Microstructure and superelastic properties of free forged Ti–Ni shape-memory alloy

Elemental titanium (Ti) and nickel (Ni) powders were consolidated by spark plasma sintering (SPS) to fabricate Ti–51%Ni (mole fraction) shape-memory alloys (SMAs). The objective of this study is to enhance the superelasticity of SPS produced Ti–Ni alloy using free forging as a secondary process. Products from two processes (with and without free forging) were compared in terms of microstructure, transformation temperature and superelasticity. The results showed that, free forging effectively improved the tensile and shape-memory properties. Ductility increased from 6.8% to 9.2% after forging. The maximum strain during superelasticity increased from 5% to 7.5% and the strain recovery rate increased from 72% to 92%. The microstructure of produced Ti–51%Ni SMA consists of the cubic austenite (B2) matrix, monoclinic martensite (B19′), secondary phases (Ti₃Ni₄, Ti₂Ni and TiNi₃) and oxides (Ti₄Ni₂O and Ti₃O₅). There was a shift towards higher temperatures in the martensitic transformation of free forged specimen (aged at 500 °C) due to the decrease in Ni content of B2 matrix. This is related to the presence of Ti₃Ni₄ precipitates, which were observed using transmission electron microscope (TEM). In conclusion, free forging could improve superelasticity and mechanical properties of Ti–51%Ni SMA.     

Bioactivity,in-vitro corrosion behavior,and antibacterial activity of silver–zeolites doped hydroxyapatite coating on magnesium alloy

Mg-based alloys received significant attention for temporary implant applications while, their applications have been limited by high degradation rate. Therefore, silver–zeolite doped hydroxyapatite (Ag-Zeo-HAp) coating was synthesized on TiO₂-coated Mg alloy by physical vapour deposition (PVD) assisted electrodeposition technique to decrease the degradation rate of Mg alloy. X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM) images showed the formation of a uniform and compact layer of Ag-Zeo-HAp with a thickness of 15 μm on the TiO₂ film with a thickness of 1 μm. The potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests indicated that corrosion resistance of Mg-Ca alloy was considerably increased by the Ag-Zeo-HAp coating. The bioactivity test in the simulated body fluid (SBF) solution showed that a dense and homogeneous bonelike apatite layer was formed on the Ag-Zeo-HAp surface after 14 d. Investigation of antibacterial activity via disk diffusion and spread plate methods showed that the Ag-Zeo-HAp coating had a significantly larger inhibition zone (3.86 mm) towards Escherichia coli (E. coli) compared with the TiO₂-coated Mg alloy (2.61 mm). The Ag-Zeo-HAp coating showed high antibacterial performance, good bioactivity, and high corrosion resistance which make it a perfect coating material for biomedical applications.     

银-沸石掺杂羟基磷灰石镁合金涂层的生物活性、体外腐蚀行为和抗菌活性（英文）

Mg-based alloys received significant attention for temporary implant applications while, their applications have been limited by high degradation rate. Therefore, silver-zeolite doped hydroxyapatite(Ag-Zeo-HAp) coating was synthesized on Ti O_2-coated Mg alloy by physical vapour deposition(PVD) assisted electrodeposition technique to decrease the degradation rate of Mg alloy. X-ray diffraction(XRD) analysis and field emission scanning electron microscopy(FE-SEM) images showed the formation of a uniform and compact layer of Ag-Zeo-HAp with a thickness of 15 μm on the Ti O_2 film with a thickness of 1 μm. The potentiodynamic polarization(PDP) and electrochemical impedance spectroscopy(EIS) tests indicated that corrosion resistance of Mg-Ca alloy was considerably increased by the Ag-Zeo-HAp coating. The bioactivity test in the simulated body fluid(SBF) solution showed that a dense and homogeneous bonelike apatite layer was formed on the Ag-Zeo-HAp surface after 14 d. Investigation of antibacterial activity via disk diffusion and spread plate methods showed that the Ag-Zeo-HAp coating had a significantly larger inhibition zone(3.86 mm) towards Escherichia coli(E. coli) compared with the Ti O_2-coated Mg alloy(2.61 mm). The Ag-Zeo-HAp coating showed high antibacterial performance, good bioactivity, and high corrosion resistance which make it a perfect coating material for biomedical applications.镁基合金作为临时植入材料的应用受到了越来越多的关注,然而,由于其降解速率高,因此应用受到了限制。为了降低镁合金的降解速率,本文作者采用物理气相沉积(PVD)辅助电沉积技术在镀氧化钛(Ti O_2)的镁合金上涂覆掺银-沸石羟基磷灰石(Ag-Zeo-HAp)涂层。X射线衍射(XRD)分析和场发射扫描电镜(FESEM)图片显示,在厚度约为1μm的二氧化钛薄膜上形成了均匀且致密的Ag-Zeo-HAp涂层,厚度约为15μm。动电位极化(PDP)和电化学阻抗谱(EIS)测试表明,通过Ag-Zeo-HAp涂层,Mg-Ca合金的耐腐蚀性大大提高。模拟体液(SBF)浸泡测试生物活性试验结果表明,在14 d后的Ag-Zeo-HAp表面上形成了一层致密且均匀的类骨磷灰石层。采用琼脂扩散法和平板涂布法对抗菌活性进行研究。结果表明,与Ti O_2涂层的镁合金(2.61 mm)相比,Ag-Zeo-HAp涂层对大肠杆菌(E.coli)的抑制区(3.86 mm)明显增大。Ag-Zeo-HAp涂层具有良好的抗菌性能、良好的生物活性和耐腐蚀性,是生物医学应用的理想涂层材料。     

自由锻Ti-Ni形状记忆合金的显微组织和超弹性（英文）

采用放电等离子烧结(SPS)法将元素钛粉和镍粉制备成Ti-51%Ni形状记忆合金(SMAs)。研究目的是采用自由锻二次加工以提高SPS合金的性能。对自由锻前后合金的显微组织、相变温度和超弹性进行比较。结果表明,自由锻可以显著提高Ti-Ni形状记忆合金的拉伸强度和形状记忆性能,自由锻后合金的韧性从6.8%提高到了9.2%,超弹性的应变范围从5%增加到7.5%,应变恢复速率从72%提高到92%。Ti-51%Ni合金显微组织中含有立方奥氏体相(B2)基体、单斜马氏体相(B19′)、第二相(Ti_3Ni_4,Ti_2Ni和TiNi_3)和氧化物相(Ti_4Ni_2O,Ti_3O_5)。自由锻后再经500°C时效处理的最终样品的马氏体相变温度向高温方向偏移,这是由于Ti_3Ni_4相(透射电镜下可以观察到)的析出而导致基体中Ni含量的减少。总之,自由锻可以提高Ti-51%Ni形状记忆合金的超弹性和力学性能。