Double Glow Plasma Surface Alloying Research Articles

High-temperature oxidation behavior of double glow plasma Cr-Y alloyed layers on Ti2AlNb alloy

A Cr-Y alloyed layer was synthesized on the surface of Ti2AlNb by double glow plasma surface alloying technique. The morphology, phase composition and oxidation behaviors at 750 °C, 800 °C, and 850 °C of Cr-Y alloyed layers were systematically investigated. The results illustrated that Cr-Y alloyed layer was approximately 10 μm thick, which the morphology of alloyed layer was uniform and compact, with a flat and uniform interface to the matrix. Oxidation kinetics for the Cr-Y alloyed layer approximately followed the parabolic law, with an oxidation weight gain significantly lower than that of Ti2AlNb. The predominant oxides of Cr-Y layer were CrNbO4, Cr2O3, and Y2O3, which effectively hindered oxygen diffusion into the substrate.

Dependence of the M choice on the properties of Hf(M)SiCN (M = Nb, Ta, Ti, Zr) ceramic coatings: ab-initio and experimental study

The HfMSiCN coatings (M = Nb, Ta, Ti, Zr) are researched using ab-initio theoretical method and double glow plasma surface alloying. The aim is to enhance the high temperature stability and wear resistance of these coatings, alongside optimizing mechanical and thermodynamic properties. Firstly, the calculated mechanical properties for Hf0.5M0.5CN correlate with those experimental measurement for HfMSiCN. Secondly, the thermodynamic parameters exhibit that the Hf0.5Zr0.5CN has the lowest thermal expansion coefficient and higher bulk modulus at high-temperatures. Moreover, the wear rate of HfZrSiCN at 500 ℃ is less than 60% of its wear rate at 300 ℃. The superior wear resistance of HfZrSiCN coating is attributed to a friction-induced composite layer including a dense amorphous nanocomposite surface layer and a nano-friction glaze layer supported by nanograins.

Combining laser surface texturing and double glow plasma surface chromizing to improve tribological performance of Ti6Al4V alloy

Ti6Al4V (TC4) alloy has been widely applied in the military, industrial, chemical, and medical fields due to their excellent thermal stability, corrosion resistance, and biocompatibility. However, titanium alloys are notorious for their poor tribological properties, such as their high friction coefficients and low surface bearing capacities. To tackle this problem, combination of laser surface texturing (LST) and double glow plasma chromizing was conducted to improve the wear resistance of TC4. LST was first conducted to produce uniform dimples with a diameter of 300 μm and gradient density of 11 % on the Ti6Al4V substrate. A chromizing coating (Cr-coating) was subsequently deposited on the surfaces of the textured and raw Ti6Al4V alloy by double glow plasma surface alloying (DGPSA). A continuous and compact Cr-coating with a thickness of about 55 μm was formed on TC4 after being maintained at a temperature of 850 °C, and the coating was mainly composed of a solid solution and intermetallic compounds of Cr2Ti phases. The surface hardness after alloying was two times higher than that of the TC4 substrate. Comparative assessments on the wear resistance of the Cr-coatings with and without LST treatment and the TC4 alloy were carried out using a ball-on-disk wear tester. The results showed that the mass loss and specific wear rate of the duplex-treated sample were 1.54 mg and 7.14 × 10−4 mm3·N−1·m−1. The mass loss and specific wear rate of the TC4 were 4.32 mg and 1.62 × 10−3 mm3·N−1·m−1. The specific wear rates of the four tested samples were in the following order: the duplex-treated TC4 < textured TC4 < chromized TC4 < polished TC4. The coating obtained by LST-double glow plasma chromizing duplex treatment exhibited an outstanding durability and the best mechanical performance. Thus, this approach be used for the protection of Ti6Al4V surface in engineering components and medical instruments.

Microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating on Inconel 718 alloy

In this paper, Al2O3/Cr composite coatings were prepared on the surface of Inconel 718 alloy by cathodic liquid plasma electrolytic deposition (CLPED) and double-glow plasma surface alloying (DGPSA) processes. The microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating were investigated. The results showed that the Al2O3 interlayer surface was fully covered with Cr coating. The interface between the Al2O3 layer and the Cr metal layer presents a mechanical interlock effect, which can absorb the deformation caused by thermal expansion, thereby reducing the adverse effects of thermal stress. The surface roughness of the Al2O3 coatings decreased after depositing Cr coating. The oxidation weight gain of the Al2O3/Cr composite coatings were significantly lower than that of the substrate, indicating that the Al2O3/Cr composite coatings improved the high-temperature oxidation resistance of Inconel 718 alloy. The oxidation weight gain of the Al2O3/Cr composite coatings at different frequencies were similar, while the Al2O3/Cr composite coating at 400 Hz was lowest. During the high-temperature oxidation process, the Al2O3 interlayer can effectively inhibit the external diffusion of Ni, Fe and other elements in the matrix, which helps to prevent the cracking of the outer oxide film, thereby reducing the oxidation rate.

Effect of C/N incorporation on structural and crystallographic properties of TaNbZr coatings deposited by double-glow plasma surface alloying on Ti-alloy substrate

The relatively low corrosion and wear resistance of Ti-alloy hinders full application of its meritorious low density-to-strength ratio. Here, we studied TaNbZr coatings by double-glow plasma surface alloying (DGPSA), with and without C- or N-incorporation, on TA15 substrate to enhance its tribological properties. The C-incorporation was introduced by adding a graphite target, which decreased the glow discharge on the Ta/Nb/Zr targets and thus reduced the deposition rate by ∼55 %. In comparison, the N-incorporation was introduced by feeding N2, partly replacing the Ar working gas flow, which reduced the sputtering yield of the metal targets that in turn reduced the deposition rate by ∼60 %. Hole and hill-in-hole structures have been observed on TaNbZrC with the size and density much higher than those on TaNbZr and TaNbZrN, which was attributed to undesired graphite particles ejected from the target and deposited directly onto the growing surface of the substrate. The localized ejection induced by the graphite particles upon the substrate-associated glow plasma gave rise to the hole and hill-in-hole structures. The C- and N-incorporation modified the surface alloying reactions, leading to different microstructure and smoothness on the surface, compositional changes of the ‘buffer’ layer at the coating/substrate interface, and varied crystallographic texturing of the coatings. Nanoindentation measurements at the cross-section across the coating/substrate interface provide evidence for the enhanced hardness, not only at the coatings but also at the near-interface regions of the substrate. These observations, together with bonding strength and tribology tests at elevated temperatures, shed new light on developing protective coatings on Ti-alloy by DGPSA.

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.

TiMoTa multi-component transition layer: Plasma in-situ diagnosis, mechanical properties and effect on diamond adhesion

The transition layer prepared on the cemented carbide surface through double glow plasma surface alloying (DGPSA) is believed to be an effective strategy to improve the adhesion between the diamond and cemented carbide. In this work, to fully reveal and understand the behavior of double glow discharge plasma, DGPSA processes were studied using optical emission spectroscopy (OES), and the effect of the as-prepared TiMoTa transition layer on the diamond growth mechanism and adhesion property was analyzed. The microstructure, composition, and adhesion properties of TiMoTa transition layers and diamond coating were analyzed using SEM, TEM, XPS, XRD, and Rockwell C indentation. The results indicated that the intensity of the plasmas (Ti, Mo, and Ta) remained stable with the deposition time with the increase of deposition temperature, the electron temperature remained in the range of 1 × 104–1.4 × 104 K during the deposition process. OES results showed that the TiMoTa transition layer with a high deposition rate and high performance can be prepared by selecting the appropriate deposition temperature and time through DGPSA technique. The TiMoTa transition interlayers with nanocrystalline structure can effectively restrain the out-diffusion of Co and the in-diffusion of C, thereby effectively improving the adhesion between diamond and cemented carbide. Hence, the TiMoTa transition layer prepared through DGPSA technique offers an effective way to develop a good adhesion diamond coating on WC-Co substrate.

