Flame Thermal Spray (FTS) coatings frequently show some porosity and reduced adherence to substrate, which affect its properties, especially its corrosion resistance. In this work, the corrosion resistance of AISI 101...Flame Thermal Spray (FTS) coatings frequently show some porosity and reduced adherence to substrate, which affect its properties, especially its corrosion resistance. In this work, the corrosion resistance of AISI 1018 carbon steel coated by different methods is compared: electroless nickel (EN) coating, NiCrFeBSi obtained by FTS, duplex coatings of an EN deposit on a layer of NiCrFeBSi obtained by FTS and a layer of NiCrFeBSi on an EN deposit. The coatings were characterized using optical microscopy and scanning electron microscopy techniques, EDS microprobe microanalysis, roughness as well as electrochemical polarization tests to obtain the corrosion rate. The results show the enhancement in the corrosion resistance in saline medium of the duplex coatings, especially of the EN coating on FTS layer.展开更多
Materials are precious resources. Different methods are employed to protect the material from degradation. Thermal spraying is one of the most effective method to protect the material from wear, high temperature corro...Materials are precious resources. Different methods are employed to protect the material from degradation. Thermal spraying is one of the most effective method to protect the material from wear, high temperature corrosion, stresses and erosion, thus increasing the life of material in use. Detonation gun spraying is one of the thermal spraying techniques known for providing hard, wear resistant and dense microstructured coatings. This paper summarizes the results of previous research done by various authors on different coatings done by detonation gun spraying technique.展开更多
WC-Co-Cr coatings are widely employed due to their improved wear resistance and mechanical properties, however, the properties and performance of these coatings are compromised by the processing parameters of each spr...WC-Co-Cr coatings are widely employed due to their improved wear resistance and mechanical properties, however, the properties and performance of these coatings are compromised by the processing parameters of each spraying technique. Therefore, this study is aimed to evaluate and determine the effect of the deposition parameters on the properties and microstructural characteristics of WC-Co-Cr coatings using a more economical thermal spray technique. In particular, the influence of flame spray parameters on the microstructure, crystal structure, hardness, and sliding wear resistance of WC- Co-Cr coatings was examined. Two parameters were considered: Type of flame (reducing, neutral and oxidizing), and the spray torch nozzle exit area. Results indicated that WC particles undergo considerable degree of decarburization and dissolution during spraying, showing substantial amounts of W2C, W, and Co3W3C, for all the considered conditions. However, the extent of phase transformation depended largely on the flame chemistry. The microstructure of the coatings was mainly affected by the spray nozzle. Regarding the sliding wear behavior, the coatings with uniform distribution of hard particles provided the best wear resistance. The decomposition of WC into W2C phase seems to have meaningless significance in the mass loss, nevertheless, the WC phase transformation to metallic tungsten and η-phase (Co3W3C) produce higher wear rates due to deficiency of carbide particles and embrittlement of the binder phase which induces cracking and delamination of the splats.展开更多
The water-cooled supersonic two-stage high-velocity oxy-fuel (HVOF) thermal spray gun was developed to make a coating of temperature-sensitive material,such as titanium,on a substrate.The gun has a combustion chamber ...The water-cooled supersonic two-stage high-velocity oxy-fuel (HVOF) thermal spray gun was developed to make a coating of temperature-sensitive material,such as titanium,on a substrate.The gun has a combustion chamber (CC) followed by a mixing chamber (MC),in which the combustion gas is mixed with the nitrogen gas at room temperature.The mixed gas is accelerated to supersonic speed through a converging-diverging (C-D) nozzle followed by a straight passage called the barrel.This paper proposes an experimental procedure to estimate the cooling rate of CC,MC and barrel separately.Then,the mathematical model is presented to predict the pressure and temperature in the MC for the specific mass flow rates of fuel,oxygen and nitrogen by assuming chemical equilibrium with water-cooling in the CC and MC,and frozen flow with constant specific heat from stagnant condition to the throat in the CC and MC.Finally,the present mathematical model was validated by comparing the calculated and measured stagnant pressures of the CC of the two-stage HVOF gun.展开更多
文摘Flame Thermal Spray (FTS) coatings frequently show some porosity and reduced adherence to substrate, which affect its properties, especially its corrosion resistance. In this work, the corrosion resistance of AISI 1018 carbon steel coated by different methods is compared: electroless nickel (EN) coating, NiCrFeBSi obtained by FTS, duplex coatings of an EN deposit on a layer of NiCrFeBSi obtained by FTS and a layer of NiCrFeBSi on an EN deposit. The coatings were characterized using optical microscopy and scanning electron microscopy techniques, EDS microprobe microanalysis, roughness as well as electrochemical polarization tests to obtain the corrosion rate. The results show the enhancement in the corrosion resistance in saline medium of the duplex coatings, especially of the EN coating on FTS layer.
文摘Materials are precious resources. Different methods are employed to protect the material from degradation. Thermal spraying is one of the most effective method to protect the material from wear, high temperature corrosion, stresses and erosion, thus increasing the life of material in use. Detonation gun spraying is one of the thermal spraying techniques known for providing hard, wear resistant and dense microstructured coatings. This paper summarizes the results of previous research done by various authors on different coatings done by detonation gun spraying technique.
文摘WC-Co-Cr coatings are widely employed due to their improved wear resistance and mechanical properties, however, the properties and performance of these coatings are compromised by the processing parameters of each spraying technique. Therefore, this study is aimed to evaluate and determine the effect of the deposition parameters on the properties and microstructural characteristics of WC-Co-Cr coatings using a more economical thermal spray technique. In particular, the influence of flame spray parameters on the microstructure, crystal structure, hardness, and sliding wear resistance of WC- Co-Cr coatings was examined. Two parameters were considered: Type of flame (reducing, neutral and oxidizing), and the spray torch nozzle exit area. Results indicated that WC particles undergo considerable degree of decarburization and dissolution during spraying, showing substantial amounts of W2C, W, and Co3W3C, for all the considered conditions. However, the extent of phase transformation depended largely on the flame chemistry. The microstructure of the coatings was mainly affected by the spray nozzle. Regarding the sliding wear behavior, the coatings with uniform distribution of hard particles provided the best wear resistance. The decomposition of WC into W2C phase seems to have meaningless significance in the mass loss, nevertheless, the WC phase transformation to metallic tungsten and η-phase (Co3W3C) produce higher wear rates due to deficiency of carbide particles and embrittlement of the binder phase which induces cracking and delamination of the splats.
文摘The water-cooled supersonic two-stage high-velocity oxy-fuel (HVOF) thermal spray gun was developed to make a coating of temperature-sensitive material,such as titanium,on a substrate.The gun has a combustion chamber (CC) followed by a mixing chamber (MC),in which the combustion gas is mixed with the nitrogen gas at room temperature.The mixed gas is accelerated to supersonic speed through a converging-diverging (C-D) nozzle followed by a straight passage called the barrel.This paper proposes an experimental procedure to estimate the cooling rate of CC,MC and barrel separately.Then,the mathematical model is presented to predict the pressure and temperature in the MC for the specific mass flow rates of fuel,oxygen and nitrogen by assuming chemical equilibrium with water-cooling in the CC and MC,and frozen flow with constant specific heat from stagnant condition to the throat in the CC and MC.Finally,the present mathematical model was validated by comparing the calculated and measured stagnant pressures of the CC of the two-stage HVOF gun.
