Self-repairing functionality and corrosion resistance of in-situ Mg-Al LDH film on Al-alloyed AZ31 surface

A novel Mg-Al LDH film was in-situ prepared hydrothermally in an alkaline aqueous solution on an Al-alloyed AZ31 substrate.The structural,chemical and functional characteristics of the film were explored by means of scanning electron microscope(SEM),X-ray diffraction(XRD),energy dispersive spectrometer(EDS),polarization curve,AC impedance and salt immersion tests,respectively.The anti-corrosion results indicated that the Mg-Al LDH film on the Al-alloyed AZ31 surface could effectively protect the AZ31 from corrosion attack even after 90 days of immersion in 3.5 wt.%NaCl solution.The protection performance is surprisingly better than most of the reported coatings on Mg alloys.More interestingly,when the Mg-Al LDH film was scratched,the exposed Al-alloyed surface might gradually release metal ions and re-generate dense LDH nano-sheets in the corrosive environment to inhibit the further corrosion there,exhibiting a self-repairing behavior.The combination of the benign long-term protection and desirable self-repairing performance in this new process of surface-alloying and LDH-formation may significantly extend the practical application of magnesium alloys.

Investigation on Cracking in the Surfacing Welding Layer of Ni_3Al Based Alloy

Investigation has been made into the causes of cracking in the Surfacing welding layer of Ni3Al based alloy by analysing both the liqu id-to-solid transformation in the molten pool and the distribution of thermal stress within the surfacing welding layer. The results show that cracking in the surfacing welding layer is directly related to the producing of eutectic phase β' (NiAl) in the interdendritic region and high thermal stress within the surfacing welding layer. When the process of electric arc surfacing welding is changed from along straight line to along' Z' pattern, cracking in the surfacing welding layer of Ni3Al based alloy is prevented due to being reduced of both the cooling rate of liquid in the molten pool and the moving speed of the heat source. Reducing the melting volume of the substrate material by lowering the output power of electric arc welding would make the content of iron atoms in the molten pool decrease. and this also can reduce the trend of the eutectic reaction in the interdendfitic region and is helpful to Suppress cracking in the surfacing welding layer.

Microstructure and properties of alloying coating on AZ31B magnesium alloy

Vacuum thermal diffusion technique was applied to preparing alloying coating on AZ31 B magnesium alloy. The microstructure and phase composition of the coatings prepared at different holding time were investigated in detail using optical microscopy（OM）, scanning electron microscopy（SEM）, energy dispersive spectrometer（EDS） and X-ray diffraction（XRD）, and so on. The microhardness tester and electrochemical workstation（PS-168a） were used to measure the microhardness and corrosion resistance of the alloying coating. The results showed that the alloying coatings gradually generated with the extension of holding time under constant temperature. And the obvious bonding interface between the coating and substrate was observed, and the bonding interface was changed from smooth to zigzag. EDS and XRD analyses showed that the microstructure of alloying coating mainly consisted of eutectic α-Mg phase and continuous network β-Al（12）Mg（17） phase. The average microhardness of the coatings increased by 113% in comparison to the substrate, and the self-corrosion potential increased from-1.389 to-1.268 V at the same time.

Effect of surface diffusion alloying on erosion wear property of ZM5 magnesium alloy

Specimens of ZM5 magnesium alloy were dipped into the mixed powder of Al and Zn at （390±5） ℃ for 8 h in argon gas protective environment and subjected to surface diffusion alloying processing （SDAP）. The erosion wear behaviors of ZM5 magnesium alloy before and after SDAP were investigated in two different erosion wear environments： oil and quartz environment; tap water and quartz environment. The surfaces of erosion wear specimens exhibited cutting scratch grooves in the oil and quartz environment. Corrosive attack was weak and cutting wear mechanism was responsible for the mass loss. When the erosion wear medium was changed to tap water and quartz environment, corrosion pits and cracks were obviously observed after erosion wear test. The corrosion from tap water and the scour from quartz intensified mass losses. Compared with the untreated specimens, the application of SDAP improved the erosion wear resistance in the same environment.

Cavitation erosion behavior of WC coatings on CrNiMo stainless steel by laser alloying

The WC powder was precoated on the surface of CrNiMo stainless steel and then made into an alloying layer by using the laser alloying technique. Phases in the layers were investigated by X-ray diffraction （XRD） analysis and surface morphologies after cavitation erosion were observed with the help of scanning electron microscopy （SEM）. The cavitation erosion behavior of the CrNiMo stainless steel and WC laser alloying layer in distilled water was tested with the help of ultrasonic vibration cavitation erosion equipment. The results showed that the thickness of the laser alloying layer was about 0.13 mm. The layer had a dense microstructure, metallurgically bonded to the substrate, and no crack had been found. The cavitation erosion mass loss rate of the laser alloying layer was only 2/5 that of the CrNiMo stainless steel. The layer had better cavitation resistance properties because of its metallurgical combination and the strengthening effects of the precipitate phases.

