High quality vacuum induction melting of small quantities of NiTi shape memory alloys in graphite crucibles

• Published in: Journal of alloys and compounds Vol. 385; no. 1-2; pp. 214 - 223
• Main Authors: Frenzel, J., Zhang, Z., Neuking, K., Eggeler, G.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 28-12-2004; Elsevier
• Subjects: Exact sciences and technology; Graphite crucibles; Interdiffusion; Melting; NiTi shape memory alloys; Physics; TiC layer; Graphite crucibles; Interdiffusion; NiTi shape memory alloys; Melting; TiC layer; Nickel alloys; Electrical properties; Induction; Cracking; Carbon; Titanium alloys; Carbon content; Shape memory alloy; Graphite; Kinetics; Metallurgy; Interface reaction; Vacuum arcs; Melts; Ingot
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2004.05.002

Binary NiTi based shape memory alloys can be produced starting from the pure elements (Ni-pellets, Ti-rods) by using vacuum induction melting (VIM). VIM ingot metallurgy is known to produce materials with a good chemical homogeneity; it, moreover, is cheaper than vacuum arc melting (VAM) when small quantities of laboratory materials are needed. In a VIM procedure, graphite crucibles are attractive because they have appropriate electrical properties. For NiTi melting, graphite crucibles are interesting because they are reasonably priced and they show a good resistance against thermal cracking. On the other hand, it is well known that melting of Ti alloys in graphite crucibles is associated with a vigorous interface reaction. And the carbon concentration of NiTi alloys needs to be kept below a certain minimum in order to assure that the functional properties of the alloys meet the required targets. Therefore, it is important to minimize the carbon pick up of the melt. The present work presents experimental results and discusses thermodynamic and kinetic aspects of the reaction of NiTi melts with graphite crucibles; a method is suggested to keep the carbon dissolution into the melt at a minimum.