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Anodizing/Anodic oxidation is the most common surface treatment of aluminum and its alloys for automobile and aerospace applications. Poor aesthetic appearance (scattered patches on the surface) is the common problem in pressure die-cast ADC12 aluminum alloy when it is subjected to anodic oxidation at higher temperature due to surface segregation. Surface segregation is inevitable in this material where it is a commercial aluminum alloy and having a high level of impurity contents. High impurity will ease to form alloy segregation in surface and subsurface during pressure die-casting and reflect poor surface appearance like yellow color patches. This case study deals to solve the poor aesthetic behavior in ADC12 alloy during the anodic oxidation process. Process condition study was done to eliminate this problem.

Biogas production from cowdung is well studied. Coconut pith is an agricultural waste available in large quantities in Kerala: the possibility of using coconut pith for biogas production was studied. It was found that coconut pith in combination with cowdung gives considerable amount of biogas, while alone it did not produce any gas. The optimum combination was found to be 60% pith and 40% cowdung. Study of dilution effect on the slurry showed that the optimum solid-liquid ratio is 1:20. Partial removal of lignin from pith increased the rate of biogas production. Gas produced from a mixture of cowdung and pith was found to have a higher methane content than that produced from cowdung only.

The water sorption isotherm of coconut pith is studied in order to get an insight into the nature of the sorption process. The surface area available for adsorption, heat of adsorption and approximate size of possible capillaries are computed from the isotherm. A considerable hysteresis effect is observed. The cell structure of coconut pith is studied using an optical microscope. On the basis of the computations and microscopic observations, the similarity of the sorption process with that of woody materials is established.

An experimental study has been made of the capacity, rate and efficiency of moisture adsorption by coconut pith. Regeneration characteristics at different temperatures have also been studied and its properties are compared with those of standard desiccants, especially silica gel. The results indicate that coconut pith shows good promise as a cheap, yet effective desiccant.

The frictional and wear behaviour and hardness of cobalt and cobalt-titania (anatase) particulate composites, developed by sediment electro-codeposition method, were studied. Frictional and wear studies, performed on a disc-on-disc type machine, show that the microhardness of the composite increases as the titania content in the composite increases. A decrease in both the coefficient of friction and specific wear rate was observed for the composites with increasing titania content in the cobalt matrix. The effect of sliding velocity and load on the coefficient of friction and specific wear rate of cobalt and cobalt titania composites was also investigated. The optical microphotographs and X-ray diffractogram reveals that the tribo-deformation is oxidation dominated for cobalt. A probable mechanism is discussed. ? 1991 Chapman & Hall.

Electroless nickel (EN) plating has received attention as a hard coating for industrial applications due to its high hardness, uniform thickness as well as excellent corrosion and wear resistance. The electroless Ni-P deposit is a supersaturated alloy in as-deposited state, and can be strengthened by precipitation of nickel phosphide crystallites with suitable heat treatments. However, the hardness of Ni-P films degrades with excessive annealing due to grain coarsening. This is the most severe barrier for electroless Ni-P deposition process from replacing chromium plating in industrial sectors. This problem is addressed in the paper by modifying the conventional electroless Ni-P bath to co-deposit tungsten to increase the hardness of the coating. Structural changes in the coating due to incorporation of tungsten are also highlighted. Deposition is done from an alkaline hypophosphite bath. Deposits with varying tungsten content are synthesized. Chemical analysis shows that tungsten incorporation reduces the phosphorus content in the deposit. Phosphorus content varied from 3 to 7 wt.% depending upon the tungsten incorporation in the deposit which in turn varied between 8 and 18 wt.%. Coatings with high tungsten content possess high hardness when compared to binary Ni-P as well as low tungsten ternary alloy deposits. � Springer Science+Business Media, LLC 2007.

The ability to codeposit ®ne particulate matter with an electroless nickel matrix is a major step in the development of processes aimed at the engineering of surfaces. The prime objective of incorporating the particulate matter is to improve wear and corrosion resistance. The most frequently studied systems are electroless Ni±P±SiC, Ni±P±Al2O3, Ni±P±diamond, Ni±P±PTFE and Ni±P±Cr3C2. Very little information is available on electroless Ni±P±Si3N4 composite coatings. Since Si3N4 has high hardness, good oxidation resistance and good chemical stability, it is worthwhile to study this combination. In the present study we codeposit Si3N4 with electroless nickel on medium carbon steel and evaluate its hardness and corrosion resistance. A proprietary high phosphorus electroless nickel plating bath was used. The pH of the bath was 4.8. Medium carbon steel coupons of 30 mm diameter and 5 mm thickness were surface ground (Ra ˆ 0:4 im) and suspended in the plating bath. The plating bath was maintained at a constant temperature of 88 1 8C. The coupons were plated for 2 h. For the preparation of composite coatings, the Si3N4 powder (size ,10 im) of a calculated quantity was mixed thoroughly with 10 ml of the plating solution using a mortar and pestle and then transferred to the plating bath. This process ensures the distribution of Si3N4 paticles throughout the bath. To obtain a uniform dispersion of Si3N4 particles in suspended form in the bath, the plating solution was stirred using a magnetic stirrer. The electroless plated samples were heat treated for 1 h at temperatures of 200, 300, 400, 500 and 600 8C to determine the change in hardness upon heating to different temperatures. In order to represent common industrial practice no special atmosphere was maintained during heat treatment. Hardness measurements were carried out using a Leitz Micro Vickers Tester employing a load of 0.1 kg. Five readings were taken on each deposit and the values were then averaged. Potentiodynamic polarization studies were carried out using EG&G PAR (Model 362) scanning potentiostat. The electrolyte used was non-deaerated 3.5% NaCl solution. The specimens were masked with lacquer so that only a 1 cm area was exposed to the electrolyte. A saturated calomel electrode (SCE) was used as a reference electrode. The corrosion potential (Ecorr) and corrosion current (icorr) were obtained from the polarization curves using the Tafel extrapolation method. Both the Ni±P and Ni±P±Si3N4 coatings did not exhibit any porosity when subjected to the ferroxyl test. Both of them were found to be adherent when tested by the bent test method, following ASTM B 571 and the thermal shock method. The thickness of the deposit was in the range of 22±25 im in all cases after 2 h of deposition. Fig. 1 shows that cross-section of the electroless Ni±P±Si3N4 deposits when viewed by optical microscopy. The incorporation of the Si3N4 particles in the deposit is clearly visible. Fig. 2 shows the weight percentage of Si3N4 particles in the electroless nickel deposit as a function of its concentration (g=l) in the plating bath. It can be deduced from the ®gure that the percentage incorporation of Si3N4 particles (the percentage of Si3N4 represents only the weight percent of Si3N4 throughout this communication unless otherwise stated) increases with an increase in concentration and reaches a maximum at a concentration of 10 g=l. Beyond this concentration of 10 g=l, a slight decrease in the percentage incorporation is observed. A decrease in the percentage of incorporation of the second phase particles was observed earlier in the electroless Ni±P±Al2O3 system by Rajagopal [1]. The increase in percentage incorporation of Si3N4 particles in the electroless Ni±P matrix with increase in its concentration in the plating bath can be

