Challenges in microstructural metrology for advanced engineered materials

Abstract

Measurement of microstructural parameters is essential for both controlling and modelling properties of and production processes for advanced materials. In the past decade new techniques such as electron backscatter diffraction have enabled a considerable increase in the amount of data and degree of detail in microstructural measurements of, for example, the extent of recrystallization in a metal deformed at high temperatures. However, the many parameters involved and automated nature of the methods can lead to artefacts and bias in calculated values, and increased resolution will lead to disagreement with more conventional methods. Examples are given of the range of microstructural measurements possible by new techniques and how different results can be obtained from the same underlying data. The need is stressed for interlaboratory comparisons to enable underpinning data to be derived on the validity, repeatability and reproducibility of measurements of key microstructural parameters.

Characterisation of local grain size variation of welded structural steel

“…ASTM grain size measurement methods, available [11]. Moreover, orientation imaging microscopy gives the operator a large degree of freedom for defining the measurement methodology and parameters such as step size, grain boundary misorientation criteria and filtering of the data [12][13][14]. For these reasons, an extensive interlaboratory round-robin [15] was carried out in order to define the grain size measurement methodology for the ISO 13067 [16] standard.…”

“…Improved grain size measurement methods are thus required to enhance the understanding between grain size distribution and mechanical properties [11]. Accurate description of the microstructural heterogeneity is also required for the mesoscale modelling of material behaviour [12]. Welds are an extreme case of heterogeneity since it is present both in macroscopic scale across the joint and in microscopic scale within a single zone; see Fig.…”

“…Najčešće saopštavana mikrostrukturna mera u literaturi je prosečna veličina zrna, iako postoji veliki izbor metoda na raspolaganju, npr ASTM metoda merenja veličine zrne [11]. Osim toga, mikroskopija sa orijentacijom slike, daje operateru veliki stepen slobode za definisanje metodologije merenja i parametara kao što su veličina koraka, kriterijumi neorijentisanosti granica zrna i filtriranje podataka [12][13][14]. Iz tih razloga, sprovedena su opsežna međulaboratorijska ispitivanja [15] kako bi se definisala metodologija merenja veličine zrna za ISO standard 13067 [16].…”

“…Poboljšane metode merenja veličine zrna traže da se poboljša razumevanje između distribucije veličine zrna i mehaničkih svojstava [11]. Precizan opis mikrostrukturnih heterogenosti je takođe potreban za međuskalno modeliranje ponašanje materijala [12]. Zavareni spojevi su ekstremni slučaj heterogenosti jer je ona prisutna i u makroskopskoj skali i na mikroskopskom nivou unutar jedne zone; vidi sl.…”

“…EBSD analiza veličine zrna se obično izvodi pomoću identifikacije zrna i određivanja veličine zrna sa investigate the influence of local grain size variation on mechanical properties. EBSD grain size analysis is typically carried out using the grain identification and determination of grain size from its surface area, often taken as the diameter of a circle with an equivalent surface area [12,36]. For homogeneous equiaxed microstructures, this assumption is justified, and values determined by circle equivalent diameter (dceq) and linear intercept are comparable within 10 % of each other [15].…”