Determination of crystallographic texture in metal sheets using ultrasound and EBSD S.B.Palmer, S. Essex, M.D.G. Potter and S Dixon* University of Warwick, Department of Physics, Coventry CV4 7AL, UK ABSTRACT The quantitative measurement of crystallographic texture through determination of the Orientation Distribution Coefficients (ODCs) can provide critical information on a sample’s suitability for being utilised in a particular manufacturing process or can be used to measure changes in the microstructure of components in service. Ultrasonic techniques have been developed by previous workers that measure three of the ODCs that describe the orientation probability distribution function for an aggregate of cubic crystallites. Electron Backscatter Diffraction (EBSD), a microscopic technique that measures the crystallographic orientations of individual crystals, has been utilised to offer an alternative method to measuring the complete range of ODCs. As a technique, EBSD provides a much more detailed measurement of texture than ultrasonic measurements ever could. Ultrasonic methods are however non-destructive, can be used on components in service and are quicker in use and are less expensive to implement that EBSD measurements. EBSD is a valuable method in validating ultrasonic measurements, and can help to guide us in determining the limitations of the ultrasonic measurements. Ultrasonic measurement of texture is and will continue to be a useful approach to measuring texture but it does have its limitations for application to real samples. Equally, one has to use EBSD properly if one is to obtain accurate and representative data for the entire sample. Keywords: texture, EMAT, EBSD, ultrasound 1. INTRODUCTION Crystallographic texture in a bulk, polycrystalline metal sample arises because of a preferential alignment of the individual crystallites or grains within the sample [1]. This preferential alignment can occur as a result of heat treatment or working processes and manifests itself as anisotropy in some of the physical properties, such as elasticity. Most sheet metals have been manufactured by a rolling process, which together with heat treatments is used to impart specific mechanical properties to a metal sheet’s particular texture properties. Quantifying texture via a non-destructive technique and validating this method is desirable to industry for determining reliably the suitability of materials for the manufacturing of particular components [2]. The level of anisotropic elasticity is typically quite small in aluminium and steel sheets, with the variation in the wave velocity or Young’s modulus as a function of angle to the rolling direction of approximately 1%. Whilst the single crystal anisotropy is much higher in steel than in aluminium, steel crystallites will tend to align with their {111} axis normal to the surface of the sheet, whereas aluminium will tend to align with their {100} axis normal to the surface of the sheet. The elastic modulus perpendicular to the {111} direction in cubic crystals is isotropic, which explains why steel sheets often have comparable, or even smaller in-plane anisotropy than aluminium sheets, despite the much higher single crystal anisotropy in steel crystals. The crystallite orientation distribution function (CODF) is a convenient way to quantify texture. The conventional method for analysing texture is x-ray pole figure analysis, which is usually used in a qualitative way [3]. The CODF w(ξ,ψ,Φ), is a probability distribution function, that defines the distribution of orientations existing within a sample. ξ, ψ and Φ are the Roe-Euler angles defining a crystallographic orientation. The CODF w(ξ,ψ,Φ) is reliant on orientation distribution coefficients (ODCs) W lmn amongst other variables (equation 1); ( ) ( ) 0 , , exp exp l l im in lmn lmn l m ln l w W Z ψ φ ξψφ ξ ∞ − − = =− =− = ∑∑∑ (1) * s.m.dixon@warwick.ac.uk ; phone 00 44 2476573877; www.warwick.ac.uk/staff/S.M.Dixon Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2008, edited by Peter J. Shull, H. Felix Wu, Aaron A. Diaz, Dietmar W. Vogel, Proc. of SPIE Vol. 6934, 69340F, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.767473 Proc. of SPIE Vol. 6934 69340F-1 2008 SPIE Digital Library -- Subscriber Archive Copy