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Morphology of the surface of titanium after cyclic oxidation at 600 • C ((a)-4 cycle/24 h, (b)-12 cycle/72 h), 650 • C ((c)-4 cycle/24 h, (d)-12 cycle/72 h) and 700 • C ((e)-4 cycle/24 h, (f)-12 cycle/72 h).
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This paper presents the results of research into the cyclic oxidation of titanium Grade 2. The value of titanium Grade 2 oxidation activation energy was determined based on an analysis of the Arrhenius diagram. The result was 205.3 kJ/mol. After cyclic oxidation at a temperature of 600 • C, the presence of oxides in an acicular system was observed...
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... The transition from the unaffected titanium sheet around the melt pool into the melted zone is clearly visible in the hardness and reduced modulus maps shown in Fig. 7b-c. The hardness of the titanium substrate sheet, averaged over the indents marked outside the melt pool in Fig. 7a, is 2.4 ± 0.7, 2.3 ± 0.4, and 2.7 ± 1.0 GPa, respectively, which is comparable to other results on commercially pure titanium grade 2 [30,31]. Within the melt pool area, the hardness and reduced modulus are enhanced and the variations are more pronounced, which reflects the distribution of TiN in Ti matrix. ...
Applying nitriding in laser powder bed fusion additive manufacturing at custom build positions requires knowledge of the spatially and temporally resolved nitriding behaviour. Here we take steps toward this goal by sequential analysis of spatially resolved structural, chemical, and mechanical information throughout the melt pool, which is not available in previous studies. Single laser nitriding tracks are produced in a laser powder bed fusion system. By re-nitriding the initially nitrided track two more times, the effect of multiple sequential nitriding steps on the spatially resolved evolution of composition, structure, morphology and mechanical properties is captured. Characterisation is carried out by X-ray diffraction on the top of the laser tracks as well as laser optical microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction, and nanoindentation on the melt pool cross sections. Nitrogen incorporation and TiN formation is observed at >200 μm melt pool depth and it is evident that multiple sequential laser passes increase the TiN fraction. The nitrogen incorporation results in a gradient of the mechanical properties with enhanced hardness and elastic modulus depending on the local nitride fraction. A maximum local hardness of ~20 GPa is observed and a melt pool hardness of 7.3 ± 1.7, 9.3 ± 3.5, and 10.3 ± 5.2 GPa is attained for one, two and three melts. Compared to the Ti substrate with a hardness of ~2.5 GPa, substantial local modifications are obtained.
... In the investigation, O800-5 was added after O800-50 failed to provide good corrosion properties. The oxide grain size increased with temperature and time because of the nucleation and aggregation of finer oxide grains 50 . The oxide grain morphology of O800-5 was coarser than that of O700-50, as shown in Fig. 6a. ...
Protective oxide layers on Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr (TC21) alloy with equiaxed microstructure considerably influence micro-hardness and hot corrosion resistance. The present work’s thermal oxidation of TC21 alloy was performed at 600, 700, and 800 °C for 5, 20, and 50 h durations. Hot corrosion methods in NaCl and NaCl + Na2SO4 salt media were applied to raw (unoxidized) and oxidized samples at 600 and 800 °C for 50 h. Hot corrosion was conducted at 600 °C for 5 cycles with 10-h steps. The best oxide layer thickness was observed at 800 °C, which increased with increased oxidation time and temperature. The surface hardness of the oxide layer at 800 °C was 900 ± 60 HV0.05 owing to the formation of TiO2 and Al2O3 phases. Raw material hardness was 342 ± 20 HV0.05, increasing threefold due to thermal oxidation. In the case of NaCl, weight loss dominated all samples except at 800 °C for 5 h. In the case of NaCl + Na2SO4, weight gain occurred at 600 and 800 °C for 5 h. Weight loss occurred for the raw samples and those processed at 800 °C for 20 and 50 h, where the oxide layer flaked off. Surface hardness increased upon hot corrosion testing because of the formation of brittle phases, such as TiO2 and Na4Ti5O12. Samples that oxidized at 800 °C for 5 h had the highest hardness and corrosion resistance.
... Titanium is a polycrystalline material that has attracted attention because it is a low-density metal, has good resistance to corrosion and good mechanical properties [1,2], which, make it have a wide variety of applications such as in the chemical, biomedical, aerospace, and military industries. Therefore, different surface treatment techniques have been sought to improve the mechanical and tribological properties of grade 2 titanium. ...
