титану після ультразвукового ударного оброблення

Структурно-фазові перетворення у поверхневих шарах стопів на основі Кобальту з карбідом титану після ультразвукового ударного оброблення

Laser Alloying of the Surface Layers of Aluminum Alloys for Improving Their Wear Resistance

The possibility of increasing the wear resistance of components made from AL25 and D16 aluminum alloys via surface alloying of the functional surfaces of the components is considered theoretically and experimentally. The mass transfer within the surface laser alloying (SLA) zone is a complex process due to the following three simultaneously occurring phenomena: the diffusion, thermocapillary convection, and incorporation of coating particle conglomerates into the melt zone during the fast evaporation of their surface layers in the field of power laser radiation. Various experimental schemes are selected using a theoretical analysis. Qualitative, quantitative, and physical studies of the process are performed. Recommendations for the selection of laser treatment conditions are given. The role of the alloying powder particle size is analyzed.

Effects of Laser Shock Peening on the Mechanical Behaviors and Microstructure of Friction Stir Processed 2A14 Aluminum Alloy

The influence of laser shock peening (LSP) on the microstructures and mechanical behaviors of the friction stir processed (FSPed) 2A14 aluminum alloy was investigated. Microhardness and tensile measurements, as well as wear test, were taken to analyze the changes in mechanical characteristics. The vibration fatigue experiments were also conducted, while the vibration fatigue life of the specimens with different treatments was compared and the fracture morphologies were observed by scanning electron microscopy. The microstructures before and after LSP were observed with electron backscattered diffraction and transmission electron microscopy. The analysis results evidenced that LSP significantly improved the mechanical properties of the FSPed specimens. Meanwhile, LSP increased the dislocation density and promoted the precipitation of the second phases on the surface layer of the FSPed 2A14 aluminum alloy, while their interactions improved the stability of the dislocation structures, which contributed to the improvement of the mechanical behaviors.

Biocompatible High Entropy Alloys with Excellent Degradation Resistance in a Simulated Physiological Environment.

Bioimplants are susceptible to simultaneous wear and corrosion degradation in the aggressive physiological environment. High entropy alloys with equimolar proportion of constituent elements represent a unique alloy design strategy for developing bioimplants due to their attractive mechanical properties, superior wear, and corrosion resistance. In this study, the tribo-corrosion behavior of an equiatomic MoNbTaTiZr high entropy alloy consisting of all biocompatible elements was evaluated and compared with 304 stainless steel as a benchmark. The high entropy alloy showed a low wear rate and a friction coefficient as well as quick and stable passivation in simulated body fluid. An increase from room temperature to body temperature showed excellent temperature assisted passivity and nobler surface layer of the high entropy alloy, resulting in four times better wear resistance compared to stainless steel. Stem cells and osteoblast cells displayed proliferation and migratory behavior, indicating in vitro biocompatibility. Several filopodia extensions on the cell periphery indicated early osteogenic commitment, and cell adhesion on the high entropy alloy. These results pave the way for utilizing the unique combination of tribo-corrosion resistance, excellent mechanical properties, and biocompatibility of MoNbTaTiZr high entropy alloy to develop bioimplants with improved service life and lower risk of implant induced cytotoxicity in the host body.

Investigation of the effect of ion implantation on the structure of the surface layer of VT20 titanium alloy

The effect of ion implantation of VT20 titanium alloys on their structural and substructural characteristics is studied. A significant change in structural characteristics has been established, which contributes to an increase in the strength properties of alloys with satisfactory ductility and heat resistance. This work was carried out as part of the state task of the Ministry of Science and Higher Education of the Russian Federation «The influence of magnetic fields and ion implantation on the structure, chemical composition and properties of titanium, aluminum alloys and elementary semiconductors».

