Glow Plasma Surface Alloying Technology Research Articles

Isothermal oxidation behavior of W-based alloy coatings doped with Ta, Cr, Ti, V

Tungsten-based multi-alloy coatings with the addition of Ta, Cr, Ti, and V were prepared by double glow plasma surface alloying (DGPSA) technology. The alloyed specimens showed bulges and pits on the surface with an island growth mechanism. The coating exhibits a single BCC phase. The hardness shows an increasing trend with the increase of alloyed elements. The maximum hardness value of WTaCrTiV is 1748 HV100g. The oxidation behavior of coatings at 800 °C was investigated, with emphasis on the effect of elemental doping on the antioxidant properties. With the addition of Ta, Cr, Ti, and V elements, the antioxidant properties of multi-alloy coatings were effectively improved compared the tungsten matrix. The WTaCrTi coating shows the optimum antioxidant properties with a dense Cr2O3 layer. As the number of elements in multi-alloy increases, the mixing entropy increases, leading to a decrease in the Gibbs free energy, which results in a more stable alloy.

High-temperature oxidation and tribological behaviors of WTaVCr alloy coating prepared by double glow plasma surface alloying technology

Tungsten-based refractory high entropy alloys (RHEAs) are a potential candidate for plasma-facing materials (PFM) due to their excellent properties. However, the oxidation resistance of W-based RHEAs is poor. Moreover, there is still a lack of research on the evaluation of room temperature wear. In this work, several WTaVCr alloy coatings were fabricated by double glow plasma surface alloying (DGPSA) technology at different temperatures and different source ratios. The microstructure of WTaVCr coatings exhibited BCC solid solution phase. The coatings were compact and uniform. The scratch test indicates that the coating combines the substrate well. The surface hardness of the samples increases significantly after alloying, which is 5 times that of the substrate. Sliding wear tests were performed on the coating as well as the substrate. The fairly low specific wear rate of the coating (W31.7Ta13.3V42.9Cr12.2) proved its excellent wear-resisting property (The wear rate was 8 × 10−7 mm3/N∙m, which was two orders of magnitude lower than that of the substrate), and the dominant wear mechanism was abrasive wear and oxidative wear. The coating (W45Ta45.4V4.5Cr5.1) showed a favorable oxidation resistance, and a continuous Cr2O3 protective layer was formed on the surface. The oxidation resistance of the coating was approximately a quarter of the W-substrate.

Nano-mechanical properties of Mo coating prepared on Invar alloy substrate by double glow plasma surface alloying

In this work, surface Mo alloying was realized on Invar alloy using double glow plasma surface alloying technology. The microstructure and phase constitution of Mo-modified coating were determined by using X-ray diffraction and scanning electron microscopy. The surface modification effect and loading strain rate (LSR) dependency of Mo coating were presented qualitatively and quantitatively via nanoindentation method based on continuous stiffness measurement technique. Results showed that the received Mo coating with a thickness of approximately 10 μm was compact and homogeneous. The phase constitution consisted of pure Mo phase. Double glow plasma surface molybdenizing improved the surface hardness and elastic modulus remarkably. Indentation response showed obvious LSR dependency. Under different LSRs, hardness and plasticity exponent increased with LSR, while elastic modulus and contact stiffness basically remained stable. Meanwhile, creep displacement and creep strain rate sensitivity exponent were positively correlated with LSR.

Microstructure and mechanical properties of W-Ta-V-Cr high-entropy alloy coatings by double glow plasma surface alloying

A W-Ta-V-Cr high entropy alloy (HEA) coating has been successfully synthesized on the tungsten-based surface by Double glow plasma surface alloying (DGPSA) technology. The effects of W-Ta-V-Cr on the microstructure and properties of the coating were systematically investigated. The results illustrated that a compact and homogeneous alloy coating with a thickness of 8.8 μm was formed on the surfaces of pure tungsten. The addition of four elements promoted the formation of BCC phase in the coating, refined the grain size and formed nanocrystalline materials. Thereby the microhardness and abrasion rate of the coating increased and decreased, respectively. The hardness value of the coating reaches 1130 HV, which is 2 times that of the substrate (∼551 HV) and the specific abrasion rate of the coating was only 1/8.5 of that of the W substrate, showing extremely excellent abrasion resistance performance. The coating effectively improves the mechanical of pure tungsten. Such high hardness and abrasion resistant can be attributed to the combined contribution from solid-solution hardening and grain refinement.

