Supersonic Atmospheric Plasma Spraying Research Articles

Effects of the second phase on the microstructure and ablation resistance of HfC coating on C/C composites

To improve the ablation resistance of HfC coating on carbon/carbon composites prepared by supersonic atmospheric plasma spraying, SiC, TaC and ZrC ceramics were added into HfC coating as the second phase. Effects of the second phase on the microstructure, interface bonding strength and ablation resistance of HfC coating were researched. The structure of HfC-SiC coating was denser and smoother than that of HfC-TaC and HfC-ZrC coatings. The dense structure, high interface bonding strength and formation of continuous Hf-Si-O glassy film resulted in the better ablation resistance of HfC-SiC coating. During ablation, the HfC-TaC coating was oxidized to a stable Hf6Ta2O17 glassy film, which could restrain the oxygen penetration. A porous HfO2-ZrO2 layer was generated on the HfC-ZrC coating after ablation, some HfO2 and ZrO2 particles may be flown away by the high-speed flame. So, the ablation resistance of HfC-ZrC coating was worse than the other two coatings.

Thermal cycling performance of La2Ce2O7/50 vol.% YSZ composite thermal barrier coating with CMAS corrosion

La2Ce2O7 (LC) is receiving increasing attention due to its lower thermal conductivity, better phase stability and higher sintering resistance than yttria partially stabilized zirconia (YSZ). However, the low fracture toughness and the sudden drop of CTE at approximately 350 °C greatly limit its application. In this study, the LC/50 vol.% YSZ composite TBC was deposited by supersonic atmospheric plasma spraying (SAPS). Compared to YSZ or double layered LC/YSZ coating, the thermal cycling life of LC/50 vol.% YSZ coating with CMAS attack increased by 93% or 91%. The latter possessed higher fracture toughness (1.48 ± 0.26 MPa m1/2) than LC (0.72 ± 0.15 MPa m1/2) and better CMAS corrosion resistance than YSZ owing to the formation of Ca2(LaxCe1-x)8(SiO4)6O6–4x with <001> orientation perpendicular to the coating surface. The sudden CTE decrease of LC was fully suppressed in LC/50 vol.% YSZ coating due to the change of temperature dependent residual stresses induced by YSZ.

Spraying power influence on microstructure and bonding strength of ZrSi2 coating for SiC coated carbon/carbon composites

The objective of this current paper was to characterize the ZrSi2 coating deposited on the SiC coated carbon/carbon (C/C) composites by supersonic atmospheric plasma spraying (SAPS) at different spraying power. The microstructure, phase composition and bonding strength were investigated. In the process of spraying, a few of ZrSi2 powders were quickly oxidized to produce ZrO2, SiO2 and ZrSiO4 ceramic phases. These phases were randomly embedded in the ZrSi2 coating to enhance the mechanical performances of the coating to some extent. In addition, t-ZrO2 and c-ZrO2 phases formed above 1473K might be converted into m-ZrO2 accompanied with 8% volume expansion, which can heal part of microcracks of the ZrSi2 coating. Therefore, only a few microcracks and pores at the spraying power of 40kW were found at the surface of ZrSi2 coating and no penetrative cracks existed in the cross section. Meanwhile, the bonding strength of the interface between the ZrSi2 and the SiC coating reached up to 11N at 40kW. In short, the SAPS technology was deemed to be a useful method to deposit the ZrSi2 coating on SiC coated C/C composites with high performance.

Wear resistance coatings of nickel alloys obtained by supersonic plasma torch

The research results of coatings of nickel alloys deposited using supersonic atmospheric-plasma spraying are presented. The main feature of the work carried out is that the plasma flow is charged by powder material using the powder ring injector designed by authors. The ring powder injector unit is equipped by a gas dynamic focusing system that makes it possible to ensure the conditions of creating coatings which are not subject to wear and tear under abrasive friction.

