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Laves phases in the Fe- and Cr-based ternary systems Fe/Cr-Al-Nb

Today there is an increasing economic and ecological need for the development of new structural materials for applications at high temperatures. Possible candidates for such materials are metallic alloys containing high-melting intermetallic phases which retain high strengths at high temperatures.

The ternary systems X-Al-Nb with X = Fe or Cr are among the potential candidates, where extended phase fields of intermetallic phases with high melting temperatures exist. The most striking intermetallic phase in this system is the Laves phase Nb(X,Al)2 which belongs to the largest class of intermetallic phases.

Microstructure of an as-cast, three-phase Al-Fe-Nb alloy consisting of primary NbAl3 surrounded by a two-phase eutectic Nb2Al + Nb(Fe,Al)2 Laves phase and a three-phase eutectic matrix NbAl3 + Nb2Al + Nb(Fe,Al)2.

A prerequisite for understanding the usually quite complex microstructures of the as-cast material and for controlling the casting process is a precise knowledge of the solidification behaviour of the ternary alloys. Therefore, the aim of the project was a detailed investigation of the liquidus surfaces and complete reaction schemes of the two ternary systems via a combination of experimental methods and thermodynamic modelling complementing each other. The work, which was funded by the Sino-German Center for Research Promotion, was performed in collaboration with Cuiyun He from the University of Nanning, Guangxi, China.

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