Cu-al-mn Shape Memory Alloys The Structure And Thermal Stability

Two kinds of Cu-Al-Mn shape memory alloys (SMA) were designed and their structure and thermostability have been studied by means of electrical resistance vs temperature (P -T) measurement, shape memory effect determination, X-ray diffraction, optical and TEM microscopy. Results show that, compared with traditional Cu-base SMA, the Cu-ll.9Al-2.5Mn (wt%) and Cu-12.4Al-3.1Mn (wt%) alloys with their compositions close to that of eutectoid have desirable thermostability (including their high resistance to martensite stabilization, martensite and parent phase decomposition).Martensite structure of Cu-11.9Al-2.5Mn(wt%) SMA as-quenched is M18R and its lattice constants are as follows: a=0.4475nm, b=0.5229nm. c=3.815nm. 3=89.6?;And the distributions of basal atoms are: I - 3/25Mn+22/25Cu, II- 3/25Al+22/25Cu, III-8/25Al-t-7/25Cu. Its excellent thermostability comes from two factors: one is that its stable 3 i parent phase is difficult to decompose at work temperature, the other is that its martensite structure approximates N18R ( 3=89.6?) which restrains the process of M18R棔 N18R and the tendency of martensite stabilization and decomposition.Martensite structure of Cu-12.4Al-3.1Mn (wt%) SMA as-quenched is M2H and its lattice constants are as follows: a=0.4459nm, b=0.5279nm, c=0.4241nm, 3=88.6?; And the distributions of basal atoms are: I - Al, II- Cu, III- 22/25Cu+3/25Mn. Its martensite transformation temperature increases and structure changes from 2H to M18R due to the deposition of Y 2 phase in early aging, which makes parent phase lack of Al and decline of electron concentration. The alloy still has good thermoelasticity after aging at 400'C for 96h with reverse martensite transformation up to 90%.