Study On Internal Friction Of Cu-Al-Mn Shape Memory Alloys During Continuous Temperature Change

Cu-Al-Mn shape memory alloys have clear targeted application requirements in practical production applications.It is very important to understand and explore the effects of thermal treatment process.At the same time,exploring the influence of Al/Mn content on the microstructure and properties of Cu-Al-Mn alloy is of great significance to regulate the preparation process and optimize its comprehensive properties.The internal friction measurement method is very sensitive to the microstructure and phase transformation process of shape memory alloy,and is an important experimental method to study the evolution of shape memory alloy microstructure and damping ability.Therefore,in this paper,Cu-Al-Mn alloys of different compositions were prepared by vacuum arc melting method,and the internal friction behavior during the heating of Cu-Al-Mn shape memory alloys were systematically studied by means of internal friction measurement.In order to provide a reference for practical production applications,the mechanism of the formation of internal friction for Cu-Al-Mn alloy was clarified,and the effect of aging time,aging temperature,quenching medium and Al,Mn element content on the damping capacity of Cu-Al-Mn alloy was clarified.In the Cu-11Al-5Mn(wt.%)alloy heating internal friction test,four typical internal friction peaks were observed,namely P1,P2,P3 and P4 peak,of which P1,P2 and P4 peaks have heating rate and measurement frequency dependence,the height of the peaks increase with the increases of heating rate,and shifts towards high temperature,decrease with the increase of measurement frequency,and have typical phase transformation peak friction characteristics.P3 peaks have distinct relaxation characteristics.The analysis showed that the generation of P1 peaks is related to the reverse martensitic transformation that occurs in Cu-Al-Mn alloy during heating.The originate of P2 peaks is related to the twin crystal refinement.According to the activation energy of P3 peak and the peak temperature position,this peak belongs to the thermally activated relaxation type internal friction peak,which is related to the formation of Cu(Al/Mn)solid solution.The P4 peak stems from the precipitation of the bainite phase at high temperatures.The microstructure state of Cu-Al-Mn shape memory alloy at different temperatures is clarified,which provides a reference for industrial production regulation.Cu-11.33Al-5.71Mn(wt.%)shape memory alloy is quenched at 850? for different aging treatments.In the heating internal friction-temperature spectrum of Cu-Al-Mn alloy after aging treatment,the peak of reverse martensitic transformation internal friction occurred.The temperature of internal friction peak is not dependent on the aging time,and the height of peak first shows an increasing pattern and then decreased.When the aging period is 20 min,the maximum internal friction is obtained.The analysis showed that the aging time is related to the micro-structural defect,and the increase of the aging time diffuses the vacancy,increases the interfacial movability,and improves the internal friction.After 20 min of aging,the equilibrium state reached.With the duration of continuation increases,the martensitic continues to grow and disappear,the energy friction of interfacial micro-slip is reduced,and the internal friction decreases.Cu-Al-Mn alloy internal friction peak temperature has no dependence on aging temperature,and the peak is reduced with the increase of aging temperature.The analysis shows that the increase in aging temperature accelerated the diffusion of vacancies,resulting in nail misalignment and an increase in the number of relative vacancies at the interface,reducing the movability of the interface,resulting in a decrease in internal friction.Cu-Al-Mn alloy internal friction peaks are significantly dependent on the quenching medium,which has different cooling rates.Internal friction peak temperature is correlated with peak and cooling rate,and the peak increases with the increase of cooling rate.The analysis shows that the faster the cooling rate is,the more easily martensite phase is generated directly from the parent phase,and the less likely it is to undergo eutectoid decomposition to form ? phase or bainite phase,which improves the ability of reverse phase transformation,and thus the internal friction increases.The change of peak temperature is caused by coherent distortion of martensite nuclei during cooling process.The internal friction peak of reverse martensitic transformation was found in the heating internal friction-temperature spectrum of five groups of Cu-Al-Mn shape memory alloys with different components.It can be seen that the internal friction peak is first raised and then decreased with the increase of Al and Mn elements.The analysis showed that within a certain range,the content of Al elements is increased,the order of martensitic is increased,the reverse martensitic phase transformation ability is improved,and the internal friction is increased.Continue to increase the Al content,easy to precipitate brittle ?2 phase,increase grain size,easy to generate stress concentration,reduce boundary sliding energy friction,internal friction is reduced.The content of Mn element increases,expands the high temperature ? phase to the low Al range,inhibits the precipitation of ? phases,increases the number of ordered martensitics,improves the reverse martensitic phase transformation ability,improves its phase change internal friction,reduces grain size,and increases the interfacial sliding energy friction,thereby increasing internal friction.With the gradually increase of the Mn content,the phase region of the ? continues to expand,the ?2 phase precipitated,the phase transformation capacity reduced,the internal friction of the phase change reduced and the grain size increased,which resulted in the concentrate of stress,the decrease of the boundary movability and decrease of internal friction.