A case study of complex metallic alloy phases: structure and disorder phenomena of Mg-Pd compounds

• Published in: Philosophical magazine (2003. Print) Vol. 86; no. 3-5; pp. 427 - 433
• Main Authors: Makongo, J. P. A., Prots, Y., Burkhardt, U., Niewa, R., Kudla, C., Kreiner, G.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Abingdon Taylor & Francis Group 21.01.2006; Taylor and Francis; Taylor & Francis
• Subjects: Alloys; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Quasicrystals; Semi-periodic solids; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Phase diagrams; Disordered alloy; Palladium alloys; Magnesium alloys; Chemical composition; Peritectic reactions; Phase stability; Order disorder; Quasicrystals; Atomic structure; Icosahedral phase; Crystal structure; Physical Sciences
• ISSN: 1478-6435; 1478-6443; 1478-6433
• DOI: 10.1080/14786430500269212

In order to achieve a deeper insight into the relation between the homogeneity range, crystal structure and disorder phenomena of complex metallic alloy phases (CMAs) we have redetermined the Mg-Pd phase diagram in the range 60-100 at.% Mg. The existence of the intermediate phases Mg 6 Pd (β), Mg 57 Pd 13 (γ), Mg 56.4 Pd 13.5 (δ), Mg 306 Pd 77 (ε), Mg 78.5 Pd 21.5 (ζ), Mg 3 Pd (η), Mg 5 Pd 2 (θ) and Mg 2 Pd (ι) has been reconfirmed. The first five of these are CMAs. The β phase melts congruently whereas the CMAs γ, δ, ε and ζ form in a cascade of peritectoid and peritectic reactions in a narrow window of approximately 30°C and 3 at.%. It is assumed that the stability of the Mackay icosahedron plays an important role in the phase formation of these CMAs. However, the β phase reveals an intricate pattern of disorder at the atomic positions of the Mackay icosahedron. Therefore, the concept of the stability of the Mackay cluster should be used only as a rule of thumb.