• Heilmaier, Martin
• Blankenburg, Malte
• Gombola, Camelia
• Kauffmann, Alexander
• Geramifard, Golnar

Abstract

Apart from the reported transition from the fibrous morphology in NiAl-34Cr to lamellae byadding 0.6 at.% Mo, further morphology transformations along the eutectic trough in the NiAl-(Cr,Mo) alloys were observed. Compositions with at least 10.3 at.% Cr have lamellar morphology while the first tendency to fiber formation was found at 9.6 at.% Cr. There is a compositional range, where both lamellae and fibers are present in the microstructure and a further decrease in Cr to1.8at.% Cr results in fully fibrous morphology. Alongside these morphology changes of the (Cr,Mo)$_{ss}$ reinforcing phase, its volume fraction was found to be from 41 to 11 vol.% confirming the trendpredicted by the CALPHAD approach. For mixed morphologies in-situ X-ray diraction experiments performed between room and liquidus temperature accompanied by EDX measurements reveal the formation of a gradient in composition for the solid solution. A new Mo-rich NiAl-9.6Cr-10.3Mo alloy clearly shows this effect in the as-cast state. Moreover, crystallographic orientation examination yields two different types of colonies in this composition. In the first colony type, the orientationrelationship between NiAl matrix and (Cr,Mo)$_{ss}$ reinforcing phase was (100)$_{NiAl}$||(100)$_{Cr,Mo}$ and $ 100 {NiAl}$||$ 100_{Cr,Mo}$. An orientation relationship described by a rotation of almost 60 about $ 111 $ was found in the second colony type. In both cases, no distinct crystallographic plane as phase boundary was observed.

Topics

• impedance spectroscopy
• morphology
• phase
• x-ray diffraction
• experiment
• Energy-dispersive X-ray spectroscopy
• lamellae
• phase boundary
• CALPHAD