Corrosion and biocompatibility of PPy/PEG coating electrodeposited on Ti6Al7Nb alloy

This work aims to improve the corrosion rate of Ti6Al7Nb alloy and to increase its biocompatibility at the same time, obtaining polymer composite films based on polypyrrole/polyethylene glycol (PPy/PEG). The elaboration method was electrodeposition. FT‐IR analysis was performed in order to emphasize the formation of the PPy‐PEG composite film by incorporating PEG into the polymer structure. The paper is focussed on PEG (400 molecular weight) effect on the corrosion in bioliquids (as tested electrochemical bioliquid was chosen Hank's balanced salt solution) and on the biocompatibility properties. The PPy film significantly improves the biocompatibility of the Ti6Al7Nb alloy. The PEG presence in the polymerization solution leads to more stable composite polymer films on the titanium alloy surface with a better corrosion resistance and a more hydrophilic behaviour comparing with the PPy film. The increase of cell viability and proliferation potential as compared to the PPy film is not important.     

AZ91HP镁合金激光熔凝层的耐蚀性和生物相容性

为提高医用AZ91HP镁合金的耐蚀性和生物相容性,采用激光熔凝技术对镁合金进行熔凝处理。结果表明,AZ91HP镁合金熔凝层相组成为α-Mg和β-Mg17Al12,凝固组织为典型的树枝晶。模拟体液中腐蚀速率结果表明,熔凝层的耐蚀性较原始镁合金显著提高。在Hank’s中浸泡21 d后,可清楚看到一些絮状物沉积在熔凝层表面;能谱分析结果表明,絮状物中Ca,P比约为1.33,接近羟基磷灰石中Ca,P比(1.67)。原始镁合金的凝血酶原时间(PT)值为11.025 s,激光熔凝层的PT值为12.025 s,熔凝层具有较好的抗凝血性。细胞毒性实验结果表明,培养1 d后,在原始镁合金周围细胞出现破碎和固缩,极少数贴壁细胞。熔凝层表面则存在许多粘附细胞,熔凝层细胞死亡率较原始镁合金大有降低。     

Corrosion behaviour of a new Ti‐6Al‐2Nb‐1Ta alloy in various solutions

A new Ti‐6Al‐2Nb‐1Ta alloy was obtained for to satisfy the mechanical and anticorrosion requirements in neutral corrosive environment. The corrosion behaviour of this new Ti‐6Al‐2Nb‐1Ta alloy in 0.1 M Na₂SO₄, 3% NaCl solutions and synthetic sea water was studied in this paper, using potentiodynamic and linear polarisation method, electrochemical impedance spectroscopy (EIS) and monitoring of the open circuit potentials. The structure of the alloy represents an α + β uniform structure with un‐oriented grains. From the potentiodynamic polarisation curves it resulted that the studied alloy is self‐passivated in all three solutions having a very good and very easy tendency to passivation. The most favourable values of the electrochemical parameters were registered in 0.1 M Na₂SO₄ solution due to its reduced corrosivity. EIS measurements proved the improvement of the passive layer resistance with the immersion time. An electric equivalent circuit with two time constants was fitted. The values of the polarisation resistances showed very good protective capacities which improved in time. The open circuit potentials have the general tendency to ennoble in time, suggesting the thickening of the passive films and the increase of their protective capacities.     

Oxidation behaviour of a PVD processed Mg‐14Ti alloy

The oxidation behaviour in air of a physical vapour deposited (PVD) Mg‐14Ti (wt. %) alloy was studied in the 325–450°C temperature range. The 2–3 mm thick deposit was grown in two stages. The first half of the deposit was mechanically worked during the process and then, deposition went on without this flailing period. The microstructure of the deposit can be divided into two parts, each one involving half of the total thickness. The oxidation resistance is strongly affected by the microstructure of the deposit, flailed or unflailed. Unflailed part of the deposit presents open boundaries with a high density of defects. Internal oxidation can proceed through this kind of boundaries. This is the reason of anomalous behaviour during the initial stages of oxidation, with maximum mass gain at 350°C. The flailed part shows a few cracks but the grain boundaries are practically free of defects. Flaws and cracks act as the starting point for the development of large intrusions, which contribute substantially to the total mass gain of the alloy, especially with increasing the temperature.     

Corrosion behaviour of an alloy formed by inductive melting of a cobalt-based alloy and AISI 4140 steel

A bimetal of Co-based alloy/AISI 4140 steel was fabricated by induction melting. The microstructure of the Co-based alloy was examined and the influence of on the alloy of acid solutions, the temperature of these solutions, and the immersion time was investigated. The results show that the microstructure of Co-based alloy consisted of a Co-rich phase, a Cr-rich phase, and W₃CoB₃. In a solution of 20% HCl and 6% FeCl₃, the Co-rich phase was attacked to form porous channels but transformed to a Si-rich passivation film to prevent further attack in the solution of 72% H₂SO₄. Therefore, the relative corrosion resistance of Co-based alloy to acid solution is 72% H₂SO₄ > 20% HCl > 6% FeCl₃.     

