Wear and corrosion behaviour of Ti–13Nb–13Zr and Ti–6Al–4V alloys in simulated physiological solution

Wear and corrosion behaviour of cold-rolled Ti–13Nb–13Zr alloy, with martensitic microstructure, and Ti–6Al–4V ELI alloy, in martensitic and two-phase (α + β) microstructural conditions, was studied in a Ringer’s solution. The wear experiments were performed at room temperature with a normal load of 40 N and sliding speeds 0.26, 0.5 and 1.0 m/s. The corrosion behaviour was studied at 37 °C using open circuit potential-time measurements and potentiodynamic polarization. It was found that Ti–13Nb–13Zr alloy has a substantially lower wear resistance than Ti–6Al–4V ELI alloy in both microstructural conditions. Surface damage extent increases with sliding speed increase and is always smallest for martensitic Ti–6Al–4V ELI alloy with highest hardness. Both alloys exhibit spontaneous passivity in Ringer’s solution. Corrosion potential values are similar for all three materials. However, Ti–13Nb–13Zr and martensitic Ti–6Al–4V ELI alloys show improved corrosion resistance comparatively to Ti–6Al–4V ELI alloy with (α + β) microstructure. Martensitic Ti–6Al–4V ELI alloy possesses the best combination of both corrosion and wear resistance, although its corrosion resistance is found to be slightly higher than that of the Ti–13Nb–13Zr alloy.     

Characterisation and corrosion resistance of the electrodeposited hydroxyapatite and bovine serum albumin/hydroxyapatite films on Ti–6Al–4V–1Zr alloy surface

A new titanium base Ti–6Al–4V–1Zr alloy covered with hydroxyapatite or bovine serum albumin/hydroxyapatite was characterized in this paper in order to be used as implant material. Following techniques were used: linear polarization, electrochemical impedance spectroscopy, scanning electronic microscopy, Fourier transform infrared spectroscopy and atomic force microscopy. For HA or BSA/HA covered alloy, the electric equivalent circuit contains two time constants (for the passive film and for coatings). The resistance of the protective films increased in time and BSA/HA coating was slightly rougher than HA coating, this situation being favourably to the cell adhesion.     

Passivation of Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys in 1 M H2SO4 and 1 M NaOH solutions

The corrosion mechanisms of Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys have been investigated by potentiodynamic and potentiostatic polarization. Very good passivation of the Al–Cr–Fe surface is exhibited from 1 M H₂SO₄ to 1 M NaOH solutions, which was confirmed by ICP-OES analysis over a period of 273 days. Potentiostatically formed passive films analysed by XPS revealed chromium enrichment in the outermost layer of the aluminium oxy-hydroxide film. Although Al–Cu–Fe–Cr showed passivation during potentiodynamic polarization, heavy active corrosion at OCP was revealed by ICP-OES. For the Al–Cu–Fe–Cr alloy, the 10% content of Cr is insufficient to maintain a protective “chemically stable” Cr oxide/hydroxide.     

Metal release from stainless steel, Co–Cr–Mo–Ni–Fe and Ni–Ti alloys in vascular implants

A seven-day immersion test using several solutions was conducted on stainless steel, Co-based alloy, and Ni–Ti alloy, which are used for stents and stent grafts. The quantitative data on the release of each metal ion and the correlation between metal ion release rate and pH were obtained. The quantities of Fe and Ni released from stainless steel gradually decreased with increasing solution pH (pH 2–7.5). For Co–Cr–Mo–Ni–Fe alloy, the quantity of Cr released steadily increased as pH decreased (pH ≤ 6) and reached nearly zero at pHs higher than 6 (pH 6–7.5). Co release was slightly affected by a variation in pH. The quantities of Ni and Ti released from Ni–Ti alloy markedly increased with decreasing pH (pH ≤ 4) and they leveled off from pH 4 (pH 4–7.5). Although the rapid increases were observed at approximately pH 2, the quantities were even higher than that of Co released from the Co–Cr–Mo and Co–Cr–Mo–Ni–Fe alloys. For further investigation of the rapid increase in the quantities of metals released at pH 2, an anodic polarization test was employed to study the passive and transpassive behaviours of Ni–Ti alloy. The critical current density for the passivation of Ni–Ti alloy markedly increased as pH decreased (pH ≤ 4) and was low (1.4 μA/cm²) at pH higher than 4 (pH 4–7.5). The potential at a current density of 10 μA/cm², by contrast, markedly rose with decreasing pH (pH ≤ 2), and was 1.2 V from pH 2 (pH 2–7.5).     

