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A novel surface modification process namely controlled ball impact peening was developed for synthesizing a nanostructured surface layer and to impart compressive residual stresses on metallic materials in order to enhance the overall surface properties. This article demonstrates the microstructural evolution, surface hardening and introduction of the residual stresses in the ball impact peened aluminium alloy surfaces, AA6063-T6. Hardened steel balls were impinged in controlled manner inducing high strain rates on the aluminium samples which are precisely moved using independent programmable logic controlled linear actuators in the controlled ball impact peening process. Mechanical properties of the nanocrystalline surface layer were investigated using dynamic ultra micro-hardness tester. The hardness of the nanocrystalline surface layer is (~. 1.3. GPa) improved compared to the matrix (~. 0.58. GPa) and the depth of the hardened layer is about ~. 350 ?m depending upon the peening conditions. The amount of compressive residual stress developed by the treatment is also studied using depth sensing indentation method. The surface compressive residual stresses induced in the ball impact peened samples is about 70-127% of yield strength of the target material depending upon the peening conditions. X-ray diffraction analysis and transmission electron microscope analysis revealed the formation of nanograin crystalline structure on the ball impact peened surface layer. The mean grain size of the peened sample determined by transmission electron microscope is about 8 � 2. nm in the top surface layer. High strain rate and repeated directional loading imparted in the contact zone generates the various dislocation activities and microstructural features which were responsible for the formation of the randomly oriented nanostructured grains on the metallic materials. With increasing strain, the various microstructural features produced in the ball impact peened aluminium samples are deformation twins, multiple shear bands, high density dislocation and dislocation pile-up at the grain boundaries as investigated by transmission electron microscope. Grain refinement on the ball impact peened aluminium surfaces resulted in the formation of high density dislocation associated with the subdivision of original grains into subgrains. The peening coverage and number of overlapping impacts depend upon the sample travelling velocity, which in turn affects the hardness, compressive residual stresses induced and grain size formed for a given ball diameter and impact velocity. � 2012.

Laser processing of Ti-SiC composite coating on titanium was carried out to improve wear resistance using Laser Engineered Net Shaping (LENS�) - a commercial rapid prototyping technology. During the coating process a Nd:YAG laser was used to create small liquid metal pool on the surface of Ti substrate in to which SiC powder was injected to create Ti-SiC metal matrix composite layer. The composite layers were characterized using X-ray diffraction, scanning and transmission electron microscopy equipped with fine probe chemical analysis. Laser parameters were found to have strong influence on the dissolution of SiC, leading to the formation of TiSi2, Ti5Si3 and TiC with a large amount of SiC on the surface. Detailed matrix microstructural analysis showed the formation of non-stoichiometric compounds and TiSi2 in the matrix due to non-equilibrium rapid solidification during laser processing. The average Young's modulus of the composite coatings was found to be in the range of 602 and 757GPa. Under dry sliding conditions, a considerable increase in wear resistance was observed, i.e., 5.91�10-4mm3/Nm for the SiC reinforced coatings and 1.3�10-3mm3/Nm for the Ti substrate at identical test conditions. � 2011 Elsevier B.V.

The present work aims to study the hardness and wear resistance of electroless Ni-B coatings. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni-B coatings. The structure, microhardness and wear resistance of electroless Ni-B coatings, both in as-plated and heat-treated conditions, were evaluated using X-ray diffraction (XRD), Leitz microhardness tester and a pin-on-disc wear test apparatus. XRD patterns reveal that electroless Ni-B coatings are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. The microhardness of the electroless Ni-B coatings increases with increase in heat-treatment temperature and exhibit two maxima in the hardness vs. heat-treatment temperature curve. The specific wear rate increases with increase in applied load from 20 to 40 N and at all applied loads, the specific wear rate and coefficient of friction are less for heat-treated electroless Ni-B deposits compared to that obtained for as-plated ones. The wear process of electroless Ni-B coatings is governed by an adhesive wear mechanism. ? 2004 Elsevier B.V. All rights reserved.

X-ray diffraction measurements were performed on titanium carbonitride coatings produced in an electron enhanced, unbalanced magnetron system. The films were deposited onto AISI 316 stainless steel substrates with an argon background pressure in the range of 0.1 Pa. A gas mixture of nitrogen and acetylene was introduced in different ratios, which alters the carbon-to-nitrogen ratio in the coating. The composition of the film was determined by glow discharge optical emission spectroscopy and wavelength-dispersive X-ray analysis. The morphology of the films was determined by scanning electron microscopy. The peak positions, integral breadths and shape parameters were determined by X-ray diffraction, and the composition influence on these parameters was investigated. The applied X-ray diffraction methods were conventional Bragg-Brentano diffraction and also parallel beam low angle diffraction. Morphological and microstructural features are found which indicate that an increased carbon content in the film gives similar results to a decrease in bias voltage. © 1995. 74-75 312 319 312-319