Development of B2 Shape Memory Intermetallics Beyond NiAl, CoNiAl and CoNiGa

Microstructure Formation in Cast TiZrHfCoNiCu and CoNiCuAlGaIn High Entropy Shape Memory Alloys: A Comparison

“…Crystallization of this composition resulted in the formation of a (Co31.7Ni26.8Cu8.5)67(Al22.1Ga10.3In0.6)33 phase surrounded preferentially by the (Co6.3Ni13.5Cu48.9)68.7(Al1.5Ga4.5In25.3)31.3 phase of Cu9In4 type. These findings are in agreement with the results [17]. In addition, small amounts of the (Co29.7Ni29.9Cu14.9)73.6(Al9.6Ga14.7In1.2)26.4 phase were observed, which could be distinguished from the previous one by SEM X-ray microanalysis.…”

“…In the as-cast state, it shows a B2 high temperature structure distorted similarly to TiZrHfCoNiCu and it also carries triclinic distortions into the tetragonal martensitic phase. TEM and DSC results clearly confirm the B2↔L1 0 type of martensitic transformation [17]. Thus, the formation of multi-component intermetallic compounds with a distorted B2 structure undergoing a martensitic transformation appears as a physical regularity, which is important for subsequent shape memory behavior.…”

“…This composition was chosen in the present study for further detailed microstructure examination because of the possibility to observe martensite crystal formation against the dendritic liquation background. Similarly, in Reference [17] the general composition of Co31.22Ni29.26Cu11.95Al16.64Ga10.39In0.55 has demonstrated high temperature martensitic transformation and, as a result, a certain amount of martensite crystals have been formed against the background of a strong dendritic liquation. In Figure 1b, it can be seen that crystallization of the non-stoichiometric Ni 67 Al 33 compound shows a two-stage behavior.…”

“…The width of the crystallization peak is also 2.5 times larger for the non-equiatomic compound (164 K, Figure 2a) than for TiNi (65 K Figures 1a and 2a), while in the case of the equiatomic one it is just 1.8 times as wide. Further cooling in the already solid state below 1090 K results in two overlapping peaks starting at 1006 K and 987 K, which have a width together of about 50 K. In the case of non-stoichiometric Co31.22Ni29.26Cu11.95Al16.64Ga10.39In0.55 deviation from the initial composition resulted not only in the appearance of a martensitic transformation [17] but also in an increase in crystallization temperature from 1500 K in Co22.33Ni22.33Cu22.33Al11Ga11In11 ( Figure 1b) to 1580 K ( Figure 2b). In Figure 2b, the width of the peak is more narrow (115 K) than for Co22.33Ni22.33Cu22.33Al11Ga11In11 (174 K, Figure 1b).…”

“…In this context, it was shown that for the TiZrHfCoNiCu system a B2↔B19' type of martensite transformation takes place [14][15][16]. Recently, an extra six component system CoNiCuAlGaIn, which emulates the B2 NiAl intermetallic compound was introduced [17]. In the as-cast state, it shows a B2 high temperature structure distorted similarly to TiZrHfCoNiCu and it also carries triclinic distortions into the tetragonal martensitic phase.…”