R Gnanamoorthy

This work deals with the influence of laser peening on the fretting wear behavior of Ti-6Al-4V. Laser peening was carried out on Ti-6Al-4V. The laser-peened surface was characterized by transmission electron microscopy. Surface roughness, nanoindentation hardness, residual stress, and tensile properties of the material in both laser-peened and unpeened conditions were determined. Fretting wear tests were conducted at different normal loads using a ball-on-flat contact geometry. Laser peening resulted in the formation of nanocrystallites on the surface and near-surface regions, increased hardness, and compressive residual stress. Laser peening did not affect the tensile properties and surface roughness significantly. There was no considerable difference between the values of the tangential force coefficient of laser-peened and unpeened samples. The fretting scar size, wear volume, and wear rate of laser-peened specimens were lower than those of unpeened samples. This may be attributed to an increase in surface hardness due to strain hardening and grain refinement at the surface and near-surface regions, higher compressive residual stress, and higher resistance to plastic deformation of laser-peened samples. © 2012 Copyright Taylor and Francis Group, LLC.

This paper deals with the effects of laser peening on fretting wear behaviour of a nickel-based superalloy, alloy 718, fretted against two different counterbody materials (alumina and SAE 52100 steel). Laser peening was carried out on alloy 718. Microstructural characterization of laser peened surface was done by electron back-scattered diffraction and transmission electron microscopy. Surface roughness, nanoindentation hardness, and residual stress of both laser peened and unpeened samples were determined. Fretting wear tests were conducted on unpeened and laser peened samples using two different counterbody materials (alumina and SAE 52100 steel balls). The results show that nanocrystallites formed in the surface and near-surface regions and compressive residual stress were induced after laser peening. Hardness increased due to grain refinement at the surface and near-surface regions. There was no significant change in the surface roughness. The laser peened sample exhibited lower tangential force coefficient values compared to unpeened samples at all loads, which may be attributed to higher hardness. Samples fretted against alumina counterbody exhibited higher tangential force coefficient compared to samples fretted against steel counterbody. Owing to increased surface hardness and higher compressive residual stress, laser peened samples exhibited lower fretting wear damage compared to unpeened samples. Due to tribochemical reactions, the wear volume of unpeened and laser peened samples fretted against alumina counterbody was higher than that of the samples fretted against steel counterbody.

Alloy 718 was subjected to surface mechanical attrition treatment (SMAT) using SAE 52100 steel balls of a 5. mm diameter for four different treatment durations (15, 30, 45 and 60. min). Fretting wear tests were conducted at different normal loads on untreated and treated samples for 25,000. cycles using alumina as a counterbody material. Microstructural features of the surface layer of samples treated by SMAT were characterized by cross-sectional optical microscopy and transmission electron microscopy. Hardness, surface roughness and residual stress were determined using a nano-indenter, surface roughness tester and X-ray residual stress analyzer respectively. SMAT resulted in the formation of nanocrystallites on the surface and near surface regions, increased hardness, increased surface roughness and compressive residual stress at the surface. Treated samples exhibited lower tangential force coefficient (TFC) compared to untreated samples. Samples treated for 60. min exhibited higher grain refinement, higher hardness, lower surface roughness and higher TFC compared to the samples treated for 30. min. The wear volume and wear rate of samples treated for 30. min were lower compared to those of the untreated samples, which may be attributed to an optimum combination of hardness and toughness and a low work hardening rate of the nanocrystalline structure at the surface of the treated samples. In contrast, the wear volume and wear rate of the samples treated for 60. min were higher than those of untreated samples, presumably due to the higher hardness and reduced toughness of the samples treated for 60. min. © 2012 Elsevier B.V.

This work is concerned with the performance of diamond-like carbon (DLC) coated Ti-6Al-4V flat samples fretted against alumina ball in two environments-ambient air and simulated body fluid (Ringer solution). Hydrogenated DLC (H-DLC) coatings were prepared by radio frequency plasma enhanced chemical vapour deposition process. Raman scattering measurements were done on the coatings. Fretting wear tests were conducted at different normal loads using a fretting wear test rig working on scotch yoke mechanism. Wear scars on the tested specimens were observed using an optical microscope. Wear volume was calculated based on wear scar diameter measured along parallel and perpendicular to the fretting direction. Tangential force coefficient (TFC) values exhibited by DLC coated samples were lower than those exhibited by uncoated specimens in both ambient air and Ringer solution. Very low TFC values and low wear volume were observed for H-DLC coated samples tested in air at lower loads of 1.9 N and 4.9 N. It was attributed to occurrence of graphitisation and formation of transfer layer on alumina ball. © 2008 Elsevier B.V. All rights reserved.

