Study of the in vitro corrosion behavior and biocompatibility of Zr-2.5Nb and Zr-1.5Nb-1Ta (at%) crystalline alloys

The in vitro corrosion behavior and biocompatibility of two Zr alloys, Zr-2.5Nb, employed for the manufacture of CANDU reactor pressure tubes, and Zr-1.5Nb-1Ta (at%), for use as implant materials have been assessed and compared with those of Grade 2 Ti, which is known to be a highly compatible metallic biomaterial. The in vitro corrosion resistance was investigated by open circuit potential and electrochemical impedance spectroscopy (EIS) measurements, as a function of exposure time to an artificial physiological environment (Ringer’s solution). Open circuit potential values indicated that both the Zr alloys and Grade 2 Ti undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Zr-1.5Nb-1Ta alloy and that this oxide has better corrosion protection characteristics than the ones formed on Grade 2 Ti or on the Zr-2.5Nb alloy. EIS study showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The fit obtained suggests a single passive film presents on the metals surface, improving their resistance with exposure time, presenting the highest values to the Zr-1.5Nb-1Ta alloy. For the biocompatibility analysis human osteosarcoma cell line (Saos-2) and human primary bone marrow stromal cells (BMSC) were used. Biocompatibility tests showed that Saos-2 cells grow rapidly, independently of the surface, due to reduced dependency from matrix deposition and microenvironment recognition. BMSC instead display a reduced proliferation, possibly caused by a reduced crosstalk with the metal surface microenvironment. However, once the substrate has been colonized, BMSC seem to respond properly to osteoinduction stimuli, thus supporting a substantial equivalence in the biocompatibility among the Zr alloys and Grade 2 titanium. In summary, high in vitro corrosion resistance together with satisfactory biocompatibility make the Zr-2.5Nb and Zr-1.5Nb-1Ta crystalline alloys promising biomaterials for surgical implants.     

Microstructure and mechanical properties of Pt-added and Pd-added Zr-20Nb alloys and their metal release in 1 mass% lactic acid solution

The effects of Pt and Pd addition to a Zr-20Nb alloy on its microstructure and mechanical property, as well as the elution of metals from the alloys in lactic acid solution, were investigated. The microstructure was characterized with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). The mechanical properties were evaluated by a tensile test. The β phase is dominantly observed in the Zr-20Nb as well as in the Pt-added and Pd-added Zr-20Nb alloys. Needle-like microstructures are observed in equiaxed grains in all alloys. Pd addition to the Zr-20Nb alloy suppresses ω phase formation more than Pt addition does. The 0.2% offset yield strength and the ultimate tensile strength of the Pt-added and Pd-added Zr-20Nb alloys increase with the Pt and Pd concentrations. XRD analysis revealed that the lattice parameter of β-Zr in the Pt-added and Pd-added Zr-20Nb alloys decreases with the Pt and Pd concentrations. Pt and Pd solute in β-Zr as a substitutional element and contribute to the increase in the strength by solid solution hardening. The addition of 2Pt and 2Pd to the Zr-20Nb alloy also improves metal elution from the alloys in lactic acid solution.     

Effects of molybdenum content on the structure and mechanical properties of as-cast Ti-10Zr-based alloys for biomedical applications