Surface‑Alloyed Nanoporous Zinc as Reversible and Stable Anodes for High‑Performance Aqueous Zinc‑Ion Battery

Metallic zinc(Zn)is one of the most attractive multivalent-metal anode materials in post-lithium batteries because of its high abundance,low cost and high theoretical capacity.However,it usually suffers from large voltage polarization,low Coulombic efficiency and high propensity for dendritic failure during Zn stripping/plating,hindering the practical application in aqueous rechargeable zinc-metal batteries(AR-ZMBs).Here we demonstrate that anionic surfactant-assisted in situ surface alloying of Cu and Zn remarkably improves Zn reversibility of 3D nanoporous Zn electrodes for potential use as high-performance AR-ZMB anode materials.As a result of the zincophilic ZnxCuy alloy shell guiding uniform Zn deposition with a zero nucleation overpotential and facilitating Zn stripping via the ZnxCuy/Zn galvanic couples,the self-supported nanoporous ZnxCuy/Zn electrodes exhibit superior dendrite-free Zn stripping/plating behaviors in ambient aqueous electrolyte,with ultralow polarizations under current densities up to 50 mA cm^(‒2),exceptional stability for 1900 h and high Zn utilization.This enables AR-ZMB full cells constructed with nanoporous ZnxCuy/Zn anode and K_(z)MnO_(2)cathode to achieve specific energy of as high as~430 Wh kg^(‒1)with~99.8%Coulombic efficiency,and retain~86%after long-term cycles for>700 h.

Cooperative effect of surface alloying and laser texturing on tribological performance of lubricated surfaces

The cooperative effect of laser surface texturing(LST) and double glow plasma surface alloying on tribological performance of lubricated sliding contacts was investigated.A Nd:YAG laser was used to generate microdimples on steel surfaces. Dimples with the diameter of 150μm and the depth of 30-35μm distributed circumferentially on the disc surface.The alloying element Cr was sputtered to the laser texturing steel surface by double glow plasma technique.A deep diffusion layer with a thickness of 30μm and a high hardness of HV900 was formed in this alloy.Tribological experiments of three types of samples(smooth,texturing and texturing+alloying) were conducted with a ring-on-disc tribometer to simulate the face seal.It is found that,in comparison with smooth steel surfaces,the laser texturing samples significantly reduce the friction coefficient.Moreover,the lower wear rate of the sample treated with the two surface techniques is observed.

Study on microstructure and properties of Mg-alloy surface alloying layer fabricated by EPC

AZ91D surface alloying was investigated through evaporative pattern casting （EPC） technology. Aluminum powder （0.074 to 0.104 mm） was used as the alloying element in the experiment. An alloying coating with excellent properties was fabricated, which mainly consisted of adhesive, co-solvent, suspending agent and other ingredients according to desired proportion. Mg-alloy melt was poured under certain temperature and the degree of negative pressure. The microstructure of the surface layer was examined by means of scanning electron microscopy. It has been found that a large volume fraction of network new phases were formed on the Mg-alloy surface, the thickness of the alloying surface layer increased with the alloying coating increasing from 0.3 mm to 0.5 mm, and the microstructure became compact. Energy dispersive X-ray （EDX） analysis was used to determine the chemical composition of the new phases. It showed that the new phases mainly consist of/3-MglTAI12, in addition to a small quantity of inter-metallic compounds and oxides. A micro-hardness test and a corrosion experiment to simulate the effect of sea water were performed. The result indicated that the highest micro-hardness of the surface reaches three times that of the matrix. The corrosion rate of alloying samples declines to about a fifth of that of the as-cast AZ91D specimen.

Tribological Properties of Dimpled Surface Alloying Layer on Carbon Steel

The effect of surface structure and coating on tribological properties of 45^# carbon steel disc was analyzed. A Nd：YAG laser was used to generate rnicrodirnples on steel surfaces. Dimples with diameter of 150 rn and depth of 50 rn were distributed in an orbicular array on disc surface. Then the alloying element Mo was sputtered to 45# carbon steel disc surface by means of double glow plasma technology. Diffusion Mo alloying layer with 30min thickness and high hardness up to 0.025 was formed on the disc surface. Tribological experiments of three types samples （smooth, texturing and texturing＋alloying） were conducted with a pin-on-disc tribometer. It is found that the dimpled-samples are most effective for reducing friction in comparison with smooth steel surthces, improving the lubricating state from boundary to hydrodynamic region.

