Produção e caracterização de ligas do sistema Al-Co-Fe- Cr e aplicações como recobrimentos para barreiras térmicas
Abstract
Since the discovery of the quasicrystalline alloys by D. Schechtamn in 1984,
many research has been done in terms of coating application of these materials
and their intermetallic approximants due to their physical and transport
properties as: high hardness, low friction coefficient, low superficial adhesion
energy, high oxidation resistance and low thermal conductivity. The low thermal
conductivity combined with the thermal expansion in the same range of the
usual metallic materials used as substrates in coatings make these alloys as
potential substitutes for the traditional ceramics thermal barrier coatings. The
alloy Al71Co13Fe8Cr8 has been studied in terms of thermal barrier applications.
This alloy presents interesting properties and characteristics for this application.
However, the information about this alloy on the literature is scarce and
contradictory. In this sense, in the present work, the Al71Co13Fe8Cr8 alloy was
selected for coating fabrication aiming to obtain a consistent structural
characterization of this alloy. Results show that the Al71Co13Fe8Cr8 alloy is not a
quasicrystalline forming composition. It is actually composed by two
intermetallic phases, one hexagonal and the other monoclic, Al5Co2 and Al13Co4
respectively, which are approximant phases of the decagonal QC with the
interesting physical and transport properties presented by the quasicrystalline
phase. The coatings were also studied in terms of the interdifusion phenomena
between the coating and a steel substrate at high temperatures. Alloys around
the Al71Co13Fe8Cr8 compositional range were also fabricated in order to
evaluate the phase formation on the aluminum rich region of the Al-Co-Fe-Cr
system. Several intermetallic phases were observed, most of them quaternary
extensions of Al-Co intermetallic phases. A quasicrystalline phase was also
observed in one of the studied compositions.