The effects of molybdenum on the structure and mechanical properties of a Ti-10Zr-based system were studied with an emphasis on improving the strength/modulus ratio. Commercially pure titanium (c.p. Ti) was used as a control. As-cast Ti-10Zr and a series of Ti-10Zr-xMo (x = 1, 3, 5, 7.5, 10, 12.5, 15, 17.5 and 20 wt.%) alloys prepared using a commercial arc-melting vacuum pressure casting system were investigated. X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer. Three-point bending tests were performed to evaluate the mechanical properties of all specimens. The experimental results indicated that these alloys had different structures and mechanical properties when various amounts of Mo were added. The as-cast Ti-10Zr has a hexagonal α′ phase, and when 1 wt.% Mo was introduced into the Ti-10Zr alloy, the structure remained essentially unchanged. However, with 3 or 5 wt.%, the martensitic α″ structure was found. When increased to 7.5 wt.% or greater, retention of the metastable β phase began. The ω phase was observed only in the Ti-10Zr-7.5Mo alloy. Among all Ti-10Zr-xMo alloys, the α″-phase Ti-10Zr-5Mo alloy had the lowest elastic modulus. It is noteworthy that all the Ti-10Zr and Ti-10Zr-xMo alloys had good ductility. In addition, the Ti-10Zr-5Mo and Ti-10Zr-12.5Mo alloys exhibited higher bending strength/modulus ratios at 20.1 and 20.4, respectively. Furthermore, the elastically recoverable angles of these two alloys (26.4° and 24.6°, respectively) were much greater than those of c.p. Ti (2.7°). Given the importance of these properties for implant materials, the low modulus, excellent elastic recovery capability and high strength/modulus ratio of α″ phase Ti-10Zr-5Mo and β phase Ti-10Zr-12.5Mo alloys appear to make them promising candidates.     

Fatigue behaviour of boron free and boron containing heat treated Ti-13Zr-13Nb alloy for biomedical applications

Fatigue behaviour of heat treated Ti-13Zr-13Nb (TZN) and Ti-13Zr-13Nb-0.5B (TZNB) alloys for biomedical implants has been investigated by rotating bending test. It was found that fatigue strength of TZN and TZNB alloys is comparable with that of conventionally used biomedical titanium alloys. Addition of boron to TZN alloy deteriorates fatigue strength.     

A novel strategy for developing α+β dual-phase titanium alloys with low Young's modulus and high yield strength

In this study,a novel strategy for developing α+β dual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1Fe alloy was developed through theoret-ical composition design and microstructure manipulation.After hot-rolling and subsequent annealing,a high volume fraction of ultrafine grained α phase embedded in metastable β-matrix was formed in the microstructure as intended.Consequently,this alloy exhibits both low Young's modulus(61 GPa)and high yield strength(912 MPa).The experimental results prove that the proposed strategy is appropriate for developing titanium alloys with superior yield strength-to-modulus ratio than those of conven-tional metallic biomedical materials.Present study might shed light on the research and development of advanced biomedical titanium alloys with low Young's modulus and high yield strength.     

Structural aspects of corrosion resistance in alloys based on the Fe3Al intermetallic phase in the cast state

This paper presents the results of investigation of four cast alloys based on the Fe₃Al intermetallic phase. Microstructure tests using light microscopy, electron scanning microscopy and X-ray diffraction methods, have been performed. On this basis, a presence of particles rich in zirconium and molybdenum, and in case of the alloy with 28 at.% aluminium and 5 at.% chromium ?? the presence of sigma phase (FeCr), has been found. Also, the results of the study of the microstructure influence on the electrochemical corrosion resistance in the 5 % NaCl solution have been presented. The Fe-26Al-2Cr-1Mo-0.1Zr-0.005B at.% and Fe-26Al-5Cr-1Mo-0.1Zr-0.005B at.% alloys exhibited increased corrosion resistance in comparison to the Fe-23Al-1Mo-0.1Zr-0.005B at.% alloy without chromium addition. The appearance of the sigma phase in the alloy of Fe-28Al-5Cr-1Mo-0.1Zr-0.005B at.% chemical composition resulted in lowering the corrosion resistance of this alloy and a change in corrosion character from the pitting to the intercrystalline one.     

Ti-12Mo-6Zr-2Fe钛合金的纳米压入特征

利用纳米压入测量仪测试了Ti-12Mo-6Zr-2Fe钛合金的硬度和模量.测试表明,Ti-12Mo-6Zr-2Fe钛合金的硬度比Ti-6Al-4V ELI高,而模量比后者低,与常规方法得到的规律一致,表明该方法能很好地表征钛合金的力学特性.对测试过程的分析表明这种方法得到的结果不能与传统方法得到的结果互换,表面状态对测量结果有一定影响.     