Performance Enhancement in Borocarburized Low-Carbon Steel by Double Glow Plasma Surface Alloying

In this paper, the performance of low-carbon steel is enhanced after introducing a borocarburized diffusion layer via double glow plasma surface alloying technology. Due to the boron-carbon gradient structure of low-carbon steel, the protective coating exhibits an excellent wear and corrosion resistance. Interestingly, the borocarburized layer consists of a 64 μm carburized layer and a 27 μm boride layer, which plays an effective role in enhancing the microhardness of borocarburized low-carbon steel, exhibiting a 1440 Vickers hardness increase in the surface microhardness of low-carbon steel. The potentiodynamic polarization measurement and impedance measurement results indicate that the boride protective film can effectively prevent aggressive chloride ions from invading the substrate, which indicates an excellent property of corrosion resistance. This systematic study paves a promising way for the future application of hard coatings in severe environments.

Wear and Deformation Performance of W/Ta Multilayer Coatings on Pure Cu Prepared by Double Glow Plasma Alloying Technique

In this study, a multilayered hard coating with a tungsten matrix and a transition layer was deposited on pure copper by double glow plasma surface alloying technology, which aimed to provide the coating superior binding force and favorable matching of mechanical properties. The micro-hardness tester was adopted to measure the surface and cross-sectional hardness of the coatings. The nanoindentation test was used to measure the elasticity modulus of the coatings. Sliding wear tests under different conditions were performed on the W/Ta multilayer coating as well as the Cu substrate and W coating. The fairly low specific wear rate of the multilayer coating proved its excellent wear-resisting property, and the wear mechanism of the multilayer coating was mainly abrasive wear. In addition, a scratch test was executed to evaluate the deformation mechanism of the coating. Compared to the W coating, the persistence of the changing elastic–plastic deformation in the W/Ta multilayer coating improved the adhesion and resistance to plastic deformation. Moreover, the changing elastic–plastic deformation region is a benefit to the wear process, and the mechanical properties of the transition layer present a linear gradient descent instead of a vertical gradient, which makes a significant contribution in the wear stage. Further, the exploration of deformation mechanisms has a significant contribution to the design for multilayered hard coatings.

Corrosion behavior of double-glow plasma copperizing coating on Q235 steel

In this paper, the copperized layerwas fabricated on the surface of Q235 steel via double glow plasma surface alloying technology to improve the marine fouling organisms attached on the surface of marine structures. The microstructure and phases composition of the coating were analyzed by SEM and XRD. The corrosion characteristics of substrate and coating were investigated in 3.5wt.% NaCl solution.The results indicated that the protective coating had a novel structure of an outermost deposition layer (85?m) and inner diffusion layer (51 ?m), which exhibited great adhesion stress because of the metallurgical bonding effects. The corrosion characteristics of substrate and coating were analyzed in detail. The corrosion products of Q235 steel were mainly ?-FeOOH, ?-FeOOH, and ?-FeOOH in the early stage of corrosion process. Then the whisker-like structure of ?-FeOOH grew on the surface of ?-FeOOH and the ?-FeOOH transformed into ?-FeOOH to achieve thermodynamical equilibrium. The dissolved copper ions in solution resulted in a unique difference in the formation of corrosion products, which inhibited the transition of iron hydroxide and promoted the formation of amorphous phases. Based on electrochemical measurement, the coating hadlower corrosion current density and higher charge transfer resistance than substrate. The corrosion resistance of copperized layer wasbetter than that of Q235 steel.

Oxidation behaviors and self-healing performance of MoSiAlY coating on γ-TiAl substrate by a surface alloying method

A novel MoSiAlY coating was deposited on a γ-TiAl alloy to improve its oxidation resistance by double glow plasma surface alloying technology. This study focused on the oxidation behaviors and self-healing performance of MoSiAlY coating during isothermal oxidation test. The coating transformations were examined by observing its morphologies, element distribution and phase structure using scan electron microscopy, energy-dispersive spectrum and X-ray diffraction respectively. The results indicated that the oxidation resistance of γ-TiAl alloy was effectively improved by MoSiAlY coating at 900 °C. The volume expansion of phases SiO2 from MoSi2 and Al2O3 from AlMo3 was responsible to the self-healing ability of MoSiAlY coating. The MoSiAlY coating would be a potential surface enhancement for Ti-Al intermetallics at high temperatures.