In the present work, multi layer perceptron feed forward artificial neural network (ANN) technique was employed to predict the fretting wear behavior of surface mechanical attrition treated and untreated Ti-6Al-4V fretted against alumina and steel counterbodies. A three-layer neural network with a gradient descent learning algorithm was used to train the network. Three input parameters normal load (L), surface hardness of the test material (H) and hardness of counterbody material (CB) were employed in construction of ANN. Tangential force coefficient (TFC), fretting wear volume and wear rate obtained from a series of fretting wear tests were used in the training and testing data sets of ANN. Ranking of the importance of input parameters on the output TFC was found to be in the order of L > CB > H. For wear volume and wear rate, it was found in the order of L > H > CB. The degrees of accuracy of predictions were 96.6%, 96.1% and 92.2% for TFC, wear volume and wear rate respectively. Owing to the good correlation between the predicted values and the experimental results, ANN can be used in the prediction of fretting wear behavior. © 2013 Elsevier Ltd.

Plasma nitriding was performed on Ti-6Al-4V samples at 520 °C in two environments (pure nitrogen and a mixture of nitrogen and hydrogen in the ratio of 3:1) for two different time periods (4 and 18 h). Fretting wear tests were conducted on unnitrided and nitrided samples for 50,000 cycles using alumina ball counterbody. Plasma nitriding reduced the tangential force coefficient of Ti-6Al-4V. The samples nitrided for 4 h exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided for 18 h. The samples nitrided in nitrogen-hydrogen mixture environment exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided in pure nitrogen. The samples plasma nitrided in nitrogen-hydrogen mixture for 4 h exhibited the highest hardness and the lowest tangential force coefficient. The wear volume and specific wear rate of the plasma nitrided samples were lower than those of the unnitrided samples. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume and specific wear rate at different loads. © 2009 Elsevier Ltd. All rights reserved.

Surface mechanical attrition treatment (SMAT) was carried out on Ti-6Al-4V. Fretting wear tests were conducted using two counterbody materials (alumina and steel). SMAT resulted in surface nanocrystallization. Due to high hardness, low tangential force coefcient (TFC) and more TiO 2 layer, fretting wear resistance of SMAT treated samples was higher than that of the untreated samples. TFC values obtained with alumina counterbody were higher than those obtained with steel counterbody. The fretting wear resistance of untreated and treated samples fretted against alumina was lower than that of the samples fretted against steel due to tribochemical reactions at the contact zone. © 2012 Elsevier Ltd.

Hydrogenated diamond-like carbon (DLC) (H-DLC), argon-incorporated DLC (Ar-DLC) and nitrogen-incorporated DLC (N-DLC) coatings were deposited on flat rectangular Ti-6Al-4V samples. The DLC coatings were characterised by Raman spectroscopy and nanoindentation. Fretting wear tests were conducted on uncoated and DLC coated samples with an alumina ball as the counterbody. As the Ar-DLC and N-DLC coatings had relatively more sp2 network compared to the H-DLC coating, they exhibited lower values of hardness and elastic modulus. At both loads of 4.9 N and 14.7 N, all DLC coated specimens showed lower values of tangential force coefficient (TFC), wear volume and specific wear rate compared to the uncoated samples. While the Ar-DLC coated sample exhibited the lowest TFC, wear volume and specific wear rate at 4.9 N load, the N-DLC coated specimen exhibited the lowest TFC, wear volume and specific wear rate at 14.7 N load. © 2009 Elsevier B.V. All rights reserved.

Hard anodizing, micro arc oxidation and detonation spraying of alumina were done on AA 6063 substrate. Fretting wear tests were done at different normal loads and a constant displacement of 55 μm for 50,000 cycles at 5 Hz. The micro arc oxidation and detonation spray coated samples exhibited lower coefficient of friction compared to hard anodizing coated and uncoated samples. Both micro arc oxidation and detonation sprayed samples showed superior fretting wear resistance compared to hard anodizing and uncoated samples. However, hard anodizing coated samples exhibited inferior fretting wear resistance compared to uncoated samples due to cracking and fragmentation of brittle and hard anodized layer. © IMechE 2013 Reprints and permissions: sagepub.co.uk/ journalsPermissions.nav.

Fretting wear tests were carried out at different normal loads on uncoated and diamond-like carbon (DLC)-coated Ti-6Al-4V samples against two counterbody materials: alumina and ultra high molecular weight polyethylene (UHMWPE). Tangential force coefficient (TFC) values obtained with alumina counterbody were much higher than those obtained with UHMWPE. A significant reduction in TFC was noticed in DLC-coated samples compared with uncoated specimens when tested against alumina counterbody at normal loads of 1.96 and 9.8 N. There was not much difference betweenTFC values of DLC-coated and uncoated specimens when tested against UHMWPE counterbody. DLC-coating reduced specific wear rate significantly at 1.96 N when the sample was tested against alumina counterbody. However, at higher loads, both uncoated and DLC-coated samples exhibited similar specific wear rates. As initial maximum contact pressure was relatively very low, no fretting scar was observed both in uncoated and DLC-coated samples tested against UHMWPE counterbody. © IMechE 2009.