Cobalt-Tungsten (Co-W) alloy coatings possessing high hardness and wear/corrosion resistance, due to their ecofriendly processing, have been of interest to the researchers owing to its various industrial applications in automobile, aerospace, and machine parts. This technical paper reports Co-W alloy coatings dispersed with multiwalled carbon nanotubes (MWCNTs) produced by pulse electrodeposition from aqueous bath involving cobalt sulfate, sodium tungstate, and citric acid on stainless steel substrate (SS316). Studies on surface morphology through SEM, microhardness by Vickers method, microwear by pin-on-disk method, and corrosion behavior through potentiodynamic polarization method for the Co-W-CNT coatings were reported. Characterization studies were done by SEM and EDX analysis. The results showed that the corrosion and tribological properties of the pulse-electrodeposited Co-W-CNT alloy coatings were greatly influenced by its morphology, microhardness, %W, and MWCNT content in the coatings.
Plasma-sprayed NiCrBSi-graphite coatings have been subjected to solid particle erosion at elevated temperatures. The work reports the erosion resistance of NiCrBSi coatings with 4, 6 and 8 wt-% addition of graphite and optimum graphite content for erosion resistance. The coatings were analyzed using optical microscopy, XRD and scanning electron microscopy. Testing was carried out using air-jet erosion test rig, at an impact velocity of 70 m s−1 and at 45°and 90°angles with sand flow rate of 1 g min−1 at RT, 500°C and 650°C. Morphology of eroded surface shows crater, lip, groove formation and chipping as visible mechanism of material removal. Coating with 4wt% distribution of graphite exhibits higher erosion resistance as compared to the coating without graphite addition and improved microhardness. Microstructure images reveal that increase in graphite content above 4% results in the segregation of graphite and leading to soft islands in the coatings thereby decreasing the erosion resistance.
Nanocrystalline cobalt-phosphorus-carbon nanotube (CNT) composite coatings on stainless steel substrates with various contents of phosphorus were prepared by a pulse electrodeposition technique involving cobalt plating bath dispersed with CNTs. Microhardness, potentiodynamic polarisation and scanning electron microscopy (SEM) studies were used to characterise Co-P and Co-P-CNT composite coatings. The microhardness of Co-P-CNT coatings is found higher than that of Co-P coating. With the increase in phosphorus content, the microhardness values for the heat treated coatings increased almost twice when compared to that of the as deposited coatings. The effects of various contents of phosphorus and CNTs on the corrosion resistance were investigated, and it was found that nanocrystalline Co-P composite coatings exhibit better corrosion resistance than Co-P-CNT coatings.
This work examines the sliding wear behaviour of nanostructured cobalt-phosphorus (Co-P) alloy electrodeposits reinforced with multiwalled carbon nanotubes (MWCNTs). Nanocrystalline cobalt-phosphorus alloy coatings reinforced with carbon nanotubes were produced by pulse electrodeposition from an aqueous bath. Tribological properties of the coatings with and without MWCNT addition were characterized. Anisotropic tribological behaviour was observed for the coatings reinforced with MWCNTs when slided against hard steel counterparts. The nanocrystalline Co-P-CNT coatings display better wear resistance and friction reduction compared with the nanocrystalline Co-P coating. The friction coefficients and wear rates of the nanocrystalline Co-P-CNT coating are influenced by the test conditions including the applied load, sliding speed and more importantly the alignment of MWCNTs in the deposits. The wear mechanisms of the nanocrystalline Co-P and Co-P-CNT alloy coatings involved in different sliding conditions are explained related to their friction and wear properties.
Many austenitic and ferritic stainless steels have a higher yield and ultimate tensile strength than duplex steels. The extent to which this is true is determined not only by the alloy’s composition but also by how it is treated. This increased strength is usually accomplished without sacrificing the alloy’s hardness, as long as the alloy does not contain any of the harmful phasing elements. Thus an attempt is made to study the duplex stainless steel being plasma sprayed on a substrate and study its microstructure, hardness, and abrasive wear resistance. The primary objective is to study the abrasive wear resistance of duplex stainless steel coatings on 316 stainless steel. Ni percentage in coatings is varied at the coating stage in weight percentages of 7.0, 7.5, and 8 % and to study its effect on the wear rate of the coatings. The composition of the coatings is confirmed using XRD. A two-body abrasive wear test is carried out to determine the wear rate of the coatings with varying percentages of Ni and varying loads. Besides, the coatings are characterized by optical microscopy. Weight loss measurements of the tested samples are carried out and the data obtained is analyzed through weight loss plots. Also, weight loss data is used to further calculate the wear rate which is analyzed using wear rate plots. Finally, the microhardness of the coatings is determined.
In this analysis, corrosion efficiency and mechanical properties of duplex stainless steel castings (DSS-4A and DSS-5A) were compared to their wrought counterparts. Cast duplex stainless steel DSS-4A and DSS-5A are characterized in two separate solution treated settings, while their wrought counterparts are characterized in both solutions treated and forged form. Optical microscopy and X-ray diffractometry were employed to perform the metallurgical characterization. Electrochemical techniques such as Tafel extrapolation and electrochemical impedance spectroscopy were used to investigate corrosion activity. An electrochemical workstation was used to perform the corrosion studies. To compare the stability and changes in corrosion properties of both grades, an ASTM standard B117 salt spray test was performed in a 3.5 percent NaCl medium. Without any intermetallic phases, the XRD showed austenite and ferrite phases. The elements were partitioned further into the phases that they promoted, according to the elemental study of the phases. The ultimate tensile strength and hardness values of DSS-5A are higher than those of DSS-4A. DSS-5A had a higher corrosion resistance than DSS-4A. When comparing the two media used (H2SO4 and NaCl), DSS-5A demonstrated superior corrosion resistance.
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