| y-Mn-based alloys have attracted a lot of interest in the industry due to the excellent damper properties,pseudoelasticity and other versatility.In this paper,the effects of thermal cycling and cyclic annealing on the damping properties,Spinodal decomposition,martensite(positive and inverse)transformation and microstructure of Mn-Cu-Al alloys were investigated by internal friction method combined with DSC,SEM,XRD and mechanical analysis.The effects of Cu content on the microstructure,damping properties and mechanical properties of Mn-Ni-Cu alloys were also investigated.The main conclusions are as follows:(1)Mn82.2Cu15.8Al2 alloy has good damping performance near room temperature,and Spinodal decomposition occurs in the temperature range of 650?845 K.The thermal cycle causes the alloy to undergo Spinodal decomposition to form a Mn-rich region and a Cu-rich region,and precipitatea-Mn.The apparent activation energy(Ea)of the low temperature relaxation internal friction peak of Mn82.2Cu15.8Al2 alloy is0.66 e V(heating)and 0.74 e V(cooling);the pre-exponential factor(t0)of relaxation time is 1.4×10-15s(heating),3.2×10-18s(cooling).After 6 cycles of thermal cycling,the low-temperature side relaxation internal friction peak Ea was 0.72 e V(cooling);t0was 1.1×10-18 s(cooling).(2)The increase of the number of cyclic annealing causes the Ms,Mf,As,Af of Mn82.2Cu15.8Al2 alloy to move to high temperature,and the thermal hysteresis becomes smaller and smaller.The sample is fully thermoelastic by controlling the temperature and number of cycles of annealing.The effect of the number of cyclic annealing on Mn82.2Cu11.8Al6 alloy is similar to that of Mn82.2Cu15.8Al2.The degree of cyclic annealing temperature and the number of cyclic annealing affect the degree of Spinodal decomposition of Mn82.2Cu17.8-xAlx(x=2,6)alloy to varying degrees.The degree of Spinodal decomposition of the alloy affects the Eatrend of the martensitic reverse transformation(RMT)process.When the cyclic annealing temperatures are693 K and 653 K,respectively,the former has a greater influence on the degree of Spinodal decomposition and RMT transition of the alloy than the latter.(3)The formation mechanism of the internal friction peak of the original sample of Mn82.2Cu11.8Al6 alloy is as follows:The P1 peak is attributed to the relaxation internal friction peak caused by martensite twinning,and its Ea=0.70 e V,t0=1.25×10-16s.The P2 peak is attributed to theg?-Mn?y-Mn transition.The P3 peak is the relaxation internal friction peak,and the formation of this peak is closely related to the diffusion of Cu and Al atoms in the Al Cu4phase,and its Ea=0.95 e V,t0=1.87×10-11s.The internal friction peak of P4 is attributed to the precipitation of a large amount ofa-Mn.The isothermal internal friction PA peak at 593 K is related to the decrease of Al Cu3 phase.(4)The addition of Cu in the Mn80Ni20-xCux alloy makes the microstructure of the alloy more uniform.The effect of Cu on the microstructure of Mn80Ni20-xCuxalloy is more obvious than that of Mn82.2Ni17.8-xCux alloy.However,the morphology of the microstructure of the different Cu content is also different.The internal friction-temperature spectrum and the unit cell parameter-temperature spectrum analysis show that the increase of Cu content can make the internal friction peak move to the low temperature side,greatly improving its damping performance.The reason is that the increase of Cu content reduces the TN of the alloy,makes TN close to Ms and the RMT and antiferromagnetic transitions are coupled to each other to obtain good damping performance.Controlling the reasonable Cu content can make the sample have good damping performance near room temperature,and expand the application field of the alloy.(5)The increase of Cu content generally reduces the hardness of Mn80Ni20-xCux(x=0,5,10),Mn82.2Ni17.8-xCux(x=0,2,4)alloys,and also affects the pseudoelasticity of the alloy.The increase in Cu content in the Mn80Ni20-xCux system reduces the deformation ability of the alloy,but the pseudoelasticity is better.For the Mn82.2Ni17.8-xCux system,a part of Ni is replaced by Cu,and the pseudoelasticity of the Mn-Ni-Cu alloy is improved compared with the binary alloy(Mn82.2Ni17.8),but in Mn-Ni-Cu ternary alloy,the proportion of Cu substituted Ni is increased,and the pseudoelasticity of the alloy is not improved much.In general,the pseudoelasticity of the Mn82.2Ni17.8-xCux system is significantly better than that of the Mn80Ni20-xCux system. |
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