Nano-Indentation Determination Of The Mechanical Properties Of The Oxide Scale Formed By High Temperature Oxidation Of Ni-Based Superalloys

摘要

Nano-indentation test was used to determine the hardness and the Young's modulus of the thermally grown oxide (TGO) formed during the high temperature isothermal oxidation of single crystal Ni-based superalloy AM1 [1]. Our previous work has shown that scratch test could be used to determine a quantitative correlation between the adherence of oxide scales formed after short term isothermal oxidation and the long term cyclic oxidation behavior of materials. Nevertheless, the values of the work of adhesion calculated using the models based on the energy balance approach during the scratch test or other testing techniques were strongly affected by the magnitude of Young's modulus of the oxide scale [2]. Variation in Young's modulus of 50 GPa resulted in errors in work of adhesion values of 10%. Usually the theoretical properties of a bulk alumina were used to assess the adhesion energy of the multi-layered TGO on superalloys. Developing an improved model of adhesion energy quantification requires the knowledge of the real mechanical behavior of the studied system. In the present work, multiple nano-indentation tests at different loads were performed on polished cross-section of AM1 after 100 h isothermal oxidation at 1100°C.The load-displacement curves were analysed to get maximum information on the mechanical behavior of the oxide scale on AM1 alloy. The effect of applied load on the measured values of hardness and Young's modulus of both substrate and oxide was observed. The measured values were used to correct the values of the work of adhesion obtained thanks to the scratch tests.