Oxidation and mechanical behavior of Al-containing MAX phase materials

Li, Xiaoqiang; Schwaiger, Ruth (Thesis advisor); Gonzalez-Julian, Jesus (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

MAX phase materials are promising for high temperature applications due to their unique combination of properties, bridging the gap between metals and ceramics. As the largest group of the MAX phase family, Al-containing MAX phase materials have attracted great attention for the application as structural materials for power generation systems considering their excellent oxidation resistance and mechanical properties. To ensure long-term operation and lifetime, the Al-containing MAX phase materials must maintain their mechanical stability even at elevated temperatures; in particular creep may lead to structure instability. Therefore, for a practical application-relevant design, Al-containing MAX phase materials with excellent oxidation resistance and mechanical properties was in the focus of the current research. In this research work, nitride Ti2AlN, carbide Ti2AlC and Ti3AlC2 were selected as most suitable representatives of Al-containing MAX phases. In particular, aiming towards an advanced characterization of different compositions, microstructures and potential associated effects on the mechanical properties, Ti2AlN, Ti2AlC and Ti3AlC2 with different microstructures were produced for further analysis. For a reliable application, a comprehensive understanding of the mechanical behavior, and in particular of the anisotropic properties is needed. Thus, nanoindentation and electron-backscatter diffraction analysis were combined to correlate elastic modulus and hardness of Ti2AlN to the crystallographic orientation. In addition, two different modeling approaches were used to better understand, validate, and as a basis for the prediction of the anisotropic mechanical behavior of MAX phase materials. Based on the models, the mechanical anisotropy of Ti2AlC and Ti3AlC2 was calculated. In addition, the elastic modulus and hardness of all the materials were determined via micro-indentation testing at room temperature. Since the abrasive behavior and the oxidation resistance are important in a number of applications, sandblasting tests were carried out and the oxidation behaviors of the Al-containing MAX phase materials were characterized. Aiming towards an understanding and improvement for long-term high temperature stability, compressive creep tests in air on bulk Ti2AlN, Ti2AlC and Ti3AlC2 were carried out. Under those testing conditions, the creep behavior of bulk Ti2AlN, Ti2AlC and Ti3AlC2 appears to be controlled by grain boundary sliding. Texturing within Ti2AlC and Ti3AlC2 has a negligible influence on the creep behavior.Overall, the investigation of the fabrication, the anisotropic mechanical properties, the abrasive resistance, the oxidation behavior as well as the high temperature creep deformation of Al-containing MAX phase materials contributes to our understanding of the properties of the materials and provides a guideline for the design and development of the MAX phase materials as structural materials in various application fields.

Institutions

• Chair of Materials in Energy Engineering (Forschungszentrum Jülich) [413410]
• Division of Materials Science and Engineering [520000]
• Chair of Ceramics and Institute of Mineral Engineering [524110]