Microstructure And Properties Of Cu-bearing TiNi-based Shape Memory Alloys

In the present study,TiNiCu alloys were prepared with the addition of Cu into TiNi alloy,which was frequently used in the clinical practice.The influence of copper content and heat treatment process on the structure and properties of TiNiCu alloy was studied systematically,and the alloy composition and heat treatment process were optimized.In order to further improve the anti-bacterial properties of TiNiCu alloy by increasing Cu content of NiTi alloy,the elements Nb was added to improve the workability of the alloy.The three-point bending properties,wear resistance,corrosion resistance,ion dissolution behavior and antibacterial properties of TiNiCu and TiNiCuNb alloy in the simulated oral environment were studied systamatically,which provide a new selection and experimental reference for the design and development of new orthodontic wire materials with both superelastic properties and antibacterial functions.The results showed thatthe microstructure of the prepared TiNiCu alloys consisted of austenite phase and Ti₂?NiCu?phase at room temperature,and Ti₂?NiCu?was distributed along the rolling direction.The grain size of the alloy increased with the increase of copper t content in NiTi alloy.TiNiCu alloy exhibited one step phase transformation upon heating and cooling,and the addition of copper increased the phase transition temperatures.After annealing and aging treatment of the prepared TiNiCu alloy,the structure of the alloy at room temperature was mainly composed of austenite and Ti₂?NiCu?,which showed the incomplete superelasticity at 37?.With the increase of copper content,the residual strain of the alloy decreased,and superelasticity increased.The superelasticity of alloy decreased with the extension of annealing time,and the superelasticity of alloy increased slightly with the extension of aging time.In general,TiNi7Cu alloy possessed better comprehensive mechanical properties.TiNi7Cu alloy after 30%cold rolling and subsequently annealing at450?for 30min or aging at 400?for 60min exhibited improved superelasticity due to the strengthening of the parent phase.In addition,TiNiCuNb alloy consisted of austenite,martensite,Ti₂?NiCu?and beta Nb phase at room temperature,the A_f temperature was 35.7?.TiNiCuNb alloy showed excellent superelasticity and residual strain of 0.4%at 37?.Compared with TiNi alloy,the microhardness of thermomechanical treated TiNi7Cu alloy annealed at 400?was higher,and the microhardness of thermomechanical treated TiNi7Cu alloy aged at 400?and TiNiCuNb alloy were slightly lower.The resistance of the aging state TiNi7Cu alloy was good under dry condition.Under the condition of wet grinding,the aging state TiNi7Cu alloy had the best wear resistance.The addition of copper enhanced the corrosion resistance of nickel-titanium alloy in neutral,alkaline,hydrogen peroxide and fluoride saliva environment containing.After immersion in the simulated saliva for different time,TiNiCu and TiNiCuNb Ni ion precipitation amount was lower than that of alloy TiNi alloy of nickel ion precipitation amount,indicating that addition of copper element into NiTi alloy decreased the release of nickel ion to a certain extent.Copper ions released from TiNiCu alloy as the time lengthened,and the released amount of copper ion in different alloys followed TiNiCuNb>aging TiNiCu>annealing TiNiCu.These three copper-bearing alloys showed antibacterial properties to escherichia coli and staphylococcus aureus,and the antibacterial effect was related to the released amount of copper ions.