Effect of thermal oxidation on the corrosion resistance of Ti6Al4V alloy in hydrochloric and nitric acid medium

The characteristics of Ti6Al4V alloy subjected to thermal oxidation in air atmosphere at 650 °C for 48 h and its corrosion behavior in 0.1 and 4 M HCl and HNO₃ medium are addressed. When compared to the naturally formed oxide layer (～4–6 nm), a relatively thicker oxide scale (～7 µm) is formed throughout the surface of Ti6Al4V alloy after thermal oxidation. XRD pattern disclose the formation of the rutile and oxygen‐diffused titanium as the predominant phases. A significant improvement in the hardness (from 324 ± 8 to 985 ± 40 HV_0.25) is observed due to the formation of hard oxide layer on the surface followed by the presence of an oxygen diffusion zone beneath it. Electrochemical studies reveal that the thermally oxidized Ti6Al4V alloy offers a better corrosion resistance than its untreated counterpart in both HCl and HNO₃ medium. The uniform surface coverage, compactness and thickness of the oxide layer provide an effective barrier towards corrosion of the Ti6Al4V alloy. The study concludes that thermal oxidation is an effective approach to engineer the surface of Ti6Al4V alloy to increase its corrosion resistance in HCl and HNO₃ medium.     

Influence of Surface Roughness on Corrosion and Tribological Behavior of CP-Ti After Thermal Oxidation Treatment

In this study, tribological and corrosion behavior of commercially pure titanium (CP-Ti) with different surface roughness values after thermal oxidation was investigated. The CP-Ti specimens were prepared with three different roughness values from silicon carbide paper, Ra = 0.1, 0.3, and 0.6 μm, and the thermal oxidization process was conducted at a temperature of 850 °C for 8 h in an O₂ atmosphere. Structural, mechanical, corrosion, and tribological properties of untreated and thermally oxidized CP-Ti with different surface roughness values were investigated through x-ray diffraction, scanning electron microscopy, microhardness, potensiostat, and pin-on-disk techniques. The corrosion and tribological behavior of CP-Ti improved as an oxide layer was formed by thermal oxidation. It was observed that the surface roughness had an effect on these characteristics. It was established that the decreased roughness improves the tribological and corrosion properties.     

热氧化对TA2耐磨和耐蚀性能的影响

选取TA2工业纯钛为研究对象进行热氧化处理,研究热氧化处理后试样表层物相构成、显微硬度、耐磨性和在浓盐酸中的耐腐蚀性。结果表明,热氧化后TA2表面形成了金红石型TiO2氧化膜,TiO2氧化层厚度随热氧化温度升高而增加;表层显微硬度随热氧化温度升高而提高。热氧化使TA2耐磨性和在36%～38%浓盐酸中耐腐蚀性明显改善,其中700℃为改善TA2耐磨性和耐蚀性的最佳热氧化工艺。     

The effects of spark anodizing treatment of pure titanium metals and titanium alloys on corrosion characteristics

This study evaluated the surface characteristics of oxide films on commercially pure titanium metals (CP-Ti; Grade 2 and Grade 3) and titanium alloy (Ti6Al4V and Ti6Al7Nb) samples formed by an anodic oxidation treatment, and investigated the effects of anodization on the corrosion characteristics. FE-SEM, XRD, and Raman spectroscopy were used to evaluate the micromorphology and crystalline structure of the oxide films. The corrosion resistance of the sample groups was evaluated using open-circuit potential and cyclic polarization tests. After anodic oxidation up to dielectric breakdown with the same electric current, 150-200 nm-sized pores were distributed homogeneously on pure titanium metal samples, partially occluded pores were observed on the Ti6Al4V alloy, and there was an inhomogeneous size and distribution of pores on the Ti6Al7Nb alloy. The titanium dioxide films formed through anodic oxidation contained a phase mixture of anatase and rutile. The cyclic polarization tests showed that all the tested sample groups were not susceptible to localized corrosion. The as-received and anodically oxidized CP-Ti grade 3 groups showed a higher corrosion resistance than the other groups. The mean E_corr values of the anodically oxidized sample groups, except for the anodized Ti6Al7Nb alloy, showed higher values than those of the respective as-received sample groups. In particular, the Ti6AL7Nb alloy showed a statistically higher E_corr value in the anodized group than in the as-received group (p < 0.05).     

