R. Vasudevan

Bio: R. Vasudevan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Plating & Residual stress. The author has an hindex of 4, co-authored 7 publications receiving 70 citations.

Fatigue strength of nickel electrodeposits prepared in ultrasonically agitated bath

Abstract: Nickel coatings are widely used 1:o prevent wear of structural steels resulting from abrasion and corrosion. When used for this purpose it may be expected that the coatings should also influence other characteristics such as mechanical woperties. As the plating alters the surface characteristics of the base metal, the fatigue properties of steels may be markedly affected by the presence of such coatings. Fatigue crack initiation generally occurs at the surface of a specimen. The internal stress of the deposit, its inherent fatigue strength relative to that of the substrate, its hardness and its thickness have all been shown to affect the fatigue limit [1-3]. In recent years, the effect of ultrasonic agitation during electrodeposition has gained popularity [4-6]. Because of the catastrophic failure due to hydrogen embrittlement in many plated highstrength steels, any effort to improve plating should attempt reduction, if not total eJimination, of this undesirable feature. Research is being continuously carried out with this as the main objective. Ultrasonics provide a solution to this problem. The present work is concerned with studying the effect of ultrasonics of the fatigue properties of nickel electrodeposits. A comparison has been made between the deposits obtained from a still bath and an ultrasonically agitated bath. The composition of a nickel Watts bath used for the present study is given in Table I. Fatigue tests were carried out in a rotating, bending fatigue testing machine of type PUNZ. Mild steel specimens prepared according to DIN 50113 standards (Fig. 1) and coated with nickel (thickness 20/~m) were employed. The mechanical properties of the base metal were: yield strength 475 MPa, tensile strength 650 MPa and hardness 194 Vicker's Hardness Number (VHN). All the fatigue tests were carried out in air at room temperature (25 °C). The thickness of deposit was measured using the gauge, Mikrotest III. The surface roughness of the plated specimens was measured by a perthometer, Perthon S5P. Fig. 2 shows the fatigue life of the specimens at different applied stresses. Three samples were tested

Wear characteristics of nickel electrodeposits in ultrasonically agitated bath

Abstract: Wear rates of nickel electrodeposits obtained from a conventional Watts bath were studied. A comparison was made between the wear rates of nickel electrodeposits obtained with an ultrasonically agitated bath and those obtained with a still bath. Deposition was done on mild steel, and wear rates were measured for unlubricated rubbing against a rotating hardened steel disc. The wear loss of the deposits obtained with the ultrasonic bath was lower than that with the still bath. When ultrasonic waves are passed through the electrolyte solution, bubbles are formed which grow and collapse due to continuous absorption of energy from alternating compression and expansion cycles of the sound waves. This results in work-hardening of the surface, which leads to higher microhardness and higher wear resistance. Nickel plating is widely used for decorative purposes. It also finds application to minimize abrasive wear in cases such as sliding contacts on 2.0 hydraulic rams. The use of ultrasound in a plating bath has been found to improve the surface quality of the deposit. The application of ultrasonic irradiation during plating affects the deposition rate and internal stress [1]. Ultrasound has decreased whisker growth, giving smoother surfaces [2], The fatigue strength of mild steel deposited with nickel is found to be improved when deposition is done in an ultrasonic field [3]. This work was aimed at evaluating the extent to which ultrasonic irradiation influences the wear resistance of the deposit. The composition of the plating bath was 250 g 1-1 nickel sulphate (NiSO4.6H20), 60g1-1 nickel chloride (NiC12.7H20) and 30g l -~ boric acid (H3BO3) in distilled water. Circular specimens, 30 mm in diameter and 5 mm thick, were plated at a current density of 3.5 A dm -2 both in an ultrasonic bath and in a still bath. The ultrasonic generator had a frequency of 22 kHz and a maximum rated capacity of 500 W. The thickness of the deposit was maintained at 40/zm for each specimen. The wear-testing rig used was as described elsewhere [4]. The mating disc was hardened steel of hardness 700 kgmm -2. Both the counter disc and the specimen were of the same diameter and the counter disc rubbed the specimen coaxially. The test Speed duration in all experiments was 30 min. The speci(r.p.m.) mens were weighed before and after the wear test. 700 The wear losses of the deposits were evaluated at 8oo different speeds. The spring load on the specimen 9oo against the counter disc was varied from 7.8 to 1000 11 kgf. 1100 Fig. 1 shows the wear rate of the specimens tested at different sliding speeds. The sliding speed is given by 27rrn/60, where n is the shaft speed in r,p.m. Wear rates were calculated using W = w/dLP, where w is the weight loss of the deposit during testing, d is the density of nickel, L is the sliding distance and P is the normal load. The wear rates of the coatings at different speeds and sliding speeds are listed in Table I. Specimens coated in an ultrasonic field showed a higher wear resistance than nickel coated under still conditions. Fig. 2 shows the wear loss per unit area at different loads, and corresponding data are given in Table II. Optical micrographs were taken after wear testing. Figs 3 and 4 show wear tracks of the specimens plated in a still bath and an ultrasonically

Effect of ultrasonic agitation on surface finish of electrodeposits

Abstract: In the present work, nickel, tin and zinc were selected to study the improvement in the nature and quality of the respective deposits when plated in ultrasonically agitated bath. Experimental procedure-Nickel, tin and zinc were electrodeposited on mild steel (O.18%C) using a Watts nickel bath, a tin fluoborate, bath and an acid zinc bath, respectively, in still and ultrasonically agitated conditions. The composition and operating conditions of these baths are shown in Tables 1-3, respectively.

