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The microstructure and oxidation behavior of Fe–B alloys have been investigated. Oxide scale cross-sectional microstructures oxidized at 1073 K for 100 h have been studied. EPMA investigations show that B 2 O 3 –SiO 2 oxides accumulates in the inner oxide layer which improves the oxidation behavior and oxide layer adhesion considerably. Cyclic oxidation kinetics data indicates that Fe–B 3.08 wt.% alloy presents the best oxidation resistance. The formation of diffusion zone in the Fe–B alloys indicate that the oxidation of the Fe 2 B boride is controlled by boron diffusion. The diffusion zone increases with time and reaches a maximum width of 60–65 μm. [ABSTRACT FROM AUTHOR]

The solidification microstructure, crystallography of eutectic precipitations and mechanical properties of high boron steel with various aluminium and chromium concentrations have been investigated extensively in the present study, as the foundation of the further analysis about the corrosion and abrasion properties at elevated temperature. The experiment results indicate that the as-cast microstructures of test alloys mainly consist of a dendritic matrix with many interdendritic precipitations. The Fe–B binary alloy is mainly composed of ferrite, Fe 2 B and pearlite and the Fe–B–Al ternary alloy consists of α-(Fe, Al) solid solution, Fe 2 B and Fe 3 AlC 0.5 . When aluminium and chromium elements are added synchronously, the as-cast microstructure changes to α-(Fe, Al, Cr) solid solution, (Fe, Cr) 2 B boride, M 7 (C, B) 3 and M 23 (C, B) 6 borocarbides. Moreover, the nucleation and growth of M 7 (C, B) 3 borocarbide is adhere to (Fe, Cr) 2 B boride because of an interphase match between crystal plane (10 1 ( — ) 0) of M 7 (C, B) 3 and (010) of Cr-rich (Fe, Cr) 2 B. Alloy Fe-1.46 wt. % B-0.22 wt. % C-11.92wt. % Cr-8.73 wt. % Al shows the highest impact toughness value. The main fracture mode is brittle fracture of boride and tough fracture of matrix. [ABSTRACT FROM AUTHOR]

Abstract Based on cold metal transfer (CMT) welding, wire-arc additive manufacturing (WAAM) technology was adopted to manufacture 2Cr13 part. The spatial periodicity of the microstructural evolution and the anti-indentation properties was explored. The results show that the as-deposited part was featured by periodic martensite laths within the block-shaped ferrite matrix in the inner layers, followed by epitaxial ferrite grains containing ultra-fine acicular martensite in the top layer only. A slightly decreased Fe intensity was caused by local elemental segregation during the re-melting process; the homogeneity of Fe and Cr was attributed to similar cooling conditions in the top layer. The martensite size gradually coarsened from the fine grain zone to the coarse grain zone and the shape transformed correspondingly from irregularly short bar-like to orderly long rod-like due to the location-related thermal history. Elongated ferrite grains exhibited a slight fiber texture in the top layer and a random crystallographic orientation in the middle region. The anti-indentation properties evolved periodically due to the periodic microstructural characteristics. The obtained experimental results confirmed higher anti-indentation properties of the as-deposited part following comparison with the as-annealed base metal, while the elastic moduli of samples were not significantly different. Graphical abstract Unlabelled Image Highlights • 2Cr13 thin-wall part with defect-free was additively manufactured by robot-assisted CMT technology. • Martensite coarsened gradually from FZ to CZ while only ultra-fine acicular martensite in the top layer. • A random crystallographic orientation in the middle region while a slightly fiber texture in the top layer • Mechanical properties were evolved periodically due to the periodic microstructural evolution. [ABSTRACT FROM AUTHOR]

The corrosion-wear behavior of Fe-3.5 wt.%B steel in liquid zinc was investigated via the block-against-ring technique. Owing to the protective ability of the Fe 2 B phase, this steel exhibited better corrosion-wear resistance than a 316L stainless steel. SEM, XRD, and EDS of the corrosion-wear interface indicated that the corrosion-wear process of Fe-3.5 wt.%B steel consists of the following steps: corrosion of the matrix, fragmentation and removal of FeZn 13 , and failure of the Fe 2 B. The intensified mechanical effect of wear resulted in significant deterioration (via fracture and removal of FeZn 13 , and spallation Fe 2 B) of corrosion-wear interface, which exacerbated corrosion, and facilitated the corrosion-wear process. [ABSTRACT FROM AUTHOR]

