Study On The Microstructure And Properties Of Shape Memory Alloys With High Damping Capacity

The microstructure and properties of TiNiCo alloy and CuAlMnRE alloys have been investigated systematically by means of optical metallographic microscope(OM),X-ray diffraction(XRD),differential scanning calorimetry (DSC),dynamic mechanical analyzer(DMA),cyclic tensile test and a semi-empirical quantitative bending test.The mechanism of the damping capacities during phase transformation,in martensite and R phase of the TiNiCo alloy has been illuminated.The influence of rare earth element(RE) on the microstructure,phase transformation behavior,shape memory effect and damping properties of CuAlMn alloys has been discussed.The experiment results show that there exist B2→R and R→B19'two step phase transformation during cooling for the Ti₅₀Ni₄₇Co₃ alloy.The damping capacity during phase transformation peak is much higher than that of single phase.The high damping capacity peak value corresponds to a sharp decrease in storage modulus.The dynamic term Q_D^-1 of single phase will disappear when the temperature rate is keep zero in the step-DMA curves.The static term Q_s^-1 of R phase is higher than that of martensite phase and parent phase.It has been found that the microstructure of CuAlMn alloys is obviously affected by the addition of RE elements(Ce and Y).The optical micrographs and the EDS results show that the grain size is clearly reduced due to the RE addition and very small amounts of the RE-riched phase disperse in the matrix can be observed.The phase transformation path of CuAlMn alloys does not change with RE addition and one-step martensitic transformation occurs during cooling and heating,however,the RE addition has apparent effect on the phase transformation temperatures.The shape memory effect(SME) of the CuAlMn alloy can be improved by an appropriate RE addition.With the increase of RE content,the SME of CuAlMn alloys increase initially and then decrease.Tensile test results show that the superelasticity(SE) of CuAlMn alloy decreases,however,the mechanical property of CuAlMn alloy can be enhanced obviously with the RE addition.The damping capacity during phase transformation and in the martensite condition decreases with the increase of RE content.In the low strain amplitude field,the damping capacity of martensite for CuAlMnRE alloys almost can not be affected by the strain amplitude.However,in high strain amplitude field,the damping capacity increases rapidly with the increase of strain amplitude.With the increase of the frequency,the damping capacity during phase transformation and in the martensite for CuAlMnRE alloy decreases gradually and then keeps constant value.