Microstructure And Strain Recovery Properties Of Ti-V-Al Shape Memory Alloy With Gadolinium Addition

Ti-V-Al shape memory alloy has a low density,which meets the requirement of lightweight,however,it does not meet the requirement of high strength for spacecraft materials such as connectors,fasteners.In order to cope with this problem,this paper attempts to improve the strength of Ti-V-Al alloy by doping rare earth Gd.The microstructure,martensitic transformation,mechanical behavior and shape memory effect were investigated systematically by SEM,TEM,DSC,XRD and tensile tests.It is shown that the doping of Gd effectively refines the grain of Ti-V-Al-Gd alloy.The grain size of the solution-treated alloy drops from more than 300 ?m to 71 ?m when the content is 1 at.%.When the Gd content reaches 0.3 at.%,the second phase Gd3(Ti,V)with orthogonal structure appears in the alloy matrices.When the Gd content increases to 1 at.%,second phase grows in number and size and is distributed along the grain boundary.Solution-treated(Ti-13V-3Al)100-x Gdx alloy matrices consist of ? " martensite.(111)I twin substructure exists both in and between martensite variants.With the increase of Gd content,he substructure of a" martensite does not change,the width of martensite lath decreases,the reverse martensitic tranformation temperature of solution-treated alloy decreases gradually.Cold rolled(Ti-13V-3Al)99.7Gd0.3 alloy matrices consists of ?" martensite.After annealed at 650?,the alloy consists of ?",?,a small amount of ? and ?.As annealing temperature increases,the contents of ?,? and ? decrease.annealing temperature increases to 800?,the alloy whole completely consists of ?".The reverse transformation temperature of martensite increases with the increase of annealing temperature.The doping of Gd also effectively improves the mechanical properties of solution-treated Ti-V-Al alloy.With the increase of Gd content,the yield strength,tensile strength and elongation firstly increase and then decrease.When the content of Gd element is 0.3 at.%,the yield strength and tensile strength reach 606.8 MPa and 925.36 MPa respectively,which increase by 17.1% and 15.7%.When the content of Gd is 0.1 at.%,the elongation reaches 20.45% which is increased by 46.5%.As Gd content increases,the recoverable strain of solution-treated Ti-V-Al-Gd alloy increases first and then decreases.When the pre-strain is 6%,the restorable strain of(Ti-13V-3Al)99.7Gd0.3 alloy reaches 4.9%.Thermomechanical treatment has a great influence on the mechanical properties of(Ti-13V-3Al)99.7Gd0.3 alloy.With the increase of annealing temperature,the yield strength decreases and the elongation increases.The recovery strain of Ti-13V-3Al alloy annealed at 700? reaches 5.0% and the recovery rate is 83.33%,which is futher improved.