Microstructure and mechanical properties of Nb4AlC3 MAX phase synthesized by reactive hot pressing

Abstract

The present study aims at synthesizing the Nb₄AlC₃ MAX phase by reactive hot pressing using Nb:Al:NbC as starting materials. In order to identify the reaction path, interrupted tests at intermediate temperatures were performed as well as differential thermal analyses (DTA) of powders. Coupling between DTA and XRD data and SEM/EDS analyses of the samples allows a better understanding of the reaction mechanisms. Pure and fully dense Nb₄AlC₃ samples were obtained and characterized for the first time by EBSD and SEM to assess, using an original method, grain size and microstructure. For instance, in the present study, an average grain length of 5–7 µm was obtained.

Standard mechanical characterizations showed interesting properties: K_Ic≈ 6 MPa m^1/2, E ≈ 350 GPa and α ≈ 7.10⁻⁶ °C⁻¹. Oxidation performance of Nb₄AlC₃ was evaluated at 1100 °C under cyclic conditions. A breakaway regime was instantaneously established for this condition, thus demonstrating the impossibility of using such an unprotected material for structural applications at high temperature in air environment.