Developing Mg–Zn surface alloy by friction surface allosying: In vitro degradation studies in simulated body fluids

A new variant of friction-assisted process named friction surface alloying(FSA)for developing surface alloys was demonstrated in the present work.In FSA,the dispersed phase is melted and allowed to react with the matrix material to form an alloy at the surface of a metallic substrate.In the present work,magnesium(Mg)sheets and zinc(Zn)powder were selected,and fine grained(~3.5μm)Mg–Zn surface alloy with improved hardness was produced by FSA.X-ray diffraction studies confirmed the formation of intermetallic phases of Mg and Zn at the surface.From the in vitro degradation studies carried out by immersing in simulated body fluids,a lower corrosion rate was observed for the Mg–Zn surface alloy compared with pure Mg.The surface morphologies after immersion studies indicated large degraded areas on the base Mg compared with Mg–Zn.The results demonstrate the potential of FSA in developing Mg-based surface alloys without melting the substrate to impart better surface properties.

Plasma Niobium Surface Alloying of Pure Titanium and its Oxidation at 900 ℃

A niobium-modified layer on pure titanium surface was obtained by means of double glow plasma surface alloying technique. The modified layer was uniform, continuous, compact and well adhered to the substrate. The niobium composition in the modified layer decreased gradually from the surface to the substrate. The oxidation behavior of the niobium-modified layer was investigated and com- pared with the untreated surface at 900 ~C for 100 h. Characterization of the layers was performed using X-ray diffraction and scanning electron microscope, respectively. The test results show that the oxidation behavior of pure titanium was improved by niobium alloying process. Niobium has a positive influence on the oxidation resistance.

Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

In this work, an in situ synthesized TiC-reinforced metal matrix composite （MMC） coating of approximately 350-400μm thickness was fabricated on a gray cast iron （GCI） substrate by plasma transferred arc （PTA） surface alloying of Ti-Fe alloy powder. Microhard- ness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy （SEM） and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual anstenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures （473 K and 623 K）, and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the sam- ples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstruc- ture and to the presence of TiC particles.

EVOLUTION OF MICROSTRUCTURE OF LASER SURFACE ALLOYING OF γ TiAi ALLOY WITH NITROGEN

Laser surface alloying of γ TiAl alloy with nitrogen was studied under the constant protective nitrogen current (20l /min). The experimental results shown that the surface multi layers formed with experimental parameters could be up to 600μm depth; it consists of TiN,Ti 2AlN,α 2 and γ phases, without AlN, and the irregular coarse continuous “flow” line,dendrite,needle and granular nitrides disperse on the fine dendrite casting α 2 and γ phases substrate. The microstructure and compositions in the nitiding layer were determined and analyzed by SEM and EPMA and the mechanism for the formation of microstructure in the nitriding layer was also discussed.

Oxidation behavior of niobized TiAl by plasma surface alloying

Plasma surface alloying of element Nb in TiAl-based alloys and the oxidation behavior were studied. The composition and microstructure of the surface alloyed layers were investigated by means of scanning electron microscopy （SEM）,energy dispersive X-ray analysis （EDX）,and X-ray diffraction （XRD）. The experimental results indicate that the diffusion layers are formed on the TiAl substrate during the plasma niobizing process. The result from oxidation resistance investigation shows that plasma niobizing greatly improves the oxidation resistance of TiAl compared with the untreated TiAl. The role of element Nb for improving the oxidation resistance is considered to be achieved by strengthening the activity of Al,which is induced by the plasma niobizing process.

Anti-oxidation characteristics of Cr-coating on surface of Ti-45Al-8.5Nb alloy by plasma surface metallurgy technique

TiAl-based alloys have received extensive attention recently due to their excellent properties. However, the weak oxidation resistance at temperatures higher than 800℃ can limit their further high-temperature structural applications.To improve the oxidation resistance of a high-Nb-content γ-TiAl alloy(Ti-45 Al-8.5 Nb, in units of at.%), a chromium(Cr)coating is prepared by using the plasma surface alloying technique, separately, at 800℃ and 1000℃. The x-ray diffraction(XRD) patterns reveal that an oxide surface layer consisting of Cr2O3, Al2O3, and TiO2 is produced on the Cr-coated Nb containing γ-TiAl substrates during the initial oxidation. However, the Cr2O3 is dominated in the oxide surface layer after being isothermally oxidized for 300 h. The oxidation kinetic curves are composed of a parabolic law stage(≤ 90 h) and a biquadratic law stage(≥ 90 h), fit by weight–gain curves. Due to diffusion in the fabrication process and oxidation process,the Cr-coated specimens have an adhesion force after being isothermally oxidized, specifically 69 N for a specimen after oxidation for 300 h. These results demonstrate that the Cr coating enhances the oxidation resistance and adhesion of a Ti-45 Al-8.5 Nb alloy, which may provide a new feasible scheme for designing oxidation protection layers.

