Double Glow Plasma Research Articles

Tribological properties of double-glow plasma Tungsten-Molybdenum alloyed layer on iron-based powder metallurgy gear materials

The Tungsten-Molybdenum (W-Mo) alloyed layer was prepared on the surface of iron-based (Fe-based) powder metallurgy (PM) gear materials by double-glow plasma surface alloying technique (DG technique), and the microstructure and properties of the alloy layer were studied in the paper. The results indicate that the alloyed layer was homogeneous and dense, and the surface microhardness was 344 HV0.1. The nanohardness and elastic modulus of the alloyed layer were 7.7 GPa and 221 GPa, respectively, which are 2.02 times and 1.43 times greater than that of substrate. The friction coefficient and the specific wear rate of the alloyed layer with the load of 470 g is 0.537 and 2.57 × 10−5 mm3 · N−1 · m−1 respectively, which is 0.254 and 81.3% smaller than that of the substrate. The wear mechanism of the alloyed layer at low load was mainly slight abrasive wear. With increasing the load, the wear intensity of the alloyed layer was not as obvious as that of the substrate, which showed excellent wear resistance.

MICROSTRUCTURE AND MECHANICAL PROPERTY CHARACTERIZATION OF MULTILAYER FREE-STANDING DIAMOND/Mo FILMS

The monolayer diamond film and free-standing diamond/Mo multilayer films were prepared by combining microwave plasma chemical vapor deposition (MPCVD) and double glow plasma surface alloying (DGPSA) techniques. The result shows that the film grain size decreases from 70–80[Formula: see text][Formula: see text]m to [Formula: see text]–20[Formula: see text][Formula: see text]m with the layer number increasing from the monolayer diamond film with a columnar crystal structure to the seven-layer diamond/Mo films, indicating that the Mo interlayer can effectively reduce the grain size. The Mo2C is formed between the Mo and diamond layers, which can improve the bonding strength. The internal stress of these films depends on the number of Mo interlayers and the Mo2C content. Moreover, the fracture strength and abrasion ratio of multilayer diamond films are effectively improved by adding the Mo interlayer. The four-layer diamond/Mo film system has the highest fracture strength and the seven-layer film system has the highest abrasion ratio.

A New Plasma Surface Alloying to Improve the Wear Resistance of the Metallic Card Clothing

A new surface strengthening process: Plasma surface chromizing was implemented on the metallic card clothing to improve its wear resistance based on double glow plasma surface metallurgy technology. A chromizing coating was prepared in the process, which consisted of a deposited layer and diffusion layer. The surface morphologies, microstructure, phase composition, and hardness were analyzed in detail. The friction behaviors of the metallic card clothing before and after plasma surface alloying were comparatively analyzed under various sliding speeds at room temperature. The results showed that: 1. The chromizing coating on the surface of metallic card clothing was dense and homogeneous without defects, and the metallic card clothing still maintained its integrity and sharpness. 2. The chromizing coating consist of [Fe,Cr], Cr, Cr23C6, and Cr7C3, which contribute to the high hardness. 3. The average microhardness of metallic card clothing increased from 365.4 HV0.05 to 564.9 HV0.05 after plasma surface chromizing. Nano hardness of the chromizing coating was approximately 1.87 times than the metallic card clothing. 4. At various sliding velocities of 2 m/min, 4 m/min, and 6 m/min, the specific wear rates of metallic card clothing were 16.38, 9.06 and 6.26 × 10−4·mm3·N−1·m−1, and the specific wear rates of metallic card clothing after plasma surface chromizing were 2.91, 3.30, and 2.95 × 10−4·mm3·N−1·m−1. Furthermore, the wear mechanism of the chromizing coating gradually changed from adhesive wear to abrasive wear as the sliding velocity increased. The results indicate that the wear resistance of metallic card clothing was improved obviously after plasma surface chromizing.

