Martensitic Transformation And Shape Memory Effect Of Ti-V-Al-Cu Shape Memory Alloys

Ti-V-Al alloys are one of the main candidate alloys for lightweight shape memory alloys in the aerospace field because of their low density,excellent mechanical processing properties,and good recoverable strain.Aerospace seals have high requirements on alloy strength and shape memory effect.Ti-V-Al alloys have low strength and cannot meet their requirements.Therefore,the experiment developed new alloys by adding Cu to Ti-V-Al alloys to meet the requirements of sealed connectors.In this paper,the influence rules and mechanisms that how Cu content and themal-mechanical treatment effect the consist of phase,microstructure,martensitic transformation,mechanical properties and shape memory effect of(Ti-13V-3Al)100-x Cux(x=0.2,0.5,1.0,1.5,2.0,2.5,5.0)alloys are systematacially investigated.It is shown that the addition of Cu element changes the room temperature microstructure of the alloy.When the Cu content is lower than 0.5 at.%,the room temperature structure of the alloy is completely ?? martensite.When the Cu content is 1.0 at.% to 1.5 at.%,the room temperature structure of the alloy is ?? martensite and ? phase.Martensite laths show a self-cooperating state,and there are twins between martensite variants in some regions.When the Cu content exceeds 2.0 at.%,the room temperature structure of the alloy is ? phase + ? phase composition.With the increase of Cu content,the martensite transformation temperature of the alloy decreases,the tensile strength increases,the elongation decreases,and the recoverable strain increases first and then decreases.Thermo-mechanical processing changes the microstructure and properties of the alloy.With the increase of annealing temperature,the martensitic transformation temperature of(Ti-13V-3Al)99.5Cu0.5 alloy increases gradually,the tensile strength decreases,the elongation increases,and the recoverable strain increases first and then decreases;The martensitic transformation temperature of the(Ti-13V-3Al)97.5Cu2.5 alloy decreases gradually,the tensile strength decreases first and then increases,the elongation first increases and then decreases,and the recoverable strain increases first and then decreases.Both exhibited the best memory effect when annealed at 750?,recoverable strains were 5.3% and 3.2%,respectively.The microstructure of(Ti-13V-3Al)99.5Cu0.5 alloy after low annealing was composed of ?? martensite,? phase and ? phase.As the annealing temperature increased,? phase and ? phase decreased,?? Martensitic preferred orientation.When the alloy was annealed at 800?,there was no ?-phase or ?-phase present in the room temperature structure.The microstructure of(Ti-13V-3Al)97.5Cu2.5 alloy after annealing at lower temperature is composed of ?? martensite,? phase and ? phase.As the annealing temperature increases,the ? phase gradually decreases,?? martensite.Body preferred orientation.After the alloy was annealed at 800 ?,no ? phase existed in the room temperature structure,and ? phase and two kinds of precipitation phases appeared.The first one was Ti2 Cu,and the second precipitation phase was rich in Cu region,and its composition needs to be further confirmed.