Ablation performance of supersonic atmosphere plasma sprayed tungsten coating under oxyacetylene torch and plasma torch

Tungsten (W) coating was prepared on SiC coated C/C composites by supersonic atmosphere plasma spraying (SAPS), aiming to improve their anti-ablation property. Under oxyacetylene torch, W coating could protect substrate above 60 s under heat flux of 2400 kW/m2. However, oxidization destroyed the intergranular and interlayer bonding of as-sprayed W coating during ablation. As a result, when heat flux of oxyacetylene torch raised to 4200 kW/m2, huge thermal and mechanical shock made W coating delaminate severely, which lead to the failure of W coating after ablated for only 30 s. During plasma ablation, argon gas offered an inert environments, which restrained oxidization of W coating. Thus, even if the temperature and mechanical erosion of plasma torch were much higher than oxyacetylene torch, W coating can successfully protect substrates above 40 s, exhibiting excellent ablation performance.

Comparison of microstructure and oxidation behavior of La-Mo-Si coatings deposited by two approaches

Abstract To investigate the effect of preparation methods on the La-Mo-Si (LMS) coatings, we developed a new LMS coating system using pack cementation (PC) and supersonic atmospheric plasma spraying (SAPS). Microstructure analysis showed that the SAPS-LMS coating possessed a higher porosity than that of the PC-LMS coating. Higher porosity can provide more channels to the oxidative and corrosive gasses to permeate the SAPS-LMS ceramic top-coat. After static oxidation for 150 h under 1773 K, the mass loss of SAPS-LMS coating (3.12 wt%) was much higher than that of the PC-LMS coating (0.05 wt%), and the parabolic rate constants presented faster oxidation kinetic in SAPS-LMS coating with respect to the PC-LMS coating. These results revealed that the protection effectiveness of SAPS-LMS coating was inferior to PC-LMS coating. Compared with SAPS-LMS coating, microscopic pores and cracks appeared in the PC-LMS coating with a thicker oxide film, which benefits from the formed La-Si-O-Al glass oxide with an excellent ability for crack healing. The reasons for poor antioxidant performance of SAPS-LMS coating are the higher volatility of La-Si-O glass containing Mo 5 Si 3 and a weak interfacial interaction between coatings and substrate.

Calcium phosphorus bio-coating on carbon/carbon composites: Preparation, shear strength and bioactivity

Microwave hydrothermal (MH) combining supersonic atmospheric plasma sprayed (SAPS) calcium phosphorus (Ca-P) bio-coatings on carbon/carbon (C/C) composite has been widely used due to their osteoconductivity and osteoproductivity. However, the erratic shear strength between coatings prepared only by SAPS (outer coating) and C/C substrates has attached more attention over the implant failure. Adding a coating prepared by MH (inner coating) before SAPS can possess superior shear strength to conventional outer coating. The inner coating with fine Ca-P particles was prepared through a unique MH method under different concentrations (10, 500 and 1000mmol/L). The influence of concentration on microstructure, phase composition, roughness and shear strength are investigated in this paper. In particularly, the roughness of inner coatings on C/C substrates was found to related to the morphologies and particle size.Results showed that inner coatings have higher roughness which was beneficial for the promotion of shear strength between the obtained Ca-P bio-coating and the C/C substrates. Subsequently, the specimens were immersed in a simulated body fluid (SBF) to investigate the bioactivity.

Effect of microwave heating time on bonding strength and corrosion resistance of Ca-P composite layers for carbon/carbon composites

Three coated Ca-P composite layers were fabricated by microwave-assisted hydrothermal (MH) and supersonic atmospheric plasma spray (SAPS) method. This multilayer coating aims to promote the bonding strength as well as the corrosion property against stimulated body fluid (SBF) on carbon/carbon (C/C) composites. The morphologies and the chemical composition of the Ca-P composite layers were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The bonding strength was evaluated by scratch test and the bioactivity was measured using SBF. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were investigated for the corrosion resistance. The results reveal that Ca-P composite layers exhibit excellent bonding strength which reaches to the loading force of 39.5 N. In SBF solution, the Ca-P composite layers can induce a new and uniform apatite layer. Additionally, potentiodynamic polarization and EIS results indicate that adding MH influences the corrosion resistance of the Ca-P composite layers. The above conclusion illustrate that MH approach could become a very useful route to enhance the long-term protection and corrosion resistance of the layers on C/C substrates for orthopedic application.