Microstructural Evolution of Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd Titanium Alloy with Carbon Additions

The effect of carbon addition on microstructural evolution was studied in a near-α titanium alloy(Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd). It was found that flake and ribbon titanium carbides with a NaCl crystal structure formed in the as-cast alloys with carbon additions of over 0.17 wt pct. Flake carbide particles are the product of eutectic transformation and precipitate from the high-temperature β phase. The ribbon carbide particles are primary phases formed prior to the nucleation of any metallic phases. The as-cast alloys with carbide precipitation after heat-treatment atβt-30℃ followed by water quenching showed the spheroidization of α lamellae and partial dissolution of carbide particles. After annealing at βt 15℃, carbide particles are mostly distributed at the grain boundary and spheroidized through mixed grain boundary plus bulk diffusions.     

XPS characterization of surface modified titanium alloys for use as biomaterials

Three different Ti alloys of biomedical interest have been studied by means of X-ray photoelectron spectroscopy (XPS) to determine their surface chemical composition in both as-received condition and after oxidation at 750 °C in air for different times. Compositions of the investigated alloys were, in wt.%, Ti-7Nb-6Al, Ti-13Nb-13Zr and Ti-15Zr-4Nb. XPS analyses showed a behaviour of the Ti-7Nb-6Al alloy different from that of the two TiNbZr alloys, evidencing the role of the chemical composition of the alloys on the oxidation mechanisms. The oxidation process generates an aluminium-oxide rich surface on the Ti-7Nb-6Al, while in the case of the TiNbZr alloys a titanium-oxide rich layer is formed. The effect of the heat treatment on the contribution of the minority elements at the surface is also discussed.     

Infrared brazing Ti-6Al-4V and SP-700 alloys using the Ti-20Zr-20Cu-20Ni braze alloy

Great efforts have been made in brazing high-strength α-β titanium alloys below their beta-phase transformation temperature in order to obtain optimized mechanical properties. The brazing temperature of the cold roll-bonded Ti-20Zr-20Cu-20Ni foil is roughly 70 °C lower than that of Ti-15Cu-15Ni filler metal. Moreover, the detrimental Cu-Ni and Cu-Ni-Zr rich Ti phases can be greatly reduced or eliminated by properly choosing the brazing thermal cycle. This research demonstrates the potential application of Ti-20Zr-20Cu-20Ni foil in brazing titanium alloys.     

The heat capacity in two-phase regions and the heat of phase transformations of some alloys in Zr-Nb and Zr-Sn systems

Analytical expressions are given for the phase boundaries of diagrams of state for Zr-Nb and Zr-Sn systems. Thermodynamically justified temperature dependences of heat capacity of Zr-1% Nb, Zr-2.5% Nb, Zr-1.5% Sn, and Zr-2.5% Sn alloys in two-phase regions are given and recommended for use. The heats of second-order phase transformations α(Zr) ? β(Zr) in alloys of Zr-Nb and Zr-Sn binary systems are obtained, and the heats of monotectoid reaction α(Zr)+β(Nb) ? β(Zr) in the Zr-Nb system and of peritectoid reaction β(Zr)+Zr₄Sn ? α(Zr) in the Zr-Sn system are calculated.     

The Mechanism of kIH in Delayed Hydride Cracking of Zr-2.5wt% Nb at 150 ℃

This work studies the KIH mechanism of delayed hydride cracking (DHC) in Zr-2.5wt% Nb alloys. A modified experimental method was developed, in which specimens are fatigued between consecutive experiments, and a constant load instead of a decreasing load is used in each experiment. The hydride clusters formed and fractured at the crack tip during different experiments are thus separated and studied individually. A new R-curve phenomenon that characterizes the resistance to DHC was observed. KIH is thus more rigorously defined. Based on the measurement of the critical hydride cluster length at different K1, the threshold phenomenon of KIH is explained.     

