Abstract
A series of NiAl-Cr-Mo systems were produced and assessed as far as their microstructure and their sliding wear resistance is concerned. The NiAl content was kept constant and seven compositions of Cr-Mo were tested, namely, 40Cr-0Mo, 30Cr-10Mo, 25Cr-15Mo, 20Cr-20Mo, 15Cr-25Mo, 10Cr-30Mo, and 0Cr-40Mo. It was observed that most of the systems contained primary phases, eutectic microconstituents, and, occasionally, intermetallic phases as the outcome of peritectic reactions. The extent and the nature of all these microstructural features was proved to be affected by the Cr/Mo relative ratio, and an attempt was conducted in order to explain the microstructural features based on solidification and other related phenomena. It was observed that the increase of the relative Mo/Cr ratio led to a significant restriction/elimination of the eutectic microconstituent. The sliding wear response of the produced system seems to diverge from the classical sliding wear laws of Archard and is based on multiple factors such as the nature of the oxide phases being formed upon sliding, the nature and the extend of the intermetallic phases being formed upon solidification, and the integrity and rigidity of the primary phases—last to solidify areas interfacial region and the factors that may influence this integrity.
Highlights
During the last decades, NiAl-based alloys have been considered as potential candidates for high-temperature applications due to their enhanced properties at such extreme servicing conditions and possible substitutes for Ni-based superalloys [1]
It is important at this stage to comment on the predictions of these models
Half of the systems show values of ∆Smix outside the range proposed for single-phase solid solution (30Cr-10Mo, 10Cr-30Mo, 0Cr-40Mo, 40Cr-0Mo, respectively), which is a strong indication for potential phase segregation in their case
Summary
NiAl-based alloys have been considered as potential candidates for high-temperature applications due to their enhanced properties at such extreme servicing conditions and possible substitutes for Ni-based superalloys [1]. The brittle nature of the NiAl intermetallic phase and their limited ductility, early enough, raised question on their possible modification so that their toughness and ductility can be improved Towards this direction, research efforts were focused on the addition of refractory metals (Cr, Mo, Ta, etc.) within the NiAl matrix in order to overcome these drawbacks and their properties were, in most of the cases, evaluated in depth [2,3,4,5,6]. The potential substitution of Ni-based super-alloys, was not the only driving force for the development of NiAl-based system. The immergence of the new class of metallic materials, high-entropy alloys (HEAs), revealed another direction of the importance of the
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