A new way to include the grain shape in texture simulations with the Taylor model
The use of the Hall-Petch relation in texture simulations with the Taylor-Bishop-Hill model is proposed as a mean to take into account grain shape effect. The results are compared with those obtained with the usual and relaxed constraint Taylor model for a simple texture and the consequences for the anisotropy coefficient are investigated On propose d'utiliser la relation de Hall-Petch dans les simulations de texture a l'aide du modele de Taylor-Bishop-Hill pour prendre en compte la forme des grains. Comparaison des resultats avec ceux du modele de Taylor classique ou relaxe dans le cas d'une texture simple; consequences pour le coefficient d'anisotropie
Digital Protocols for Statistical Quantification of Microstructures From Microscopy Images of Polycrystalline Nickel-Based Superalloys
This paper presents new digital image analysis protocols and workflows for the quantification of size distributions of key microstructural features (e.g., grain size, γ’ size) and γ’ volume fraction in polycrystalline nickel-based superalloys. These digital protocols leverage recently established image analyses algorithms that have been shown to be computationally efficient and scalable. They allow consideration of very large sample sizes (both larger scan sizes and larger number of images), and the extraction of reliable and reproducible microstructure statistics. For grain size analysis, electron backscatter diffraction was used to characterize the polycrystalline microstructure, and angularly resolved chord length distribution (AR-CLD) analysis was performed to reliably quantify the grain size and morphology distribution. For γ’ size and volume fraction analysis, back-scattered electron imaging in the scanning electron microscopy (BSE-SEM) was used to characterize the microstructure at the sub-grain level, and a robust image segmentation workflow was developed and used to identify the γ’ pixels in the gray-scale image. AR-CLD analysis was also performed on these segmented images to determine size distributions of the γ’ precipitates. The digital protocols developed in this work are demonstrated on three different nickel superalloy specimens subjected to very different cooling rates (labeled as slow-cool, moderate-cool, and fast-cool), which resulted in vastly different γ’ size distributions. It is demonstrated that the effect of the cooling rates on the γ’ size distributions can be reliably quantified using the digital protocols presented in this study.
Changes in Quartz During Heating and the Possible Effects on Si Production
In Si and FeSi production, the main Si source is SiO2, in the form of quartz. Reactions with SiO2 generate SiO gas that further reacts with SiC to Si. During heating, quartz will transform to other SiO2 modifications with cristobalite as the stable high-temperature phase. Transformation to cristobalite is a slow process. Its rate has been investigated for several industrial quartz sources and has been shown to vary considerably among the different quartz types. Other differences in behavior during heating between these quartz sources, such as softening temperature and volume expansion, have also been studied. The quartz-cristobalite ratio will affect the rate of reactions involving SiO2. The industrial consequences and other implications of the observed difference between quartz types are discussed. Initial studies of industrial quartz were published by Ringdalen et al. In the current work, a new experimental method has been developed, and an investigation of several new quartz sources has confirmed the earlier observed large variation between different sources. The repeatability of the data has been studied and the effect of gas atmosphere investigated. The results from the earlier work are included as a basis for the discussion.