Microstructure and tribological behavior of W-Mo alloy coating on powder metallurgy gears based on double glow plasma surface alloying technology

In the present paper, plasma surface alloying was implemented on powder metallurgy gears to improve its wear resistance based on double glow plasma surface metallurgy technology. A W-Mo alloy coating was obtained in the process. The morphology, microstructure and phase composition were investigated by SEM, EDS and XRD. The hardness was examined by Vickers hardness test and nanoindentation test. The tribological behavior of powder metallurgy gears before and after plasma surface alloying was evaluated on a ball-on-disc reciprocating sliding tribometer under dry sliding condition at room temperature. The results indicate that the W-Mo alloy coating is homogeneous without defects, which includes deposition layer and interdiffusion layer. The average microhardness of powder metallurgy gears before and after plasma surface alloying is 145.8 HV0.1 and 344.4 HV0.1, respectively; Nano hardness of deposition layer and interdiffusion layer is 5.76 GPa, 14.35 GPa, respectively. The specific wear rate of W-Mo alloy coating is lower than original PM gears. The wear mechanism of W-Mo alloy coating is slight adhesive wear. The W-Mo alloy coating prepared by double glow plasma surface alloying technology can effectively improve wear resistance of powder metallurgy gears.

Plasma surface tantalum alloying on titanium and its corrosion behavior in sulfuric acid and hydrochloric acid

An anti-corrosion Ti-Ta alloy coating was prepared on pure titanium surface by double glow plasma surface alloying technology. Electrochemical corrosion test was applied to test the anti-corrosion property of Ti-Ta alloy layer. The microstructure and the phase composition of Ti-Ta alloy coating were detected before and after corrosion process by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results showed that the Ta-Ti alloy layer has a thickness of about 13–15 μm, which is very dense without obvious defects such as pores or cracks. The alloy layer is composed mainly of β-Ta and α-Ti. The Ta alloy layer improves the anti-corrosion property of pure titanium. A denser and more durable TiO2 formed on the surface Ta-Ti alloy layer after immersing in strong corrosive media may account for the excellent corrosion resistant.

Preparation and characterization of Cr/CrC multilayer on γ-TiAl alloy by the double glow plasma surface alloying technology

Hard ceramic and ductile metal materials combined in multilayered structures provide superior wear and oxidation resistance to the single layer, which has been applied extensively to components subjected to high-temperature oxidation and wear. In this paper, the oxidation and wear properties of Cr/CrC multilayer coating obtained on γ-TiAl alloy by an emerging technology, that is double glow plasma surface alloying technology, were reported. Sliding wear and oxidation tests were performed on Cr/CrC multilayer as well as on chromising reference coating. The friction coefficients of Cr/CrC multilayer at room and high temperature were 0.2 and 0.175 respectively, about only 22.2% and 35% of the γ-TiAl substrate. The Cr/CrC multilayer oxidized approximately parabolically, with lower oxidation rate than the chromising coating. The oxidation mechanism of the Cr/CrC multilayer was mainly dominated by carbide oxidation and dense Cr2O3 scale oxide development.

Effect of plasma surface tungstenising on the friction and wear of Ti2AlNb-based alloys

ABSTRACTTo obtain a strong bond between W coatings and the substrate, a novel graded tungstenised layer on Ti-Al-Nb alloys was produced using a double glow plasma surface alloying technology and a special graded tribological coating was designed. The microstructural results showed that the tungstenised layer was distributed in a graded manner and was mainly comprised of W- or Ti-rich TixW1−x phases. Varying the friction conditions indicated that an increase in the load and sliding speed led to an increase of the friction coefficient and wear rate of the tungstenised layer at room temperature. These changes were mainly caused by the graded distribution of the W composition and the change in surface contact status. The results indicated that the friction and wear properties of Ti-Al-Nb alloys were greatly improved by the surface tungstenising.