Highlights: [•] The as-received microstructure of bulk Fe2B comprises iron and silicon borides. [•] The orientation of Fe2B in liquid zinc strongly affects on corrosion resistance. [•] The Fe2B/FeB phase transition process of bulk Fe2B in liquid zinc occurs. [•] Phase transition and spalling dominate corrosion of Fe2B in liquid zinc. [Copyright &y& Elsevier]

Abstract: The microstructure and crystallography of eutectic borides and secondary precipitations in 18wt.% Cr–4wt.% Ni–1wt.% Mo–3.5wt.% B–0.27wt.% C steel have been investigated extensively. The results show that the as-cast microstructure of Cr–Ni–Mo-containing Fe–B steel is composed of a dendritic martensite with large interdendritic eutectic borides. Transmission electron microscopy (TEM) results confirm that the borides are indexed to Cr- and Mo-rich M2B-type borides with the chemical formulas of Fe(1.35–1.36)Cr(0.92–1.05)B0.96 and Fe0.73Cr0.45Mo0.78B, respectively. The cluster-like boride possesses a possible orientation relationship between body-centred orthorhombic Cr-rich M2B and martensite with //〈110〉α growth direction. After destabilization, M23(C, B)6 secondary borocarbide with a specific orientation relationship precipitates first and thereafter coarsens following the appearance of M7(C, B)3 precipitation with the increasing destabilization temperature at the same soaking time, thus leading to a large decrease of Cr content in the martensite. However, no M6(C, B) secondary borocarbide is found in as-destabilized Fe–B steel. Destabilization treatment has no effect on the morphology of eutectic borides. The secondary borocarbides have the stoichiometry of (Fe18.26Cr4.74)(B, C)6 and (Fe3.86Cr3.14)(B, C)3 respectively. The high-resolution TEM results indicate that the nucleation and precipitation of M23(C, B)6 occur at the grain/subgrain boundaries as well as partial within martensite, and a subsequent transformation from M23(C, B)6 to M7(C, B)3 takes place in situ, which is probably owing to the crystalline defects of dislocations and stacking faults in the structures caused by lattice distortion. [Copyright &y& Elsevier]

Abstract: The interfacial morphology and corrosion resistance of low carbon Fe–B cast steels in zinc bath at 520°C were investigated. The results show Fe–B cast steel containing high Cr and Ni exhibits the best corrosion resistance to liquid zinc. The corrosion layers are composed of Γ-Fe3Zn10, δ-FeZn10, ξ-FeZn13 and η-Zn. The corrosion behaviour of Fe–B cast steels includes the following processes: the preferential leach and dissolution of Cr and Ni, the formation of Fe–Zn compounds controlled by zinc atom diffusion, and the spalling of borides without the supporting role of α-(Fe,Cr) matrix corroded by liquid zinc. [Copyright &y& Elsevier]

Extreme High-Speed Laser Metal Deposition (EHLMD) is an efficient additive manufacturing technology that can quickly form difficult-to-machine materials. However, the rapid melting and solidification of EHLMD has the characteristic of forming a metastable microstructure. This study examines the effect of different aging temperatures on the microstructure and properties of EHLMD K648 superalloy. It is found that the formation of long needle-like α-Cr phase and γ' phase at lower aging temperatures (750 °C and 800 °C) is more beneficial for improving the strength of EHLMD K648 superalloy. The tensile strength was highest at 750 °C (1236 MPa) but its elongation was low (9.4 %). As the aging temperature increased (850–900 °C), the α-Cr phase transformed into rods and small particles, resulting in a decrease in tensile strength and an increase in elongation. At 900 °C, the tensile strength was 918 MPa and the elongation was 21.0 %. With further increase in aging temperature (>900 °C), coarse carbide and α-Cr phase precipitated in EHLMD K648 superalloy, causing its tensile strength and elongation to decrease. When the aging temperature reached 1000 °C, the tensile strength and elongation decreased to 790 MPa and 13.3 %, respectively. • The microstructure and mechanical properties of EHLMD K648 superalloy were investigated by different aging temperature. • The α-Cr phase evolves from long needle-like to rod-like and coarse particles with increase of aging temperature. • As the aging temperature increases, the tensile strength gradually decreases. [ABSTRACT FROM AUTHOR]

