Fucheng Yin

The traditional preparation process of fluozirconic acid is carried out in a reaction kettle, where zirconium oxide reacts with concentrated hot hydrofluoric acid. However, the use of concentrated hot hydrofluoric acid leads to high process and equipment costs, severe environmental pollution, significant safety hazards. Moreover, the purity of the original solution after dissolution is low, and the phase composition is complex. In this paper, a preparation method for fluozirconic acid solution with controllable phase composition is studied. This is a dissolution method that using 99.8% purity sponge zirconium and 8N purity hydrofluoric acid of medium concentration as raw materials under normal temperature and pressure. The optimal dissolution process was determined experimentally as a hydrofluoric acid concentration of 35% and a liquid-solid ratio of 5 mL·g⁻¹. Under these conditions, the HZrF₅ phase content in the solution reached its maximum, thereby creating favorable conditions for the subsequent hydrometallurgical preparation of high purity zirconium tetrafluoride (ZrF₄), creating conditions for the subsequent preparation of high purity zirconium tetrafluoride through hydrometallurgy. At the same time, this paper also conducts certain explorations on the phase characterization of the solution.

With the development of marine science and technology, marine construction is entering a new period of modern ocean development and utilization. The scale of marine development is expanding constantly. The lifespan of aircraft engines faces new challenges in marine environments. This paper reviews recent progress in the development of high-temperature coatings for aero-engines designed to resist marine atmospheric corrosion, with a focus on corrosion mechanisms, detection technologies, current research on marine atmospheric corrosion, standards for evaluating coating resistance, and novel advancements in coating materials.

The CoCrFeNiMn high-entropy alloys were treated by powder-pack boriding to improve their surface hardness and wear resistance. The variation of boriding layer thickness with time and temperature was studied. Then, the frequency factor D₀ and diffusion activation energy Q of element B in HEA are calculated to be 9.15 × 10⁻⁵ m²/s and 206.93 kJ/mol, respectively. The diffusion behavior of elements in the boronizing process was investigated and shows that the boride layer forms with the metal atoms diffusing outward and the diffusion layer forms with the B atoms diffusing inward by the Pt-labeling method. In addition, the surface microhardness of CoCrFeNiMn HEA was significantly improved to 23.8 ± 1.4 Gpa, and the friction coefficient was reduced from 0.86 to 0.48~0.61.

The service performance of single crystal blades depends on the crystal orientation. A grain selection method assisted by directional columnar grains is studied to control the crystal orientation of Ni-based single crystal superalloys. The samples were produced by the Bridgman technique at withdrawal rates of 100 μm/s. During directional solidification, the directional columnar grains are partially melted, and a number of stray grains are formed in the transition zone just above the melt-back interface. The grain selected by this method was one that grew epitaxially along the un-melted directional columnar grains. Finally, the mechanism of selection grain and application prospect of this grain selection method assisted by directional columnar grains is discussed.

By combined numerical simulations and unidirectional solidification experiments, the temperature field evolution of seeding for nickel-based single-crystal superalloys was studied. At the steady state, the position of the mushy zone in the seed moves down as the melt is poured into the mold. The holding time required for the temperature field of the seed segment to reach the steady state is less for seeds with casting than for those without casting. The holding time required to completely eliminate randomly oriented broken dendrites in the melt-back zone is much longer than that required for the temperature field to achieve a steady state. A short incubation stage is required before the temperature field evolution process; then, the migration rate of the isotherm gradually increases until it is the vicinity of the withdrawal rate. Finally, the effect of temperature field evolution on the formation of stray grains in seed segments is discussed.

The microstructure, interfacial characteristics, and corrosion resistance of Fe-W-Mn-Al-B alloys in molten zinc at 520 °C have been investigated using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and electron probe micro-analysis (EPMA). The experimental results indicate that the Fe-B alloy with 11 wt.% W, 7 wt.% Mn, and 4 wt.% Al addition displays a lamellar eutectic microstructure and excellent corrosion resistance to molten zinc. The toughness of M₂B-type borides in the hyper-eutectic Fe-4.2B-11W-7Mn-4Al alloy can be more than doubled, reaching 10.5 MPa·m^1/2, by adding Mn and Al. The corrosion layer of the Fe-3.5B-11W-7Mn-4Al alloy immersed in molten zinc at 520 °C comprises Fe₃AlZn_x, δ-FeZn₁₀, ζ-FeZn₁₃, and η-Zn. The lamellar borides provide the mechanical protection for α-(Fe, Mn, Al), and the thermal stability of borides improves as the fracture toughness of the borides increases, which jointly contribute to the improvement of the corrosion resistance to the molten zinc.

The corrosion of galvanizing equipment parts by liquid zinc is an urgent problem that needs solving. In this work, FeB-30 wt.% Al_0.25FeNiCoCr cermet coating was deposited on the surface of 316L stainless steel by AC-HVAF to protect galvanizing equipment parts from corrosion by liquid zinc. The microstructures and phase compositions of powders and the coating were determined by SEM, EDS, and XRD in detail. Additionally, the microhardness, fracture toughness, abrasion wear resistance, and corrosion resistance of the coating to liquid zinc were also studied. The results indicate that the abrasion wear resistance and corrosion resistance of the coating are much better than that of the 316L stainless steel substrate. The failure of the coating in liquid zinc is mainly due to the penetration of liquid zinc into macro-cracks, which causes the coating to peel off.

In this paper, the corrosion behavior of X80 pipeline steel weld joints in an acidic red soil solution was studied. The results show that uniform corrosion occurs on the entire surface of the weld joint after 840 h immersion. The corrosion degree of heat affected zone (HAZ) is more serious than that of base metal (BM) and weld zone (WZ). The corrosion rate of HAZ specimen is always higher than those of WZ and BM specimens throughout the separated immersion. The accelerating corrosion of HAZ may come from its microstructure change, its corrosion sensitivity and the deterioration of mechanical performance of corrosion product on it.