In situ impedance spectroscopy study of the electrochemical corrosion of Ti and Ti–6Al–4V in simulated body fluid at 25 °C and 37 °C

The corrosion resistance of Ti and Ti–6Al–4V was investigated through electrochemical impedance spectroscopy, EIS, potentiodynamic polarisation curves and UV–Vis spectrophotometry. The tests were done in Hank solution at 25 °C and 37 °C. The EIS measurements were done at the open circuit potential at specific immersion times. An increase of the resistance as a function of the immersion time was observed, for Ti (at 25 °C and 37 °C), and for Ti–6Al–4V (at 25 °C), which was interpreted as the formation and growth of a passive film on the metallic surfaces.     

Corrosion and tribo-corrosion enhancement of SS301 and Ti–6Al–4V substrates by amorphous hydrogenated SiN/SiC/a-C multilayer coating architecture

Amorphous hydrogenated silicon-based multilayer coatings were deposited on 301 stainless steel (SS301) and Ti–6Al–4V alloy substrates using plasma enhanced chemical vapor deposition (PECVD), in order to integrate the advantages of the respective layers. Corrosion and tribo-corrosion behaviors of the complete coating/substrate system on different substrates were investigated. The SiN/SiC double-layer coating substantially improved the corrosion resistance of the metals: For SS301, the corrosion current, i_corr, was reduced by more than three orders of magnitude, and the breakdown voltage was increased from 0.34 to 1.37 V. For Ti–6Al–4V, the i_corr was decreased by a factor of ~ 50. Particularly, the Ti–6Al–4V/SiN/SiC multilayer system exhibited excellent anti-corrosion properties according to potentiodynamic polarization measurements, due to the superior corrosion resistance of both the Ti–6Al–4V substrate and the silicon-based coatings. Further enhancement of the tribo-corrosion resistance has been achieved by applying an amorphous hydrogenated carbon (a-C) coating as a top layer in the three-layer system. In the tribo-corrosion test in 1 wt.% NaCl solution, the SiN/SiC/a-C coating reduced the wear rate and the friction coefficient by a factor of ~ 175 and ~ 4, respectively, compared with the bare Ti–6Al–4V. The Ti–6Al–4V/SiN/SiC/a-C multilayer system integrates in synergy the advantages of the respective layers, and its versatility makes it a particularly attractive candidate for applications in different harsh working environments.     

Electrochemical behaviour of Ti–6Al–4V alloy and Ti in azide and halide solutions

Electrochemical techniques including open circuit potential measurement, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion and passivation behaviour of Ti–6Al–4V alloy in sodium azide (NaN₃) solutions compared to the behaviour of its pure base metal Ti. The results showed that increasing azide concentration increases the rate of corrosion (i_corr) and shifts negatively the rest potential (E_f), as well as decreases the spontaneous thickening rates of the inner and outer layers constituting the passive oxide film on each sample. These effects are more accentuated for the alloy than for the metal. Moreover, the electrical resistance (R_ox) and the relative thickness (1/C_ox) of the oxide films on the two samples exhibit an almost linear decrease vs. NaN₃ concentration. The results suggested that addition of Al and V to Ti, although improves its machinability, yet it decreases the performance of its surface oxide film to protect the degradation of the metal. The alloy was found to be more susceptible to corrosion than its base metal, since Ti expresses higher apparent activation energy (E_a) for the corrosion process than Ti–6Al–4V. Electrochemical behaviour of Ti in azide medium was also compared with that in various halide solutions. It was found that Ti has a stronger propensity to form spontaneous passivating oxide layers in bromide more than in azide and other halide media, where the positive shift in the value of E_f and the simultaneous increase in the oxide film resistance (R_ox) follow the sequence: Br⁻ > > Cl⁻ > I⁻ > F⁻.     

Influence of silicon on the corrosion behaviour of Al–Zn–In–Mg–Ti sacrificial anode

The influence of Si on the corrosion behaviour of Al–5Zn–0.03In–1Mg–0.05Ti (wt.%) alloy was investigated by the microstructure observation and electrochemical measurements in order to improve its corrosion non-uniform and electrochemical properties. The main precipitates in Al–5Zn–0.03In–1Mg–0.05Ti–0.1Si (wt.%) alloy is Mg₂Si phase, which decrease the galvanic corrosion because the potential difference between Mg₂Si and a-Al is smaller than that between MgZn₂ and a-Al. The addition of Si improves the corrosion uniformity of the anode due to the fine equiaxed grains and grain boundaries where Mg₂Si particles uniformly distributed. The results indicate that the microstructure, electrochemical characteristics and corrosion uniformity can be improved significantly after adding 0.1 wt.% Si into Al–5Zn–0.03In–1Mg–0.05Ti (wt.%) alloy.     