Korrosionseigenschaften dünner Schichten im System Ti?B?N

Corrosion properties of thin coatings in the Ti? B? N system Thin titanium nitride TiN, boride TiB₂ and boronitride Ti(B, N) hard coatings were deposited on titanium substrates by the PVD-process Magnetron-Sputter-Ion-Plating (MSIP). They were characterized by X-ray diffractometry, SEM and WDX-analysis. With increasing B-content the Vickers hardness of the coatings increases. Photoelectron spectroscopic measurements show that all coatings are covered in atmosphere by thin oxid layer. Titanium nitride is electrochemically in 1 N sulphuric acid stable up to 1.3 V (SHE), above 1.3 V it becomes oxidized to titanium oxide TiO₂ and nitrogen N₂. The oxidation products were detected with XPS. Corrosion tests in nitric acid HNO₃ show that the corrosion resistance of titanium nitride is lower than the resistance of titanium. The corrosion of titanium boride and titanium boronitride in sulphuric acid is more intensive compared to titanium nitride. The borides cannot be passivated, but dissolve completely by anodic polarization.     

Hochtemperaturkorrosion des 2.25Cr-1Mo-Stahls unter simulierten Müllverbrennungsbedingungen

High temperature corrosion of 2.25Cr-1Mo in simulated waste incineration environments The corrosion of the 2.25Cr-1Mo steel was investigated by thermogravimetry in He? O₂? HCl? SO₂ at 500°C with and without deposits, taken from a waste incinerator. Additions of 500 vppm HCl to He-O₂ without deposits lead to accelerated corrosion due to the formation of FeCl₂ at the metal/oxide interface, its evaporation and oxidation lead to Fe₂O₃ at the outer surface (“active oxidation”). SO₂ causes FeS₂ formation on the FeCl₂ which retards the corrosion process. Under deposits, accelerated corrosion was observed in He-O₂ due to the reaction of alkalichlorides of the deposits with the oxide scale to ferrate and chlorine, which causes active oxidation. In He? O₂? HCl occurs strongly accelerated corrosion, due to transformation of the sulfates in the deposits by reaction with HCl to alkalichlorides. Addition of SO₂ shifts this equilibrium to enhanced stability of the sulfates, thus the corrosion in He? O₂? HCl? SO₂ is reduced.     

Oxidation resistance and corrosion behavior of hot-dip aluminized coatings on commercial-purity titanium

Aluminizing is an effective method to protect alloys from oxidation and corrosion. In this article, the microstructure, morphology, phase composition of the aluminized layers and the oxide films were investigated by SEM, EDS and X-ray diffraction. The high temperature oxidation resistance and electrochemical behavior of hot dip aluminizing coatings on commercial-purity titanium had been studied by cyclic oxidation test and potentiodynamic polarization technique. The results show that the reaction between the titanium and the molten aluminum leads to form an aluminum coating which almost has the composition of the aluminum bath. After diffusion annealing at 950 °C for 6 h, the aluminum coating transformed into a composite layer, which was composed of an inner layer and an outer layer. The inner layer was identified as Ti₃Al or Ti₂Al phase, and the outer layer was TiAl₃ and Al₂O₃ phase. The cyclic oxidation treatment at 1000 °C for 51 h shows that the oxidation resistance of the diffused titanium is 13 times more than the bare titanium. And the formation of TiAl₃, θ-Al₂O₃ and compact α-Al₂O₃ at the outer layer was thought to account for the improvement of the oxidation resistance at high temperature. However, the corrosion resistance of the aluminized titanium and the diffused titanium were reduced in 3.5 wt.% NaCl solution. The corrosion resistance of the aluminized titanium was only one third of bare titanium. Moreover, the corrosion resistance of the diffused titanium was far less than bare titanium.     

热氧化提高钛及钛合金表面性能的研究进展

热氧化作为一种引起广泛关注的钛及钛合金表面改性技术,具有工艺简单、原位生长、薄膜厚度大以及性价比高等特点。通过热氧化表面处理技术能够在钛及钛合金表面形成较厚的由钛氧化层和氧的扩散层组成的硬质氧化膜,氧化膜对材料起到有效的保护作用,提高了材料单一耐磨性、耐蚀性以及生物活性或综合表面性能。从热氧化工艺原理及其对钛及钛合金表面性能影响的角度,综述了热氧化对钛及钛合金表面硬度、耐磨性、耐蚀性、生物相容性等性能影响的研究进展,并对其以后的研究方向进行了展望。通过合理控制氧化温度、氧化时间、氧化气氛及冷却方式等工艺条件,从而得到连续、致密且疲劳性能较好的金红石型TiO_2和氧的扩散层是改善钛及钛合金性能的关键。将热氧化处理与其他工艺相结合,针对性地提高膜层厚度及材料的耐磨性、耐蚀性、生物性能等,以实现复合涂层的制备将是热氧化在钛及钛合金性能改善方面的研究方向。     

