PSI - Issue 53

Serhii Lavrys et al. / Procedia Structural Integrity 53 (2024) 246–253

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Serhii Lavrys et al. / Structural Integrity Procedia 00 (2019) 000 – 000

1. Introduction Due to the excellent combination of high specific strength and corrosion resistance, titanium alloys are promising materials in many industries [1 – 3]. For example, titanium alloys have the excellent corrosion resistance in many oxidizing and some diluted reducing acids due to the instantaneous formation of the protective oxide film, which has high chemical stability. Therefore, titanium and its alloys are candidate materials for the chemical, petrochemical, metallurgical and energy industries. For example, titanium is widely used as corrosion resistance material for the production of pumps, piping systems, coolers, filters and valves [4 – 6]. However, the widespread use of titanium alloys is usually limited because of the high manufacturing cost. It is associated with complicated conventional manufacturing technology and subsequent energy-consuming machining of titanium semi-finished products [7, 8]. It is possible to reduce the high cost of products made of titanium alloys due to the use of new and advanced technologies for their production – additive manufacturing (AM). The main advantage of AM compared to the conventional technology is the ability to form complex architectural configurations of products with satisfactory geometric accuracy [8, 9]. That is, AM allows to fabricate titanium alloy parts without the use of the energy-consuming machining (turning, cutting, welding, etc.). Another advantage is that AM can be classified as a green technology. AM builds the product layer by layer, reducing material consumption and waste. The waste (unused titanium or titanium containing powder mixture) generated in the process is reused in manufacturing and does not lose any of its properties. However, AM titanium alloys are characterized by lower anti-corrosion properties compared to the conventional manufactured (wrought) ones. This is explained by the structural features of AM titanium alloys, such as structural or chemical heterogeneity, anisotropy, porosity, and a typical martensitic structure [9 – 13]. For instance, B. Wu et al. established that the corrosion behaviour is anisotropic due to corresponding anisotropy in microstructure, phase structure, grain size and orientation within the AM Ti6Al4V alloy. Compared to standard wrought Ti6Al4V alloy, the AM Ti6Al4V alloy had a slightly inferior corrosion resistance owing to the formation of asymmetrical structures with acicular α’ phases [10]. A.H. Ettefagh et al. showed that the corrosion rate of AM Ti6Al4V alloy is by almost sixteen times worse than the wrought one, which is explained by the presence of non-equilibrium martensitic phase [13]. One of the methods of eliminating structural anisotropy and martensitic structure, and therefore improving the corrosion resistance of AM titanium alloys, is post heat treatment (HT). It should be noted that, depending on the AM method, it is possible to obtain titanium alloys similar in chemical composition, but with different phase-structural states. As a result, in order to improve the anti-corrosion characteristics by post HT (annealing), the time-temperature regimes of the treatment should be determined based on the specific titanium alloy. Therefore, the aim of this study is to determine the effect of post heat treatment on the corrosion resistance of Ti6Al4V titanium alloy produced by the selective laser melting method.

Nomenclature AM

additive manufacturing;

HT

heat treatment;

K W A

constant (8.76 × 10 4 ); weight loss, [g]; exposure time, [h]; density, [g/cm 3 ]; corrosion potential, [V]; exposed area sample, [cm 2 ];

T D

E corr

i corr and і pass

corrosion and passivation current density, [A·cm

− 2 ], respectively;

R S , R f , R ct and R p CPE1 and CPE2

solution, oxide film, charge transfer and polarization resistance [Ω·cm oxide film and electric double layer capacitance [Ω − 1 cm − 2 s n ], respectively;

2 ], respectively;