Thermoelastic martensite in an ausaged FeNiTiCo alloy

A thermoelastic martensite which is related to a shape memory effect has been observed mainly in nonferrous alloys such as Ti--Ni, Cu--Zn, Cu--Al--Ni. For ferrous alloys, only two alloys have been found to exhibit the thermoelastic martensite, i.e., one is an ordered Fe-- approx 25 at.%Pt (f.c.c. < - > b.c.t.) and the other is an Fe-- approx 30 at.%Pd (f.c.c. < - > f.c.t.). Based on the results of previous researches on Fe--Ni--C thin plate martensite and on Fe--Pt thermoelastic (thin plate) martensite, an Fe--Ni--Ti--Co alloy was selected as a candidate for new ferrous thermoelastic martensite and the possibility of thermoelastic transformation in this alloy system was examined. It was found that the martensite in properly ausaged Fe--33%Ni--4%Ti--10%Co alloy possesses all the characteristics of a thermo-elastic martensitic transformation, and exhibits a shape memory and a pseudoelastic behavior. The transformation behavior in this martensite is shown. This is the second ferrous alloy which undergoes the thermoelastic martensite during f.c.c. < - > b.c.t. transformation. 8 ref.--AA