Anodic oxide coatings were synthesised on Ti-6Al-4V substrates using aqueous electrolytes containing dissolved calcium and phosphorus. Different coatings were produced by varying the time of synthesis. Inherent features of the coatings were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Uniform corrosion, electrochemical polarisation and ac impedance tests were performed in simulated body fluid (SBF). Small amounts of calcium and phosphorus are deposited from the electrolyte on to the coating and their levels increase with increasing duration of synthesis. Maximum values of porosity and thickness are obtained for oxides coated for 3 h. Coatings produced from shorter times showed very good resistance to the attack of SBF. � 2006 Institute of Metal Finishing.

Electrodeposited anodic oxide coatings were produced on Ti-6Al-4V substrates using aqueous electrolytes containing dissolved calcium and phosphorus. Different coatings were produced by varying the time periods. The coatings were characterised by XRD technique and TEM. The coatings were exposed to Simulated Body Fluid (SBF). Electrochemical polarisation and ac impedance studies too were performed on the coatings in SBF. Pins were coated and run against wooden disc in pin-on-disc type of wear tests. Coatings produced from long time electrolysis showed very good resistance to the attack of SBF and less wear compared to those produced from short time exposure. � 2007 Springer Science+Business Media, LLC.

Nickel composite coatings have been prepared on mild steel substrates by sediment electro-co-deposition (SECD) technique. Silicon nitride, fly ash and calcium fluoride are used as the reinforcements. Metallographic studies, microhardness, friction and wear tests under various loads and sliding speeds have been carried out on these coatings. Optical and scanning electron microscopy (SEM) studies on the worn surfaces were conducted. A theoretical model was used to predict the wear rates of the composite coatings. All the composite coatings exhibited a lower coefficient of friction and better wear resistance when compared with nickel coatings at all loads and sliding velocities studied. However, nickel-calcium fluoride composite coatings possessed the lowest coefficient of friction and wear rates. Significant effect of load and sliding speed on both the coefficient of friction and wear rates of nickel, nickel-silicon nitride and nickel-fly ash coatings has been observed. SEM studies of the worn surfaces reveal delamination process at higher loads. The predicted wear rates are in reasonable agreement with the experimental values. ? 2003 Elsevier Science B.V. All rights reserved.

The effect of ultrasonic vibration on microhardness, residual stresses and surface finish of nickel electrodeposits was investigated. A comparison was made between the results obtained with an ultrasonically agitated bath and those with a still bath. Ultrasonic agitation increased the deposition rate and limited current density. The deposit from the bath with ultrasound gave a smoother surface and exhibited increased microhardness. The residual stresses of the deposits were reduced with an ultrasonically agitated bath.

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[No abstract available]

This article deals with the effect of the microstructural changes, due to transformation of delta ferrite, on the associated variations that take place in the tensile and stress corrosion properties of type 316 L stainless steel weld deposits when subjected to postweld heat treatment at 873 K for prolonged periods (up to 2000 hours). On aging for short durations (up to 20 hours), carbide/ carbonitride was the dominant transformation product, whereas sigma phase was dominant at longer aging times. The changes in the tensile and stress corrosion behavior of the aged weld metal have been attributed to the two competitive processes of matrix softening and hardening. Yield strength (YS) was found to depend predominantly on matrix softening only, while sig-nificant changes in the ultimate tensile strength (UTS) and the work-hardening exponent, n, occurred due to matrix hardening. Ductility and stress corrosion properties were considerably affected by both factors. Fractographic observations on the weld metal tested for stress-corrosion cracking (SCC) indicated a combination of transgranular cracking of the austenite and interface cracking. ? 1995 The Minerals, Metals & Material Society.

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

[No abstract available]

[No abstract available]

Lattice parameters of α γ2, δ, and θ-phase alloys from the copper-aluminium system have been measured by X-ray diffraction in the temperature range 20 to 850°C. The results have been used, along with values for the pure metals, to evaluate volume changes on alloying which have been found to correlate well with previously measured enthalpies and excess entropies of formation of the same alloys. The results also tend to confirm the view that alloys in the region of 40 at.- % aluminium exist as a separate phase (δ) with a γ-brass structure containing 50 atoms and two vacancies, instead of the normal 52 atoms, per unit cell.