Effect of Stacking-Fault Energy on the Deformed Structures and Work Hardening of Ag and Ni after Scratching during Early Loading Stage

Friction wear are accompanied by the formation of refined structures and shear bands in the surface layers of metals and alloys. The propensity for refinement and shear band formation is mainly determined by the stacking-fault energy (SFE). Despite the fact that significant studies have been dedicated to plastic deformation during friction, little effort has been directed toward elucidating the early stages of deformation hardening that is accompanied by the effects of SFE. The research results presented herein focused on the initiation of twin and lamellar shear bands, transformation of nano-grained structures during shear banding, and the deformation hardening of surface layers during the scratching of metals with low and high SFE. Flat samples of low (Ag) and high (Ni) SFE were scratched with a diamond indenter for one to ten friction cycles. The friction surfaces were examined with a field-emission scanning electron microscope. It was shown that the scratch track sizes and amounts of pile-up material were lower for Ag than those for Ni. High deformation hardening of Ag relative to Ni was confirmed by the inhibition of cross-slip and the formation of ultra-fine structures. The deformed structure of Ag after ten scratch cycles was characterized by the formation of core shear bands that were bent in the depth of the deformed layers. It was shown that the balance between deformation hardening and softening was crucial in preserving a steady friction state and forming wear particles.

A protective superhydrophobic Mg–Zn–Al LDH film on Surface-Alloyed Magnesium

A novel approach was developed to fabricate a protective superhydrophobic LDH film on a Zn–Al alloyed surface of AZ31 Mg alloy. The alloyed surface layer not only provided essential divalent and trivalent cations and a base for the direct growth of a Mg–Zn–Al LDH film in a sodium nitrate hydrothermal solution, but also offered additional corrosion and mechanical protection for the substrate magnesium alloy. Further modification with low surface energy lauric acid (LA) could change the micro/nano hierarchical topographic surface of the LDH film from hydrophilicity to super-hydrophobicity. The long-term anti-corrosion performance, super-hydrophobicity, wear resistance, chemical stability and adhesion strength of the LA-modified LDH film on the surface-alloyed AZ31 were experimentally verified.

The influence of chromium content on wear and corrosion behavior of surface alloyed steel with Fe(16−x)Crx(B,C)4 electrode

In this study, the electrodes containing Fe(16−X)CrX(B,C)4 (X = 3,4,5) were used for surface alloying on an AISI 1010 steel substrate. The alloy structure of the coating exhibits in-situ composite structure with a large amount of reinforcing carbides and borides phases as to be hypoeutectic and hypereutectic structure in the surface alloyed layer. The obtained composition of the alloy shows that it contains much more interstitial hard phases in the alloyed layer than the conventional hardfacing alloys used in the industrial applications for the hardfacing of the steels. The morphological and microstructural properties showed that layer microstructure changed from hypoeutectic to hypereutectic structure with an increase in chromium content. The results of these studies revealed that the microstructure of hardfacing layers consists of interstitial phases of α(Fe-Cr) and (Fe,Cr)23(C,B)6 as major phases, (Fe,Cr)2(C,B) and (Fe,Cr)7(C,B)3 as minor phases in the in-situ composite structure. The composite hardness’ in the alloyed surface layers of the Fe(16−X)CrX(B,C)4 alloys ranged from 711 HV to 1164.3 HV. Wear test against alumina ball shows that the friction coefficients of the surface alloyed layers decreased with increase in applied loads and decrease in chromium content in the Fe(16−X)CrX(B,C)4 alloy composition. Coefficient of friction ranged from 0.55 to 0.79 in the present study. Wear rates of the surface alloyed steels caused to increase with decrease in chromium content and increase in applied loads. The wear rates of the alloyed layer changed between 3.07 × 10 and 5 mm3/m and 6.95 × 10−5 mm3/m. The corrosion resistance of the alloyed layers was measured by a potentiostatic polarization test. Icorr and Ecorr of the coated layers changed from 1.813 to 9.965 µA/cm2 and −704.786 to −745.792 mV, depending on alloyed layer compositions. With increasing chromium content, the corrosion resistance of the coating layer has changed in a nobler side.

