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Here, we present a comprehensive study on atomic-scale in-situ biasing/heating scanning transmission electron microscopy ((S)TEM) of Al-amorphous SiO2–SiC interface. The investigation includes electrical, chemical, and structural analysis of the interface at different temperatures (25–600 °C). The results show that at ~ 500 °C the electrical (three-orders of magnitude resistivity drop), chemical (dissolution of SiO2 amorphous layer), and microstructural features (e.g. formation of Al2O3, Si and Al4C3) of the interface start to change. According to the results, amorphous SiO2 dissolves in Al, leading to formation of α-Al2O3 and Si within the Al. In contrast, elemental interdiffusion (Al3+ ⇄ Si4+) between Al and SiC occurs resulting in formation of Al4C3. From the results, we can infer that reaction mechanism between Al and crystalline SiC is different with that between Al and SiO2 amorphous phase. It is believed that structural similarities between SiC and Al4C3 play an important role in paving the way for elemental interdiffusion. [ABSTRACT FROM AUTHOR]

Al‐Si3N4 couples were heat‐treated at 850‐1150°C for 250 hours. The thickness of the interacted area was measured by scanning electron microscopy (SEM) and scanning/transmission electron microscopy (TEM/STEM). The interaction rate increases exponentially with inverse temperature, with an activation energy of 194.23 kJ/mol and diffusion pre‐coefficient of 5 × 10−9 m2/s, indicating that the interaction is diffusion‐dependent. As the results showed, the interfacial area is comprised of Al alloy channels, Si precipitates, and AlN grains. Al‐Si transfer through the solid solution (Si3‐xAlxN4‐y) at the interface of Al alloy and β‐Si3N4 grains controls the kinetic of the interaction. When concentration of Al in solid solution exceeds a certain amount, it undergoes a topotactic phase transformation to form Al1‐xSixN1+y (viz., AlN). Next, the Al1‐xSixN1+y grains detach from the β‐Si3N4 grains and subsequently new Al‐Si3N4 interfaces are established. These interfaces repeat the interaction process, continuing until all the reactant is depleted. Thus, the interaction kinetics consist of a sequence of associated parabolic stages, precluding the observation of parabolic kinetics. [ABSTRACT FROM AUTHOR]

The present work reports the SEM, EPMA and TEM examination of reactions at the interface of Al7075 alloy and a 50/50 wt% mixture of BaAl2Si2O8 + CaAl2Si2O8feldspars at 850 °C, 1150 °C and 1250 °C. Sintering of the feldspar mixture at 1450 °C caused dissolution of ~1.0 wt% Ca in BaAl2Si2O8and 0.5 wt% Ba in CaAl2Si2O8. The interaction of the Al alloy with the sintered feldspars shifted the alloy composition to the Al–Si–αBaAl2Si2and Al–Si–βaAl2Si2compatibility triangles. The feldspars underwent a series of phase transformations, leading ultimately to the formation of Al2O3. [ABSTRACT FROM AUTHOR]

The present work reports an investigation of the interactions of Al 7075 alloy and anorthite at 850°C (150 h) and 1150°C (24 h). Transmission electron microscopy, electron probe microanalysis, X-ray diffraction, and scanning electron microscopy coupled with energy-dispersive spectroscopy were used to identify the mineralogical and microstructural changes at the metal-ceramic interface. At 850°C, the phase formation mechanisms were (a) Si4+-Al3+ interdiffusion between the Al alloy and anorthite to form calcium dialuminate ( CA2) and Ca2+-Mg2+ interdiffusion between the Al alloy and calcium dialuminate to form spinel. At 1150°C, spinel + Al2O3 and calcium hexaluminate ( CA6) + CA2 were the major and minor phase mixtures, respectively in the corroded area. A thin layer of calcium monoaluminate ( CA), gehlenite, and Si was present in the immediate vicinity of anorthite. The early stages of corrosion at 1150°C and 850°C were identical. However, due to thickening of the corroded region ( viz., spinel formation) and enhanced evaporation of Mg at the higher temperature, the interdiffusion path evolves from Si4+-Al3+ + Ca2+-Mg2+ to Si4+-Al3+ + Ca2+-Al3+, thus establishing the following phase evolution path at the interface: [ABSTRACT FROM AUTHOR]

A corrosion cup test was undertaken using BaAl2Si2O8 and Al4.1Zn3.2Mg alloy, heated in air for 150 h at 850°C. Electron probe microanalysis, X-ray diffraction, and scanning electron microscopy coupled with energy dispersive spectroscopy were used to identify the mineralogical and microstructural changes at the interfaces. The microstructural results revealed three microstructural areas: (1) Spinel layer with large numbers of Al alloy channels; (2) interfacial area with mainly alumina, spinel, and BaAl2Si2O8; and (3) interdiffusion zone chemically close to barium hexaaluminate. The principal observations are: BaAl2Si2O8 was highly resistant to molten Al alloy corrosion owing to sluggish kinetics, as evidenced by the observation of unreacted BaAl2Si2O8 grains in the interfacial area., The nature of the microstructure, particularly an interdiffusion zone instead of a continuous layer of precipitated alumina at the interface between the Al alloy channels and the unreacted BaAl2Si2O8 supports the conclusion that the corrosion mechanism is governed by interdiffusion (Si/Ba and Al/Mg) and substitution., The formation and limited retention of an MgO layer at the metal-ceramic interface played a critical role in alloy oxidation and the consequent interfacial phenomena. [ABSTRACT FROM AUTHOR]

Al‐Si3N4 couples were heat‐treated at 850‐1150°C for 250 hours. The thickness of the interacted area was measured by scanning electron microscopy (SEM) and scanning/transmission electron microscopy (TEM/STEM). The interaction rate increases exponentially with inverse temperature, with an activation energy of 194.23 kJ/mol and diffusion pre‐coefficient of 5 × 10−9 m2/s, indicating that the interaction is diffusion‐dependent. As the results showed, the interfacial area is comprised of Al alloy channels, Si precipitates, and AlN grains. Al‐Si transfer through the solid solution (Si3‐xAlxN4‐y) at the interface of Al alloy and β‐Si3N4 grains controls the kinetic of the interaction. When concentration of Al in solid solution exceeds a certain amount, it undergoes a topotactic phase transformation to form Al1‐xSixN1+y (viz., AlN). Next, the Al1‐xSixN1+y grains detach from the β‐Si3N4 grains and subsequently new Al‐Si3N4 interfaces are established. These interfaces repeat the interaction process, continuing until all the reactant is depleted. Thus, the interaction kinetics consist of a sequence of associated parabolic stages, precluding the observation of parabolic kinetics. [ABSTRACT FROM AUTHOR]