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Surface Damage Mitigation of Titanium and Its Alloys Via Thermal Oxidation

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Surface Damage Mitigation of Titanium and Its Alloys Via Thermal Oxidation Rev. Adv. Mater. Sci. 2019; 58:132–146 Review Naiming Lin*, Ruizhen Xie*, Jiaojuan Zou, Jianfeng Qin, Yating Wang, Shuo Yuan, Dali Li, Lulu Zhao, Luxia Zhang, Zhenxia Wang, Yong Ma, Pengju Han, Wei Tian, Xiaoping Liu, Zhihua Wang, and Bin Tang Surface damage mitigation of titanium and its alloys via thermal oxidation: A brief review https://doi.org/10.1515/rams-2019-0012 1 Introduction Received May 28, 2018; accepted Oct 04, 2018 Abstract: Titanium (Ti) and its alloys have been exten- Titanium (Ti) used to be considered a rare metal in 1800s sively applied in various fields of chemical industry, ma- [1]. According to statistics Ti had been turned out to be rine, aerospace and biomedical devices because of a spe- the ninth most abundant element on earth and the fourth cific combination of properties such as high strength to most abundant metal in the following century [2, 3]. Ti weight ratio, exceptional corrosion resistance and excel- and its alloys obtained considerable development since lent biocompatibility. However, friction and wear, corro- the pure metal (Ti sponge) firstly became commercially sion which usually occur on the surfaces of Ti-base com- available by Kroll process in the middle of 20th century [4]. ponents can lead to degradation in both properties and Ti and its alloys initially made their names in aerospace performance. Thermal oxidation (TO) of titanium and its and chemical industries due to their promising strength- alloys under certain conditions can accomplish significant to-weight ratios, high tensile strength and excellent corro- improvements both in wear resistance and corrosion resis- sion resistance [4]. While widespread use of Ti-base met- tance, without special requirements for substrate geome- als were limited somewhat by cost at that time [2, 3]. In tries. In this review, the studies and applications of TO pro- nowadays, Ti and its alloys are one kind of the most im- cess in surface damage mitigation titanium and its alloys portant structural metallic materials in in various indus- were reviewed and summarized. trial fields. Due to their relatively low modulus, good fa- tigue strength, promising formability/machinability, anti- Keywords: Surface damage; titanium; titanium alloys; sur- corrosion property and exceptional biocompatibility, in- face strengthening;thermal oxidation creasing usage has been found in automotive applications, chemical processing equipment, pulp and paper industry, marine vehicles, biomedical devices and sporting goods af- *Corresponding Author: Naiming Lin: Research Institute of Sur- face Engineering, Taiyuan University of Technology, Taiyuan, ter wide technical investigations and estimations [5, 6]. 030024, P. R. China; Shanxi Key Laboratory of Material Strength Nevertheless, Ti and its alloys cannot meet all of the re- and Structure Impact, Taiyuan University of Technology, Taiyuan, quirements during engineering service. The drawbacks of 030024, P R China; Department of Chemical and Materials Engineer- low surface hardness, high/unstable friction coefficient in ing, University of Alberta, Edmonton, AB T6G 1H9, Canada; Email: sliding contacts against common bearing materials, severe [email protected] *Corresponding Author: Ruizhen Xie: Department of Civil Engi- adhesive wear and susceptibility to galling are harmful neering, Taiyuan University of Technology, Taiyuan, 030024, P R for the direct application of Ti-base materials. Insufficient China wear resistance is a major technological problem threat- Jiaojuan Zou, Jianfeng Qin, Yating Wang, Shuo Yuan, Dali Li, ening to limit the extensively application of Ti and its al- Lulu Zhao, Luxia Zhang, Zhenxia Wang, Yong Ma, Xiaoping loys as they are subjected to aggressive and harsh working Liu, Bin Tang: Research Institute of Surface Engineering, Taiyuan conditions during operation [7–9]. Because of removing University of Technology, Taiyuan, 030024, P. R. China Pengju Han: Shanxi Key Laboratory of Material Strength and Struc- or minimizing materials degradation/failure is nowadays ture Impact, Taiyuan University of Technology, Taiyuan, 030024, necessary by existing raw materials and energy shortage, P R China; Department of Civil Engineering, Taiyuan University of Technology, Taiyuan, 030024, P R China Wei Tian: Research Institute of Surface Engineering, Taiyuan Uni- versity of Technology, Taiyuan, 030024, P. R. China; China United Zhihua Wang: Shanxi Key Laboratory of Material Strength and Northwest Institute for Engineering & Research, Xi’an, 710082, P. R. Structure Impact, Taiyuan University of Technology, Taiyuan, China 030024, P R China Open Access. © 2019 N. Lin et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License Surface damage mitigation of titanium and its alloys via thermal oxidation: A brief review Ë 133 Figure 1: High-temperature metal oxide formation diagram, (a) adsorption of oxygen, (b) diffusion of oxygen, (c) formation of film/scale, (d) growth of film/scale and (e) formation of thick oxide layer. material scientists