Digital Repository, CONVEGNO IGF XXII ROMA 2013

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Fracture behaviour of cast TiAl based intermetallic alloys
A. Brotzu, F. Felli, D. Pilone

Last modified: 2013-06-27


The γ -TiAl based intermetallic alloys have received considerable attention as candidate materials
for high-temperature aerospace applications, power generation and automotive industry, with the efforts being
directed toward the replacement of Ni-based superalloys in many interesting applications. In fact TiAl-based
alloys’ density is about 4 g/cm3 which is about half of that of commonly used Ni-based superalloys, and
therefore these alloys have attracted broad attention as potential candidate for high-temperature structural
applications in the fields for example of turbocharger manufacture. Specific composition/microstructure
combinations are believed to be capable of improving mechanical properties while maintaining satisfactory
oxidation resistance, creep resistance and high temperature strength for targeted applications.
Different casting methods such as conventional sand casting, investment casting, low pressure casting,
centrifugal casting, shell mould casting have been used for producing TiAl based alloys.
In our experimental work specimens were produced by means of centrifugal casting, the main advantage of this
method being the production of castings completely free from any porosity.
Tests carried out on several samples characterized 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 cracks
initiation and growth have been analysed in order to identify the factors causing these very high residual stresses
that often produce explosive crack propagation throughout the casting.

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