Effect of processing factors on the microstructure and gradual diffusion of tungstenized layers

The refractory tungsten (W) coating due to its low sputtering yield is not easy to be obtained, and the bonds between the W coating and its substrate are weak and easily broken. A novel gradual tungstenized layer as the plasma facing armor material is prepared by using the double glow plasma surface alloying technology (DGPA). The effects of process factors on the microstructure and micro-hardness of the alloyed layers are investigated. It is found that TixW1-x gradual layers are formed in the alloyed layer. Due to the fact that the tungsten content in the gradual tungstenized layer gradually decreases from surface to the substrate, the layer is composed of both pure tungsten coating and transitional coatings (e.g. TixW1-x (x>0.5) and TixW1-x (x<0.5) coatings). Hence, the gradual layer can enhance the bond strength between the layer and substrate, and the improved mechanical properties such as high hardness can also be obtained. The fact is that vacancies, dislocation and crystal defects could form on the surface of the substrate due to the effect of the double glow plasma bombardment. Therefore, a particular attention is paid to the diffusion mechanisms of W atoms in the W gradual layers and a diffusion model is proposed to explain the forming process of the gradual layers according to the Fick's first law. The findings reported here demonstrate the potential of an effective surface modification method for improving the diffusivity of W atoms. The present work provides a better understanding of the gradual diffusion process of tungsten element.

Double-glow plasma fabrication of graphene-oxide film and its UV photo-induced surface behavior

We demonstrated a new method by preparing a large-area graphene-oxide (GO) film on the quartz plates using the double glow plasma surface alloying technology (DGPSA). The relationship between UV photo-induced wettability and tribological performance was investigated. The results indicated that GO film exhibited the special hydrophilic-hydrophobic conversion under the ultraviolet irradiation. The wettability of GO film increased from 32° to 75° after 5min of irradiation, indicating a photo-induced hydrophobic surface. In view that UV irradiation induced the hydrophobicity of graphene, the friction coefficient of the obtained GO film after UV irradiation is lower than that before UV irradiation and their wear-proof properties are also improved. This work aims to confirm that the GO film prepared by DGPSA can display the obvious surface hydration behaviors and the tribological properties under the UV irradiation.

The large-area preparation and photoelectrochemical properties of graphene/ZnO nanorod composite film

We proposed a new method for preparing a single-crystalline (002)-oriented ZnO nanorod (ZnONR) array and graphene/ZnO nanorod (GZN) composite film on quartz plates using double glow plasma surface alloying (DGPSA) technology.

Study on preparation, microstructure and luminescent properties of Er-ZrO2 layer

To further explore the material early-warning application of the luminescent coating, we demonstrated a new method by preparing a mixture layer of metallic erbium and oxidized zirconium (Er-ZrO2 layer) using the double glow plasma surface alloying technology with Zr and Er co-sputtering under oxygen plasma exposure. The microstructure, composition and luminescence properties of the layers were characterized by scanning electron microscopy, X-ray diffraction, Raman and photoluminescence spectra. The dependence of the luminescence on the gradual concentration was studied. Results indicated that the contents of Zr, Er and O in the layer decreased gradually along the depth direction. The luminescence properties were concentration-dependent. X-ray diffraction analysis showed that the crystalline structure of ZrO2 layer transferred from a mixture phase of tetragonal and monoclinic to pure monoclinic phase with the Zr-Er co-sputtering. The Raman bands of the layers depended on its local ZrO2 crystal structures. Photoluminescence characteristics of Er-ZrO2 layer revealed that the main emission bands were assigned to 2H11/2→4I15/2 and 4S3/2→4I15/2 transition under the excitation at 325 nm. The fact suggested that the plasma surface alloying is an effective method to obtain luminescent layer.

