Annealing of nickel/titanium alloys

Abstract

Abstract 1461202 Annealing nickel-titanium alloys TEXAS INSTRUMENTS Inc 10 Dec 1974 [21 Dec 1973] 53344/74 Headings C7A and C7N An alloy containing by 50-58 wt per cent Ni and balance Ti is maintained under a tensile stress of 30,000-100,000 p.s.i. while it is annealed at a temperature above (preferably about 50‹C above) the temperature at which a first diffusional phase transformation occurs above the martensitic transformation range, that limiting temperature being identified by the incidence of a negative slope in the graph of electrical resistivity v. temperature. The alloy may be in wire form which is passed continuously through a hot zone. The process both increases tensile strength and reduces the tendency to relaxation on cycling through the martensitic transformation. The product may have a tensile strength exceeding 175,000 p.s.i., martensitic elongation activity of at least 2 per cent under a tensile stress greater than 100,000 p.s.i., and is resistant to fatigue failure for #10<SP>6</SP> cycles through the martensitic transformation under a stress such that the activity is 2 per cent. As exemplified a 54.3 per cent Ni alloy showed a first transformation temperature of 375‹C and was annealed at 425‹C under 35,000 p.s.i. stress.

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