Effect of Er incorporation on structural and element distribution of Zr alloyed layers prepared using double glow plasma surface alloying

ABSTRACTA special target structure for erbium (Er)-zirconium (Zr) co-deposition is proposed, based on the hollow cathode effect. To study the effect of rare earth on the alloyed layer, Zr-Er alloyed layers with different quantity proportion of Er and Zr elements were prepared on Ti-based substrate using double glow plasma surface alloying. The microstructure and composition of the alloyed layers were analysed by XRD and SEM-EDS. Results showed that Er element grows perpendicular to the Ti-based substrate in the alloyed layers, and it was found that the growth structure had an opposite effect on the diffusion of the Zr element. Interestingly, as the concentration of Er element increases, the addition of Er element to a certain extent affects the crystallisation of the Zr-Er alloyed layer and reduces the diffusivity of the Zr element.

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.

Effect of laser surface texturing (LST) on tribological behavior of double glow plasma surface zirconizing coating on Ti6Al4V alloy

In the present work, double glow plasma zirconizing technique combined with laser surface texturing (LST) were applied to improve the wear resistance of Ti6Al4V (TC4) alloy. A zirconium coating (Zr-coating) was firstly synthesized on TC4 alloy by double glow plasma surface zirconizing. Laser surface texturing (LST) was subsequently conducted to produce uniform dimples on the surfaces of Zr-coating and raw TC4 alloy. The dimple texture with a diameter of 300 μm and gradient densities of 5%, 7%, 11% were distributed in a square array on the surfaces of coated and uncoated TC4 alloy disks, respectively. Comparative assessments on the wear resistance of the related Zr-coating and TC4 alloy were carried out using a ball-on-disk wear tester. The results showed that the Zr-coating with a thickness of about ~50 μm, was tightly adhered to the TC4 alloy matrix. The textured specimens with a texture density of 5% revealed the lowest mass loss values in comparison to other samples, and the wear rate decreased by 20% and 26.6% compared with that of the TC4 alloy and Zr-coating without dimple texture on their surfaces. The wear rate value of the four tested samples were finally sorted in the sequence of the duplex treated TC4 < zirconized TC4 < textured TC4 < polished TC4.

Electrochemical characteristics of iridium coating by double glow plasma discharge process on titanium alloy substrates

ABSTRACTIridium coating was fabricated by a double glow plasma discharge process on titanium alloy substrates. The electrochemical behaviours of the coating and the substrate were studied and compared. The coating exhibited a preferred (220) orientation. The coating was rough and many defects were present in the coating; the electrochemical activity of the coating was strong. The corrosion potential of the coating was more positive than that of the substrate, and corrosion current density of the coating was higher than that of the substrate. Although the polarisation resistance of the coating was less than that of the substrate due to the defects in the coating and the performance of the oxide film formed, such as conductive Ir oxides film and non-conductive ceramic oxide film on the substrate surface, the coating with a high corrosion potential and high width of the capacitive loop had significant benefit for anti-corrosive properties of titanium alloy substrate.

EFFECT OF SUBSTRATE TEMPERATURE ON TANTALUM CARBIDES INTERLAYERS SYNTHESIZED ONTO WC-Co SUBSTRATES FOR ADHERENT DIAMOND DEPOSITION

Tantalum carbides (TaXC) interlayers have been synthesized by double glow plasma surface alloying (DG-PSA) method at different temperature for subsequent deposition of diamond coatings. The evolution of the microstructures, phase composition and adhesion of the interlayers dependent on substrate temperature has been discussed. The results show that the layers are composed of TaXC (i.e. Ta2C, TaC) with nanocrystalline microstructure and small amounts of CoTa2. The layer produced at 700∘C is formed of specific flower-shaped rings embedded in smooth structures. As the temperature increases to 800∘C, interacted rings are covered the full surface, and the surface roughness is increased. As the temperature increases further, the rings are replaced by irregular-shaped pits, caused a decreasing surface roughness. Besides the special microstructure with interactional rings and relatively high roughness, the layer prepared at 800∘C possesses higher adhesion, better wear performance and higher hardness than those of other layers. The coating obtained on the interlayer pretreated at 800∘C exhibits the best adhesion. Thus, the TaXC interlayers synthesized at 800∘C are demonstrated as a suitable option for adherent diamond coatings deposited onto WC-Co substrates.