Corrosion behaviour after anodising of pre-nitrided CP-Ti

Abstract

This study presents corrosion characterisation of CP-Ti after nitriding, anodising and duplex surface treatment. The structural properties and corrosion characteristics were investigated by using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and electrochemical polarisation unit. After anodisation and duplex treatment, the porous oxide layer including anatase phase and unshaped or circular pores formed on CP-Ti surface. Size and shape of the pores were changed according to the anodising parameters. It was observed a double layered structure including porous layer on the top and a dense columnar layer beneath that section formed on duplex treated CP-Ti surface at low temperature of anodisation process. Pitting corrosion was observed on all of the samples after the electrochemical polarisation tests. Dense columnar microstructure provided good corrosion resistance via acting as a barrier. As a result, double oxide layer provided an important improvement in corrosion resistance in contrast with nitriding and anodisation processes.     

Optimization of Oxidation Temperature for Commercially Pure Titanium to Achieve Improved Corrosion Resistance

Thermal oxidation of commercially pure titanium (cp-Ti) was carried out at different temperatures, ranging from 200 to 900 °C to achieve optimum corrosion resistance of the thermally treated surface in simulated body fluid. Scanning electron microscopy, x-ray diffraction, Raman spectroscopy and electrochemical impedance spectroscopy techniques were used to characterize the oxides and assess their protective properties exposed in the test electrolyte. Maximum resistance toward corrosion was observed for samples oxidized at 500 °C. This was attributed to the formation of a composite layer of oxides at this temperature comprising Ti₂O₃ (titanium sesquioxide), anatase and rutile phases of TiO₂ on the surface of cp-Ti. Formation of an intact and pore-free oxide-substrate interface also improved its corrosion resistance.     

不同Cr含量的Ni-Cr合金熔覆层的高温氧化和热腐蚀特性

采用激光熔覆技术制备了Cr质量分数为10%、20%和40%的Ni-Cr合金熔覆层,研究了其在900 ℃下的高温氧化特性和600 ℃下Na₂SO₄+25% K₂SO₄混合盐中热腐蚀特性。结果表明,Cr含量对熔覆层的高温特性起着关键作用。提高Cr含量对提升熔覆层抗硫酸盐诱导的热腐蚀能力比提升抗循环高温氧化能力更有效。Cr40涂层抗高温氧化和热腐蚀性能最佳。Cr10的氧化产物以NiO为主,极易脱落,内部氧化严重。虽然Cr40表面可以形成单一的Cr₂O₃层,但热应力和生长应力引起的富Cr氧化物内部开裂,使Cr40的抗循环高温氧化能力仅略好于Cr20。面对热腐蚀时,Cr10表面呈现层状NiO和Ni₃S₂叠层分布的腐蚀产物,内部腐蚀区也生成了Ni的硫化物。Cr20表面Cr₂O₃层被破坏,内部腐蚀严重,生成了CrS。Cr40表面生成了致密的Cr₂O₃保护层,有效地防止了进一步腐蚀。     

Investigation of wear behavior of titanium oxide films, produced by anodic oxidation, on commercially pure titanium in vacuum conditions

The wear performances of titanium oxide films, produced by anodic oxidation, in vacuum conditions were investigated. Anodic oxidation treatments were carried out at − 3 and 40 °C temperatures using H₂SO₄(1.5 M)-H₃PO₄(0.3 M) solution and voltage of 200 V. Wear tests were performed at ambient air, pressures of 10^− 3 mbar and 10^− 6 mbar. Anodizing process produced a porous oxide layer on the surface. Although the pore size decreased with increasing process temperature, surface roughness decreased. Hardness results showed that anodic oxidation at lower temperatures produced oxide film with higher hardness. Wear rate of CP-Ti significantly decreased with anodic oxidation treatment in all wear conditions since oxide film acted like a solid lubricant. The best wear resistance was obtained from the hard-anodized samples both in ambient air and vacuum conditions.     

Inhibitive Effect of Tannic Acid on the Corrosion of Copper in Acid Solutions

Abstract

The behaviour of copper has been studied in lM solutions of HCl, HNO₃ and an HCl–HNO₃ mixture, containing various amounts of tannic acid (0 · 25, 0·5 and 1·0%). As tannic acid is a mixture of galloylglucoses, the same acids containing gallic acid (0·1, 0·2 and 0·5%) or glucose (0·1, 0·5 and 1·0%) have also been studied.

Glucose inhibits the corrosion of copper in HNO₃ solution to a very slight extent and has no effect in other solutions. Gallic and tannic acids have no effect in HCl but, at the highest concentrations tested, show an inhibitive efficiency of 80% and 70%, respectively, in HNO₃ and about 65–70% in HCl–HNO₃ mixtures.

