Functional multi-layer nitride coatings for high temperature solar selective applications

• Applicability of the CAPVD technique for optical coatings generation is highlighted.
• A new high temperature stable solar selective coating has been demonstrated.
• The TiAlCrN/TiAlN/AlSiN coating is found to be optically stable even at 700 °C.
• The observed high stability is attributed to the nature of nitrides chosen.

A solar-selective functional multi-layered coating for high temperature applications has been developed on copper and stainless steel substrates using an industrially viable cathodic arc physical vapor deposition technique. The selective coating was formulated in such a way that the constituent functional layers are mainly high temperature stable nitride materials which are also hard and capable of imparting protection against wear. A multi-layer structure comprising TiAlCrN as IR reflector, TiAlN as absorber and AlSiN as anti-reflective layer was found to exhibit promising results. The stacking of these three materials with appropriate thickness in a systematic manner, viz. Cu/TiAlCrN/TiAlN/AlSiN with high Cr and Al contents in TiAlCrN and TiAlN layers, respectively, yielded high absorptivity (αAM1.5=0.91) and low emissivity (ε=0.07) values corresponding to an attractive optical selectivity (α/ε) of 13. The open air high temperature performance of the optimized multi-layer structure was also investigated in the temperature range 27–700 °C and the stability of the coatings at high temperatures with respect to optical properties was established.