Phase stability,oxidation, and interdiffusion of a novel Ni−Cr−Al−Ti−Si bond-coating alloy between 900 and 1100°C

A novel, low-expansion experimental Ni–Cr–Al–Ti–Si bond-coating alloy was investigated in the as-cast state concerning its phase stability, oxidation resistance in air, and interdiffusion with single-crystal IN-100 at 900, 1000, and 1100°C. Isothermal oxidative thermogravimetry was employed up to 500 hr. Interdiffusion was compared to a commercial Ni–Co–Cr–Al–Y alloy on IN-100. Oxidized Ni–Cr–Al–Ti–Si specimens and diffusion couples were characterized by metallography, SEM, EDX, XRD, and XRF. The Ni–Cr–Al–Ti–Si alloy provides good oxidation resistance in air at least up to 1000°C. The alloy is an alumina former. Due to its coarse microstructure, other oxides (e.g., rutile) may form and considerably dominate the oxidation behavior. The kinetics of oxidation were correlated with temperature, formation of phases, and morphology of oxides. Interdiffusion fluxes between Ni–Cr–Al–Ti–Si and IN-100 were mainly directed to the superalloy. They were faster than in Ni–Co–Cr–Al–Y/IN-100 diffusion couples.     

Effect of Cr, Yb and Zr additions on localized corrosion of Al–Zn–Mg–Cu alloy

The effect of Cr, Yb and Zr additions on localized corrosion of Al–Zn–Mg–Cu alloy has been investigated. Additions of Cr, Yb and Zr to Al–Zn–Mg–Cu alloy stabilized the deformation-recovery microstructure with low angle grain boundaries on which grain boundary precipitates distributed discretely. The exfoliation and stress corrosion cracking of Al–Zn–Mg–Cu alloys propagated along the high angle recrystallized grain boundaries. The unrecrystallized Al–Zn–Mg–Cu–Zr–Cr–Yb alloy exhibited higher resistance to stress corrosion cracking and exfoliation corrosion, compared to the partial recrystallized Al–Zn–Mg–Cu–Zr alloy with high angle grain boundaries.     

Corrosion behaviour of laser gas nitrided Ti–6Al–4V in HCl solution

Laser surface nitriding of Ti–6Al–4V alloy was carried out with a Nd:YAG pulsed laser. The microstructure and corrosion behaviour of the nitrided samples were examined, using SEM, XRD, XPS, and anodic polarization tests in 2 M HCl solution. Laser nitriding produced a thin continuous TiN layer followed by TiN dendrites and TiN_0.3 needles. The laser nitrided specimen exhibited less corrosion current density, passivated more readily and also, maintained a lower current density over the duration of the experiment. This was correlated with the formation of very thin, continuous TiN_xO_y film, which could retard chloride ions ingress into the substrate.     

Corrosion product analysis on crevice corroded Alloy-22 specimens

Surface analytical techniques were applied to characterize corrosion products formed during the crevice corrosion of the Ni–Cr–Mo(W) Alloy-22 in 5 mol/L NaCl at 120 °C. Micro-Raman spectroscopy demonstrated the formation of polymeric molybdates within the crevice corroded region where intergranular corrosion dominated. The location and chemical speciation of the Mo and W species formed was investigated by Raman mapping. Crevice corrosion was found to propagate preferentially across the alloy surface rather than to penetrate deeply at localized sites, a feature which appears to be linked to the formation and build-up of polymeric molybdates.     

Mechanical properties of metals for biomedical applications using powder metallurgy process: A review

The uses of biomaterials have been revolutionizing the biomedical field in deployment as implants for humans. During the past five decades, many implant materials made of metals have been put into practical use. Powder metallurgy techniques have been used to produce controlled porous structures, such as porous coatings applied for dental and orthopedic surgical implants, which allow bony tissue ingrowth within the implant surface, thereby improving fixation. This paper examines various important metals using powder metallurgy technology to produce elements of a total hip replacement. These alloys are 316L stainless steel alloy, Co−Cr−Mo alloy, and Ti−6Al−4V alloy. Also, this paper examines current information on the mechanical properties. Mechanical properties are discussed as a function of type of materials and process of fabrication. This article addresses the engineering aspects concerning the advantages and disadvantages of each type of material.     

Nano-porous surface states of Ti–Y–Al–Co phase separated metallic glass

A novel nano-porous state was fabricated at the surface of the Ti-based metallic glass by selective etching technique. By transforming the surface of the Ti₄₅Y₁₁Al₂₄Co₂₀ phase separated alloy from smooth towards rough with nano-pores in an oxidised state, the passivation behaviour of the glassy alloy in simulated body fluid condition was remarkably improved leading to corrosion resistance significantly higher than that of the Ti–6Al–4V alloy, one of the favourite candidate materials for implant applications.     

