Evaluation of the Effect of Minor Additions in the Crystallization Path of [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xMx Metallic Glasses by Means of Mössbauer Spectroscopy

Understanding the crystallization of metallic glasses is fundamental in the design of new alloys with enhanced properties and better glass-formability. The crystallization of a series of Fe-based metallic glasses of composition [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xMx (M = Mo, Nb and Zr) has been studied by means of differential scanning calorimetry and transmission Mössbauer spectroscopy. This latter technique allows the following of the microstructural evolution of the studied alloys through the identification and quantification of the several Fe-containing crystalline phases and also through the changes in the amorphous structure at the initial stages of crystallization. The results show that the crystallization products are the same for all the studied compositions (α-Fe, Fe2B, (FeCo)23B6 and a paramagnetic remnant) although with different relative proportions and the crystallization of a phase without Fe in the alloys with Zr. Moreover, the addition of Zr favors the crystallization of α-Fe causing a detrimental effect on the glass forming ability, while the increase in Mo content up to 6 at% favors the crystallization of (FeCo)23B6. The different amount of α-Fe and borides is presented as a measure of the glass forming ability of this type of alloys.

Crystallization behavior of ternary γ–γ′ Co–Al–W alloy

In the investigation, crystallization behavior of ternary γ–γ′ alloy based on Co–Al–W system was analyzed. The alloy with nominal composition Co–9Al–9W (at.%) was prepared via vacuum induction melting. Solidification characteristics of the investigated superalloy were obtained by a method of thermal analysis based on temperature measurement of metal solidifying in a mold. After casting, obtained metallic materials were investigated by differential thermal analysis in order to determine characteristic temperatures and compare results with those of obtained in the first thermal analysis. Furthermore, a description of primary microstructure was performed for ingots solidified with two different cooling rates. The analysis was made using X-ray diffraction, optical microscopy and scanning electron microscopy. The crystallization path of alloy was investigated. The solidification range of alloy was narrow. The crystallization in a sand mold resulted in the dendritic microstructure containing γ single phase. The as-cast microstructure after solidification with higher cooling rate was comparable; however, observed crystals were mostly columnar, while sand cast was characterized by equiaxed crystals structure.

Deducing Crystallization Sequence of Magmas from Spatial Distribution of Crystals in Rocks

The order of crystallization of minerals from melt is of prime importance for an understanding of magma fractionation and chemical differentiation from the magma chamber to the planetary scale. Determination of the crystallization sequence based on petrographic observations, however, is often ambiguous; especially in multiply saturated, nearly eutectic felsic melts. This paper presents a novel approach to estimate the order of crystallization of minerals in igneous systems based on a quantitative study of their spatial distributions. Statistical modelling of crystallization demonstrates that later crystallizing mineral phases are generally more clustered. A simple inversion model is then derived to calculate the crystallization sequence and the volume fraction of older minerals present in the system at the onset of crystallization of a later (younger) phase. Application of the model to a sample of equigranular granodiorite (Fichtelgebirge granite batholith, Germany) indicates that plagioclase was the first liquidus phase. It was followed by biotite, K-feldspar, and quartz at 41, 48, and 63 vol. % crystallized, respectively, which is in qualitative agreement with experimental phase equilibria results for moderately hydrous granitic melts. If phase equilibria for a given composition are known or assumed, the crystallization sequence thus constrains the intensive variables (e.g., water content) and their evolution during magma solidification. The model thus provides a novel and independent approach to reconstruct the magma crystallization path that would be inaccessible by other methods.

Mafic glass compositions: a record of magma storage conditions, mixing and ascent

The trans-crustal magma system paradigm is forcing us to re-think processes responsible for magma evolution and eruption. A key concept in petrology is the liquid line of descent (LLD), which relates a series of liquids derived from a single parent, and therefore tracks the inverse of the crystallization path. It is common practice to attribute multiple magma compositions, and/or multiple melt compositions (from melt inclusions and matrix glass), to a single LLD. However, growing evidence for rapid, and often syn-eruptive, assembly of multiple magma components (crystals and melts) from different parts of a magmatic system suggests that erupted magma and melt compositions will not necessarily represent a single LLD, but instead may reflect the multiple paths in pressure–temperature space. Here, we use examples from mafic magmatic systems in both ocean island and arc settings to illustrate the range of melt compositions present in erupted samples, and to explore how they are generated, and how they interact. We highlight processes that may be deduced from mafic melt compositions, including the mixing of heterogeneous primitive liquids from the mantle, pre-eruptive magma storage at a range of crustal and sub-Moho depths, and syn-eruptive mixing of melts generated from these storage regions. The relative dominance of these signatures in the glasses depends largely on the water content of the melts. We conclude that preserved melt compositions provide information that is complementary to that recorded by the volatile contents of crystal-hosted melt inclusions and coexisting mineral compositions, which together can be used to address questions about both the pre- and syn-eruptive state of volcanic systems. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

Sol-Gel Derived Mullite-Gahnite Composite

Mullite-gahnite composites with different phase-proportions were prepared using sol-gel process. Crystallization path was determined using differential thermal analysis (DTA). X-ray powder diffraction (XRD) was used to study the crystal phases development. The course of the thermal reactions is dominated by the intermediate formation of two spinel phases. The former phase was attributed to gahnite, while the latter to Al-Si spinel. Zn loading decreases amounts of mullite and α-alumina, while increases gahnite and amorphous phase. The observed microstructure of sintered bodies is characterized by fine gahnite particles distributed among larger mullite grains, which is highly favourable for ceramics with high mechanical requirements.