Wear Resistance Enhancement of Al6061 Alloy Surface Layer by Laser Dispersed Carbide Powders.

In this paper, results of the experimental study on improving wear resistance in sliding friction of Al-based alloy are presented. The technique used involves the formation of a metal matrix composite (MMC) in the alloy surface layer by laser dispersion of carbide powders such as WC, TiC and SiC. For WC and TiC MMC surface coatings fabricated under conditions typical for most of the technologically relevant solid-state lasers (wavelength range of 0.8–1.1 μm), the nearly inversely proportional dependence of the required laser energy density on the powder mass density is observed. Highly homogenous distribution of powder particle content (up to 40%) in the MMC surface coatings of a thickness between 0.8 and 1.6 mm obtained by multiple scanning is observed in the cross-section of specimens processed within a rather narrow parameter window. Tribological tests and comparison to untreated material reveal wear resistance increases by five- and ten-fold, observed in samples with laser-dispersed TiC and WC powders, respectively. Results indicate that substantial modification and reinforcement of the surface layer can be achieved in Al alloy in a one-step process without substrate preheating.

The influence of the energy density of the electron beam on the morphology of surface and mechanical properties of the surface layer of NiTi alloy

This work comprises a study of the influence of the energy density E s of the low-energy high-current electron beam (LEHCEB) exposure on the morphology of surface and mechanical properties of the surface layer of nickel titanium alloy (NiTi alloy). It was found that the formation of crater-like relief on the surface of NiTi alloy after electron beam treatment is determined by the structure and distribution of the particles of second and impurity phases. The mechanical properties in a modified surface layer of no more than ∼ 500 nm thickness change at different values of the energy density E s of electron beam.

Preparation of platinum-silver alloy nanoparticles and their catalytic performance in methanol electro-oxidation

Platinum-silver alloy nanoparticles (PtxAgy NPs) were synthesized in a molten salt system without using any organic surfactants or solvents; the catalytic role of Ag in the methanol electrooxidation reaction (MOR) in alkaline electrolyte over PtxAgy NPs was investigated. The TEM images suggest that Pt52Ag48 nanotubes (NTs) can be obtained when the Pt/Ag ratio in the molten salt precursor reaches 1. The methanol electrooxidation reaction test results indicate that the Pt52Ag48 NTs with a clean surface exhibits a much better catalytic performance than the conventional Pt black in MOR. Meanwhile, the catalytic activity of the Pt52Ag48 NTs is greatly related to the positive potential limit; the peak current of MOR reaches 1.61 mA/μgPt with a positive potential limit from –1.0 to 0.5 V (vs. SCE), which is 1.92 times higher than that with a positive potential limit from –1.0 to 0.1 V (vs. SCE). The Ag element in the surface layer of PtxAgy alloy may promote the MOR through a redox process during the electrochemical cycle. The insight shown in work should be beneficial to the application of PtxAgy alloy in the direct methanol fuel cells (DMFCs).

Heat Transfer in Surface Layer of a T15k6 Heterogeneous Hard Alloy under Pulsed High-Energy Irradiation

A one-dimensional model of a hard alloy is proposed, which takes into account the heterogeneity of the physical properties of a composite material by representing it as a sequence of 2 μm TiC and WC carbide particles. The influence of the energy density of pulsed high-current electron beams on the melted layer depth and microstructure is investigated. A comparison of the penetration depths of the hard alloy obtained by calculation and experimentally shows their good agreement. It is found out that with an increase in the beam energy density due to melting of the carbides a (Ti, W)C supersaturated tungsten solid solution is formed and a WC→W2C transformation occurs during crystallization.

