Microstructure Evolution During Strengthening And Toughening Via Grain Refining And Its Effect On The Damping Property Of A CuAlMn Shape Memory Alloy

Cu-based shape memory alloys(SMAs)have broad application prospects because of their unique shape memory effect and high damping capacity.However,these alloys still have the problems of poor mechanical properties and intergranular fracture because of their very coarse grains.Therefore,in this paper grains of the Cu-11.9Al-2.5Mn(wt.%)SMA were effectively refined by a novel inoculant.The evolution rule of microstructures,change rule and associated mechanisms of mechanical and damping properties were also investigated.The results showed thatAl-La-B inoculant had obvious refining effect on the grains of CuAlMn SMA.When the addition amount of Al-La-B inoculant reached 2.5 wt.%,the refining effect was the best: the average grain size of the quenched alloy could be refined to36 ?m from 313 ?m of the unrefined alloy,and the average grain size of hot rolled and quenched alloy could be refined to 85 ?m from 530 ?m of unrefined alloy.On this basis,the grains of the alloy could be further refined by adding 0.1 wt.% Ce element: the average grain size of the quenched alloy could be refined to 25 ?m,while the average grain size of the hot rolled and quenched alloys could be refined to 80 ?m.The optimal heat treatment process of the refined CuAlMn SMA was: quenching at900 ?after holding for 15 min,and then rapidly heating up to 350 ?and aging for 15 min.The main purpose of aging treatment after quenching was to improve the order degree of the alloy,and effectively eliminate supersaturated vacancies formed during rapid quenching,so as to stabilize the transformation point.The mechanicalproperties of resultant materials wasinvestigated.It was found that the hardness,tensile strength and elongation of the CuAlMn SMA increased significantly with the decrease of grain size.When the Al-La-B content was 2.5 wt.%,the three properties reached their maximum values.In addition,with the decrease of grain size,the tensile fracture mode of the CuAlMn SMA gradually changed from intergranular brittle fracture to transgranular ductile fracture.Hot rolling could further enhance the three mechanical properties.The damping test results showed that with the decrease of grain size,the damping of the CuAlMn SMA refined by Al-La-B inoculant increased,while the damping of the CuAlMn SMA refined by Ce element decreased firstly and then increased.It was believed that this was due to the effect of grain refinement on the two opposite aspects of the damping capacity.Firstly,grain refinement could reduce the lamellar spacing of martensite,which would increase the number of interfaces in unit volume,thus contributing to theincrease of damping capacity.Secondly,with the decrease of lamellar spacing,the adjacent compressive stress and the binding force of grain boundaries increased,which resulted in the decrease of interfacial slip and the decrease of damping capacity.Therefore,the overall damping property of the material was the result of the combined effect of the two factors.