Influence of forging deformation and heat treatment on microstructure of Ti-xNb-3Zr-2Ta alloys

Ti-xNb-3Zr-2Ta alloys (x = 33, 31, 29, 27, 25) (wt.%) were fabricated by vacuum non-consumable arc melting and hot forging. The hot-forging specimens were solid solution treated at 1053 K for 1.8 ks followed by water quenching (WQ) and air cooling (AC) respectively. The microstructure of hot-forging specimens with different deformation rate and solid solution treated at different temperatures was investigated. The result showed that a large amount of α" martensite appeared in the WQ group while only a little amount of α" phase could be found in the AC group. Moreover, for the WQ group, less niobium resulted in more diffraction peaks of α" phase in XRD profiles. This result suggested that the stability of β phase decreased with the decrease of Nb content. The microhardness of Ti-xNb-3Zr-2Ta (wt.%) alloys was improved significantly with the decreasing Nb content in both WQ group and AC group. Increasing deformation ratio could effectively refine β grains for Ti-25N-3Zr-2Ta (wt.%). Both acicular martensite and lath martensite were found in the transmission electron microscope observation of Ti-25Nb-3Zr-2Ta (wt.%) alloy. Martensitic internal twins were identified as well.     

Production of some amorphous alloys in ternary systems Zr-(Pd,Ru, Mo)-(Si,B)

The possibility of producing amorphous alloys in ternary systems Zr-(Pd, Ru, Mo)-(Si, B) has been investigated. Using a specially designed splat-cooling apparatus, some of the mentioned alloys were obtained in the amorphous state.     

Development of high Zr-containing Ti-based alloys with low Young's modulus for use in removable implants

This research focuses on the development of new titanium (Ti) alloys with a low Young's modulus for use in removable implants. In this study, Ti-30Zr alloy was selected as the base alloy, and the effect of Mo addition on the microstructures, Young's moduli, and tensile properties of Ti-30Zr-(0–8 wt.% Mo) alloys was investigated in this study to assess the mechanical compatibility of these alloys for biomedical applications. Further, the cytocompatibility of a part of the designed alloys was examined. The experimental results indicate that both the microstructures and the mechanical properties of the designed alloys are strongly affected by the Mo contents. The Ti-30Zr-(6, 7 wt.%) Mo alloys, located near the boundary of (β + ω)/β with a metastable structure, show a good combination of a low Young's modulus, high tensile strength, fairly large elongation. In addition, Ti–30Zr–7Mo alloy is highly cytocompatible.     

Joining of zirconia using zirconium-based alloys

The contact angles of Zr-Ni, Zr-Cu and Zr-Co alloys against PSZ were measured by the sessile drop method. Each alloy wetted PSZ very well. Zr-Co alloys showed a different behaviour. Joints of PSZ plates were obtained using Zr-17Ni alloy. At the joint interface, internal oxidation of zirconium occurred. The fracture shear strength of this joint was 55 MPa.     

锆合金表面Cr基涂层的耐高温氧化性能

用磁控溅射法在锆合金基体表面制备Cr和CrAl层,并使其在1200℃/1 h水蒸汽中氧化,用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)等手段表征氧化前后涂层和Zr合金基体的微观结构,研究了两种涂层在(反应堆失水(LOCA)事故情况下的)高温蒸汽环境中的抗氧化性能。结果表明：在1200℃/1 h水蒸汽中氧化后没有涂层的锆合金基体表面生成厚度约为100 μm的氧化膜;而在Cr涂层表面生成的致密Cr₂O₃层其厚度约为4 μm,表明氧化速率显著降低。CrAl涂层氧化后表面生成致密的Cr₂O₃和Al₂O₃混合氧化层,其厚度只有0.8 μm,表明氧化速率进一步降低。这些结果表明: 用磁控溅射法在锆合金表面制备的Cr和CrAl涂层,在1200℃水蒸气环境中均表现出良好的耐氧化性能。在Cr涂层表面生成的氧化膜厚度约为未涂层锆合金氧化层的1/25,CrAl涂层氧化膜厚度低于锆合金表面氧化层的1/100。     

Formation of amorphous anodic oxide films of controlled composition on aluminium alloys