Gallic acid may be considered to be a cathodic inhibitor that does not interfere directly with the cathodic process but modifies the corrosive environment. Tannic acid behaves both as a cathodic inhibitor and also as an anodic inhibitor due to the formation of an oxidation compound that is adsorbed on the copper surface.     

Effect of voltage on microstructure and corrosion resistance of microarc oxidation coatings on CP-Ti

The surface modification of commercially pure titanium (CP-Ti) by microarc oxidation (MAO) under different voltages was investigated using 1%H₃PO₄ solution as an electrolyte. The microstructure, phase composition and elemental distribution of ceramic coatings were investigated using scanning electron microscopy (SEM) and X-ray diffraction. The corrosion behaviour of the coating was also examined by potentiodynamic polarisation testing in a 3·5 wt-%NaCl solution. Micropore oxide films were formed on all the sample groups by MAO. The thickness and micropore size of the MAO coating increased with the increasing voltage. Energy dispersive X-ray spectroscopy results indicate that Ti, O and P became incorporated into the MAO coatings. At a low voltage of 250 V, the MAO coatings were composed of amorphous, P₂O₅, TiP₂O₇ and titania phases (rutile and anatase). Variation of treatment voltages increased the ceramic coatings from an amorphous structure to a phase structure, and the P₂O₅ phase disappeared. The corrosion potential Φ_corr of the MAO sample shifted towards nobler directions, and the corrosion density I_corr fell significantly compared with that of the bare CP-Ti. Corrosion testing showed that the sizes of the micropore of the MAO samples obviously decrease, and the MAO surface becomes smooth.     

Cyclic Oxidation Behavior of IN 718 Superalloy in Air at High Temperatures

Ni-base superalloy IN 718 was cyclically oxidized in laboratory air at temperatures ranging from 750 to 950 °C for up to 12 cycles (14 h/cycle). The kinetic behaviour as well as the surface morphology, and the oxide phases of the scales were characterized by means of weight gain measurements, cyclic oxidation kinetics, scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) analysis techniques. The results showed that as the oxidation temperature increased, the oxidation rate, the external scale thickness, and internal oxidation zone increased. It was suggested that the oxidation rate was controlled by the diffusion of substrate elements in the alloy and the inward diffusion of oxygen through the oxide scale. The oxidation kinetics followed a sub-parabolic rate law and, the activation energy of oxidation was 249 ± 20 kJ mol^?1. The scaling process was controlled mainly by the diffusion of chromium, titanium, manganese, and oxygen ions through the chromia scale. IN 718 showed low weight gain and very slow reaction rates of substrate elements at 750 °C. At 850 °C, a continuous and very thin oxide scale was formed. At 950 °C, XRD and EDS-elemental mapping analysis revealed that a complex oxide scale had formed. It consisted of an outermost layer of TiO₂?CMnCr₂O₄ spinels, inner layer of Cr₂O₃, and the inner most layer composed of Ni₃Nb enriched with Nb, Ti and Al oxides underneath the chromia layer. The oxide scale at this temperature seemed to be thicker layer, significant spallation and volatilization had apparently occurred, and greater internal corrosion was identified. The doping effect of titanium was observed, where it was found to be diffused through the chromia scale to form TiO₂ at the oxide-gas interface as well as internally and at the oxide alloy interface. The amount of rutile (TiO₂) at the oxide surface increased with temperature. In view of Mn contents in the alloy, the manganese?Cchromium spinel oxide was inferred to have played an important role in cyclic oxidation behaviour of IN 718, where the change in oxidation kinetic was noted. The Al contents would cause internal Al-rich oxide formation at grain boundaries.     

阳极氧化法制备TiO2膜在模拟深海热液区的耐腐蚀性能

以恒压阳极氧化方法在钛基体上制备TiO₂氧化膜,使用水热釜模拟深海热液区的条件研究其耐腐蚀性能。采用XRD、SEM、接触角测定仪对氧化膜以及腐蚀试样产物进行晶型、表面结构、化学成分和亲疏水性能测定,使用动电位扫描方法对其进行极化曲线测试。结果表明,钛试样和阳极氧化钛试样在模拟深海环境条件下,经过腐蚀反应在表面都生成了一层非致密的TiO₂ 膜,对基体并不能起到保护作用,而阳极氧化生成的致密TiO₂ 膜对基体能够起到很好的保护作用。经腐蚀后钛试样表面有TiH₂相的形成,腐蚀电位负移0.45 V。而阳极氧化钛试样表面没有TiH₂相的形成,且腐蚀电位负移较小,表现出良好的耐腐蚀性能。     

