Shape memory alloy with ductility and a process of making the same

#A shape memory alloy with ductility and a making process of the same Field of the invention The present invention relates to a Ti—Ni shape memory alloy and a making process of the same. More particularly, the present invention relates to a new Ti—Ni shape memory alloy which is excellent in mechanical properties with which the Ti—Ni shape memory alloy can be put to practical use as an actuator for micro machines such as a micro valve. The present invention also relates to a making process of the Ti—Ni shape memory alloy.

#A Ti—Ni alloy has been known as a shape memory alloy. A making process in which the Ti—Ni shape memory alloy is produced as a thin film has also been known. Besides, it has been known that a Ti—Ni alloy with excessive Ti, the amount of which is 50˜66 atomic % in a composition, has higher R-phase transformation temperature than those of Ti—Ni alloys either with excessive Ni in a composition or with a composition in which Ti and Ni have an equal atomic ratio.

#While these Ti—Ni alloys with lower transformation temperature has been put to practical use, the Ti—Ni alloy with excessive Ti has so poor mechanical properties and is so brittle that, in fact, it has not been used so far.

#FIG. 1 is a photo showing a structure of a Ti—Ni alloy thin film obtained by annealing at 773K for 5 minutes;

#FIG. 2a is a photo showing a structure of a Ti—Ni alloy thin film obtained by annealing at 873K for 3 minutes;

#FIG. 2b is a photo showing a structure of a Ti—Ni alloy thin film obtained by annealing at 873K for an hour;

#The present invention provides a Ti—Ni shape memory alloy with ductility, which includes Ti of 50˜66 atomic % in a composition and in which precipitation of Ti2Ni phases at grain boundaries is suppressed. More particularly, the present invention provides a Ti—Ni shape memory alloy with ductility, which exhibits plastic strain of not less than 15% at room temperature.

#The present invention further provides a making process of a Ti—Ni shape memory alloy with ductility, which includes Ti of 50˜66 atomic % in a composition. The process comprises the steps of crystallizing an amorphous Ti—Ni alloy at 600˜900K for less than an hour and then cooling down to room temperature slowly in order to suppress precipitation of Ti2Ni phases at grain boundaries. More particularly, the present invention provides a making process in which the crystallization is conducted at 800˜900° C. for less than 10 minutes.

#Suppressing precipitation of Ti2Ni phases at grain boundaries remarkably improves mechanical properties of a Ti—Ni alloy with excessive Ti.