Strong bonding of infrared brazed α2-Ti3Al and Ti–6Al–4V using Ti–Cu–Ni fillers

Infrared dissimilar brazing of α₂-Ti₃Al and Ti–6Al–4V using Ti–15Cu–25Ni and Ti–15Cu–15Ni filler metals has been performed in this study. The brazed joint consists primarily of Ti-rich and Ti₂Ni phases, and there is no interfacial phase among the braze alloy, α₂-Ti₃Al and Ti–6Al–4V substrates. The existence of the Ti₂Ni intermetallic compound is detrimental to the bonding strength of the joint. The amount of Ti₂Ni decreases with increasing brazing temperature and/or time due to the depletion of Ni content from the braze alloy into the Ti–6Al–4V substrate during brazing. The shear strength of the brazed joint free of the blocky Ti₂Ni phase is comparable with that of the α₂-Ti₃Al substrate, and strong bonding can thus be obtained.     

Thermal relaxation of residual stress in laser shock peened Ti–6Al–4V alloy

Laser shock peening (LSP) induced residual stresses in Ti–6Al–4V, and their thermal relaxation due to short-term exposure at elevated temperatures are investigated by an integrated modeling/simulation and experimental approach. A rate and temperature-dependent plasticity model in the form of Johnson–Cook (JC) has been employed to represent the nonlinear constitutive behavior under both LSP and thermal loads. By comparing the simulation results with experimental data, model parameters for Ti–6Al–4V are first calibrated and subsequently applied in analyzing the thermal stability of the residual stress in LSP-treated Ti–6Al–4V. The analysis shows that the magnitude of stress relaxation increases with the increase of applied temperature due to material softening. Most of stress relaxation occurs before 10 min to 20 min exposure in this study, and stress distribution becomes more uniform after thermal exposure. An analytical model based on the Zener–Wert–Avrami formula is then developed based on the simulation results. The activation enthalpy of the relaxation process for laser shock peened Ti–6Al–4V is determined to be in the range of 0.71 eV to 1.37 eV.     

Composition and processing effects on the electrochemical characteristics of biomedical titanium alloys

The electrochemical behaviour of the Ti–13Nb–13Zr and Ti–6Al–4V ELI alloys with martensitic microstructures was investigated by polarization and electrochemical impedance spectroscopy (EIS) in Ringer’s solution. The impedance spectra were interpreted by a two time-constants equivalent circuit. Both investigated alloys showed high corrosion resistance, but the thin and uniform passive film on the Ti–6Al–4V ELI alloy surface was more protective. The inner barrier and outer porous layer were highly resistant and capacitive. However, thicker and more porous passive film on the Ti–13Nb–13Zr alloy surface may be beneficial for osteointegration. The suitable thermomechanical processing improved the corrosion resistance of Ti–13Nb–13Zr alloy.     

Interfacial reactions between molten Al and a Co–Cr–Mo alloy with and without oxidation treatment

The effect of the formation of an oxide layer on the interfacial reactions between a Co–Cr–Mo alloy (CCM alloy) and molten Al is investigated. In the absence of an oxide layer, the CCM alloy reacted rapidly and an interfacial two-layer structure formed between the CCM alloy and molten Al. Upon oxidation, a uniform (Cr,M)₂O₃ (M: doped elements) oxide layer formed on the CCM alloy surface, which effectively inhibited the reaction between the CCM alloy matrix and molten Al for more than 2 h.     

Experiments and finite element simulations on micro-milling of Ti–6Al–4V alloy with uncoated and cBN coated micro-tools

This paper presents experimental investigations and finite element simulations on micro-milling of Ti–6Al–4V alloy with fine grain uncoated and cBN coated micro-end mills. Micro-milling of Ti–6Al–4V using uncoated and cBN coated tungsten carbide micro-end mills are conducted; surface roughness, burr formation and tool wear are measured. Effects of machining parameters on surface roughness, burr formation, and tool wear for uncoated and cBN coated micro-tools are investigated. Finite element modelling is utilized to predict forces, temperatures, and wear rate for uncoated and cBN coated micro-tools. Predicted temperature and tool wear contours for uncoated and cBN coated micro-tool edges reveal advantages of cBN coatings. Optimization studies on the experimental results are also conducted to identify the optimum process parameters which minimize both surface roughness and burr formation concurrently.     

Passivation and corrosion behaviours of cobalt and cobalt-chromium-molybdenum alloy

Passivation and corrosion behaviour of the cobalt and cobalt-base alloy Co30Cr6Mo was studied in a simulated physiological solution containing chloride and bicarbonate ions and with pH of 6.8. The oxido-reduction processes included solid state transformations occurring at the cobalt/electrolyte interface are interpreted using theories of surface electrochemistry. The dissolution of cobalt is significantly suppressed by alloying it with chromium and molybdenum, since the alloy exhibited “chromium like” passivity. The structural and protective properties of passive oxide films formed spontaneously at the open circuit potential or during the anodic polarization were studied using electrochemical impedance spectroscopy in the wide frequency range.