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Al2O3 particle-modified Fe66Cr10Nb5B19 metallic glass matrix coatings were deposited on carbon steel substrates by detonation spraying of the corresponding powder mixtures. The microstructure, mechanical and tribological properties of the coatings were investigated. In the microstructure of the coatings, the Al2O3 particles were located between the layers of the Fe66Cr10Nb5B19 amorphous alloy. The bonding strength between the substrate and composite coatings was ~ 130 MPa. The wear behavior of the coatings was studied under dry linearly reciprocating conditions in a ball-on-flat mode using a WC-6Co ball as a counterbody. It was found that the friction coefficients of the Al2O3-free coating and composite coatings were close to each other and varied in the range of 0.64–0.70. The specific wear rate of the coatings modified with 1.5 and 4 vol.% of Al2O3 was 2.5 × 10−5 and 3.1 × 10−5 mm3 N−1 m−1, respectively, which is about one-fifth of the specific wear rate of stainless steel. It was suggested that the dominating wear mechanisms of the Fe66Cr10Nb5B19-Al2O3 composite coatings are fatigue and abrasion wear. [ABSTRACT FROM AUTHOR]

In the present work, Fe66Cr10Nb5B19 metallic glass coatings deposited by detonation spraying (DS) on carbon steel substrates were structurally characterized and tested in 3.5 wt.% NaCl solutions with pH values of 3.0, 5.5, and 10.0 under potentiodynamic polarization conditions. The coatings had low porosity (2.9-4.5%) and showed a predominantly amorphous structure. The concentration of an amorphous phase in the detonation coatings was 97.5-99.5 wt.%. Such high concentrations were not observed in thermally sprayed Fe-Cr-Nb-B coatings obtained by other research groups. Under the test conditions, the coatings exhibited low corrosion current densities (of the order of 10-6 A cm-2) and low passive current densities (below 10-3 A cm-2) while showing extended passive regions (stable within 1.5 V from the corrosion potential). The Fe66Cr10Nb5B19 coatings produced by DS showed a much better corrosion resistance than the carbon steel substrate. Furthermore, the corrosion resistance of the Fe66Cr10Nb5B19 DS coatings was superior to that of flame-sprayed or high-velocity oxygen fuel-sprayed Fe-Cr-Nb-B coatings reported to date. These results open new prospects for the use of affordable and Cr-lean Fe-Cr-Nb-B glassy coatings for carbon steel protection, where chloride-induced corrosion is the major degradation risk, such as metallic components for marine applications. [ABSTRACT FROM AUTHOR]

This study presents the results of the morphological dependence of alumina granules obtained by spray freeze drying (SFD) with twin‐fluid atomization. It is shown that the introduction of 1‐, 2‐ and 4‐wt.% polyvinyl alcohol (PVA) as a binder in an alumina suspension leads to the formation of irregular granules. Depending on atomization conditions, spherical, "tadpole‐like," granule‐satellite and granule aggregates may form during SFD. Increasing the flight time of droplets before the fixing of their shape when they come in contact with liquid nitrogen effectively contributes to the spheroidization of alumina granules. Compacting PVA‐free SFD granules leads to the formation of diagonal flaws in a green‐body structure. Adding PVA prevents the abovementioned defects by increasing the strength of alumina granules. Increasing the amount of PVA leads to an increase in "tadpole‐like" granule content and, consequently, a decrease in a green‐body density. [ABSTRACT FROM AUTHOR]

• In many studies, a liquid phase forms during spark plasma sintering (SPS) • The formation of liquid can be concurrent or stimulated. • The origin of the liquid phase formation during SPS is analyzed. • Experimental evidence of melting at inter-particle contacts is summarized. • Problems of description of SPS with a liquid phase involved are discussed. Spark plasma sintering (SPS) is a modern sintering technique based on the application of pulses of direct electric current and pressure to the powder sample. SPS is often regarded as a solid state sintering technique. At the same time, in many studies, the formation of a liquid phase during SPS was observed as an effect concurrent to the powder consolidation. Furthermore, in some cases, the formation of a liquid phase was intentionally stimulated. In this article, we aim to analyze the origin of the liquid phase formation during SPS and discuss its role in the microstructure development of different materials. Two situations are considered: melting occurring when the whole sample reaches a temperature required for the liquid to appear and melting of local character associated with overheating of the inter-particle contacts. The problems of the description of the SPS processes with liquid phases involved are discussed and possible future research directions in this area are proposed. [ABSTRACT FROM AUTHOR]