Procedures for interface residual stress determination using neutron diffraction: Mo-coated steel gear wheel Giovanni Bruno a,b, * , Carlo Fanara c , Darren J. Hughes a , Nicolas Ratel b a Manchester Materials Science Centre, Grosvenor Street, Manchester M1 7HS, UK b ILL, Diffraction Group, 6, rue Horowitz, BP 156, F-38042 Grenoble, France c WERC, School of Industrial and Manufacturing Science, Building 46, Cranfield University, MK43 0AL Cranfield, UK Received 21 September 2005; received in revised form 29 November 2005 Available online 21 February 2006 Abstract Residual stresses were determined in steel gear wheels coated with molybdenum using neutron diffraction. A systematic procedure was developed to assess them in both the molybdenum coating and in the steel substrate. A detailed description of the problems associated with measurements of this type is given, together with a procedure aimed at rationalising their solution. Precise sample positioning was developed using a new experimental method and advanced metrology equipment allowing off-line sample alignment and mounting. This reliably replaces the inefficient use of entrance scans, usually adopted in residual stress analysis by neutron diffraction. Corrections were applied to overcome the presence of pseudo-strains and data reduction was performed to coher- ently interpret the results, including the determination of the centre-of-mass of the diffracting volume. The full three-dimensional stress profile was determined in the coating and the substrate. The data analysis methodology is fully described and recommendations are given for this kind of measurement. Ó 2006 Elsevier B.V. All rights reserved. PACS: 07.10.Pz; 85.40.Xx; 61.12.q Keywords: Residual stress; Neutron diffraction; Metallic coating; Gauge volume; Surface strain scanning 1. Introduction 1.1. Near surface residual stress determination Coatings are applied in many engineering situations to reduce wear and corrosion. Recent steps have been made in the development of coatings in engine and transmission components for example spray coated synchronizer gears [1]. However, in order to fully understand the in-service behaviour of these components and to meet quality assur- ance protocols it is necessary to determine the residual (or locked in) stresses. These stresses arise not only during the manufacture of the substrate component but also due to application of the coating material. The residual stresses exist in both the substrate and coating. A limited number of techniques are available to non- destructively determine residual stress in coatings and these are mainly based around the diffraction technique. The crystal lattice of the specimen is effectively used as a strain gauge, changes in strain relating to shifts in diffraction angles. Historically, laboratory X-ray generators were used, employing the classical sin 2 w method [2]. However, because of the generally small penetration depth in engi- neering materials, its applicability to depth resolved residual stress determination is limited. Modifications of the procedure like the layer removal technique [3] are no longer non-destructive and require long preparation times and complicated analysis to relate the measured strains to the original stresses of the component. 0168-583X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.01.002 * Corresponding author. Present address: Corning SAS, CETC, CS&S, BP3, F-77211 Avon, France. Tel.: +33 164 697040; fax: +33 164 697454. E-mail address: brunog@corning.com (G. Bruno). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 246 (2006) 425–439 NIM B Beam Interactions with Materials & Atoms