This document is the deliverable D1.1 of the project POLYPHEM. It is planned in the framework of the Work Package 01 (R&D ON SOLAR RECEIVER). Task 1.1 of the POLYPHEM project deals firstly with the choice of a more competitive metallic alloy than the reference one, the alloy 600, in order to manufacture the solar receiver modules, more precisely, the environment protective layer. Secondly, the mechanical properties and microstructure of the best alloy and the reference one are examined using representative mock-ups. This deliverable presents the main results of the POLYPHEM Task 1.1.