Numerical Analysis of High-Velocity Oxygen Fuel Thermal-Spray Process for Fe-Based Amorphous Coatings

High-velocity oxygen fuel (HVOF)-sprayed amorphous alloy coatings usually have advantages of a dense structure that improve their resistance to corrosion, wear, and fatigue in the substrate. The flame flow characteristics and particle behaviors during the spray process have a significant influence on the amorphous coating structure and properties. In this study, a computational fluid dynamics model is enforced to analyze the flame flow and Fe-based amorphous alloy particle behavior in an HVOF spray process. The flame flow temperature, velocity characteristics, and the Fe48Cr15Mo14C15B6Y2 Fe-based amorphous alloy particles’ velocities, temperatures, flight trajectories, and mass concentration distribution characteristics are simulated. Moreover, the effects of the oxygen/fuel ratio, particle morphology parameter, particle-injection rate, and angle on the particle behavior are also investigated. Judging from the simulation results, the optimum amorphous alloy particle size varies between 20 and 30 μm, the shape factor is within the range of 0.9–1, the optimum O/F ratio is 3.4, the optimum injection angle is 45°, and the optimum injection rate is 10 m/s. With these conditions, most of the particles settled toward the centerline of the spray gun and are in a semisolid or solid state before affecting the substrate, giving the materials optimal coating structure and performance.

Features of nanocomposite powder paints spreading with the addition of aluminum oxide nanofibers

The paper studies the effect of violation of the spreading of powder paints when they are compounded with nanofibers of aluminum oxide. It is shown that with the addition of small fractions of aluminum oxide nanofibers equal to 0.05 wt%, the grains of the powder paint do not have time to wet each other, the crosslinking of the coating structure occurs up to this point, which is fixed by a characteristic granular texture. The paper also illustrates the features of the distribution of nanofibers of aluminum oxide in the coating. The increase in cohesion energy leads to a natural increase in the surface tension in the paint, which we observe in the form of the characteristic morphology of the coating. Investigation of coatings of a reference powder paint and a modified addition of aluminum oxide nanofibers) were carried out using an optical microscope. Separately, the morphology of the resin was investigated by scanning electron microscopy. Increasing the proportion of the flow agent based on acrylic compounds in the polyester resin from 0.8 to 1.8 wt% solves this problem, while the strengthening effect of nanofibers of alumina in the paint is retained.

Formation of the Diffusion Zone in Explosion Welded Composite Cr20Ni80 - AD1 at Liquid-Phase Interaction

The paper presents the investigation on the structure, chemical and phase composition of the diffusion coating formed during the liquid-phase heat treatment in the explosion-welded Cr20Ni80 + AD1 bimetal. It is shown that the coating structure consists of NiAl3, CrAl7, Ni2Al3 intermetallic inclusions, as well as a metastable ternary compound – τ2-phase (Al77.5Cr12.5Ni10) of different dispersion and morphology. There are no crystallization defects in the coating structure.

Back-trap mottle: A review of mechanisms and possible solutions

Print mottle is a serious and common uneven printing defect that occurs when printing coated paper by the offset multicolor printing process. It is characterized by a non-uniform appearance in terms of brightness, gloss, or color density that appears mostly in solid printed areas. Back-trap print mottle and water-interference print mottle occur when the quality of the paper substrate, especially the coating layer quality, is not satisfactory. To cope with this quality problem of coated papers, the understanding of the offset printing process, the requirements of coated-paper quality, and the reasons for this problem should be addressed. In this review, the basic process of offset printing and the mechanisms of print mottles were explored, the importance of coating uniformity in both the coating structure and process was reviewed, and the approaches to cope with print mottle were introduced.