Investigation of the Correlation between Texture and Microstructure on a Submicrometer Scale in the TEM

Abstract

In recent years the investigation of local texture and microstructure by analysis of electron backscatter diffraction patterns (EBSP) in the SEM has become a very powerful and popular method. With the introduction of SEM with field emission guns (FEG) the spatial resolution of EBSP measurements could be enhanced from 500 nm with a tungsten emitter to better than 50 nm. This evolution of SEM techniques raises the question whether transmission electron microscopy (TEM) still has fields of application in texture research. The present article answers this question with a clear “yes” and presents three examples of investigations where TEM is indispensable. The three examples comprise the investigation of the correlation between dislocation structure and deformation texture, a study on nucleation mechanisms of recrystallization in highly deformed metals and the investigation of microtexture and microstructure in nanocrystalline materials. Together with the presentation of these cases some of the necessary measurement techniques are described briefly. It is shown that TEM has to be applied when highest spatial resolution of orientation determination and imaging and high accuracy of orientation determination are to be reached, when the three‐dimensional and quantitative characterization of lattice defects is required or when materials with a high density of lattice defects are to be investigated.

Multiple twinning in pure hexagonal close-packed titanium

“…Mechanical twinning is a particularly important deformation mode in -titanium (Vedoya et al, 1988;Philippe et al, 1995;Fundenberger et al, 1997;Zaefferer, 2003). It is an important factor in the control of the properties of titanium such as ductility and fracture strength (Kocks & Westlake, 1967;Partridge, 1967;Mahajan & Williams, 1973;Yoo, 1981).…”

“…Twins can be described by elegant methods in mathematical crystallography (e.g. Nespolo & Ferraris, 2000, 2003Nespolo, 2004). Several authors of this paper have also applied mathematical methods imported from number theory, notably Bezout's theorem (Zhang et al, 2010), to develop a general method to determine twinning elements.…”

Investigation of the Correlation between Texture and Microstrucure on a Submicrometer Scale in the TEM

“…[6] In order to understand and model the texture evolution of various titanium alloys, it is important to know which glide systems (which kind of dislocations) are activated and, at best, to know their relative critical resolved shear stresses. This problem has been studied by detailed TEM investigations for three different titanium alloys by Zaefferer [7,8] and some aspects of these investigations are presented here.…”

Characterization and modeling of heterogeneous deformation in commercial purity titanium

“…4,5 The primary slip system is { } 10 10 1210 < >prismatic slip because it has the lowest critical resolved shear stress. 4 There are three other slip systems, { } 0001 1210 < > basal, { } 10 11 12 10 < > pyramidal <a> slip, and { } 10 11 2 1 13 < > pyramidal <c+a> slip, that can be activated with high resolved shear stress. There are also four twinning systems in α-titanium 6 that can contribute to deformation, two tensile (extension) twinning modes (T1 and T2), and two compressive (con-traction) twinning modes (C1 and C2).…”

“…The evolution of the plastic gradient, F p , is given by Equation 2, where the plastic velocity gradient, L p , resulting from activity on all deformation systems is described as Equation 3 with P α = m α  n α as the Schmid matrices with respect to the undeformed state,  g 0 3 1 10 = − − s as reference shear rate, n the constant stress exponent, t α the resolved shear stress, and s α is the shear resistance. The evolution of s α during deformation is written as Equation 4. The resolved shear stress t α = P α : S, where S is the second Piola-Kirchhoff stress S = C : E e .…”