Effect Of Cu/Ti/Mn/Si On Microstructure And Properties Of Fe-Mn-Si Based Shape Memory Alloys

Fe-Mn-Si-based shape memory alloys are characterized by low cost of raw materials,easy processing and manufacturing,and excellent mechanical properties,making them one of the most likely shape memory alloys to be used in industry on a large scale.In addition to shape memory properties,corrosion resistance is becoming another important indicator of the excellent performance of this material.Seven alloys with different compositions were designed for this project.The effects of Cu/Ti/Mn/Si on the organization and properties of Fe-Mn-Si based SMAs were investigated,and the shape memory properties of the alloys were improved by adjusting the sintering temperature and holding time of spark plasma sintering.This project aims to explore the use of discharge plasma sintering combined with mechanical alloying to produce Fe-Mn-Si-Cr-Ni shape memory alloys with excellent mechanical properties,shape memory properties and good corrosion resistance.Firstly,the effect of Cu content on the organization and properties of Fe-20Mn-6Si-8Cr-5Ni-0.5Ti alloy was investigated.The results showed that the addition of Cu element can promote the passivation of the fcc phase of the alloy,thus improving the corrosion resistance of the alloy.However,the addition of Cu elements will increase the α’-bcc phase content,reduce the alloy yield strength,superelastic strain and shape recovery rate,and only the alloy block with Cu content of 3 wt.% shows plastic behavior after compression.Next,the effects of sintering temperature and holding time on the organization and properties of the alloy with Fe-20Mn-6Si-8Cr-5Ni-0.5Ti-3Cu were investigated,and the results showed that under the sintering parameters ranging from 950℃ to 1050℃ and holding time from 10 min to 60 min,changing sintering temperature and holding time has little effect on the corrosion resistance of the alloy.Increasing the sintering temperature and prolonging the holding time can increase the uniformity of the two-phase distribution,which improve the fracture strength of the alloy.When the holding time reaches 60 min and the sintering temperature reaches 1050℃,the microstructure defects appear inside the alloy,and the yield strength and compression rate of the alloy decrease.The optimum sintering parameters are held at 1000℃ for 30 min.Under these sintering parameters,the yield strength of the alloy is 1259 MPa,the fracture strength is 1911 MPa,the compression rate is18.9%,and the superelastic strain is 2.1%.Finally,the effect of Ti/Mn/Si content on the organization and properties of Fe-20Mn-6Si-8Cr-5Ni-3Cu alloy was investigated.The results showed that decreasing Mn and Si elements would promote the precipitation of the α’-bcc phase,reducing the yield strength and compression ratio of the alloy.Among all kinds of alloys in this study,the alloy without Ti held at 1000℃ for 30 min has the lowest mean crystallite size and the highest lattice microstrain,and has the best shape memory performance.The superelastic strain is 2.6%and the shape recovery strain is 1.2%.At the same time,the alloy without Ti has the best mechanical properties.The yield strength is 1655 MPa,the fracture strength is 1745 MPa,the compression rate is 15.3%,the relative density is 97.2%,and the hardness is 545 HV.