Ablation resistance of supersonic-atmosphere-plasma-spraying ZrC coating doped with ZrO2 for SiC-coated carbon/carbon composites

To improve the ablation resistance of ZrC coating for carbon/carbon (C/C) composites, the C/Zr ratio of the coating was changed by doping ZrO2 using supersonic atmosphere plasma spraying (SAPS). The SAPS ZrC coating with 10vol.% ZrO2 showed a significant improvement on ablation resistance compared with SAPS ZrC coating without ZrO2 and could protect C/C composites for more than 90s at heat flux of 2.4MW/m2. The oxycarbides in the coating attenuated the destructiveness from gas products. The decreased C/Zr ratio and increased relative content of ZrCxOy in the multiphase coating reduced the CO evolution and contributed to the improvement on ablation resistance. An optimal oxycarbide was ZrCx (0.61<x<1.0, y=0) based on thermodynamic calculation. Excessive doping of ZrO2 deteriorated the ablation resistance due to many potential oxygen penetration paths produced during heating and cooling and the probably increased vaporization of the coating.

Oxyacetylene torch ablation resistance of Co-modified WC coating deposited on C/C composites by supersonic atmosphere plasma spraying

Abstract Cobalt (Co) was chosen as an additive to improve the ablation resistance of WC coating for SiC coated C/C composites, SiC modified WC coating and pure WC coating which were prepared and tested for comparative purposes. Results showed that the thermal shock resistance of WCC (WC-10%Co) coating was better than pure WC coating and WCS (WC-10%SiC) coating. Furthermore, the produced oxide layer on WCC coating was found to be more stable due to the reaction of CoO and WO 3 . As a result, during oxyacetylene torch ablation test, compared with pure WC coating and WCS coating, WCC coating keeps excellent dimensional stability with the linear ablation rate decreased by 67% and 62%, respectively, showing a significant improvement of the ablation resistance.

Improvement of interfacial adhesion in PP/PS blends enhanced with supersonic atmosphere plasma spraying surface‐treated carbon fiber

The effects of surface treatment of a carbon fiber (CF) by supersonic atmosphere plasma spraying (SAPS) on the interfacial adhesion behavior and morphology of polypropylene/polystyrene (PP/PS) matrix blends filled CF composites were investigated. Effects of surface treated a commercial CF on mechanical properties are studied. Contact angle was measured to examine the changes in wettability of the CF. The chemical and morphological changes were characterized by using X‐ray photoelectron spectroscopy and scanning electron microscopy. PP/PS/CF composites were fabricated with and without SAPS treatment, and their interlaminar fracture toughnesses were compared. The results showed that the interlaminar shear strength of composites has been greatly improved filled SAPS modification CF. The water contact angle of resin sample decreased 50% after addition of SAPS surface‐treated CF. Scanning electron microscopy results on the fractured surface exhibited PP/PS blends adhered well around the CFs of the SAPS‐treated specimen compared with that of the untreated specimen. This attributed to the CF interlock, and it improves the wetting between fibers and resins. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Fabrication of W/Cu composite coatings by supersonic atmosphere plasma spraying and their anti-ablation performance under oxyacetylene torch

W/Cu composite coatings were prepared by supersonic atmosphere plasma spraying (SAPS) on SiC coated C/C composites. Results indicated that 45 kW is suitable to prepare W/Cu coating, and the micro-hardness of W/Cu coatings decrease with the increase of Cu content. The average bonding strength between W/Cu coatings and SiC coated C/C composites exceed 20 MPa. The anti-ablation property of W/Cu coatings with different Cu content was studied under oxyacetylene torch, W12Cu (wt. 12% Cu) coating shows excellent anti-ablation performance. Compared with pure W coating, the linear ablation rate of W12Cu coating decrease by 63% under heat flux of 2.4 MW/m2 and 87% under heat flux of 4.2 MW/m2, respectively. During oxyacetylene ablation, molten Cu film that formed on the surface of coating protected coating from oxidization, sweating and cooling effect of Cu phase decreased the surface temperature of W/Cu coating 300 °C at most, these were beneficial to good ablation resistance property of W/Cu coating.

