EFFECTS OF BORON ADDITION ON MICROSTRUCTURE AND MECHANICAL-PROPERTIESOF TI-TD-NI HIGH-TEMPERATURE SHAPE-MEMORY ALLOYS

The application of Ti-Pd-Ni high-temperature shape memory alloys to pr actical use is restricted due to their low critical stress for slip at high temperatures. About 0.2 at.% boron was added to a Ti50Pd30Ni20 a lloy to improve its high-temperature mechanical properties including h igh-temperature shape memory characteristics. The influence of boron o n martensitic transformation temperatures, microstructure and high-tem perature mechanical properties was studied. The results show that TiB2 precipitates with an average size larger than 1 mu m are produced in Ti50Pd30Ni19.8B0.2 alloy due to proper heat treatments described in th e text. These TiB2 precipitates seem to be distributed within grains, rather than to segregate to grain boundaries. The addition of boron is beneficial to high-temperature ductility of Ti-Pd-Ni alloy. The addit ion of boron has no noticeable influence on high-temperature shape mem ory characteristics of Ti50Pd30Ni20 alloy, and the reason for this is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.