A Semi-Automatic System for the Ultrasonic Measurement of Texture

Abstract

The texture (preferred grain orientation) of rolled metal plates influences a number of important mechanical properties such as their ability to be plastically formed into complex shapes. X-ray diffraction techniques can characterize texture in great detail but are unsuitable for real time process control. Furthermore, x-rays only sample the properties of a near surface layer, whereas the average properties throughout the thickness may be of greater interest. This paper describes an alternate texture characterization approach based on ultrasonic measurements of the anisotropy of plate wave velocities. Relationships have recently been established between the macroscopic elastic constants of a rolled metal plate and the coefficients of an expansion of the crystallite orientation distribution function (CODF) in terms of generalized Legendre functions [1]. It has also been shown that these coefficients can be determined from velocity measurements of ultrasonic plate modes [2,3]. Here a system is described which implements these ideas in a semi-automated fashion as would be required for process control applications. The measurement system consists of two sets of EMAT transducers and associated electronics, one for SH_O mode measurements and the other for S_O mode measurements. Each set consists of one transmitter and two receivers, separated by a fixed distance and placed at a variable angle with respect to the rolling direction of the plate. The pair of received signals are digitized and processed to determine the coefficients W₄₀₀, W₄₂₀ and W₄₄₀, which can, in turn, be used to make first order predictions of pole figures. These steps are reviewed in detail and future directions are discussed.