Effect of site occupation on thermal and mechanical properties of ternary alloyed Mo5Si3

The fundamental thermophysical properties of Mo5Si3 have been investigated. The pronounced mismatch in the coefficient of thermal expansion (CTE) between the c- and a-directions of monolithic Mo5Si3 was reduced significantly by alloying additions. 25 at.% Cr reduced the CTE-mismatch to 1.45 in Mo3Cr2Si3, while 25 at.% Ti resulted in a mismatch of 1.32. Rietveld refinement of neutron powder diffraction data of the studied compounds reveals that Cr, having a smaller radius than Mo, has preference for the 4b chain sites of the D8(m) unit cell of Mo5Si3. In contrast, Ti atoms, being larger than Mo, occupy almost entirely the l6k sites in the unit cell interior. Compression tests of cast Mo5Si3 at 1573 K indicate that 25% Ti or Nb additions both result in brittle fracture, whereas Mo5Si3 containing 25% Cr deforms plastically. 25% Cr additions decreases the yield strength to approximately half of that of monolithic Mo5Si3 at 1573 K. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved