Effects of the manufacturing process on fracture behaviour of cast TiAl intermetallic alloys

A. Brotzu, F. Felli, D. Pilone

Abstract


The ? -TiAl based intermetallic alloys are interesting candidate materials for high-temperature
applications with the efforts being directed toward the replacement of Ni-based superalloys. TiAl-based alloys
are characterised by a density (3.5-4 g/cm3) which is less than half of that of Ni-based superalloys, and therefore
these alloys have attracted broad attention as potential candidate for high-temperature structural applications.
Specific composition/microstructure combinations should be attained with the aim of obtaining good
mechanical properties while maintaining satisfactory oxidation resistance, creep resistance and high temperature
strength for targeted applications.
Different casting methods have been used for producing TiAl based alloys. In our experimental work,
specimens were produced by means of centrifugal casting. Tests carried out on several samples characterised by
different alloy compositions highlighted that solidification shrinkage and solid metal contraction during cooling
produce the development of relevant residual stresses that are sufficient to fracture the castings during cooling
or to produce a delayed fracture. In this work, crack initiation and growth have been analysed in order to
identify the factors causing the very high residual stresses that often produce explosive crack propagation
throughout the casting.


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DOI: http://dx.doi.org/10.3221%2FIGF-ESIS.27.08