Binary, non-equilibrium Al-29at%Nb, Al-44at%Ta, Al-19at%Ti, Al-25at%Ti and Al-32at%Zr alloys were prepared by magnetron sputtering and subsequently anodized at high Faradaic efficiency to grow barrier-type anodic films. Examination in the transmission electron microscope revealed amorphous anodic films of relatively uniform compositions across the film thicknesses, except for a layer of relatively pure alumina, of about 5% of the film thickness, present at the film/electrolyte interface of the Al-Ta alloy. The film compositions, from Rutherford backscattering spectroscopy, indicate that the alloy constituents are oxidized in their alloy proportions to form films comprising intimately mixed units of the various oxides, namely alumina, niobia, titania, tantala and zirconia. The films grow by co-operative transport of metal and oxygen ions under the electric field with formation of film material by both migration of metal ions outwards and of oxygen, and possibly hydroxyl, ions inwards. The average migration rates of Al³⁺, Nb⁵⁺, Ti⁴⁺ and Zr⁴⁺ ions are similar, to within 10%, but Ta⁵⁺ ions migrate more slowly than Al³⁺ ions. The results of the study show that a wide range of compositions of amorphous oxide films can be readily formed by anodic oxidation of appropriate alloys, including compositions containing units of normally crystalline anodic oxides, namely TiO₂ and ZrO₂.     

AES study of passive films formed on a type 316 austenitic stainless-steels in a stress field

The type AISI 316 stainless steel, in addition to the principal alloying elements chromium and nickel, contains 2.5–3.5% of molybdenum. This element is added to improve the mechanical properties and the pitting resistance of austenitic alloys. Concerning the Stress Corrosion Cracking (SCC) resistance of austenitic stainless steels, molybdenum additions to alloys have a variable effect: the effect is detrimental for small additions of Mo, and it is beneficial for the alloy containing more than 4% Mo. Thus the Mo concentration on passive film plays an important role on the SCC resistance of steels. On the other hand, in a previous investigation, it was shown that the composition of passive films formed on the stressed 302 alloy depended on the compressive or tensile nature of stresses. Consequently, the aim of the present work is to study the composition of passive films formed on 316 steel and the migration of molybdenum in a stress field. Thus, Auger electron spectroscopy spectra were recorded to determine the chemical composition of the passive films formed on both sides of the type AISI 316 stainless steel U-bend samples. The results obtained show that the behaviour of chromium and oxygen in passive films formed on 316 steel in the stress field was nearly similar to that formed on 302 steel. Concerning the molybdenum diffusion outwards the passive film formed on the 316 steel was reduced by either the tensile or compressive stress field.     

Effects of minor Zr and Sr on as-cast microstructure and mechanical properties of Mg–3Ce–1.2Mn–1Zn (wt%) magnesium alloy

The effects of minor Zr and Sr on the as-cast microstructure and mechanical properties of the Mg–3Ce–1.2Mn–1Zn (wt%) alloy were investigated. The results indicate that adding minor Zr and/or Sr to the Mg–3Ce–1.2Mn–1Zn alloy does not cause an obvious change in the morphology and distribution of the Mg₁₂Ce phase. However, the grains of the Zr- and/or Sr-containing alloys are effectively refined. Among the Zr- and/or Sr-containing alloys, the grains of the alloy with the addition of 0.5 wt%Zr + 0.1 wt%Sr are the finest. Furthermore, adding minor Zr and/or Sr to the Mg–3Ce–1.2Mn–1Zn alloy can improve the tensile properties. Among the Zr- and/or Sr-containing alloys, the alloy with the addition of 0.5 wt%Zr + 0.1 wt%Sr obtains the optimum tensile properties. In addition, adding minor Zr and/or Sr to the Mg–3Ce–1.2Mn–1Zn alloy also can improve the creep properties, and the creep properties of the three alloys with the additions of 0.5 wt%Zr + 0.1 wt%Sr, 0.5 wt%Zr, and 0.1 wt%Sr are similar.