Thermal cycling property of supersonic atmospheric plasma sprayed thermal barrier coatings reinforced by Ni-coated YSZ fibers

Fiber reinforcement is wildly used in the metal matrix composites to restrict the initiation and propagation of cracks. In thermal barrier coatings (TBCs), the thermo-mechanical stresses lead to formation and propagation of detrimental cracks which usually cause premature failure of TBCs. In our study, the reinforcement effect of yttria-stabilized zirconia (YSZ) fibers in TBCs Ni20Al bond coat has been investigated and the wettability of YSZ fibers was taken into account. Electroless plating was conducted on the surface of YSZ fibers to enhance the interfacial compatibility between YSZ fibers and Ni20Al. TBCs with Ni20Al bond coat and YSZ top coat were deposited onto the In738LC superalloys by supersonic atmospheric plasma spraying. The microstructure and morphology of TBCs with and without YSZ fibers were estimated. The cyclic oxidation behaviour was investigated at 1050°C, and the TBCs with Ni-coated YSZ fibers show better cyclic oxidation resistance than conventional TBCs, which indicates that the addition of YSZ fibers can improve the cyclic life of TBCs. Further analysis shows that the fibers improved the thermal cycling resistance which could be attributed to the fiber bridging process.

Effect of LaB6 content on the gas evolution and structure of ZrC coating for carbon/carbon composites during ablation

ZrC coatings with different contents of LaB6 for SiC-coated carbon/carbon composites were fabricated by supersonic atmosphere plasma spraying. The mechanism of gas evolution during oxidation at ultra-high temperatures and the oxide scale structure evolution of the coating after addition of LaB6 with different contents were studied. Results showed that rare earth borate rather than rare earth oxide mainly reduced the melting resistance of the oxide scale. The oxide scale for ZrC coating with 10% LaB6 was unfavorable to the gas escape. After addition of 20% LaB6, the oxide scale was favorable to the gas escape but disadvantageous to the coating applied in the environment containing scouring because of the reduced melting resistance. High content of LaB6 also could cause evident boiling of B2O3, leading to producing big pores in the oxide scale during ablation. Appropriate content of LaB6 for ZrC coating was found to be 15%.

Ca-P bioactive coating prepared by combining microwave-hydrothermal and supersonic atmospheric plasma spraying methods

Ca-P based coatings on carbon/carbon composite (C/C) were manufactured via a combined method comprising of microwave-hydrothermal (MH) and supersonic atmospheric plasma spraying (SAPS) techniques. However, a weak mutual interaction between the coating and C/C substrate has been a critical issue for a long time. Herein, we reported a new method for shear strength enhancement without compromising the osteoconductivity and osteoproductivity. Results showed that the inner layer has a strong mechanical interlocking with C/C substrate and the failure mode of outer layer changed from the coating cohesion (within the coating) to adhesive (at the coating/substrate interface) fracture. The shear strength between Ca-P bioactive coating-C/C substrate by MH/SAPS was significantly improved as compared to that prepared by SAPS. The Ca-P bioactive coating exhibited a good bioactivity as evidenced by the formation of a uniform carbonate-apatite layer formed on coating after immersing into stimulated body fluid for a specified period of time.

Ablation Mechanism of HfC-HfO2 Protective Coating for SiC-Coated C/C Composites in an Oxyacetylene Torch Environment

To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an HfCxOy-HfO2 transitional layer was generated in the coating, which resulted from the active oxidation of HfC. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO2.