PROSPECTS FOR THE APPLICATION OF ION-PLASMA METHODS FOR INCREASING THE FATIGUE STRENGTH OF TRIBOSYSTEMS

Intensive research and development of multicomponent functional coatings and methods of their application on the surface with precision processing, which is required by the components of modern units of aircraft construction, space technology and other industries, are now being carried out in Ukraine and in the world. The Avinit N plasma precision nitriding methods widely used in industrial production of JSC FED have significant differences and advantages over traditional furnace methods of gas nitriding, namely: a significant reduction in the duration of diffusion saturation with nitrogen of the surface layer of iron-based alloys with an overall reduction in the technological time processing cycle up to 3-5 times; completely avoid hydrogen embrittlement; ensure dimensional preservation (nitriding “to size”) and high surface finish, reduction of the brittleness of the nitrided layer and the formation of nitride zones of all compositions without pores, as a result of which surface refinement after nitriding is not required. The article presents the results of tribological studies of the effect of plasma nitriding according to JSC FED technology on the contact strength from fatigue of steel 20X3MVF GOST 20072 during rolling friction with slipping surfaces and comparing the results with the contact fatigue strength of the same steel hardened by traditional gas cementation technology. They showed that the wear resistance of specimens reinforced with Avinit N nitriding is significantly higher than that of specimens hardened by traditional carburizing. The integrated multi-cycle resistance to fatigue wear (fracture) of samples hardened by nitriding Avinit N is more than 10 times higher than that hardened by cementation. This is due to the mechanisms of fatigue failure of cemented samples (spalling along the boundary of the defect). The results of the work can serve as the basis for conducting research on the use of ion-plasma nitriding technologies instead of cementing in order to increase the contact strength of the surface of the parts, taking into account also the advantages of this technology, such as maintaining the size and high purity of the surface treatment, as a result of which there is no need for their mechanical refinement after hardening.

Effect of Ultrasonic Surface Rolling Treatment on Corrosion Behavior of Alloy 690

The nanograins (NG) on the top surface layer of alloy 690 were successfully prepared by ultrasonic surface rolling treatment (USRT). The average grain size of NG alloy 690 was 55 nm, and the thickness of the NG surface layer was about 1 μm. Meanwhile, the surface roughness was significantly reduced after surface nanocrystalliztion. The corrosion behavior of alloy 690 before and after USRT was studied in a secondary side environment containing chloride. Electrochemical corrosion experiments demonstrated that the passive film generated by USRT was denser than that formed on coarse-grained (CG) alloy 690. Pitting corrosion was prone to occur in grain boundaries of CG alloy 690, and the pits on the surface of NG alloy 690 were smaller than those generated on CG alloy 690 after 1000 h of an immersion experiment.

ANALYSIS OF CHANGES IN THE PHASE AND STRUCTURAL STATE OF AN ALUMINUM ALLOY 1933 SURFACE LAYER, MELTED BY A PULSED ELECTRON BEAM

The structural and phase changes in the surface layer of an aluminum alloy 1933 caused by the action of a relativistic pulsed electron beam are studied. The structural and phase state of this layer is determined by the impact action of the electron beam and by the kinetics of crystallization from the melt under ultrafast cooling. The impact of a pulsed electron beam is accompanied by the formation of a developed surface relief and the appearance of microcracks on it. The structure of the modified layer is nonequilibrium. X-ray diffraction studies and the results of energy dispersive X-ray microanalysis made it possible to determine that magnesium oxide inclusions are present in the remelted layer. MgO inclusions are generally uniformly distributed in the remelted layer. The maximum size of MgO inclusions does not exceed 1 μm. The causes and mechanisms of the formation of magnesium oxide during the action of a pulsed electron beam are discussed.