and engineers have long devoted them- technique that has been industrially used to strengthen selves to design and produce new materials which are si- the Ti and its alloys [26]. Its popularity is mainly assign multaneous with promising wear and corrosion resistance to its cost effectiveness, simplicity and rapidity. Further- that can meet the increasing challenges and demands more, the TO treatment has no special requirements for over wide range of modern industrial applications [10]. An- geometrical shapes of components [27]. TO process has other way of achieving this is utilizing appropriate sur- been confirmed that it can afford combined improvements face treatment techniques, e.g. surface strengthening (de- in wear resistance and corrosion resistance [28, 29]. The formation/phase transformation treatment), surface cov- benefits conferred by the TO process are attributed toboth ering (coating/layer/film) and surface diffusion (thermo- the formation of an external rutile oxide ceramic layer (in- chemical treatment or laser/plasma/electron beam alloy- ert/passivation capability) and an internal oxygen diffu- ing) on the surfaces of existing materials [1]. Surface treat- sion (solid solution strengthening) zone [30]. In this re- ments are able to realize a favorable compromise between view, the technological principle was briefly introduced, the cost and the performance by endowing the mate- surface damage mitigation of titanium and its alloys via TO rial surfaces with high hardness value, effective friction- treatment was presented and summarized. This work is ex- reduction, excellent corrosion resistance and promising pected to create database and provide reference informa- mechanical performance, meanwhile the desirable bulk at- tion, thereby furtherly broaden the practical applications tributes of the materials are maintained [11]. of TO treatment on titanium and its alloys. A variety of surface treatment technologies, such as thermochemical surface treatment (nitriding, carburizing, surface alloying), micro arc oxidation (MAO)/plasma elec- 2 Thermal oxidation of titanium trolytic oxidation (PEO), physical vapor deposition (PVD), chemical vapor deposition (CVD), ion implantation, ther- and its alloys mal spraying, thermal oxidation (TO), laser surface treat- ment and electro-spark deposition (ESD), also several du- A number of studies reported that a complete TO process plex treatments have been conducted to improve the sur- of metals generally contains five steps (Figure 1) [2]: 1 ab- face performance of titanium and its alloys [12–25]. Among sorption of oxygen, 2 dissolution of oxygen, 3 formation the existed surface treatment technologies, thermal oxi- of thin oxide film, 4 growth of oxide layer, 5 formation of dation (TO) which taking the advantage of high chemi- thick oxide layer. The oxidation reaction of Ti with oxygen cal affinity between Ti and oxygen (O), is an ideal surface 134 Ë N. Lin et al. is shown in Eq. (1): Ye et al. [33] firstly processed the thermal oxidation treatment on commercially pure titanium (CP-Ti, TA2) at Ti + O = TiO (1) 2 2 500∘C, 600∘C, 650∘C, 700∘C, 750∘C and 850∘C for 210 min. With respect of Ti alloys, taking Ti6Al4V as an exam- It was seen that the thermally oxidized samples revealed ple, other alloying elements will also react with oxygen as thicker TiO2 layers than the authigenic TiO2 layer on pure ∘ shown in the following Eqs. of (2) and (3): titanium, only as the TO temperature was above 600 C. Meanwhile it was found that higher temperature bene- 4 2 Al + O = Al O (2) 3 2 3 2 3 fited the thickening of TiO2 layer. All of the TO treated pure titanium presented improved corrosion resistance in 4 2 36%-38% HCl at room temperature and in 30% H O at V + O = V O (3) 2 2 3 2 3 2 3 36.5∘C. The most promising corrosion resistance was re- ∘ Under permanent temperature and pressure condi- ceived when the TO treatment was conducted under 700 C 0 for about 330-500 min. tions, the standard Gibbs energy change (∆GT) can be ob- tained from the following equation [31]: Yan et al. [34] found that an oxide film composed of ru- tile TiO was formed on the surface of pure titanium after T T 2 Z Z ∘ 0 0 0 ∆Cp atmospheric thermal oxidation treatment (600-900 C/0.5- ∆G = ∆H − T∆S + ∆Cp dT − T dT (4) T 298 298 T 24 h). When the oxidation temperature is low and the time 298 298 is short, the oxide film is well bonded to the substrate. With 0 where ∆H298 is the standard free energy of formation the increase of oxidation temperature and time, the bind- 0 at 298 K (kJ/mol), T the is temperature in Kelvin, ∆S298 is ing force decreases. Between the oxide film and pure tita- the standard absolute entropy at 298 K, ∆Cp is the heat ca- nium is a layer of oxygen-permeating layer composed of pacity. Eq. (4) can be furtherly simplified as follows: an α-phase Ti-O solid solution. With the increase of oxida- tion temperature and the prolongation of time, the oxygen ∆G0 = ∆H0 − T∆S0 (5) T 298 298 content in the oxygen-permeating layer increases, and the 0 thickness of the oxygen-permeable layer both inside and For all of the reactions, the values of ∆GT belonging to TiO2, Al2O3 and V2O3 can be calculated according to outside increases.
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