HfC-ZrC-SiC multiphase protective coating for SiC-coated C/C composites prepared by supersonic atmospheric plasma spraying

HfC-ZrC-SiC (HZS) multiphase coating was deposited on the surface of SiC-coated carbon/carbon composites by supersonic atmospheric plasma spraying. The morphology and microstructure of HZS coating were characterized by XRD and SEM. The as-prepared coating was composed of different carbides and oxides. The structure was dense and crack free. Each element distributed uniformly in the coating. Ablation resistance test was carried out by oxyacetylene torch. During ablation, the outer coating underwent a process of solid state sintering and formed a dense Hf-Zr-Si-O layer on the surface of coating gradually, which could prevent the oxygen diffusing inward. The inner coating was oxidized gradually with the oxygen permeation and the structure was loose. In addition, the newly formed HfSiO4 and ZrSiO4 were generated after cooling, which could play a pinning effect and prevent crack extension.

Effect of vacuum re-melting on the solid particles erosion behavior of Ni60-NiCrMoY composite coatings prepared by plasma spraying

Ni60-NiCrMoY composite coatings prepared by supersonic atmospheric plasma spraying were subjected to vacuum re-melting. The effect of vacuum re-melting on erosion behavior of the as-sprayed coatings was examined at various impact angles. The erosion mechanism of the as-sprayed and re-melted coatings were also investigated. At low impact angles, metal removal of coatings and substrate was controlled by microcutting. The erosion resistance of the coatings was higher than that of substrate, and the re-melted coatings exhibited best erosion resistance. With increasing the impact angle, the erosion rate of substrate first increased and then decreased, while that of the coatings increased gradually. The highest erosion rate of substrate occurred at an impact angle of 45°, which was lower than that of the as-sprayed coatings and higher than that of the re-melted coatings. Vacuum re-melting broadened the range of the impact angles which the as-sprayed coating can bear. At high impact angles, the substrate showed serious ductile fracture. The as-sprayed coatings exhibited significant brittle fracture, and the lamellar spalling caused by crack initiation and propagation. The erosion of the re-melted coatings was carried out both by ductile and brittle fracture. Vacuum re-melting greatly improved the bonding strength and erosion resistance of the as-sprayed coatings.

Deposition and ablation resistance of HfC-based coatings prepared on SiC-coated C/C composites by supersonic atmospheric plasma spraying

In order to improve the ablation properties of C/C composites, HfC-based coatings with different mass ratios of SiC were deposited on the surface of SiC-coated carbon/carbon composites by supersonic atmospheric plasma spraying. The morphologies and microstructures of the HfC-based coatings were characterised. The ablation resistance test was carried out by oxyacetylene torch. The results show that the as-prepared coatings are multiphase coatings consisting of HfC, HfO2, SiC and SiO2. The structure of different coatings is dense. After ablation for 60 s, the ablation centre region of coating is smooth without obvious microcrack and pinhole, and no interlaminar crack can be observed at the cross-section. An Hf–Si–O compound oxide layer is generated on the surface of coating, which is beneficial for protecting the C/C composites from being ablated. Meanwhile, the further generated HfSiO4 can play a pinning effect, which can prevent crack extension.

Effect of Monolithic LaB6 on the Ablation Resistance of ZrC/SiC Coating Prepared by Supersonic Plasma Spraying for C/C Composites

Ablation resistance of monolithic LaB6-doped ZrC coating for SiC-coated carbon/carbon composites by supersonic atmospheric plasma spray was investigated under an oxyacetylene torch with a heat flux of 4.18 MW/m2. Result shows that ZrC coating with 10 vol.% LaB6 has a good ablation resistance compared with pure ZrC, ZrC with 20 vol.% LaB6 and SiC-doped ZrC coating. After ablation for 15 s, the weight is increased by 1.12 mg/s. The good ablation resistance is ascribed to the formation of a stabilized scale which consists of protective La2Zr2O7-containing molten phase and ZrO2 particles keeping the integrity of the coating.