Formation of Structure and Properties of Boron-Rich Fe–B–C Alloys Alloyed with Cr, V, Nb or/and Mo
O. V. Sukhova
Oles Honchar Dnipro National University, 72 Gagarin Ave., UA-49010 Dnipro, Ukraine
Received: 05.05.2020; final version - 11.02.2021. Download: PDF
The effects of substitution of Fe in the boron-rich Fe–B–C alloys, containing 10.0–14.0% B and 0.1–1.2% C, 0–5.0 % Cr, V, Mo or/and Nb (in % wt.), are studied with combined analysis of optical microscopy, X-ray diffractometry, scanning electron microscopy, energy dispersive spectroscopy. The microstructure of the master Fe–B–C alloys consists mainly of primary dendrites of Fe(B, C) solid solution and Fe$_2$(B, C) crystals peritectically formed from Fe(B, C) phase and the rest of the melt. As found, chromium or vanadium have high solubility in the constituent phases of the Fe–B–C alloys, with preferential solubility observed in the Fe(B, C) dendrites, where Cr or V occupy Fe positions. The addition of Cr or V to the Fe–B–C alloys helps to modify their brittleness: while it slightly decreases microhardness values, addition of these elements notably improves the fracture toughness of the constituent phases. Molybdenum or niobium are shown to be present in secondary phases identified as Мо$_2$В, Мо$_2$(B, C) or NbB$_2$, respectively. The level of Mo or Nb contents in the Fe(B, C) and Fe$_2$(B, C) solid solutions and quantity of the observed secondary phases indicate a very small Mo and no Nb solubility in the constituent phases. The Mo or Nb enhances a hardness of the master Fe–B–C alloy due to secondary phases’ precipitation. To enhance performance characteristics of the boron-rich Fe–B–C alloys, the 1.0–2.0% Cr, 0.5–1.0%V, 1.0–3.0% Nb, 1.0–3.0% Mo are simultaneously added to the master alloy. The properties improve due to the formation of Cr- and V-containing Fe$_2$(B, C) and Fe(B, C) solid solutions as well as Mo- and Nb-based secondary phases. The developed multicomponent alloy is recommended as a filler of macroheterogeneous composite coatings for strengthening of parts working in abrasive or gas-abrasive media at elevated temperatures.
Key words: boron-rich iron-based alloys, alloying elements, microstructure, solid solutions, secondary phases, mechanical properties.
PACS: 06.60.Vz, 62.20.M-, 68.08.De, 81.05.Ni, 81.40.Ef, 81.40.Np
Citation: O. V. Sukhova, Formation of Structure and Properties of Boron-Rich Fe–B–C Alloys Alloyed with Cr, V, Nb or/and Mo, Metallofiz. Noveishie Tekhnol., 43, No. 3: 355—365 (2021)