A. Iyer

Bio: A. Iyer is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Cobalt & Nitride. The author has an hindex of 3, co-authored 4 publications receiving 31 citations.

Tribological properties of cobalt-partially stabilized zirconia (PSZ) composites in dry sliding conditions

Abstract: Particulate strengthened cobalt-partially stabilized zirconia composites were produced by conventional electro-codeposition method. Tribological properties of the deposits were evaluated against a hardened steel disc under dry sliding conditions on a thrust bearing type disc on disc machine. Dispersion of the particles improved the hardness and tribological properties of cobalt. Load and sliding velocity variations at the interface significantly influence the tribological properties of the deposits. Partially stabilized zirconia showed phase transformations during wear.

Corrosion characteristics of cobalt-silicon nitride electro composites in various corrosive environments

Abstract: The corrosion characteristics of electro codeposited cobalt-silicon nitride composites in neutral sodium chloride and sulphuric acid solutions are presented. The electro composites showed greatly improved corrosion resistance over pure cobalt in nondeaerated 3.5% sodium chloride solution, but they induced significantly less galvanic corrosion on steel in the same medium. Galvanic current and dissolution current measurements showed a linear variation with the cathode-to-anode area ratio, while the galvanic potential showed a logarithmic variation with the same. Composites of cobalt-silicon nitride also showed improved passivation properties in 1 N sulphuric acid.

Tribomechanical properties of cobalt-silicon nitride composite coatings

Abstract: Cobalt-silicon nitride composites were produced on mild steel by conventional electrocodeposition from a sulphate bath. These deposits showed better performance than pure cobalt in friction and wear tests against a hardened steel disc under dry sliding conditions. Changes of load and sliding velocity at the interface were also found to influence the tribological performance.

Electrodeposition and sliding wear resistance of nickel composite coatings containing micron and submicron SiC particles

Abstract: SiC particles of three different sizes, namely 5, 0.7 and 0.3 μm, were codeposited with nickel from Watts’ solutions. It was found that for a given number density of particles in the plating solution, the number density of particles in the coating increases with decreasing particle size. The friction and wear behavior of these composite coatings was evaluated in uni- and bi-directional sliding tests against corundum balls. The best sliding wear resistance was obtained with Ni–SiC composite coatings containing 4–5 vol.% submicron SiC particles.

Effect of electrodeposition conditions and reinforcement content on microstructure and tribological properties of nickel composite coatings

Abstract: In this work, pure nickel and nickel composite coatings (Ni–Al 2 O 3 , Ni–SiC, and Ni–ZrO 2 ) were deposited from Watts bath using direct current (DC), pulsed current (PC), and pulsed reverse current (PRC) electrodeposition conditions. Detailed investigations on the effect of deposition conditions on the evolution of surface microstructure, crystallographic micro-texture, microhardness, and sliding wear behavior of pure nickel and nickel composite coatings are presented. For all the coatings, the PC and PRC deposition conditions resulted in more random/weak crystallographic texture compared to DC deposition. The composite coatings deposited using PC and PRC deposition also exhibited significant improvement in microhardness and wear resistance due to enhanced reinforcement of nanoparticles in the coatings. Also, the effect of nanoparticle content of the electrolyte bath on the surface microstructure, tribological properties, and level of reinforcement in the Ni–Al 2 O 3 composite coating is investigated. The reinforcement of nanoparticles in the Ni–Al 2 O 3 composite coatings increased linearly with the amount of nanoparticle loading in the electrolyte bath. The microhardness and wear resistance of the Ni–Al 2 O 3 composite coatings also improved with increasing Al 2 O 3 content in the coatings.

Electrochemical studies on electroless ternary and quaternary Ni-P based alloys

Abstract: The autocatalytic (electroless) deposition of Ni–P based alloys is a well-known commercial process that has found numerous applications because of their excellent anticorrosive, wear, magnetic, solderable properties, etc. It is a barrier coating, protecting the substrate by sealing it off from the corrosive environments, rather than by sacrificial action. The corrosion resistance varies with the phosphorus content of the deposit: relatively high for a high-phosphorus electroless nickel deposit but low for a low-phosphorus electroless nickel deposit. In the present investigation ternary Ni–W–P alloy films were prepared using alkaline citrate-based bath. Quaternary Ni–W–Cu–P films were deposited by the addition of 3 mM copper ions in ternary Ni–W–P bath. X-ray diffraction (XRD) studies indicated that all the deposits were nanocrystalline, i.e. 1.2, 2.1 and 6.0 nm, respectively, for binary, ternary and quaternary alloys. Corrosion resistance of the films was evaluated in 3.5% sodium chloride solution in non-deaerated and deaerated conditions by potentiodynamic polarization and electrochemical impedance (EIS) methods. Lower corrosion current density values were obtained for the coatings tested in deaerated condition. EIS studies showed that higher charge transfer resistance values were obtained for binary Ni–P coatings compared to ternary or quaternary coatings. For all the coatings a gradual increase in the anodic current density had been observed beyond 740 mV. In deaerated condition all the reported coatings exhibited a narrow passive region and all the values of Ep, Etp and ipass were very close showing no major changes in the electrochemical behavior. In the non-deaerated conditions no passivation behavior had been observed for all these coatings.

On the wear characteristics of cobalt-based hardfacing layer after thermal fatigue and oxidation

Abstract: High temperature wear characteristics of Stellite 6 alloy containing Cr3C2 after thermal fatigue and oxidation treatment at 700°C were investigated. The hardfacing layer was deposited by plasma transferred arc (PTA) process. After thermal fatigue treatment, cracks propagated along boundaries of incoherent chromium carbide particles. Significant oxidation occurred mainly on the clad layer containing Cr3C2. The wear test results revealed a slightly higher wear volume on Stellite 6 with Cr3C2 due to the existence of cracks. The formation of oxide on the surface could effectively reduce the wear volume by reducing the real contact area between mating surfaces. Lower sliding speed resulted in higher wear volume. The mechanism was interpreted by the friction coefficient change during sliding wear. Wear test results were further interpreted by investigating the wear trace via SEM. Possible wear mechanisms were postulated. Analysis of wear debris showed severe oxidation on the Stellite 6 with Cr3C2. It could be concluded that oxidation on the clad layer was beneficial to the wear resistance at elevated temperature. Thermal fatigue cracking on the surface might be detrimental to the wear resistance, however, this could be partly compensated by the existence of oxide.

Electrodeposition and characterization of Ni–Zn–P and Ni–Zn–P/nano-SiC coatings

Abstract: Alloy coatings and metal based composites have been given special attention for their unique properties. In the present study, a novel electroplating bath was introduced. Ni–Zn, Ni–Zn–P nickel rich alloy coatings and Ni–Zn–P/nano-SiC nickel rich composite coating were successfully deposited on low carbon steel substrates. The optimum bath composition was found by comparing the amount of coating cracks checked by a scanning electron microscope (SEM). The presence of nearly homogeneous SiC nanoparticles in the coating was confirmed by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and MAP analysis. The effect of operating conditions on the mechanical properties of nanocomposite coatings was investigated. The wear resistance of the coatings was examined by pin on disk wear tests. The nanocomposite coatings had a lower weight loss compared to the Ni–Zn–P coatings in the wear test.