In present study, Fe-based composite layers were fabricated on steel substrate by laser cladding with or without the addition of Nb and B 4 C in Fe-based alloy powders. The phase composition, microstructure evolution, microhardness and wear properties of Fe-based composite layers were studied. The results showed that the phases in the Fe-based composite layer were mainly α-Fe, Fe 2 B, Cr 7 C 3 and Cr 23 C 6. The addition of Nb and B 4 C resulted in the in-situ formation of NbC phase, an increase in the amount of Fe 2 B phase, and the refinement of the microstructure in the Fe-based composite layer. The microhardness of the Fe-based composite layer was increased by 269.5 HV 0.5 and the wear resistance was improved to about 1.5 times the original wear resistance when the 5% Nb and 5% B 4 C powders were added. The wear mechanisms of both two Fe-based composite layers were abrasive wear and adhesive wear. • A new Fe-based composite layers were fabricated by laser cladding. • In-situ NbC phase was generated. • The microstructure evolution mechanism were proposed. • The microhardness and the wear resistance was improved by adding Nb and B 4 C. [ABSTRACT FROM AUTHOR]

Abstract The crack-free H13 block was deposited through additive manufacturing with the cold metal transfer technology. The internal 3D pore distribution, the microstructural evolution, and the mechanical performances were explored. A negligible porosity with dispersive-distribution and spherical-shape below 0.001% guaranteed a sound metallurgical bonding within the as-deposited part. The martensite laths growth direction varied dramatically with a very short position variation, as well as the block-like size-inconsistent δ-ferrite presence in the overlap zone, which were mainly generated by the thermal flux direction from the center to margin within a single arc track. Massive second-phase particles with morphology-diversity and size-nonuniformity were precipitated, indicating a strong dependency with the intrinsic heating treatment. The enhanced microhardness in the body zone was attributed to the martensite strengthening mechanism, while slightly low hardness was produced due to the soft δ-ferrite formation. When compared with the other zones, the enhanced ultimate tensile strength was obtained in the body zone at the expense of tensile ductility, revealing a positive relationship with the rise of hard martensite percentage. This work demonstrated that a crack-free H13 block with limited porosity and desirable mechanical properties was deposited using the present technology, despite the nonhomogeneous microstructures. Highlights • A crack-free H13 block part innovatively and firstly deposited using the robotic CMT technology. • A negligible porosity even below 0.001% guaranteed a sound metallurgical bonding behavior. • Varied microstructural evolution with a very short position variation within a single arc track. • Desirable mechanical performances due to martensite strengthening and precipitation strengthening. [ABSTRACT FROM AUTHOR]

Highlights • A new and simple method for producing steady disturbance wave is mentioned in this research. • The droplets formation process experienced different breakup mode at different nozzle diameters. • The wavelength of surface wave decreased with the rose of the disturbance frequency. • With the increase of the disturbance frequency, the size of droplets diameter decreased. Abstract The continuous-ink-jet printing technology is of great importance in many fields of the industrial and scientific applications due to its low-cost, simplicity, and flexible to a wide variety of material, which entail important technological advantages over existing technology. The perturbation imposed on the surface of the jet-flow is one of the primary parameters to control droplets formation. Therefore, a simple method for producing steady disturbance is presented in this article for further development the technology of continuous-ink-jet printing. Using high-speed photography technology along with image processing, the formation of droplets are investigated at different nozzle diameter and disturbance frequency. The results showed that the droplets formation experienced different breakup modes at different nozzle diameters. The satellite droplet was produced by breakup of jet-tip at the nozzle diameter of 0.15 mm. When the nozzle diameter was increased to 0.33 mm, the satellite droplet was produced by breakup of the trailing of primary droplet. The vibration region of uniform droplets could be controlled by the change of the gas pressure. The wavelength of surface wave decreased with the rose of the disturbance frequency, and a model was established to illuminate the relationship between the disturbance frequency and the wavelength of surface wave. The diameter of droplets decreased with the rose of the disturbance frequency. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) technology was adopted to deposite 2Cr13 thin-wall part using robotic cold metal transfer (CMT) equipment; the process stability, phase identification, microstructural evolution, and tensile properties in different layers were investigated. The results showed that a smooth surface was obtained for each layer due to the stable droplet transfer process, which ensured a stable deposition process. Positions in different layers had no significant influence on the structural aspects of the as-fabricated part according to XRD results. Elongated ferrite grains and fine-grained acicular martensite within the matrix in the top layer were recrystallized, instead of a spatial periodicity of martensite laths within equiaxed ferrite grains in the inner layers. Martensite content was increased gradually away from the base metal in the 05–25 th layers except nearly 100% martensite in the first layer. Long axis of martensite laths was randomly distributed in the X-Y plane in the both top and middle regions, while an epitaxial growth parallel to the building direction was found in the X-Z and Y-Z planes. Higher homogeneous ultimate tensile strength (UTS) and strong anisotropy in poorer ductility were obtained for the AM part when compared with the as-solutioned counterpart. Fracture behavior was transformed from ductile to mixed-mode, and finally to brittle from the 01 st layer to the 25 th layer. [ABSTRACT FROM AUTHOR]

