Anisotropic thermal lattice expansion and crystallographic structure of strontium aluminide within Al-10Sr alloy as measured by in-situ neutron diffraction

Abstract The aluminium strontium master alloy Al-10Sr has been investigated by in-situ neutron diffraction upon a heating-cooling cycle, revealing composition, crystallographic structure, lattice evolution and linear thermal expansion coefficients. Expansion of the Al matrix between [23.5 … 26.7]·10−6 K−1 depends on temperature and fits well to the literature values, extrapolating to higher temperature at 800 K. Thermal expansion is highly anisotropic for tetragonal Al4Sr by a factor of 1.86 with values of 20.8 and 11.1·10−6 K−1 in a and c-axis. The even larger discrepancy to the Al matrix is prone to residual intergranular phase stresses explaining the brittleness of such composite material. Upon first heating, recovery of the initially plastically deformed material is observed until 600 K and 700 K, for Al4Sr and Al. Rietveld analysis refines the 4e Wyckoff positions of the I 4/m m m crystal structure to z = 0.39 revealing that local tetrahedrons are regular while local hexagons are stretched, in contrast to literature. Its lattice parameters report to aI = 4.44240(48) A, cI = 11.0836(15) A at 300 K. Furthermore, the manuscript demonstrates full technical analysis of the neutron data. Findings feed into data bases and an outlook for improving mechanical properties of Al4Sr composites is given.