PSI - Issue 59

Olexandr Ivanov et al. / Procedia Structural Integrity 59 (2024) 622–628 Olexandr Ivanov et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Results and discussion Microstructures of sample materials presented on Fig. 1. As can be seen, structure of sample 1 (a) is characterized with two different areas with clear border between them. There is also an absence of traces of any polygonal phases which indicates the absence of Fe(Mo, B) 2 phase. This, most likely, caused with low percentage of Mo in initial material. Also, clear formation based on Ti, such as TiC, TiB 2 , cannot be found in the observed area. This could be due to the higher formation energy of such phases and (or) chemical features of the initial Ti material. Microstructure of sample 2 (b) differs with presence of prolonged polygonal particles distributed in the material. Microstructure of sample 3 (c) characterized with lesser ferrite phase and higher amount of polygonal particles with higher size and more square-formed in comparison to sample b. Such particles can be described as Fe(Mo, B) 2 . Inside of Fe(Mo, B) 2 particles small round-like grains can be seen, which are grains of TiC. Temperature formation of TiC is higher than it is for Fe(Mo, B) 2 so it works as modifier for Fe(Mo, B) 2 formation. Such influence leads to formation of uniformly distributed particles with size of the same order. According to The Materials Project (https://next-gen.materialsproject.org/) the phase Fe(Mo, B) 2 is one of the favorable for formation in B-Fe-Mo system: Mo ₂ FeB ₂ crystallizes in the tetragonal P4/mbm space group. Mo² ⁺ is bonded in a distorted hexagonal planar geometry to six equivalent B³ ⁻ atoms. There are two shorter (2. 33 Å) and four longer (2.34 Å) Mo–B bond lengths. Fe² ⁺ is bonded in a square co- planar geometry to four equivalent B³ ⁻ atoms. All Fe –B bond lengths are 2.33 Å. B³ ⁻ is bonded in a 9- coordinate geometry to six equivalent Mo² ⁺ , two equivalent Fe² ⁺ , and one B³ ⁻ atom. The B –B bond length is 1.85 Å. For sample d Fe(Mo, B) 2 phase can be seen in particles with size that differs a lot as well as it differs with form, that in some particle seen prolonged in one direction, which is caused by a small amount of Ti in the initial electrode. In this structure lack of Ti leads to lesser formation of TiC and, as a result, lesser modifier for Fe(Mo, B) 2 formation. Structure also characterized with lesser ferrite phase, which can be result of features of formation of high molybdenum alloys.

Fig. 1. SEM images of hardfacing samples 1 (a), 2 (b), 3 (c) and 4 (d).