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.

MECHANICAL PROPERTIES OF THE Fe-Al-Nb COATING BY DOUBLE GLOW PLASMA SURFACE METALLURGY

The Q235 steel was covered by Fe–Al–Nb alloyed coating to improve the mechanical properties of the Q235 steel. This double glow plasma surface metallurgy (DGPSM) surface modification technique was carried out at 1023[Formula: see text]K and pressure of 38[Formula: see text]Pa for 4.5[Formula: see text]h. The surface morphology represented the typical Volmer–Weber mode, an island structure which was accumulated by numerous small particles, and most of the angles formed between three islands were about 120[Formula: see text] where there was no appreciable defect. Meanwhile, in the cross-sectional morphology of the Fe–Al–Nb coating, there was a deposition layer, a diffusion layer and two transition regions between the different adjacent interfaces, and the coating approximate 17[Formula: see text][Formula: see text]m was found to be metallurgically adhered to the Q235 steel. The basic mechanical properties of the Fe–Al–Nb coating and Q235 steel including the hardness, elastic modulus and friction performance were measured and compared. The results showed that the formation of Fe3Al, FeAl, and Fe2Nb intermetallic compounds and Nb carbides in the coating can enhance the mechanical properties of the treated sample. The nanoindentation tests indicated that the hardness and elastic modulus of Fe–Al–Nb coating were 8.08[Formula: see text]GPa and 260.03[Formula: see text]GPa which were much higher than Q235 steel. The sliding friction tests showed that Fe–Al–Nb coating significantly improved the friction performance of Q235 steel at the speed of 300, 600 and 900[Formula: see text]rpm with load 320[Formula: see text]g for 15[Formula: see text]min.

Effect of Substrate Pre-carburizing on Properties of TiN (Ti) Hard Coatings Deposited on Ti-6Al-4V Alloy

Interface fracture often occurs in systems of soft substrate and hard coatings during the service process, which is related to the weak interface strength and the unstable expansion of cracks along the interface induced by the residual thermal stress. The residual thermal stress mainly comes from the mismatch of thermal physical properties between matrix and hard coatings. In this study, a gradient carburized layer was prepared on TC4 substrate before the deposition of TiN(Ti) coatings using double glow plasma carburization. And then the mono- and multilayer TiN(Ti) coatings were synthesized on the carburized layer, forming composite hard coatings. The effect of substrate carburizing on properties of coatings was studied. The results show that the composite coatings' hardness can be increased nearly 2 times and the bonding strength is enhanced to over 80 N, compared with that of mono-and multilayer TiN(Ti) coatings. Also the interface brittle fracture tendency is restrained obviously by the hardened substrate, and the coordinative deformation ability of the coating at extra load is optimized. The composite coating composed of pre-carburized layer and TiN hard coating shows a higher strength and toughness.

Isothermal Oxidation Behavior of Zr-Y Coating on γ-TiAl by Double Glow Plasma Surface Metal Alloying Technique

Oxidation resistance of Zr-Y coating on γ-TiAl alloy prepared by a double-glow plasma surface alloying technique was investigated in static air at 750 °C, 800 °C and 850 °C for 100 h. A pure Zr coating was also prepared for comparison. Addition of Y improved high-temperature oxidation resistance of the alloying coating because of its refining effect and inhibition of cationic diffusion. Oxidation kinetic curves indicated that the high-temperature oxidation resistance of the Zr-Y coating was about eight times higher than that of the bare substrate and about 3 times higher than that of pure Zr coating.

Sliding wear behaviour of Ni-Cr alloying on Ti6Al4V based on double-glow plasma surface metallurgy technology

To improve the wear resistance of Ti6Al4V alloy, Ni-Cr alloy coatings with 40 at.%Ni were prepared on Ti6Al4V alloy surface by double-glow plasma surface metallurgy technique. The friction and wear behaviour of the coatings sliding against Si3N4 at room temperature and 500 °C were comparatively studied. The results show that the alloy coatings comprise a deposited layer, a diffusion-modified layer and a heat-affected zone. The deformed deposition layer plays an anti-friction effect as a soft film. The tribological behaviour of diffusion layer is abrasive wear. Ni-Cr surface alloying process significantly reduces the friction coefficient of Ti6Al4V alloy and improves the wear resistance properties of Ti6Al4V alloy.

