Anisotropic secondary phases in Mo(Si,Al)2 ceramics investigated by neutron diffraction

Mo(Si,Al) 2 ceramics offer improved oxidation resistance over MoSi 2 , enhancing performance in resistive heating elements. However, formation of the anisotropic secondary phase Mo 5 (Si,Al) 3 during processing also promotes crack formation. While coefficients of thermal expansion (CTE) data exist for the Mo(Si,Al) 2 matrix phase and Al-free Mo 5 Si 3 , it is unclear how Al-incorporation affects the thermal expansion behaviour of Mo 5 (Si,Al) 3 . In this work, high-temperature neutron diffraction was used to measure phase-specific anisotropic thermal expansion in Mo(Si,Al)₂ ceramics, with and without Al-addition. The Mo₅(Si,Al)₃ phase was confirmed to be anisotropic, independent of Al-content. This study provides the first CTE-data for Mo₅(Si,Al)₃ embedded in the matrix phase and with Al-addition, offering valuable insight for designing reliable heating elements for high-temperature industrial applications. Typical microstructure of Mo(Si,Al) 2 ceramics and the ratio of temperature dependent lattice parameters, c over a , illustrating the anisotropy of the Mo 5 (Si,Al) 3 secondary phase. • Neutron diffraction used to study Mo(Si,Al) 2 ceramics up to 1100 °C. • First coefficients of thermal expansion reported for Mo 5 (Si,Al) 3 embedded in a matrix phase. • Secondary Mo 5 (Si,Al) 3 phase shows strong anisotropy, unaffected by Al-substitution. • Thermal anisotropy of Mo 5 (Si,Al) 3 lower than literature due to matrix constraint effects.