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FGH 97 alloy (FG) and its composite with TiC addition (FT) were prepared by spark plasma sintering. The TiC particles were dissolved into the alloy matrix during ball milling, but precipitated out in-situ as MC solid solution with semi-coherent interface after sintering, leading to a homogeneous and fine microstructure. After exposure to 900 °C for 300 h, its grain size grew by only 31%. The fine microstructure promoted selective oxidation of Al and ensured high oxidation resistance of the composite FT. The precipitated carbides increased oxidation resistance of FT and endows its oxide scale with self-healing ability for long-term oxidation. • PM Ni-based superalloy with TiC addition is prepared by spark plasma sintering. • TiC transforms to nanoscale semi-coherent MC solid solution after sintering. • The composite possesses homogeneous and fine microstructure, promoting selective oxidation of Al. • The composite exhibits high thermal stability and oxidation resistance. • Alumina scale re-grows at surface of the composite after it is removed. [ABSTRACT FROM AUTHOR]

Abstract: Experimental investigations have been carried out for liquid films flowing on the vertical coated division tube. A new thermal tracing technique was developed to measure the mixing effect and liquid film velocity of falling liquid film on the coated division tube. In general, mixing of solution could refresh the interface of bulk liquid, and hence lead to the more efficient heat transfer within the liquid film. By using the high speed video camera and thermal imaging technique, the flow patterns and mixing effect of liquid film on the coated division tube were investigated experimentally. Flow visualization experiments revealed that the liquid film formed a bifurcate flow at the upper edge of the vertical coated regions. The bifurcate flow converged and resulted in stronger mixing that drove the thermal tracing liquid particles from the interface to the internal of liquid film. There was deformation of temperature distribution on the coated division tube. The average mixing intensity on the coated division tube was about 1.2 times larger than that on the bare brass tube. [Copyright &y& Elsevier]

Enamel coating, which is of low thermal conductivity and high chemical stability, has been employed for the protection of many hot parts against oxidation. It is composed of multiple oxides, and each oxide component plays a certain role on thermophysical properties. In this paper, a type of silicate enamel coating with different contents of oxide component Al 2 O 3 was prepared on K444 superalloy. Its microstructural evolution and cyclic oxidation behavior at 1000 °C were investigated. Results indicated that the A0 enamel coating, which was free of Al 2 O 3 in composition, suffered from serious crystallization at high temperature. The formation of quartz, cristobalite and SrSiO 3 crystals resulted in significant mass loss during cyclic oxidation. However, precipitation of these crystals was almost completely prohibited in the A10 and A15 coatings with 10 and 15 wt% Al 2 O 3 , respectively. The A10 coating had no mass loss after cyclic oxidation. But much high content of Al 2 O 3 resulted in the formation of abundant long strip crystals of SrAl 2 Si 2 O 8 in the A15 coating, which led to minor spallation. Furthermore, enamel coatings with Al 2 O 3 (above 6 wt%) promoted the formation of a continuous alumina scale at the enamel/alloy interface, which improved oxidation resistance and increased bonding strength. The well grown alumina scale at interface as well as the mild crystallization ensured high spallation resistance of the enamel coating A10. [ABSTRACT FROM AUTHOR]

The effect of CoO and NiO on the adherence between enamel coating and steel is investigated experimentally in this study. Enamel coatings are applied to the steel using a wet process with slurries. A total of five enamels were prepared including three single layer enamels: blank enamel ( BL), NiO bearing enamel ( MTNi3), CoO bearing enamel ( MTCo3), and two double layer enamels: BL- MTNi3, BL- MTCo3, which consisted an inner layer of BL and an outer layer of MTNi3 or MTCo3. Falling-weights tests were performed and the cross-sections at the enamel/steel interface were analyzed with a scanning electron microscopy ( SEM) coupled with an energy dispersive spectroscopy ( EDS) and electron probe microanalysis ( EPMA). Results show that the increases of adherence for MTCo3 and MTNi3 coated steel are attributed to the micro-alloys precipitation at the enamel/steel interface. These micro-alloy precipitations grow parallel to the steel/enamel interface for MTNi3, while they are dendritic and perpendicular for MTCo3. Compared with MTCo3, the negative reaction energy between NiO and FeO for MTNi3 causes micro-alloy precipitations formed far away from the enamel/steel interface, resulting in different morphology and adherence. [ABSTRACT FROM AUTHOR]

