Eutectics and peritectics in the solidification processing of Nb silicide based alloys
July 17-21, 2016
There is strong industrial preference for cast Nb silicide alloys, in particular for directionally solidified (DS) alloys, owing to familiarity of industry with production and use of cast Ni superalloys for more than 30 years.
Solidification processing of the new alloys can “control” their microstructures via the reactions L ® (Nb) + Nb3Si, L + bNb5Si3 ® Nb3Si, Nb3Si ® (Nb) + aNb5Si3 and L ® (Nb) + bNb5Si3, of which the former can be suppressed in favour of the latter that is metastable in the Nb-Si binary.
In the open literature the solidification processing of Nb silicide based alloys has attracted very little attention compared with their microstructures, mechanical properties and oxidation, owing to the difficulty of scaling up from small arc melted buttons and the limited availability of facilities for melting and casting ultra-high temperature alloys (most of the developmental alloys have Tliquidus > 2273 K) and for their secondary processing.
The presentation will discuss the above reactions in model Nb silicide based alloys with particular emphasis on the formation and stability of the Nb3Si and bNb5Si3. New data about the dependence of the formation of the Nb3Si on solidification conditions will be presented for the first time and discussed. The experimental data will be from cast and heat treated alloys that were prepared using arc and plasma melting and optical floating zone (OFZ) melting.
Conor McCaughey and Panos Tsakiropoulos, "Eutectics and peritectics in the solidification processing of Nb silicide based alloys" in "Beyond Nickel-Based Superalloys II", Chair: Dr Howard J. Stone, University of Cambridge, United Kingdom Co-Chairs: Prof Bernard P. Bewlay, General Electric Global Research, USA Prof Lesley A. Cornish, University of the Witwatersrand, South Africa Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/superalloys_ii/47