Topical Problems in Manufacturing Semi-Products (Bars and Wires) from TiNi-Based Shape-Memory Alloys

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

“…The purity of commercial titanium is appropriate for our study; it is not quite as good as that of our nickel pellets (Ti, >99.7 wt.%; C, 0.01 wt.%; O, 0.0281 wt.%; Fe, 0.02 wt.%; N, 0.011 wt.%; H, 0.0007 wt.%). Special care was taken to produce clean Ti-surfaces by grinding prior to melting (80 grid SiC emery paper) as was recommended in [22].…”

“…VIM in combination with graphite crucibles is attractive because (i) graphite crucibles can be easily handled, (ii) it is the least expensive method and (iii) provides alloys of excellent chemical homogeneity. It has been known for a long time that melting NiTi shape memory alloys in graphite crucibles results in increased carbon contents in the alloys [13][14][15][16][17][18][19][20][21][22]. The carbon in NiTi alloys forms TiC, increases the Ni-concentration [16,17] and thus results in a decrease of phase transition temperatures [11,12].…”

“…Melting processes have been reviewed on a number of occasions and especially vacuum induction melting (VIM) and vacuum arc melting (VAM) have been described in the literature [13][14][15][16][17][18][19][20][21][22]. Both processes are commercially exploited and ingots ranging from several grams to several thousand kilograms can be produced.…”