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Abstract
The effect of the elemental composition of AlxSi1−xN coatings deposited on Cu substrates by magnetron sputtering on their structure, mechanical properties and thermal cycling performance is studied. The coatings with Al-Si-N solid solution, two-phase (AlxSi1−xN nanocrystallites embedded in the SixNy tissue phase) and amorphous structure were obtained by varying Al/Si ratio. It is shown that polycrystalline coatings with a low Si content (Al0.88Si0.12N) are characterized by the highest thermal cycling resistance. While the coatings with a high and intermediate Si content (Al0.11Si0.89N and Al0.74Si0.26N) were subjected to cracking and spallation after the first cycle of annealing at a temperature of 1000 °C, delamination of the Al0.88Si0.12N coating was observed after 25 annealing cycles. The Al0.88Si0.12N coating also exhibited the best barrier performance against copper diffusion from the substrate. The effect of thermal stresses on the diffusion barrier performance of the coatings against copper diffusion is discussed.
Highlights
Due to their high thermal conductivity and excellent corrosion resistance, Cu and its alloys are extensively used in many heat exchange applications
Rapid degradation of the coating was due to tensile thermal stresses arising on heating owing to difference in coefficients of thermal expansion (CTEs) of the coating and the substrate as well as to changes in elemental and phase compositions of the coating caused by copper diffusion from the substrate
The coating with a low Si content (Al0.88 Si0.12 N), the main phase of which was polycrystalline AlN, was characterized by the highest thermal cycling resistance, which can be attributed to its rather low elastic modulus that ensured a substantial decrease in the thermal strain and stress
Summary
Due to their high thermal conductivity and excellent corrosion resistance, Cu and its alloys are extensively used in many heat exchange applications. Copper is commonly utilized as a substrate for solar selective absorbers in solar thermal collectors [1,2], while Cu alloys are widely used as combustion chamber liner materials in rocket engines [3]. During operation in these applications, copper components suffer from extremely high thermal loads. Cu atoms penetrate through above layers and react with oxygen to form copper oxide hillocks on the surface [1,2] This mechanism leads to material depletion and the formation of Kirkendall voids in the copper substrate causing porosity and loss of strength [1]. Protective barrier coatings with high thermal stability and oxidation
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