Abstract
Classical sessile drop experiment was performed for intensive microstructure and phase composition studies of the reaction product region (RPR) formed because of high temperature interaction between the aluminum–copper alloy (Al—16.7 at.% Cu) and SiO2 (amorphous) substrate. The experiment was performed in vacuum at 1173 K for 2 hour contact time. Scanning and transmission electron microscopy techniques were applied to reveal the details of the complex microstructure of reactively formed product zone at the drop/substrate interface. Three regions of different structure and phase composition were well distinguished in the RPR: the first layer was composed of large-faced Al2O3 crystals of alpha type surrounded by the Al2Cu metallic channels, the second one had the same phase composition but different morphology of the alpha alumina and with silicon as an extra component (dissolved within these phases and as precipitates). The third area revealed very fine-grained (100–200 nm) microstructure, in which Al2Cu and Si grains were embedded in orthorhombic δ-Al2O3 matrix. Moreover, the presence of the deformation twins in silicon, twinned on (1–11) plane was related to large strains present in the area close to the SiO2 substrate and coming from the volumetric mismatch of SiO2 and the freshly formed Al2O3.
Highlights
Classical sessile drop experiment was performed for intensive microstructure and phase composition studies of the reaction product region (RPR) formed because of high temperature interaction between the aluminum–copper alloy (Al—16.7 at.% Cu) and SiO2 substrate
Scanning and transmission electron microscopy techniques were applied to reveal the details of the complex microstructure of reactively formed product zone at the drop/substrate interface
Three regions of different structure and phase composition were well distinguished in the RPR: the first layer was composed of large-faced Al2O3 crystals of alpha type surrounded by the Al2Cu metallic channels, the second one had the same phase composition but different morphology of the alpha alumina and with silicon as an extra component
Summary
The composite materials based on Al–Al2O3 system are characterized by the unique set of properties such as high hardness, good resistance to abrasion, low density, and thermal and electrical conductivities, accompanied by a low price. The alloying elements may change both the phase composition and the morphology of reactively formed phases, affecting the properties of the final product. Information on the effect of alloying elements on the type and morphology of reactively formed alumina is of practical importance. The study by Sobczak et al [5] using optical microscopy (OM) and scanning electron microscopy (SEM) techniques did not show any new reactively formed phases after alloying Al with 16.7 at.% Cu (near eutectic composition with corresponding low melting temperature of 550 K) and subsequent long-term contact with SiO2 at 1273 K. The thickness of reaction product region (RPR), as a measure of reactivity in the system, was decreased from 1.2 mm in Al/SiO2 to 0.5 mm in Al16.7Cu/SiO2. Santhage [6] has reported (after Strange and Breslin [7] and Evarts [8]) the influence of Al–Cu melt composition on the domain sizes of reactively formed alumina in the
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