模拟体液中纯钛及Ti6A14V合金的腐蚀行为

采用电化学测试技术研究了人体医用金属材料工业纯钛和Ti6A14V合金在人工模拟体液中的腐蚀行为,结果表明,阳极极化后两种合金均未发现点蚀,工业纯钛的维钝电流密度小于于Ti6A14V合金,前者的阳极极化性能优于后者,Ti6A14V合金缝隙试样在阳极电位超过＋2000mV(vsSCE)后,电流开始急剧增大,发生了缝隙腐蚀;通过电子探针分析发现,在缝隙内Al和V两种元素发生活性溶解。工业纯钛在电位达到＋4000mV/(vsSCE）时仍没有发生缝隙腐蚀。     

Ni元素对非晶合金Mg_(65)Cu_(25)Gd_(10)在NaCl溶液中腐蚀行为的影响

采用析氢腐蚀实验比较了非晶合金Mg65Cu25Gd10和Mg65Cu20Ni5Gd10在1%NaCl溶液中腐蚀性能。利用电化学测试技术和场发射扫描电子显微镜(FESEM)对两非晶合金在NaCl溶液中的腐蚀行为进行了研究。析氢腐蚀实验表明,Ni的加入大大提高了非晶合金Mg65Cu25Gd10抗蚀性能,极化曲线测试结果也表明Mg65Cu20Ni5Gd10非晶合金的腐蚀电流远远小于Mg65Cu25Gd10非晶合金。EIS测试表明,电化学阻抗谱测试结果显示Mg65Cu20Ni5Gd10非晶合金电荷转移电阻高于Mg65Cu25Gd10非晶合金。腐蚀产物形貌观察表明,Ni的加入使非晶合金Mg65Cu20Ni5Gd10腐蚀表面膜更为致密。结合各测试结果,探讨了Ni的加入提高镁基非晶合金耐蚀性机理。     

富钛的TiNi记忆合金薄膜组织结构

探讨了用ＨＣＤ法在玻璃基板上制备的Ｔｉ－４３．２７％Ｎｉ形状记忆合金薄膜和经不同热处理后的组织结构，结果表明，当镀膜的基板温度较高时，所得的薄膜基本晶化，其组织为由马氏体、Ｒ相、母相和Ｔｉ２Ｎｉ析出相等组成的多晶体。经热处理后，母相量增加，马氏体量减少，表明热处理使Ｍｓ点下降，利用这一现象，可扩大记忆合金薄膜的旷工 由曙加热到１１０℃的动态观察中发现，多晶体中的马氏休逐步缩小，消失，转变成母相、Ｒ     

钒与V-5Cr-5Ti合金在氯离子溶液中的电化学腐蚀行为

采用电化学腐蚀测试技术对钒与V-5Cr-5Ti合金在氯离子溶液中的电化学腐蚀行为进行了研究。结果表明,在50μg/gCl-的氯化钾溶液中,钒的腐蚀电位高于V-5Cr-5Ti合金而具有更好的热力学稳定性;相对于V-5Cr-5Ti合金,钒具有较大的极化电阻和较小的腐蚀电流;钒与V-5Cr-5Ti合金具有相似的阴极极化行为;在阳极极化过程中,钒主要表现为Tafel行为,而V-5Cr-5Ti合金具有"伪钝化"和钝化行为;二者均具有负的循环极化滞后环;钒的抗腐蚀性能优于V-5Cr-5Ti合金。     

Corrosion behaviour of AA2024 aluminium alloy in different tempers in NaCl solution and with the CeCl3 corrosion inhibitor

The paper analyses the corrosion behaviour of naturally and artificially aged AA2024 alloy in NaCl solution and in the presence of an environment-friendly corrosion inhibitor, CeCl₃. On the basis of the values of polarisation resistance and corrosion current density, the corrosion resistance of the protective inhibitor film is established as well as the general corrosion resistance of this aluminium alloy. Resistance to pit formation is determined based on the difference in pitting and corrosion potentials while resistance to pit growth is determined based on the amount of charge consumed during pit growth. A scanning electron microscope is used to examine the morphology of the pits formed during the pitting corrosion testing, as well as to determine the cerium content on intermetallic particles and the matrix AA2024 alloy. The corrosion behaviour of AA2024 alloy is investigated after different test periods in NaCl solution and in the same solution with the CeCl₃ inhibitor. The corrosion resistance of both tempers of AA2024 alloy is more than one order of magnitude higher in the presence of CeCl₃. An explanation of the observed differences in the corrosion behaviour of the naturally and artificially aged AA2024 alloy is proposed. Different corrosion behaviour of the alloy after different test periods is also explained.     