Highlights: [•] The experiment of circumferential coated tubes at high temperature is conducted. [•] The higher heat transfer coefficients of falling film absorption are gained. [•] The mass transfer coefficient of the circumferential coated tube is lower. [Copyright &y& Elsevier]

Tribocorrosion tests were performed on the Cast and SPS Ni20Cr alloys sliding against Si 3 N 4 in 3.5 wt% NaCl solution to investigate the grain size effect on the synergy of corrosion and wear. An appealing result was that the SPS alloy with finer grains exhibited less intense corrosion-induced wear, but more severe wear-induced corrosion, compared to the coarse-grained Cast alloy. The mechanism responsible for the significant difference was attributed to the composition and microstructure of the tribo-layer influenced by grain refinement. The finer grain structure facilitated the rapid replenishment of thicker Cr-rich tribo-layer, while meanwhile the dense layer exhibited high hardness and greatly reduced the wear rate of SPS alloy. • Tribocorrosion behaviors of the Cast and SPS Ni20Cr alloys were investigated, focusing on the grain size effects. • The SPS alloy with finer grain structure displays lower wear rate and COF during tribocorrosion. • The SPS alloy exhibit less intense corrosion-induced wear, but more violent wear-induced corrosion. • The rapid replenishment of thicker and denser Cr-rich tribo-layer greatly reduces the wear rate of SPS alloy. [ABSTRACT FROM AUTHOR]

A Ni-based superalloy composite (FTSC) was successfully prepared by spark plasma sintering with Ti 3 SiC 2 (15 vol%) and FGH97 alloy powders as precursors. During sintering, the weakly bonded Si layers de-intercalate from Ti 3 SiC 2 and the remaining TiC is eroded by the elements of the matrix, which promoted in-situ precipitation of MC and M 6 C carbides. MC with core-shell structure builds up a semi-coherent interface with the alloy matrix: (1 ¯ 1 1 ¯) γ/γ' ‖ (1 1 ¯ 1) MC with [110] γ/γ' ‖[110] MC. The Zener pinning effect of ultra-fine duplex carbides results in refinement of alloy grains and notably improvement in mechanical strength. Comparing to the alloy FGH97, the composite FTSC possesses 55% higher microhardness, 100% higher compressive yield strength and 92% higher flexural strength. On the other hand, the refined grains ensured fast formation of a protective alumina scale at surface, which provides high oxidation resistance for the composite. [Display omitted] • A novel Ni-based composite is prepared by SPS with Ti 3 SiC 2 and FGH97 powders as raw materials. • The decomposition of Ti 3 SiC 2 during sintering promotes the in-situ uniformly precipitation of MC and M 6 C carbides. • MC had a semi-coherent orientation relationship with the matrix. • The composite exhibits enhanced mechanical strength but moderate high fracture toughness. • The composite exhibits high oxidation resistance at 900 °C. [ABSTRACT FROM AUTHOR]

Corrosion of three SiO 2 –B 2 O 3 –Al 2 O 3 –CaF 2 -R 2 O (R = Na and K) based enamels with different ZrO 2 contents in H 2 SO 4 and NaOH solutions was studied. The addition of ZrO 2 reduced acid resistance of enamels. Especially for enamel with 5 wt% zirconia, the weight loss reached 4.04 mg/cm2 after 30-day corrosion. On the contrary, substituting ZrO 2 for SiO 2 greatly improved the alkali resistance of enamel, since the weight loss of enamel with ZrO 2 was only 0.3 mg/cm2 after 20-h corrosion, which decreased to less than one third of that of enamel without ZrO 2. Corrosion mechanism was comparatively discussed in these two solutions. [ABSTRACT FROM AUTHOR]