Coordinately Improving the Wear and Fatigue Properties of Ti6Al4V Alloy by Designed CrZr-alloyed Layer

A CrZr-alloyed layer was prepared through a pre-zirconizing and subsequent chromizing treatment on a Ti6Al4V substrate.After the removal of the top Cr deposit and Ti4Cr layers,a（Cr,Zr）-Ti solidsolution layer was obtained.The microstructure,composition,microhardness and toughness of the（Cr,Zr）-Ti solid-solution layer were evaluated.The results showed that the pre-addition of Zr played an important role in inhibiting the precipitation of the soft Ti4Cr phase,which in turn allowed us to obtain a material characterized by a remarkable hardness.Wear and fatigue tests showed that the（Cr,Zr）-Ti solid-solution layer could coordinately improve the properties of the Ti6Al4V alloy.This was mainly due to the good match of hardness and toughness of the（Cr,Zr）-Ti solid-solution layer.In addition,the gradual change in composition and mechanical properties was conducive to the coordinated deformation between the（Cr,Zr）-Ti solid-solution layer and the Ti6Al4V substrate during fatigue tests.This reduced the stress concentration in correspondence of the interface between the two materials.

Influence of Boron on the Mechanical Properties and Microstructure of Surfaced Alloy

In this paper, the influeuce of B on mechanical properties and microstructure of weld metal from B4C surfacing alloy is studied’ Results show that increasing boron content leads to sharp increasing of harduess and wear-resistance of weld metal’ And micrestructure transforms gradually from hypoeutectoid to hypereutectic with Fe3C-type carbide transforming into Fe3 (C, B)- and Fe23 (C, B ),-type carbon-boride. And in hypereutectic micrestructure even segregates out high-hardness phase Fe2B. As eutectic mainly consists of a phase and Fe23 (C,B),’ Fe3 (C,B) and distributes homogenously in network, which makes surfaced alloy have kigh impact resistance.

Effects of C,N-Codoped on the Corrosion Resistance of TiO_2 Films Prepared by Plasma Surface Alloying and Thermal Oxidation Duplex Process

C,N-codoped TiO 2 films have been deposited onto stainless steel substrates using plasma surface alloying and thermal oxidation duplex process.Composition analysis shows that the films shield the substrates entirely.The TiO 2 films are anatase in structure as characterized by X-ray diffraction.The electrochemical measurements show that the equilibrium corrosion potential positively shifts from-0.275 eV for bare stainless steel to-0.267 eV for C,N-codoped TiO 2 coated stainless steel,and the corrosion current density decreases from 1.3×10-5 A/cm2 to 4.1×10-6 A/cm2.The corrosion resistance obtained by electrochemistry noise also reveals that the C,N-codoped TiO 2 films provide good protection for stainless steel against corrosion in stimulated body fluid.The above results indicate that C,N-codoped TiO 2 films deposited by plasma surface alloying and thermal oxidation duplex process are effective in protecting stainless steel from corrosion.

Use of a Laser/TIG Combination for Surface Modification of Ti-6Al-4V Alloy

The surface modification of materials such as Ti-6Al-4V is necessary to improve their wear resistant properties for use in tribological applications. In this paper it is shown that a laser with low power and tungsten inert gas (TIG) can be combined together for surface modification of Ti-6Al-4V alloy, and when performed in a controlled atmosphere of pure nitrogen or a mixture of nitrogen and argon, can produce a wear-resistant surface alloy. Compared with laser processing, a cheaper surface modification process has been developed involving a shorter processing time, which is free of stringent requirements such as a vacuum system.

Microstructure and Properties of Laser Surface Alloying 304 Stainless Steel with Si

Silicon was added to the surface of 304 stain- less steel by laser melting the sprayed preplaced Si powders.The optical microscopy,X-ray diffraction and EPMA were employed to investigate the microstructure and chemical composition of the laser surface alloyed layer.The hardness of the al- loyed layer was measured by microhardness test and wear resistance was evaluated by scratch test. Corrosion resistance of laser alloyed sample was studied in 1N H_2SO_4+0.1N NaCl and 0.5N HCl+0.5N NaCl aqueous solutions.A microcrystalline intermetallic compound coating with smooth surface and good chemical homogeneity without porosity and crack is ob- tained.The hardness is about 720 HV.The wear re- sistance is 2 times better than that of the substrate. The corrosion resistance of the laser alloyed sample is much better than that of 304 stainless steel sample.