Quantitative characterization of micro-topography a bibliography of industrial surface metrology

Abstract: 3

Ultrasound-assisted electrodeposition of composite coatings with particles

Abstract: The electrodeposition of multifunctional composite coatings has rapidly emerged in the last decade due to the enhanced mechanical properties and corrosion resistance that such composite coatings exhibit compared to electroplated single metal and alloy deposits. Many studies have indicated that the implementation of ultrasound in composite electroplating processes can bring about many benefits, not only as a tool to improve the dispersion and de-agglomeration of particles in the electroplating bath, but also to enhance the incorporation of finely dispersed and uniformly distributed particles into the metal matrix. The present paper summarizes the fundamentals of the use of ultrasound and acoustic cavitation and how it may influence the electrodeposition of composite coatings with particles by commenting on some of the most significant works on this topic presented by the scientific community in the last 10 years. This paper will review these investigations and discuss how the ultrasonic parameters may affect the dispersion of the particles in the electrolyte and its effect on the characteristics of the composite coatings, generally resulting in the enhancement of the mechanical properties and corrosion resistance of the composite coatings. In addition, this paper will review some of the issues that may arise when using ultrasound in such processes and the pros and cons of the different transducer systems available, highlighting the need for detailed information regarding the ultrasonic parameters and equipment used when utilising sonication.

A comparative study of the effect of mechanical and ultrasound agitation on the properties of electrodeposited Ni/Al2O3 nanocomposite coatings

Abstract: In our study, Ni/Al 2 O 3 nanocomposite coatings were obtained by electrochemical deposition of alumina nanoparticles from nickel Watts baths with different concentrations of Al 2 O 3 particles in solution. A comparison of the effects of mechanical (300 rpm) and ultrasonic (24 kHz, 38 W cm − 2 ) stirring on the properties of electrodeposited Ni/Al 2 O 3 composite coatings was performed, observing an enhancement of the Al 2 O 3 incorporation in the composite coating and an improvement of the uniformity of particles distribution in the nickel metal matrix when ultrasonic energy was applied to the process. Moreover, the characterization of the coatings also showed that for both types of agitation, the incorporation of Al 2 O 3 nanoparticles led to changes in the morphology and structure of the nickel matrix leading to an improvement of its tribological properties. These properties were further enhanced when ultrasonic stirring was used during the composite coating electrodeposition.

Synthesis and characterization of Ni-TiO2 composite coatings by electro-co-deposition

Abstract: Ultrafine TiO 2 dispersed nickel composite coatings have been prepared by direct current deposition process on steel substrate from Watt's bath to improve the surface mechanical property of conventional nickel coating. To resist agglomeration of ultra fine particles in plating bath due to high surface free energy and to get homogeneous coating, magnetic stirring was applied during deposition with prior ultrasonic agitation. For de-agglomeration, Hexa decylpyridinium bromide (HPB) was used in varying quantity in plating bath as surfactant. Characterization of TiO 2 powder as well as microstructure, hardness and wear properties of the coatings were studied by means of XRD, SEM, microhardness tester and ball-on-plate type wear tester. TiO 2 incorporation in the coatings was uniform and dispersion of TiO 2 was below 100 nm size along with the faceted nickel matrix. Selective amount of HPB addition produces hard orientation of nickel in the composite coating along with better TiO 2 co-deposition rate leading to higher microhardness and wear resistance. Wear is mainly adhesive in nature and the worn out TiO 2 particles shift it nominally to abrasive mechanism.

Ultrasound-assisted electrodeposition of nickel: Effect of ultrasonic power on the characteristics of thin coatings

Abstract: The effect of ultrasonic power on the characteristics of low-frequency ultrasound-assisted electrodeposited Ni coatings from an additive-free Watts bath has been evaluated by different methods. XRD analysis showed that, while mechanical agitation favoured the electrocrystallization of Ni in the [211] direction, ultrasound promoted the electrodeposition of Ni with a [100] preferred orientation. FIB-SEM images of the surface of Ni deposits not only indicated that the surface structure agreed to some extent with the XRD results, but also that ultrasound refined, to a certain extent, some of the grains of the surface of the coatings. FIB-SEM images of the cross-section of the coatings confirmed this effect of ultrasound on the microstructure of the deposits. Such change in the microstructure of Ni, along with work-hardening by ultrasound, resulted in an increase in the hardness of the deposits. The characteristics of the deposits depended on the ultrasonic power employed, and it was found that Ni coatings electrodeposited using an ultrasonic power of 0.124 W/cm3 presented the higher proportion of crystals with a [100] preferred orientation, the highest degree of grain refinement in the surface and the highest microhardness values. Nevertheless, these deposits also presented visible erosion marks on the surface of the coatings due to the formation of transient bubble structures near the surface of the cathode during the electrodeposition. These erosion marks might be considered the main drawback to the use of ultrasound during the electrodeposition.