Double-Glow Plasma Surface Alloying of BTi-62421S Alloys: Regulation of Microstructure Properties

In order to meet the design requirements of lightweight artillery and adopt the method of double-glow plasma nitriding to solve the problem of low hardness and poor abrasion resistance of Ti alloy, the BTi-62421S high-performance titanium (Ti) alloy was selected as the experimental material to replace gun steel. To study the effect of different nitrogen (N) concentrations on the heat resistance scouring performance of BTi-62421S high-performance Ti alloy and investigate the influence of alloying elements on the heat resistance scouring performance under the same parameters compared with the commonly used TC4 Ti alloy, argon was used as the protective gas by continuously increasing the N concentration (Ar/N2 = 1:1, 1:2, 1:3). It was found that the honeycomb structure on the surface of the sample and the thickness of the coating increased continuously, reaching a thickness of 15 μm, while the depth of the nitride particles extending from the coating to the substrate also increased, reaching a maximum depth of 26 μm. The orientation of TiN changed from 37° to 62°. The hardness of the coating showed a negative correlation with the coefficient of frictional abrasion, which significantly improved the heat-resistant scouring performance of BTi-62421S high-performance Ti 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.

Microstructure and wear behavior of (ZrTaNb)C/N quaternary ceramic coatings prepared by double-cathode glow plasma surface alloying on titanium alloy

Multi-principal component coating is a new type of surface protection material developed in recent years. To improve the surface hardness and wear resistance of aviation titanium alloy, (ZrTaNb)C, (ZrTaNb)N and ZrTaNb coatings were prepared by double cathode glow plasma surface alloying. The microstructure, mechanical properties and high temperature tribological behavior of quaternary ceramic coatings were studied. The results show that the quaternary ceramic coating has an FCC cubic structure, which is different from the BCC structure of the ZrTaNb coating. Meanwhile, the solid-soluble C and N elements improve the surface hardness and toughness of the multi-principal component coating, resulting in a significant reduction in wear rate, which is only 1/10 and 1/5 of that of the substrate and pure metal coating (25 °C). When the temperature increases to 500 °C, the compliant islets of oxidized and compacted debris are gradually activated as a wear-resistant oxidation glaze layer. The gradient structure of amorphous-nanocrystalline composite is formed in the subsurface layer, which can effectively improve the surface strength and wear resistance. This study provides an effective strategy for improving the wear resistance of titanium alloy surface in a wide temperature range.

Tribological behavior of diamond particles reinforced hafnium matrix composite coatings on Ti6Al4V

The diamond particles reinforced hafnium matrix composite coatings are prepared by the double glow plasma surface alloying technique combined with the microwave plasma chemical vapor deposition process (MPCVD). The effect of the Hf diffusion layers and diamond particles on their phase transformation, microstructure evolution, and wear behavior is systematically investigated. The results reveal that the surface of the Hf-alloying coating which is fabricated by plasma surface metallurgy emerged discrete micropores due to the Kirkendall effect during the plasma reverse sputtering. With the reverse sputtering time increasing, the general pore size increases, and the deposition layer has been completely sputtered out, leaving the Hf diffusion layer with a thickness of about 10 μm. After diamond particles deposition by MPCVD, the diamond particle reinforced hafnium matrix composite coatings with carbide and diamond coexisting were formed. The wear experiments were conducted in ambient air with a reciprocating friction tester, demonstrating that the diamond particle reinforced hafnium matrix composite coatings exhibited good antifriction performance with the decrease of wear rate by ∼8 times due to the lubrication effect of the diamond and graphite particles.

Effects of TiMoTa nano-crystalline interlayer on nucleation, adhesion and tribological behaviors of diamond coating

To investigate the influence of the transition layer on diamond nucleation and growth, the TiMoTa multi-alloy interlayers were firstly prepared on WC-6%Co cemented carbide by double glow plasma surface alloying technique, and diamond was then deposited using microwave plasma chemical vapor deposition system. The thickness of the TiMoTa interlayers increased from 1.2 μm to 2.7 μm with the deposition temperature increasing from 800 to 900 °C. Due to the formation of nano-crystalline structure and hard phase, the as-prepared TiMoTa interlayer exhibited high micro-hardness. In the diamond deposition process, the nano-carbide particles preferentially formed at the TiMoTa interlayers can effectively prevent the further diffusion of C, so the surface carbon concentration rapidly accumulates to the critical value required for the nucleation and growth of diamond microcrystals. Finally, a microscale wear-resistant diamond coating with good adhesion was grown on the transition layer, the crack propagation radius of the diamond coating is ∼162 μm, and can reach Hf 2–3 grade. Therefore, our prepared TiMoTa nano-crystalline interlayer provides a new path for the development of a high-quality diamond coating with good adhesion on cemented carbide.

