Papers by Keyword: Cu-Al-Mn

Abstract: The effect of ageing temperature on damping capacity of the Cu-20.4Al-8.7Mn alloy at room temperature was investigated by internal friction measurements. The results indicated that damping capacity of the alloy exhibits a non-monotonous changing trend with ageing temperature. Ageing at lower temperature of less than 150oC, damping capacity rapidly increses even up to maximum of 0.01 with the increasing ageing temperature, the reason of which should relate with the increased amount of twin boundaries and phase interfaces between martensites due to the thinning and splitting of martensitic plates, whereas when the ageing temperature exceeds 150oC, the damping capacity trends to steeply decrease as the ageing temperature increases until close to a constant in last corresponding to the ageing at higher temperature due to the occurrence and complete finish of transformation of martensites to austenites.

Abstract: The ductility of Cu – Al – Mn shape memory alloys at room temperature depends on the aluminium content. High aluminium contents make Cu – Al – Mn very brittle and unsuitable for plastic shaping. Two Cu – Al – Mn shape memory alloys were investigated. The ductile alloy CuAl7.8Mn9.5 (all contents in wt. %) could be easily cold rolled by 86 %. The alloy CuAl12Mn4.3 could be cold rolled by only 12 - 14 %. The amplitude dependence of damping of austenitic specimens increased with increasing degree of cold work, whereas the damping of martensiticaustenitic specimens decreased. These observations can be explained by the creation of stress induced martensite and therefore by new moveable interfaces like phase- and twin boundaries, which contribute to damping. Plastic deformation increases the dislocation density, too. Both the increase of dislocation density and the increase of martensite content can lead to a decrease of damping mainly for high deformation degrees. Same shape memory alloys have shown negligible hardness increase during cold rolling, too. This behaviour, untypical for metals, can be explained by the generation of new martensite and by the fact that the hardness of martensite is smaller than the hardness of austenite. Some aging effects of the specimen after cold rolling, which lead to decrease of damping, were detected. This can be explained by pinning of moveable interfaces by point defects and/or retransformation of martensite into austenite.

Abstract: The mechanical and fatigue properties of Cu - Al - Mn shape memory alloys with different phase fractions at room temperature were investigated. The specimens with different chemical compositions (Al: 8.9 - 12.5 wt. % and Mn: 3.3 - 9.3 wt. %) were tensile loaded with 10-3 s-1 tensile strain rate. Austenitic specimens have the highest tensile strength and fracture strain. Yield strength, tensile strength and elongation of martensitic alloys were lower compared with austenitic alloys. Fracture strain of martensitic alloys depend only little on the chemical composition. Specimens of martensitic, austenitic and three different multiple phase specimens were tested in the high cycle fatigue range at room temperature. The Woehler curves for multiple specimens depend on the phase fraction at testing temperatures. Different elements as Co, Ni, Fe and Si were alloyed to CuAl11.6Mn5. All decreased the ductility of the specimens, and their fatigue properties. Maxima could be detected in the strain amplitude dependence of damping for multiple phase specimen. These maximum are shifted to lower damping and to higher strains with increasing number of mechanical cycles, compared to the as cast condition for not cycled specimen. The strain amplitude dependence of damping in martensitic and austenitic Cu – Al – Mn shape memory alloys does not change much during mechanical cycling.

Abstract: The influence of thermal cycling between - 196 °C and 200 °C and equivalent heat treatment at 200 °C on the amplitude dependence of internal friction at room temperature has been studied in as cast Cu – Al - Mn shape memory alloys with different chemical compositions. Using X-ray diffraction one composition was found to be austenitic and two others martensitic with two martensite types (2H and 18R) at room temperature. All specimens were thermally cycled for 100 times. During one thermal cycle the specimen underwent altogether two phase transformations one in each direction. Thermal cycling causes microstructural changes in the specimens due to atomic reordering, thermal stresses, which are generated in the martensitic state due to the anisotropy of thermal expansion, or due to the nucleation and propagation of interphase cracks in parent phase. During repeated thermal cycling the transition peaks obtained in mechanical spectroscopy became narrower due to an enduring change of the microstructure and annealing effect at 200 °C. To compare between the effects of thermal cycling and heat treatment one martensitic specimen was annealed at 200 °C. For selected cycle numbers and heat treatment times the amplitude dependence of damping was measured at room temperature. The influence of thermal cycling of martensitic specimens on the damping level was found to be similar to the influence of heat treatment at 200 °C. It is most likely that the highest heat treatment temperature is more important for the amplitude dependence of damping than the temperature change during thermal cycling. Cracks due to thermal cycling were found in all cycled specimens. They have no significant effect on the amplitude dependence of damping of the martensitic samples, whereas some small influence could be observed in austenitic samples at room temperature.