Improving tribological properties of Ti-5Zr-3Sn-5Mo-15Nb alloy by double glow plasma surface alloying

Molybdenum, an alloying element, was deposited and diffused on Ti-5Zr-3Sn-5Mo-15Nb (TLM) substrate by double glow plasma surface alloying technology at 900, 950 and 1000°C. The microstructure, composition distribution and micro-hardness of the Mo modified layers were analyzed. Contact angles on deionized water and wear behaviors of the samples against corundum balls in simulated human body fluids were investigated. Results show that the surface microhardness is significantly enhanced after alloying and increases with treated temperature rising, and the contact angles are lowered to some extent. More importantly, compared to as-received TLM alloy, the Mo modified samples, especially the one treated at 1000°C, exhibit the significant improvement of tribological properties in reciprocating wear tests, with lower specific wear rate and friction coefficient. To conclude, Mo alloying treatment is an effective approach to obtain excellent comprehensive properties including optimal wear resistance and improved wettability, which ensure the lasting and safety application for titanium alloys as the biomedical implants.

Formation process and cross-sectional hardness of a Cr-alloyed layer on Ti6Al4V alloy

A Cr-alloyed layer consisting of five sublayers was prepared on Ti6Al4V substrate via double glow plasma surface alloying technology at 800°C. The formation process and cross-sectional hardness of the Cr-alloyed layer were studied in detail. The results showed that a set of new phase layers (i.e., Cr, TiCr2, Ti4Cr, (βTi,Cr) and (αTi,Cr) sublayers) formed at 800°C; however, the (βTi,Cr) phase decomposed and separated out the Ti4Cr phase when the temperature decreased. Additionally, the TiCr2 phase had the highest hardness while Ti4Cr phase had the lowest hardness. Precipitation of the soft Ti4Cr phase from the (βTi,Cr) phase therefore limited the improvement of the hardness and led to an unusual change: increasing the Cr content led to a lower hardness.

Temperature dependence of W metallic coatings synthesized by double glow plasma surface alloying technology on CVD diamond films

W metallic coatings were synthesized on free-standing chemical vapor deposition (CVD) diamond films using double glow plasma surface alloying (DGPSA) technology. The influence of varying metalizing temperatures on the microstructures, phase composition and adhesion of the W metallic coatings were investigated. Likewise, the effectiveness of the W metallic coatings was preliminary evaluated via examining the shear strength of the brazing joints between W-metalized diamond films and commercial cemented carbide (WC–Co) inserts. The results showed that continuous and compact W metallic coatings were formed on the diamond films in the temperature range of 750–800°C, while cracks or cavities presented at the W/diamond interface at 700°C, 850°C and 900°C. Inter-diffusion of W and C atoms preformed, and WC and W2C were formed at the W/diamond interfaces at all temperatures except 700°C, at which only W2C was formed. Moreover, etched cavities appeared at the W/diamond interface when the temperature exceeded 850°C. The critical loads for coating delamination, as measured with the scratch test, increased as the temperature rose from 700°C to 800°C, while decreased with further increasing temperature. The maximum load was obtained at 800°C with a value of 17.1N. Besides, the shear strength of the brazing joints depicted the similar trend with the critical load. The highest shear strength (249MPa) was also obtained at 800°C.

Effects of combined plasma chromizing and shot peening on the fatigue properties of a Ti6Al4V alloy

A plasma chromizing treatment was conducted on Ti6Al4V samples by employing the recently developed double glow plasma surface alloying technology. The Cr-alloyed layer consisted of four sub-layers, namely the Cr deposition, Cr2Ti, CrTi4, and Cr-Ti solid-solution layers. The local hardness and moduli were determined via nanoindentation. In addition, the fatigue properties of the samples were evaluated by using a rotating-bending fatigue machine under a given load. The results showed that the hardness or elastic moduli of the adjacent sub-layers differed significantly and the fatigue properties of the Ti6Al4V alloy deteriorated with the plasma chromizing treatment. This deterioration stemmed mainly from cracks initiated at the interfaces between the sub-layers and the microstructural changes of the substrate; these changes were induced by the high temperature used in the plasma chromizing process. However, the fatigue life of the plasma-chromized samples was increased by a shot peening post-treatment. The fatigue life of the samples resulting from this combination of treatments was slightly higher than that of the single-shot-peened Ti6Al4V substrate. In fact, the sample retaining only the Cr-Ti solid-solution layer (that is, the first three sub-layers were removed), when shot-peened, exhibited the highest fatigue life among all the tested samples; this was attributed to that sample having the highest residual compressive stress, the significant work hardening, and the good hardness to toughness balance.