Effects of Cold Rolling on the Microstructure and Corrosion Resistance of the Double-Glow Plasma Ni-Cr Alloying Layer on Q235 Steel.

A Ni-Cr alloyed layer was prepared on the surface of Q235 steel using double-glow plasma surface alloying (DGPSA) technology and the alloyed layer was cold-rolled with different deformation rates. The microstructure, composition distribution and phase composition of the alloyed layer were characterized using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and an electrochemical workstation. On this basis, the corrosion resistance of the alloyed layer was analyzed. The results showed that a Ni-Cr alloyed layer formed on the surface of Q235 steel following double-glow plasma nickel-chromium alloying. The alloy elements of Ni and Cr were distributed in a gradient from the outside to the inside and the main phases were FeCr0.29Ni0.16C0.06, Cr23C6 and γ solid solution. The alloyed layer, once cold-rolled with different deformation rates, underwent synchronous plastic deformation with the substrate, with no fracturing and spalling. The self-corrosion potential of the cold-rolled specimens in 5% H2SO4 and 3.5% NaCl solution is close to that of 304L stainless steel, and the corrosion currents are much lower. The corrosion resistance of the cold-rolled specimens is comparable to the original specimens, with no significant changes.

Improvement of plasma carbonitriding modified layer on TA15 surface by RASP-assisted DGPSA treatment

In this paper, a dual process combining rotationally accelerated shot peening (RASP) and double glow plasma surface alloying (DGPSA) was designed to prepare Ti(C,N) modified-layer on titanium alloys. The improvement effect of RASP pretreatment on DGPSA technology was analyzed by comparing the surface phase composition, wear resistance and fractography of plasma-carbonitriding (PCN) layers with and without RASP pretreatment. It was found that RASP pretreatment promoted the diffusion and deposition of carbon and nitrogen atoms on the surface of titanium alloy, forming a thick and dense modified layer with a gradient variation in hardness. There is a large residual compressive stress on the surface of the modified layer after RASP-assisted DGPSA treatment. The near-surface fracture morphology indicates that RASP pretreatment can alleviate the adverse effects of surface brittleness and severe grain coarsening caused by heat treatment and improve the surface mechanical properties. The gradient reinforced layer formed by the dual treatment on the subsurface effectively supports the dense compound layer on the surface, resulting in excellent wear resistance.

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.

The preparation and lubrication properties of a CrN/Cr multilayer using the double glow plasma surface alloying technique

Metal sealing rings with high hardness can improve wear resistance and reduce internal leakage. In this study, the double glow plasma surface alloying (DGPSA) technique was employed to produce the necessary conditions for a metallurgical bond and lubricant storage. Four primary stages are required in deposition processing: evaporation, destruction, atomization, and ionization. A Cr layer (including a 5 μm interdiffusion layer and a 45 μm pure metallic layer in thickness) and a thin (1–2 μm) CrN layer were prepared using the DGPSA technique. The obtained interdiffusion layer can reduce the mismatch in mechanical properties between the Cr layer and the substrate. When the atomic coverage of N atoms is higher than 1.5 ML, the stable adsorption structure is essentially nonexistent, indicating that improving the N2 ionization rate is more valuable than increasing the nitrogen partial pressure. When the Ar/N2 flow ratio is 2:1, the CrN/Cr multilayers provided microreservoirs for lubricants and improved wear and plastic deformation resistance. For the CrN/Cr multilayer, a higher contact pressure resulted in superior frictional properties.