Currently, different surface treatments have been studied to improve wear resistance and increase the hardness values of grade 2 titanium, based on morphological and structural changes. For this work, the impact of the annealing temperature on grade 2 titanium surfaces obtained by the electrochemical anodization technique using HCl in aqueous solution at a concentration of 3 M and a constant potential of 11.5 V for 2 h was studied. Annealing temperatures were 400, 450, 500, 550, and 600 °C for 4 h. It was found that the plates treated at 600 °C presented the best results, where a hardness of up to 5.57 GPa and coefficient and wear rate values of 0.28 and 1.56 × 10–4 mm3/Nm, respectively, were obtained. The oxide layers exhibited a combination of anatase and rutile crystalline phases in X-ray diffraction and Raman-active vibrational modes of anatase and rutile.
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... Thermal oxidation is a technique that, by subjecting titanium to high temperatures, allows the surface of the titanium to be modified, obtaining a uniform oxide layer over the entire metal surface, thus improving its corrosion resistance, and its mechanical and tribological properties [3,[9][10][11]. According to previous research, titanium Grade 2 has been studied because this material has a good affinity with oxygen and it is possible to obtain a compact oxide layer on its surface to improve its resistance to wear [9,[12][13][14]. Based on the consulted literature, the thermal oxidation parameters used to increase the hardness values and improve titanium wear resistance have been temperatures from 500 to 900 °C and oxidation times from 20 min to 72 h [7]. ...
This article presents oxidation tests of titanium Grade 2 subjected to temperatures of 450 °C, 550 °C, 650 °C, 750 °C, and 1000 °C for 2 h. An analysis of the morphology of the oxidized surfaces was carried out and it was possible to observe the formation of oxide crystals from 750 °C. The cross section of the oxidized samples was analyzed to obtain thicknesses and it was found that the increase in temperature promoted the growth of the oxide layers, obtaining thicknesses of up to 3.27 ± 0.65 µm. A combination of phases with rutile TiO2 and Ti3O was found in the oxidized samples starting from 650 °C. Based on surface analysis, a growth of oxide grains was observed that caused an increase in Ra and Rz roughness values up to 78.32 ± 4.19 nm and 202.73 ± 25.65 nm, respectively. It was found that titanium oxidized at a temperature of 750 °C showed the best results, with a hardness value of 10.60 GPa, a friction coefficient of 0.573 ± 0.03, and a volumetric wear of 2.26 × 10–5 ± 1.82 x10⁻⁵ mm³/Nm. In addition, under these oxidation conditions, higher compressive stresses were observed, which were also beneficial for the sample.
... The crystallographic constants are a = 0.465 nm, b = 0.465 nm, and c = 0.297 nm [13,14]. With the extension of the oxidation time, oxygen ions diffuse through the TiO2 layer into the specimen, forming an oxygen diffusion zone between the Ti matrix and the TiO2 oxide layer [15,16]. Under high temperature conditions, the The influence of processing temperature on the ∆rG of reactions (1) is shown in Figure 2. When the value of ∆rG is less than zero, the reaction can occur. ...
... The crystallographic constants are a = 0.465 nm, b = 0.465 nm, and c = 0.297 nm [13,14]. With the extension of the oxidation time, oxygen ions diffuse through the TiO 2 layer into the specimen, forming an oxygen diffusion zone between the Ti matrix and the TiO 2 oxide layer [15,16]. Under high temperature conditions, the pure Ti matrix undergoes a configuration transformation from α-Ti to β-Ti, and 884 ± 2 • C is the phase transition temperature of the two structures. ...
Pure titanium was treated by atmospheric oxidation, and the effect of the treatment temperature on its performance was studied. X-ray diffraction, scanning electron microscopy, wear testing, and scratch testing were used to evaluate the performance of the treated specimens. In order to evaluate the difficulty of compound formation during the different processing temperatures, Gibbs free energy was calculated. The experimental results show that the surface hardness of the sample can be improved at a certain oxidation treatment temperature. When the processing temperature is 850 °C, the surface hardness reaches the maximum value. The results of the scratch testing show that the hardened layer produced at this processing temperature has excellent peeling resistance. In addition, the wear depth and wear width are also at their minimum values at this processing temperature. Since the specimen treated at a processing temperature of 850 °C provides sufficiently high surface hardness and wear resistance in this research report, it is considered to be the optimal condition during practical application.