Corrosion of three bulk enamels with different silica contents in sulfuric acid was studied. Catastrophic corrosion happened for enamel with 54.6 wt% silica. Its weight loss reached 36.90 mg/cm 2 after seven-day corrosion. A porous leached layer with tremendous cracks formed at surface during corrosion, which favored acid invading and further corrosion. On the contrary, the durability of enamels with silica content over 60 wt% was guaranteed by their highly connected silicate network and a developed dense gel layer that clogged corrosion pits. Their weight losses were less than 0.2 mg/cm 2 after seven-day corrosion. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the effect of co-incorporation of two different kinds of nano materials with different forms, layers (Na-MMT) and mesoporous silica particles (MCM-41), into the polymer matrix on the corrosion performance of epoxy resin. Correspondingly corrosion performance of the coatings was studied by electrochemical impedance spectroscopy (EIS) in 3.5% NaCl aqueous solution and salt spray test. The X-ray diffraction (XRD) measurement showed that the Na-MMT layers were exfoliated and the hexagonal framework structure of MCM-41 was retained during and after the composite preparation. The co-incorporation of Na-montmorillonite (Na-MMT) and MCM-41 into the epoxy coating possessed the best corrosion resistance than incorporating either Na-MMT or MCM-41 particles separately due to different interfacial structures between the fillers and the matrix. [Copyright &y& Elsevier]

• Enamel composite coatings with addition of Ni, Fe or ZrB 2 are prepared on TiAl alloy. • The enamel composite coating with ZrB 2 nanoparticles provides well oxidation protection and high thermal shock resistance. • Cracks are self-healed in the enamel composite coating at temperature of 700 or 800 °C. Enamel coating only provides high oxidation resistance for alloys at temperatures below or close to softening temperature, where cracks are difficult to self-heal due to the high viscous. In this study, the enamel composite coating with nanoparticles of Ni or Fe suffers cracking and local spallation under thermal shock from 700 °C to room temperature. With addition of nanoparticles of ZrB 2 , The enamel composite coating provides well oxidation protection meanwhile high thermal shock resistance at temperatures of 700 and 800 °C. Cracks are able to heal owing to the high thermal stability of ZrB 2 and its unique oxidation products. [ABSTRACT FROM AUTHOR]

The steam oxidation behavior of three heterogeneous HR3C alloys was investigated at 650 °C comparatively. After a long-term oxidation process for 1000 h, the results demonstrated that the commercial HR3C alloy already exhibited a high oxidation resistance. However, the spallation resistance of the oxide scale was low during the initial oxidation period. The addition of a moderate amount of Nb into the alloy (1#HR3C) increased the oxidation resistance of the alloy. In addition, the improvement of the microstructural stability was substantially influenced by solid solution strengthening and fine grain strengthening. However, the addition of excessive Nb could significantly affect the growth model of the oxide scale and negatively affect the oxidation performance and microstructural evolution of the alloy (2#HR3C). [ABSTRACT FROM AUTHOR]

• Water vapor accelerates greatly the oxidation and corrosion of CB2 steel at 650 °C. • An inorganic composite coating was easily prepared by air spraying process. • The coatings improve both of the oxidation and corrosion resistance at 650 °C. • A thin continuous Cr-rich oxide scale formed beneath the coatings. Inorganic silicate composite coatings were developed to inhibit the oxidation and corrosion of ZG12Cr9Mo1Co1NiVNbNB (CB2) stainless steel in air and water vapor containing environment at 650 °C. The results indicated that water vapor accelerates greatly the oxidation and corrosion of CB2 steel by transforming the protective Cr 2 O 3 scales into non-protective multilayered scales. The excellent inhibition action of the coatings was attributed to barrier effect accompanying with the consumption of O 2 and water by NiCrAlY powders. The Cr-rich oxide layer grew at the interface of the coatings and substrate steel retards the outwards diffusion of Fe and Cr. [ABSTRACT FROM AUTHOR]