The interfacial morphologies and erosion-corrosion behavior of directional Fe-3.5 wt.% B steel in flowing liquid Zn-0.30 wt.% Al were investigated. Adding 0.30 wt.% Al to liquid zinc significantly improved the erosion-corrosion resistance of directional Fe-3.5 wt.% B steel, which possesses greater erosion-corrosion resistance when the [002] orientation of Fe 2 B is perpendicular to the erosion-corrosion interface. The erosion-corrosion interface consisted of an inhibition layer, determined by 0.30 wt.% Al, liquid zinc temperature and Fe 2 B orientation. This interface inhibited the diffusion, controlled Fe 2 B failure mode, resisted micromechanical scouring, and suppressed erosion-corrosion. Deterioration of the inhibition layer at the erosion-corrosion interface resulted in severe erosion-corrosion damage. [ABSTRACT FROM AUTHOR]

The effects of orientation and lamellar spacing on the interface microstructure and corrosion behavior of a directionally solidified (DS) Fe-B alloy in a hot-dip galvanization bath were investigated. The results indicated that the microstructure of the DS Fe-B alloy consisted of oriented α -Fe and Fe 2 B grains. The oriented Fe 2 B with [002] preferred growth orientation displayed low-angle grain boundaries on the Fe 2 B (001) basal plane. The DS Fe-B alloy with Fe 2 B vertical to the corrosion interface possessed the best corrosion resistance to liquid zinc owing to the formation of an interface-pinning multilayer induced by the Fe 2 B orientation. The epitaxially grown columnar ζ-FeZn 13 products were controlled by the geometric constraint of Fe 2 B grain orientation and size, and a mechanism model that explains the interfacial orientation-pinning behavior is discussed in detail. Transmission electron microscopy (TEM) results revealed that the possible orientation relationships of the oriented Fe 2 B and columnar ζ-FeZn 13 products are (001) Fe2B //(−402) ζ-FeZn13 and [002] Fe2B //[110] ζ-FeZn13 . The corrosion damage of the DS Fe-B alloy with Fe 2 B [002] orientation vertical to the corrosion interface in liquid zinc was governed by the competitive mechanisms of Fe 2 B/FeB transformation and microcrack-spallation resistance, which is proposed as being the result of a multiphase synergistic effect in the micro-structures. [ABSTRACT FROM AUTHOR]

• Temperature effect on oxidation resistance of a Fe-Cr-B-Al-C-Mn-Si alloy is studied. • The oxidation resistance is best at 900 °C; it decreases with rising temperature. • The formation mechanism of oxide scale with bilayer/monolayer structure was discussed. • MnCr 2 O 4 oxides promote protective α-Al 2 O 3 oxide formation. • Selective oxidation of Al suppresses outward diffusion of Cr and Mn. The effect of temperature on the oxidation resistance of a novel wear-resistant Fe-10Cr-1.5B-6Al-0.3C-0.8Mn-0.6Si alloy is investigated. The mass growth rate shows that this alloy exhibits superior oxidation resistance at 900 °C. As the oxidation temperature increases from 900 °C to 1100 °C, the structure of the observed oxide scales transforms from a porous bilayer to a flat monolayer, while the oxidation rate increases sharply. The selective oxidation of Al suppresses the outward diffusion of Cr and Mn to form MnCr 2 O 4 oxides in the monolayer oxide scale, thereby decreasing the oxidation resistance at 1100 °C. [ABSTRACT FROM AUTHOR]