Hydrogen-free nitriding of ZrTiAlV by double glow plasma discharge improving the wear resistance

ABSTRACTA hydrogen-free nitriding method through double glow plasma metallurgy is exploited and a nitrided layer was formed on ZrTiAlV alloy. The nitrided layer was characterised through X-ray diffraction, optical microscopy, scanning electron microscopy and energy-dispersive spectroscopy techniques, as well as through Vickers hardness and friction and wear tests. Results showed that the nitrided layer is 580 µm thick, homogeneous and dense. It mainly consists of TiN, Ti2N and ZrN phases. The hardness of the nitrided layer on the surface of the ZrTiAlV alloy is nearly 2.5 times higher than that of the ZrTiAlV substrate. The friction coefficient and wear resistance of the alloy considerably improved after nitriding.

Double glow plasma surface Cr-Ni alloying of Ti6Al4V alloys: Mechanical properties and impact of preparing process on the substrate

Surface Cr-Ni alloying of Ti6Al4V alloys was achieved by double-glow plasma surface metallurgy technology. The adhesion strength and nano-indentation hardness of Ti-CrNi alloy coatings with 20, 40, 60, and 80 at% Ni contents were investigated respectively. Effects of process on the metallographic structure, tensile strength and fatigue resistance of Ti6Al4V alloys were analyzed in detail. The results show that Ti-CrNi alloy coatings were dense, uniform, and compact, including a complete structure of deposited layer, interdiffusion layer, and sputtering-affected zone. With increasing of Ni, the adhesion of the deposited layer raised. However, the nano-hardness of the deposition layer gradually declines. The addition of Ni does not have significant impact on the nano-hardness of interdiffusion layer. Plasma alloying treatment resulted in the α-phase grain size of Ti6Al4V increased and a “net structure” appeared. After plasma alloying, the tensile strength of Ti6Al4V was about 2.1% higher than the solid solution annealing state. However, the fatigue life of Ti6Al4V after plasma alloying process declined.

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.

Microstructural characterization and tribological behavior of surface plasma Zr-Er alloying on TC11 alloy

The Zr coating and Zr-Er coating are grown on TC11 substrate by double-glow plasma surface metallurgy technique, followed by the wear tests at ambient temperature and 500 °C. The data of nanohardness and elastic modulus of the samples are collected by the nano-indentation test. The adhesion strength of coatings is investigated by means of the scratch test. The study of wear resistance is performed using a ball-on-disc wear test system by running against the Si3N4 ball and measured by scanning electron microscope (SEM) and X-ray diffraction (XRD). Experimental results indicate that the nanohardness of the Zr coating and Zr-Er coating are 5.94 GPa and 7.98 GPa, respectively, which are 1.79 times and 2.41 times greater than that of TC11 substrate. Zr coating and Zr-Er coating realize the metallurgical bonding with TC11 substrate with continuous and compact structure. Compared with the Zr coating and TC11, the Zr-Er coating presents the lowest specific wear rates, which are 1.689 × 10−6 mm3 Nm−1 and 1.851 × 10−6 mm3 Nm−1 at ambient temperature and 500 °C respectively, indicating the excellent and improved wear resistance of TC11.

Oxidation behaviour of plasma surface alloying on Ti6Al4V alloy

ABSTRACTTi–CrNi alloy coatings with 20, 40, 60 and 80 at-%Ni were prepared on Ti6Al4V alloy surface by double glow plasma surface alloying technique. The cyclic oxidation behaviour of the coatings was investigated at 750, 850 and 950°C. The results show that each coating has a complete structure of settled layer, mutual diffusion layer and sputtering affected zone. When the Ni content was 40 at-%, the Ti–CrNi alloy coating showed the best cyclic oxidation resistance. The oxide scale with ‘Cr2O3 film+NiO film’ structure showed the best resistance to peeling.

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.