Ep. George et al., CHARACTERIZATION, PROCESSING, AND ALLOY DESIGN OF NIAL-BASED SHAPE-MEMORY ALLOYS (REPRINTED FROM MATERIALS CHARACTERIZATION, VOL 32, PG 139-160, 1994), Materials characterization, 39(2-5), 1997, pp. 665-686
The microstructures and phase transformations in binary Ni-Al, ternary
Ni-Al-Fe, and quaternary Ni-Al-Fe-Mn shape memory alloys (SMAs) were
investigated by light and electron microscopy, electron and X-ray diff
raction, and differential scanning calorimetry. The effects of alloyin
g additions (B, Fe, and Mn) on martensite stability, shape recovery, a
nd tensile ductility were also studied. NiAl-based SMAs can be made du
ctile by alloying with B for enhanced grain boundary cohesion and Fe f
or improved bulk properties. Iron has the undesirable effect that it d
ecreases the martensite --> austenite transformation temperatures (A(p
)) Fortunately, A(p) can be increased by decreasing the ''equivalent''
Al content of the alloy. In this way, a high A(p) temperature of simi
lar to 190 degrees C has been obtained without sacrificing ductility.
Recoverable strains of similar to 0.7% have been obtained in a Ni-Al-F
e alloy with A(p) temperature of similar to 140 degrees C. Manganese a
dditions (2-10%) lower A(p), degrade hot workability, and decrease roo
m temperature ductility. Good-quality, ductile SMA ribbons have been p
roduced by melt spinning. However, additional alloy design is required
to suppress the aging-induced embrittlement caused by Ni5Al3 formatio
n.