The corrosion behavior of Ti3SiC2 in common acids and dilute NaOH

Hot isostatically processed bulk, fine (3-5 μm) grained samples of Ti₃SiC₂ were immersed in concentrated and dilute hydrochloric, HCl, sulphuric, H₂SO₄, nitric, HNO₃, dilute hydrofluoric, HF, acids and sodium hydroxide, NaOH, solutions at room temperature. Based on six-months weight changes the dissolution rates of Ti₃SiC₂ in concentrated and dilute HCl, H₂SO₄ and dilute NaOH were found to be negligible (<2 μm/yr). In dilute HF and concentrated HNO₃ the corrosion rates were, respectively, ≈5 μm/yr and 13 μm/yr respectively. In contrast to Ti metal, the weight losses of Ti₃SiC₂ in dilute HNO₃ were higher (≈250-320 μm/yr) and depended on concentration. Post-immersion scanning electron microscopic micrographs of samples immersed in HNO₃ indicated that an oxygen rich Si-based layer forms on the surface of the samples. This implies that the Ti atoms are leached out into the HNO₃ solution, leaving behind a Si-rich layer that is ultimately oxidized. Cyclic polarization and potentiostatic i-t transients in dilute HCl and H₂SO₄ acids, strongly suggest that a thin irreversible electrically insulating layer forms on the surface of Ti₃SiC₂. Exposing a sample to a constant current density of 0.6 mA/cm² for two days resulted in the formation of a 5 μm thick SiO₂-based layer on the surface. The presence of such a layer would explain the excellent corrosion resistance of Ti₃SiC₂ in these acids.     

Selective Oxidation of Chromium by O2 Impurities in CO2 During Initial Stages of Oxidation

This study shows that the corrosion behaviour of 12 wt% Cr steel in CO₂ at 550 °C is determined in the first stage of oxidation by reaction with O₂ impurities. Depending on the amount of theses impurities and the thermal ramp rate, selective oxidation of chromium could lead to the formation of a protective chromium-rich oxide. An oxidation model describing qualitatively the nature of the oxide layer formed in the initial period of oxidation is presented. From these observations, surface engineering processes for protecting 9–12 wt% chromium steels from fast corrosion rate have emerged.     

The Effect of Colored Titanium Oxides on the Color Change on the Surface of Ti-5Al-5Mo-5V-1Cr-1Fe Alloy

In the present investigation, a color change on the surface of Ti-5Al-5Mo-5V-1Cr-1Fe alloy was studied through thermal oxidation experiments in the temperature range of 100-1000 °C with an interval of 50 °C. The phase composition and morphology of oxide layer were characterized by x-ray diffraction and light optical microscopy, respectively. The result shows that the achieved colors after thermal oxidation followed a chromatic scale which went from silver white to light yellow to golden yellow to blue and then to light green and brownish black. The color change on the alloy mainly resulted from the different colored titanium oxides in the oxide layer. The silver white, yellow, and blue on the alloy with the oxidation temperature below 600 °C were the results of TiO₂ white tint, TiO golden tint, and Ti₂O₃ blue color, respectively. The light green was the mixed color of TiO golden tint and Ti₂O₃ blue color in the oxidation temperature range of 600-700 °C. However, at the oxidation temperatures exceeding 750 °C, the color turned to be brownish black. It might be associated with the thick, porous, and multilayered oxide layer. Consequently, it can be suggested that the illustration of the color change is vitally necessary for assessing the quality of the final workpieces according to the color change on titanium alloys.     

相对流速对316L钢焊缝在液态铅铋合金中腐蚀行为的影响

在核工业领域,316L不锈钢因其优异的性能常被作为核用钢种,液态铅铋合金常作为加速器次临界驱动系统(ADS)的冷却剂,高速流动的液态铅铋合金(LBE)会对316L不锈钢焊缝造成氧化腐蚀,同时氧化腐蚀后的产物也会对液态LBE造成污染,所以研究316L不锈钢焊缝在液态铅铋合金中的腐蚀行为具有重要意义. 文中对比研究了使用母材作为焊丝进行TIG焊的316L不锈钢焊缝在550 ℃动态(相对流速为1.70,2.31,2.98 m/s)液态LBE中的耐腐蚀性能,试验时间为1 500 h. 结果表明,三组试样都生成了双氧化层,外氧化层主要为Fe₃O₄,内氧化层主要为FeCr₂O₄,内氧化层相对于外氧化层较致密;随着流速的提高,元素的传质过程变快,氧化腐蚀加剧,内氧化层增厚.