Non-destructive Materials Characterization and Evaluation

The propagation of ultrasonic waves through materials is essentially governed by its elastic and anelastic properties. Following the basics of interatomic forces and elasticity, ultrasonic velocities in single crystals and polycrystalline materials are discussed in chapter 1 in detail, providing means for materials characterization using ultrasonic velocity measurements. The third-order elastic constants in polycrystalline materials describe the acoustoelastic constants which form the basis for the evaluation of elastic stresses in materials. Stresses lead to anisotropic velocities and so do textures. It is discussed how these can be separated. The anisotropy of the constituents of the microstructure of a material leads to ultrasonic scattering and therefore to attenuation of the propagating waves, whereas the anelasticity in lattice structure leads to internal friction. Both effects are discussed with various examples. Fatigue and creep manifest themselves in the parameters describing ultrasonic propagation and hence can be exploited for non-destructive materials characterization (NDMC). Thus, in chapter 1, we emphasize the principles forming the basis for NDMC using ultrasonics and demonstrate their applications through suitable examples.

This chapter discusses the physical principles and the applications of non-destructive materials characterization (NDMC) techniques using X-rays, neutrons, electrons, and positrons. Various means of generation and detection of X-rays are presented followed by the basics of their interaction with materials. These interactions lead to attenuation and diffraction, which are elucidated by examples from different metallurgical and material science applications of NDMC. The basics of X-ray diffraction and their applications for the measurement of elastic stresses at different length scales and of textures are discussed as well. The specific differences of the interaction of neutrons with materials as compared to X-rays in radiography and scattering studies are worked out. Applications of electron and positron annihilation for NDMC are also discussed.

In this chapter, electro-magnetic (EM) and micro-magnetic (MM) techniques for applications in non-destructive material characterization (NDMC) are discussed. While EM techniques can be used for all electrically conducting and ferromagnetic materials, MM techniques are applicable only to ferromagnetic materials. There are many commonalities between the EM and MM techniques in terms of the sensors’ primary excitation and reception of secondary magnetic fields. After explaining the basic concepts of conductivity, electromagnetism, and magnetic properties of materials, applications of these for the characterization of microstructures and stresses are presented. The effects of conductivity and permeability of materials on the amplitude and phase of eddy current signals are analyzed for use in NDMC. Furthermore, the physical principles underlying various magnetic hysteresis loop parameters and MM parameters are discussed, followed by their applications in the field of metallurgical engineering and material science. The analogy of the dislocation movement under stress fields, which determines the mechanical properties, and the domain-wall movement under magnetic fields governing the magnetic properties provide the means for NDMC.