The dependence of electron work function, Φ, on the thickness of Ti layers was investigated by making use of the Kelvin method under ambient conditions. Layers were produced by vacuum phase deposition and were analyzed by x-ray photoelectron spectroscopy and transmission electron microscopy. A quantum size effect was revealed finding work function to increase as the layer thickness, z, decreased below 4 nm. The extent of increase, ΔΦ, was understood in terms of a simple particle-in-a-box model arriving at the function ΔΦ=ℏ2π2/2mez2. This equation being free of any adjustable parameter, consisting only of the Planck constant and electron mass, seems to be a reasonable first approximation.
This paper presents the characterisation of micromechanical and tribological properties of titanium Grade 2 before and after cyclic oxidation. The oxidation process was carried out at temperatures of 600C, 650C, and 700C in 4 and 12 cycles. Microscopic studies showed that oxide particle size increased with increasing oxidation temperature and the number of cycles. Titanium Grade 2 showed up to 3 times higher hardness after cyclic oxidation. The highest hardness (8.4 GPa) was obtained after 12 cycles of titanium oxidation at 650C. Tribological tests were conducted in pairs with different materials (Al2O3, ZrO2, bearing steel 100Cr6). The presence of oxide layers obtained on the titanium surface resulted in a significant reduction in specific wear rate. Titanium Grade 2 showed the best resistance to sliding wear after cyclic oxidation at 600C during sliding interaction with ZrO2 and 100Cr6 balls (unmeasurable wear under assumed test conditions). In the other test variants, the reduction in wear ranged from 37 to 96%.
Diamond-like carbon (DLC) is a promising solid lubricant owing to its excellent anti-friction and wear-resistance characteristics. However, the high hardness of DLC causes two-body abrasion to its counterpart, which generally are ferrous and brass metals having a relatively low hardness, resulting in severe wear of counterpart. Therefore, it is required to solve the wear-imbalance issue, leading to noise and vibration in tribo-system. In this study, we aimed to investigate the wear behavior of counterparts sliding against DLC. We used four-3d-transition metals (Ti, Fe, Ni, and Cu) as the counterpart of DLC, based on the chemical properties for carbon and oxygen, i.e., the activation energy of oxidation and work of separation with carbon. Our finding is suggested that the wear of transition metals was governed by oxidative wear rather than mechanical wear (e.g., adhesive wear and abrasive wear). Moreover, their oxidative wear was prevented by carbon-containing tribofilm, which is transferred from DLC continuously. It revealed that severe oxidational wear was caused in copper and iron, because of their chemical properties.
In this study, the effect of temperature on the morphology, crystal structure, chemical composition, roughness, wettability, Vickers microhardness, and corrosion resistance of thermally oxidized Ti-15Zr-xMo (x = 0, 5, 10, and 15 wt%) samples were evaluated. Thermal oxidation treatments were performed in air, at temperatures between 773 K and 1173 K, for 21.6 ks. Oxide layers were composed preferentially by Ti, with traces of Zr, in TiO2 and ZrO2. The temperature and bulk chemical composition influenced the phase composition, showing formation of different fractions of TiO2 (anatase and rutile) together small amounts of tetragonal and monoclinic ZrO2. The morphology showed the presence of a smooth inner layer with some oxide precipitates in the outer layer, with thickness ranging from 1 µm to more than 100 µm. Roughness and contact angle values changed according to the growth of precipitates in the oxide layers. Vickers microhardness exhibited a sharp increase with the growth of the oxide layers, remaining higher than that for bulk samples. The results indicated that a favorable combination of surface properties could be achieved when optimizing the thermal oxidation treatment, which could assist in broadening the biomedical applications of the Ti-15Zr-Mo based alloys.Ti-15Zr-15Mo alloy thermally oxidized at 973 K exhibited enhanced corrosion resistance, and emerged as the best candidate for use as orthopedical implants.
This study investigated the corrosion behaviors of Ti6Al4V alloy during the hot salt and hot salt - water vapor tests. Ti6Al4V suffered from slight oxygen erosion at the initial stage, while chlorine greatly accelerated the oxide growth. The initial and accelerated oxidation reactions resulted in a continuous mass gain of Ti6Al4V during the hot salt test. Ti6Al4V experienced severe corrosion degradation during the hot salt - water vapor test. The reaction between oxides, chloride salt and water induced the formation of hydrochloric acid (HCl), while chlorine reacted with water to form HCl. The HCl subsequently reacted with the alloy to form gaseous chlorides, that volatilized to the outside and consequently led to a significant mass loss of Ti6Al4V. These results confirmed that the oxidation - hot salt - water vapor synergism effect showed a strong damage on the hot end components of titanium alloy during the marine service.