Characterization and properties of NbN–Nb bilayer formed on titanium for bipolar plates

In this study, the NbN/Nb bilayer structure was prepared by duplex-treatment (plasma surface alloying + nitriding) on titanium used as bipolar plates for proton exchange membrane fuel cells (PEMFCs). Niobium coating was deposited on titanium by means of double glow plasma surface alloying technique. Then, a thin NbN layer was created by plasma nitriding. The corrosion resistance and electrical conductivity of samples were measured in simulated PEMFCs environments. The result shows that at an applied potential of 0.6 V the corrosion current density of duplex-treated sample is two orders lower than that of untreated titanium. After corrosion testing at 0.6 V for 4 h, the interfacial contact resistance is 5.1 mΩ cm2 compared with 29.7 mΩ cm2 for untreated titanium.

Design of Ta gradient layer to improve adhesion strength between Cu substrate and DLC film

Tantalum (Ta) gradient transitional layer, which was prepared by double-glow plasma surface alloying technology, was designed to improve the adhesion strength between Cu substrate and diamond-like carbon (DLC) film. The microstructure, morphology, mechanical and tribological properties of samples were characterized and analyzed. The results showed that the adhesion strength and tribological properties were improved greatly by Ta interlayer. The surface roughness of the sample was mainly depended on the Ta deposition layer, increased with prolonged alloying time. The adhesion strength between Cu substrate and DLC film increased obviously with Ta interlayer. Notably, the sample with Ta alloying time of 30 min showed highest critical load arise from that Ta gradient interlayer can form intertwined planes near Cu substrate and Ta2C near DLC film. Furthermore, it showed lower friction coefficient (∼0.22) and the lowest wear rate (3 × 10−5mm3/Nm), which was attributed to the highest content of sp3C, lower surface roughness and more content of Ta2C grains in the sample.

Fabrication of porous micro/nano structured Cr coating with superhydrophobic and ultrahigh adhesion properties by plasma reverse sputtering process

In this study, a superhydrophobic Cr porous surface with better abrasive resistance was prepared on Ti6Al4V substrates by double glow plasma surface alloying and the plasma reverse sputtering process. These results showed that the Cr coating with rough and porous micro-nano structures was formed on the surface of Ti6Al4V alloy, which could be attributed to the Kirkendall effect during the process of the plasma reverse sputtering. The role of the reverse sputtering time on the structure and performance of the Cr porous coatings was investigated systematically. The thickness of Cr diffusion layers increased from 13 μm to 28 μm as the reverse sputtering time increased to 45 min. The friction behavior was revealed by wear test, demonstrating prominent improvement of wear resistance. Meanwhile, the as-prepared micro-nano structured Cr coatings exhibited superhydrophobic properties with ultrahigh adhesion.

Characterization of Quasi-Static/Dynamic Contact Mechanical Properties of Mo Surface-Modified TC4

By using the double glow plasma surface alloying technique, a Mo surface-modified layer is prepared on Ti6Al4V(TC4). The element concentration and microstructure are characterized with a glow-discharge optical emission spectroscope and a scanning electron microscope. The results indicate that the Mo modified layer is compact in structure and gradation in composition, which consists of a pure Mo deposition layer and a thick Mo diffusion layer. Nanoindentation test results indicate that the surface hardness of TC4 is significantly improved after surface modification. Therefore, the initial part of the Mo diffusion layer has higher hardness than the Mo deposition layer. The impact tests for 10,000 cycles at different loads demonstrate that impact load 100 N only causes small plastic deformation, while impact loads 300 N and 500 N could result in cracks. Combining nanoindentation test with finite element reverse analysis, plastic parameters of the Mo modified layer are quantitatively determined. By using the impact test and finite element forward analysis, the dynamic contact mechanical properties of Mo surface-modified TC4 are characterized. When the impact cycles are fixed, ring cracks firstly occur and then radial cracks occur with the impact load increase on the graded layer. The ring cracks are mainly caused by impact stretch fatigue and corresponding cyclic stress is between 3.53 and 2.62 GPa. The radial cracks are mainly related to the tension-compression fatigue and corresponding cyclic stress is between 3.92 and −0.97 GPa.