Mechanical fatigue of Cu-based shape memory alloy after different heat treatment

Shape memory alloys, Part I: General properties and modeling of single crystals

“…Due to the lower percentage of martensitic transformation associated with elevated test temperatures, a higher fatigue life is observed. NiTi alloys Melton and Mercier (1979b) 10 3 6 N f 6 10 4 (5% P e t P 4%) Ni50.1Ti49.9 and Ni50.3Ti49.7; pseudoelastic cycling under stress control; different alloy compositions and applied heat treatments result in different fatigue life McNichols et al (1981) 7 · 10 3 6 N f 6 2 · 10 5 (8.3% P e t P 4.4%) Ni50Ti50; thermal cycling; strong linear correlation between the cycles to failure and the applied cyclic strain amplitude Miyazaki (1990) and Miyazaki et al (1999) 10 2 6 N f 6 10 5 (3.5% P e t P 2%) Ni50Ti50 and Ti50Ni40Cu10; pseudoelastic cycling under strain control; maximum recovery strain and stress hysteresis decrease with increasing Cu content; fatigue life for both alloys increases with decreasing testing temperature Bigeon and Morin (1996) 10 6 N f 6 10 4 (50 MPa 6 r 6 800 MPa) Ti48.8Ni45.2Cu6; thermal cycling; reduction of the applied stress rapidly increases the fatigue life Tobushi et al (1997Tobushi et al ( , 1998 10 2 6 N f 6 10 4 (1.4% 6 e t 6 3%) Ni50.2Ti49.8; pseudoelastic cycling under strain control; fatigue life increases with decrease of testing temperatures; longer fatigue life: 10 5 6 N f 6 10 7 (0.5% 6 e t 6 1%) is observed for the R-phase transformation Lagoudas et al (2000) and Bertacchini et al (2003) 10 3 6 N f 6 5 · 10 4 (54 MPa 6 r < 247 MPa) Ni50Ti40Cu10; thermal cycling; transformation strain is in the range 2% 6 e t 6 4%; fatigue life increases for smaller transformation strains and stress levels; heat treatments also influence the fatigue life Cu based alloys Melton and Mercier (1979a) 5 · 10 4 6 N f 6 10 5 Cu68.1Znl8.2Al13.7; pseudoelastic cycling under strain control; increasing M s induces longer fatigue life; stress-induced range used is 30 MPa 6 r 6 100 MPa Sure and Brown (1985) 3 · 10 3 6 N f 6 5 · 10 4 (0.8% P e t P 0.5%) Cu69.2Al27.6Ni3.2; pseudoelastic cycling under stress control; stress-induced range used is 15 MPa 6 r 6 280 MPa; grain size growth reduces fatigue: for grain size of %150 lm, 3 · 10 3 6 N f 6 5 · 10 3 , while for grain size %20 lm the number of cycles to failure is N f % 5 · 10 4 Morin and Trivero (1994) N f % 10 4 (r % 100 MPa) Cu69.5Al26.8Ni3.7; thermal cycling; e t % 2.5%; very low influence of thermal cycling on SME and transformation temperatures; significant creep-like deformation observed during the first 1000 cycles Bigeon and Morin (1996) N f 6 10 3 (10 MPa 6 r 6 200 MPa) Cu75Zn11Al14; thermal cycling; transformation strain range is e t 6 7%; reduction of the applied stress rapidly increases the fatigue life Lu et al (1996) 4 · 10 3 6 N f 6 2.1 · 10 4 Cu77.5Zn17.5Al5; pseudoelastic cycling under strain control; fatigue life decreases for higher annealing temperatures, while slower cooling rates increase it; pre-straining structural elements impacts the fatigue life…”

“…Cooling rates can also affect the fatigue life. Methods such as step quenching (Lu et al, 1996) have been shown to increase the fatigue life. Thermally induced transformation fatigue life can be increased by lowering the applied stress level (Bigeon and Morin, 1996).…”