Теплоперенос в поверхностном слое гетерогенного твердого сплава Т15К6 при импульсном высокоэнергетическом воздействии

Теплоперенос в поверхностном слое гетерогенного твердого сплава Т15К6 при импульсном высокоэнергетическом воздействии

Electrochemical formation of composite coatings by cobalt alloys in a pulsed mode

Electrodeposition of refractory metals and zirconium in composite alloys with cobalt allows to obtain coatings with a unique combination of physicochemical properties that are unachievable while using other methods of covering. By varying the composition of the electrolyte in galvanostatic mode it is impossible to obtain high-quality composite coatings with a high content of refractory components and current efficiency. As an alternative, it was suggested the use of pulsed electrolysis mode that allows to improve the producing of composite coatings. The selection of the ratio of pulse duration and pause allows avoiding the introduction of expensive additives and co-depositing metals in the alloy, which is not possible in the galvanostatic mode. Therefore, the purpose of the work was to determine the parameters for electrochemical deposition of cobalt coatings with refractory metals and zirconium from non-toxic electrolytes by pulsed electrolysis. The use of pulse mode at a ratio of the pulse duration 1×10-3-20×10-3 s and a pause duration of 2×10-3-20×10-3 s and an amplitude of the cathodic current density of 2-10 A/dm2 allows to obtain cobalt-based composite alloys with an increased content of zirconium, molybdenum and tungsten as comparing with stationary modes. Increasing the operating current densities causes the increase of the refractory metals content in composite alloys that contain molybdenum, and also decreases the grain size of the Сo-Mo-WхОy alloy surface layer. Based on the analysis of the experimental studies, the dependencies of current amplitude and pulse frequency on the current efficiency and composition of Сo-Mo-WхОy, Co-W-ZrO2 and Co-Mo-ZrO2 alloy coating were determined. The control of the composition of Сo-Mo-WхОy, Co-W-ZrO2 and Co-Mo-ZrO2 galvanic alloys in a quite wide range of alloying components concentrations is being achieved by varying the parameters of the pulse electrolysis, which allows adapting of the deposition technology to the needs of the modern market.

The impact of laser surface treatment on the microstructure, wear resistance and hardness of the AlMg5 aluminum alloy

Light metal alloys due to several unique properties such as low density and high corrosion resistance are increasingly used in various technical applications, where the automotive industry is one of the most important sectors. The automotive applications use mostly aluminum alloys, where the strength to density ratio of the material plays a crucial factor. Unfortunately, relatively low mechanical properties limit their applications for parts where a high surface hardness and wear resistance is expected. The classic heat treatment of aluminum alloys can only in some limited ranges improve the bulk material properties. Despite this, surface treatment with laser processing has developed significantly over the past 20 years. The laser beam treatment allows the introduction of a wide range of alloying elements to the surface layer of an aluminum alloy and thus, as a result of the precipitation of numerous intermetallic phases, significantly increases hardness, and abrasion resistance. The purpose of this work was to modify the aluminum surface layer using high-power fiber laser (HPFL). During this process, a mixture of titanium and iron powders (90/10 wt.%) was introduced onto the surface of the AlMg5 alloy. The microhardness tests carried out by the Vickers method and tribological tests showed a significant increase in mechanical properties in the entire volume of the obtained layer. Research on light and scanning microscopy revealed fragmentation of primary precipitates and the formation of numerous intermetallic phases rich in titanium and aluminum.

Influence of high current pulsed electron beam on microstructure and properties of Ni–W alloy coatings

Ni–W alloy coating layers were successfully materialized through an innovative surface alloying approach, high-current pulsed electron beam (HCPEB) irradiation. Two levels of HCPEB irradiation, 10 and 20 pulses, were applied to tungsten powders coated on nickel substrate. In the case of 10 pulses HCPEB irradiated sample, surface defects were formed on the Ni–W alloy surface layer. As the number of HCPEB pulse increased to 20, the surface became much smoother as compared to that of 10 pulses irradiated one. During irradiation, W particles were dissolved into the Ni substrate, and the newly formed Ni–W alloy layer was mainly composed of two major phases, NiW and Ni. After HCPEB irradiation, the microhardness was significantly increased, and the coefficient of friction (COF) and wear rate were reduced, which is attributed to the ultrafine W particles formed in the Ni substrate. Moreover, the corrosion property was enhanced after HCPEB irradiation.