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The use of pre-alloyed powders as high-entropy alloy (HEA) coating precursors ensures a predetermined (unaltered) elemental composition of the coating with regard to the feedstock powder. At the same time, it is interesting to tackle a more challenging task: to form alloy coatings from powder blends (not previously alloyed). The powder-blend-based route of coating formation eliminates the need to use atomization or ball milling equipment for powder preparation and allows for the introduction of additives into the material in a flexible manner. In this work, for the first time, a HEA was obtained using detonation spraying (DS) followed by spark plasma sintering (SPS). A powder mixture with a nominal composition of 10Al-22.5Fe-22.5Co-22.5Ni-22.5Cu (at.%) was detonation-sprayed to form a multicomponent metallic coating on a steel substrate. The elemental composition of the deposited layer was (9 ± 1)Al-(10 ± 1)Fe-(20 ± 1)Co-(34 ± 1)Ni-(27 ± 1)Cu (at.%), which is different from that of the feedstock powder because of the differences in the deposition efficiencies of the metals during DS. Despite the compositional deviations, the deposited layer was still suitable as a precursor for a HEA with a configurational entropy of ~1.5R, where R is the universal gas constant. The subsequent SPS treatment of the substrate/coating assembly was carried out at 800–1000 °C at a uniaxial pressure of 40 MPa. The SPS treatment of the deposited layer at 1000 °C for 20 min was sufficient to produce an alloy with a single-phase face-centered cubic structure and a porosity of <1%. Interestingly, the hardness values of the as-sprayed and SPS-treated coatings were close to each other (~320 HV0.3). The hardness of the coatings measured in two perpendicular directions did not differ significantly. The features of the DS–SPS route of the formation of HEA coatings and its potential applications are discussed. [ABSTRACT FROM AUTHOR]

The goal of this work was to study the phase and microstructure changes involved in the process of coating formation by detonation spraying of Ti3Al, TiAl, and TiAl3intermetallics. The O2/C2H2ratio was varied between 1.1 and 2.0, and the explosive charge was 30–40% of the barrel volume. In most experiments air was used as a carrier gas; selected experiments were performed with argon. We found that depending on the spraying parameters, TiAl3essentially retains in the coatings or partially decomposes forming TiAl and Ti3Al as minor phases. Detonation sprayed Ti3Al reacts with nitrogen and oxygen partially transforming into titanium nitrides TiN/Ti2N and titanium oxynitrides TiNxOy. TiAl partially decomposes forming Ti3Al, which further reacts with oxygen and nitrogen as the particle temperature and the content of oxygen in the explosive mixture increase. Thein situformed titanium nitrides and oxynitrides show a reinforcing effect increasing the hardness of the coatings. [ABSTRACT FROM PUBLISHER]

Tungsten is a promising material for plasma-facing components of thermonuclear reactors. In the present work, tungsten coatings of low residual porosity (1%) were deposited on copper substrates by detonation spraying. Calculations of the particle temperatures and velocities were conducted for tungsten particles of different sizes using a previously developed model. These calculations helped selecting the spraying parameters enabling the formation of high-quality tungsten coatings in the experiments. A proper selection of the stand-off distance allowed achieving a high deposition efficiency of the powder (60%). The coatings showed a high bonding strength to the copper substrates, which was found to be 100 MPa, and a high hardness (850 HV). The coatings were shown to accumulate compressive stresses, which are beneficial for the structural integrity of coatings up to 500 μm thick. • Tungsten coatings of low porosity were obtained by detonation spraying. • Velocities and temperatures of the particles leaving the gun barrel were calculated. • No oxidation or carbidization of tungsten took place during spraying. • The W coatings showed a high bonding strength to a copper substrate (100 MPa). • The W coatings possessed a high Vickers hardness (850 HV). [ABSTRACT FROM AUTHOR]

In the area of metal matrix composites, novel reinforcing options are currently being evaluated. Particles of amorphous alloys present an interesting possibility to reinforce soft metals. In the present work, the interaction between Fe 66 Cr 10 Nb 5 B 19 metallic glass and aluminum during spark plasma sintering (SPS) was studied for the first time. In order to trace the phase and microstructural changes upon sintering, mixtures containing 20 vol% and 50 vol% of metallic glass were subjected to SPS at 500–570 °C. After SPS at 500 °C, no reaction layer between the metallic glass particles and aluminum was observed. After SPS at 570 °C, a reaction layer containing Fe 2 Al 5 and FeAl 3 formed around the Fe-based cores. The Vickers hardness of composites obtained from mixtures containing 20 vol% Fe 66 Cr 10 Nb 5 B 19 at 540 °C was 75 HV and increased to 280 HV after sintering at 570 °C due to the formation of thicker reaction layers at the interface. The hardness of the composite sintered from the mixture containing 20 vol% Fe 66 Cr 10 Nb 5 B 19 at 570 °C was between the values predicted by Reuss and Voigt models. Comparison of results of SPS of the powder mixtures with those of SPS of a pre-compacted pellet and electric current-free annealing suggests that local heating at the interface caused by interfacial resistance may be an important factor influencing the reaction advancement at the interface and the formation of Al-containing intermetallics. • Interaction between Fe 66 Cr 10 Nb 5 B 19 metallic glass and Al during SPS was studied. • After SPS at 500 °C, no reaction layer between the alloy and Al was observed. • After SPS at 570 °C, a layer of Fe 2 Al 5 and FeAl 3 formed around the alloy cores. • Reaction advancement is influenced by local heating at the interface during SPS. • Hardness of composites is compared with values given by Voigt and Reuss models. [ABSTRACT FROM AUTHOR]