Corrosion behaviors of a new titanium alloy TZNT for surgical implant application in Ringer's solution

A new near α-titanium alloy Ti12.5Zr2.5Nb2.STa (TZNT) for surgical implants was designed. The potentiodynamic technique was per-formed to investigate the corrosion behaviors of TZNT in Ringer's solution, and Ti6A14V, Ti6A17Nb, and TA2 were taken as comparison. The structure of the passive film was analyzed using an X-ray photoelectron spectrometer (XPS). The results indicate that TZNT possesses better corrosion resistance, when compared with Ti6A14V, Ti6A17Nb, and TA2. The passive film formed on the TZNT surface is composed of oxides, such as TiO_2, ZrO_2, Nb_2O_5, and Ta_2O_5. The elements Zr and Ta are rich, whereas Ti and Nb are poor in the passive film. The addi-tion of Zr, Nb, and Ta with relatively low electrochemical reaction potentials can reduce the anode activity and improve passive properties. Other than that, oxides such as ZrO_2, Nb_2O_5, and Ta_2O_5 with the nobler equilibrium constants make the passive film more stable.     

Effect of Gd on microstructure and refinement performance of Al-5Ti-B alloy

Al-5Ti-B and Al-5Ti-B-Gd master alloy refiners were fabricated by fluorine salt casting method. The microstructure and phase constitution of the master alloys were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Al-Ti-B alloy refiner consists of Al₃Ti phase and TiB₂ phase. After Gd is introduced into the intermediate alloy, Ti₂Al₂₀Gd phase appears in the alloy, the size of Al₃Ti is significantly reduced, and Ti-Al-Gd phase is found in the edge of Al₃Ti phase. At the same time, some independent Ti-Al-Gd phases appear in local areas, which are Ti₂Al₂₀Gd phase determined by micro-area electron diffraction analysis. Analysis and calculation results of the high-resolution images of the Ti₂Al₂₀Gd/Al structure show that there is no other compound at the junction between the Ti₂Al₂₀Gd phase and Al, and Ti₂Al₂₀Gd phase has a great difference in atomic space with the α-Al, which cannot be directly used as heterogeneous nucleus. But, after being decomposed in the aluminum melt, the Ti₂Al₂₀Gd phase can promote the refinement effect of the refiner. In the Al-Ti-B-Gd master alloy, there are many dispersed Al₃Ti particles with a size of less than 1 µm, which can promote the Al-5Ti-B refining effect.

     

Corrosion behaviour and mechanism of 6082 aluminium alloy in NaCl and Na2SO4 etchants

The corrosion behaviour of 6082 aluminium alloy was studied by measuring the electrochemical impedance spectra and electrode polarization curves. After the electrochemical tests, a microstructural analysis of the samples was conducted by using optical microscopy and electron scanning microscopy techniques to determine the corrosion mechanism. The results show that the Nyquist plot of the electrochemical impedance data in the NaCl solution consists of high- and low-frequency capacitive impedance loops. When ions are added to the NaCl etchant, the Nyquist plots of the electrochemical impedance data are composed of two different curves: a high-frequency capacitive impedance loop and a low-frequency inductive impedance loop. The corrosion current density increases with increasing concentration, and as a result, the corrosion resistance of the aluminium alloy decreases. The microstructures of 6082 aluminium alloy consist of Mg₂Si secondary particles in a large α-Al matrix. Pitting corrosion initially occurs at the boundary between the matrix and secondary particles because the electrode potentials of the matrix and secondary particles are different. Then, corrosion paths develop along the network-like grain boundaries, and finally, massive network-like corrosion occurs throughout the entire alloy.     

Effect of surface preparation on corrosion properties and nickel release of a NiTi alloy

Surface preparation is potentially important to the corrosion and biomedical properties of NiTi shape memory alloys.The effect of surface preparation on corrosion properties and nickel release of a Ti-56 wt.%Ni alloy has been studied.Surface of the NiTi coupons were prepared by four methods, namely, chemical etching, electropolishing, mechanical polishing and oxidizing, and then examined by corrosion test system.Furthermore, the Ni ion releases from NiTi samples with different surface preparations dipped in 1% HCl solution were analysed.Compared with the surface after chemical treatment, mechanical polishing and thermal oxidation, electropolished surface has better corrosion resistance and less nickel release for not only its lower surface roughness, but also the composition and property of its surface film.     

Corrosion resistance of hot‐dipped zinc and zinc alloy coated sheet steels under offshore atmospheric environment

The application of hot‐dipped zinc and zinc‐aluminum alloy coatings were introduced. Exposure tests of the steels with these coatings were conducted in the offshore atmosphere in Qingdao and Xiamen for 12 years separately. Effects of the coating thickness, alloy composition and atmospheric environment on the corrosion performance were studied. Results of the onsite exposure tests were compared with the results of a previous indoor salt spray accelerated corrosion tests. The study supports that zinc‐aluminum alloy coatings are useful in providing better corrosion resistance and can be further developed for future applications.