Double Glow Discharge Technique Research Articles

Diffusion and plasma oxidation mechanism of Fe–Al coatings

Al coatings were deposited using a pure Al target directly onto pure iron substrates at different temperatures by double glow discharge technique. Then, the Fe–Al coatings were plasma oxidised at 580°C. The results indicated that the aluminide layer was nanocrystalline with many crystal defects after the aluminising process. The oxidation kinetics showed a two-stage behaviour. The energetic O ions with higher driving force diffused into the coatings at the beginning of the oxidation. Then, O ions diffused via short circuit diffusion caused by the existence of large amounts of grain boundaries and crystal defects. After oxidation, α-Al2O3, γ-Al2O3 and Fe2O3 phases were detected. Large amount of voids filled with oxide ions were formed at the outermost aluminide layer owing to the different intrinsic diffusivities of Fe and Al.

Al2O3 reinforced Fe–Al composite coatings prepared by double glow discharge technique

Alumina (Al2O3) particles reinforced iron aluminide coatings (Fe–Al coatings) were prepared on the surface of 316L stainless steel at only 580°C by a novel approach, namely double glow discharge technique. The chemical composition and morphology of the coatings were characterised by means of glancing angle (1°) X-ray diffractometry, X-ray photoelectron spectroscopy and scanning electron microscopy (SEM) respectively. The hardness, wear and corrosion behaviours of the aluminide coatings were also evaluated. The results indicated that the aluminide coatings exhibited a good wear and corrosion resistance since Al2O3 particles were well distributed in the coatings. The friction coefficient of the composite coatings increased first and then decreased with the increment of Al2O3 particles, meanwhile the corrosion potential and microhardness tended to increase. Finally, the wear mechanisms of the coatings were discussed.

Characterization of W Coating on Cu Substrate Prepared by Double-Glow Discharge

In this study, tungsten (W) was coated on a copper (Cu) substrate by using double-glow discharge technique using a pure W panel as the target and argon (Ar) as the discharge and sputtering gas. The crystal structure of the W coating was examined by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was performed with cross-section images to investigate the penetration depth of W into the Cu body. Additionally, the properties of wearability resistance, corrosion resistance and mechanical strength of the W coated Cu matrix were also measured. It is concluded that in double-glow plasma, W coated Cu can be facilely prepared. It is noticed that the treatment temperature heavily dominates the properties of the W-Cu composite.

Friction and Wear Properties of W,Mo,Co Alloyed Layer on T8 Steel by Double-Glow Technique

In this paper, cobalt, tungsten and molybdenum were co-diffused into the surface of T8 steel by double glow discharge technique. A carbide layer with M6C＋MC was formed on T8 steel. Under the carbide layer was a diffusion layer of W,Mo,Co. Hardness of carbide layer is high over 1200~1400 HV0.025 and can improve to 1400~1600 HV0.025 after solution and ageing treatment. Hardness of the diffusion layer is only 400~550 HV0.025, but it can improve to 800~1000 HV0.025 after solution and ageing treatment. The carbide layer combides with the substrate in metallurgy and can not peel off from the substrate. The carbide layer on T8 steel possess same good tribological properties of M2 steel.

Effects of sputtering condition on tribological properties of tungsten coatings

Tungsten coating is often used for tribological applications, especially for those at elevated temperatures due to its high melting point and good wear resistance. In this study, research was conducted to investigate the tribological behavior of tungsten coatings produced at various temperatures using a double glow discharge technique. The relationships among the coating’s microstructure, their properties and the deposition temperature were studied. The microstructure of the coatings was examined using optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Hardness and elasticity of the coatings were evaluated using a nano/micro-mechanical probe. Wear and friction of the coatings against a ceramic ball at various temperatures were evaluated using a high-temperature pin-on-disc tribometer. It was demonstrated that raising the substrate temperature from 400 to 1100 °C changed the microstructure of tungsten coatings from tapered grains with voids at boundaries to finer fibrous structure with fewer voids. The results illustrated that the mechanical and tribological behavior of a tungsten coating was strongly affected by its microstructure. The coating that was formed at the highest substrate temperature, 1100 °C showed, the best friction and wear behavior.

Plasma Surface Alloying

A new plasma assisted surface alloying method, termed the ‘double glow discharge technique’, is described. The technique has been used to produce diffusion coatings of tungsten, molybdenum, chromium, and titanium on plain carbon steels. The maximum alloy contents obtained were up to 20 wt- %, to a depth commonly in excess of 50 μm.