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Vacuum brazing of TiAl alloy is achieved using TiZrNiCu fillers and BNi-2 fillers. The oxidation behavior of the two kinds of TiAl alloy joints is investigated in air at 800 °C. The influence of high-temperature oxidation on the microstructure and mechanical properties of the joints are characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and shear tests. It is found that long-term oxidation does not have a large effect on the microstructure of joints. However, the fillet of the brazed joint achieved via BNi-2 fillers forms longitudinal solidification cracks, which proved that the brazed joint using TiZrNiCu fillers shows more excellent oxidation resistance.

The properties of hexagonal boron nitride (hBN) were explored to improve the chemical and thermal performance of a three-dimensionally interconnected hBN (3Di-hBN)-reinforced Cu0.7–Ni0.3 (3Di-hBN CuNi) composite, prepared via a simple two-step process. The chemical performance was examined by potentiodynamic polarization and electrochemical impedance spectroscopy, whereas the thermal performance was investigated by thermogravimetric analysis and high-temperature oxidation experiments. The 3Di-hBN CuNi composite exhibited a corrosion resistance six times higher than that of a powder metallurgy (PM) CuNi alloy (without hBN). Furthermore, during high-temperature oxidation experiments at 900 °C, the 3Di-hBN CuNi composite gained ~ 36% less mass than the PM CuNi alloy, indicating its superior high-temperature oxidation resistance. The improved chemical and thermal stability of the 3Di-hBN CuNi composite were attributed to the impermeability and thermal stability of hBN, that is, its ability to obstruct the penetration and diffusion of atoms, ions, and molecules at high temperatures. [ABSTRACT FROM AUTHOR]

The conventional Zircaloy cladding may react with coolant in light water reactors and elicit severe accident at high temperature, which constraint the safe and efficient development of nuclear energy. To avoid the tragedy happened in Fukushima, the concept of Accident Tolerant Fuel (ATF) was developed around the globe to secure the steady operation for nuclear power plants. As a short-term solution, deposition of protective coatings upon the cladding tubes are proved to be effective. Among the coatings, Chromium is one of the most outstanding choices. This paper reviews the recent study results about the performance and failure mechanisms of Cr-coated Zr cladding, including mechanical, irradiation, high-temperature oxidation tests, etc. under normal and/or accident conditions. The experiments and tests collectively suggest that Cr coating possesses excellent comprehensive properties for integrity protection of claddings and provides a promising future of the commercial application in reactor cores. Finally, this review proposes ambiguities and questions needed to be analyzed and clarified in future works.

The high-temperature oxidation behavior of Ni–11Fe–10Cu–6Al alloy at 750, 850 and 950 °C in air was investigated. Its oxidation kinetics follow the parabolic rate law at all temperatures and are significantly lower than those of Ni–11Fe–10Cu and Ni–11Fe–10Cu–6Al–3Y alloys. The doping of Al to Ni–11Fe–10Cu alloy can improve not only the adherence of oxide scale but also the oxidation resistance. The structure and growth mechanism of multilayer oxide scale formed on Ni–11Fe–10Cu–6Al alloy are studied. The effect of doping Al on the high-temperature oxidation behavior of Ni–11Fe–10Cu alloy is also discussed. [ABSTRACT FROM AUTHOR]

Whether used as hot rollers or hot forging dies, the high-temperature oxidation resistance of cemented carbides is closely related to their lifetime. In the context of the above applications, a WC–Co–Ni alloy with Cr 3 C 2 –CeO 2 –WS 2 mixed additives is designed based on the principles of oxidation resistance and self-lubrication at elevated temperatures. The results of continuous oxidation at 700 °C for 16 h show that the oxidation rate of WC–6Co–6Ni–1.2Cr 3 C 2 –1.0CeO 2 –0.4WS 2 (alloy 2#) with ultrafine dispersion phase Ce 2 O 2 S 2 decreases by 23.7% and 15.4%, respectively, compared with WC–6Co–6Ni (alloy 1#) and WC–6Co–6Ni–1.2Cr 3 C 2 (alloy 3#). The additives of Cr 3 C 2 and CeO 2 can promote the in situ atomic recombination in the binder phase and rapid nucleation of (Ni,Co,Cr)WO 4. As a result, a 2.3 times and 1.6 times higher MWO 4 (M = Co, Ni, Cr) in quantity is formed on the oxidized surfaces compared with the counterpart alloy 1# and alloy 3#. The high proportion of dense (Ni,Co,Cr)WO 4 phase and the Ce 2 O 2 S 2 third phase resistant to high-temperature oxidation can form a double obstacle to the diffusion of oxygen atoms and delay the kinetic process of oxidation reaction. • WC–Co–Ni–Cr 3 C 2 –CeO 2 –WS 2 alloy with Ce 2 O 2 S 2 ultrafine dispersion phase is developed. • The developed alloy features high strength and superior resistance to oxidation. • Nucleation and crystal growth mechanism of MWO 4 is proposed. • The fact that combination of Cr and Ce favors MWO 4 rapid formation is revealed. • Double obstacle mechanism to O atom diffusion is proposed for the developed alloy. [ABSTRACT FROM AUTHOR]

The paper discusses the effects of B _4 C particle (B _4 C _p ) content on the microstructure and high-temperature oxidation resistance of B _4 C _p /Ti-5.4Al-4.03Mo-3.93V-2.37Cr-0.01Zr composite prepared by powder metallurgy. The results demonstrate that grain size of the composites decreases by increasing reinforcement content from 1 to 3 wt.%, suggesting that B _4 C _p can refine grain of the materials. For the composites with increasing B _4 C _p content from 0 to 3 wt.%, the apparent porosity increase from 3.23 to 6.89%, indicating that the density of materials decreased with the increase of B _4 C _P content. In addition, the hardness of the materials have been greatly improved. Comparing to the substrate 434.02 HV, the 1, 2, and 3 wt.% B _4 C _P specimens are increased by 37.2%, 57.5%, and 84.7%, respectively. The weight of the oxidation product is reduced and the oxidation rate is slowed down, as the B _4 C _P content increases. Moreover, the thickness of the oxide layer is greatly reduced, and the thickness of oxidation layer in composites with 0, 1, 2 and 3 wt.% B4CP specimens were 60, 55, 47 and 40 μ m, indicating that B _4 C _P can improve the high-temperature oxidation resistance.

The binary intermetallic compounds Mo 5 Si 3 (T1) and Ti 5 Si 3 are prone to rapid oxidation below 1000 °C. Recent investigations on (Mo,Ti) 5 Si 3 , however, revealed that macro-alloying with 40 at.% Ti can result in a very good oxidation resistance in a wide temperature range (750–1300 °C) due to the formation of a duplex layer composed of a silica matrix with dispersed titania. Additionally, Ti decreases density making (Mo,Ti) 5 Si 3 a promising key constituent of quaternary Mo-Si-B-Ti alloys considered for ultrahigh temperature structural applications. The aim of this study is to obtain an in-depth understanding of the influence of different Ti concentrations as well as of nitrogen on the oxidation behavior of (Mo,Ti) 5 Si 3 at intermediate and elevated temperatures. The microstructure and oxidation mechanisms were analyzed using various experimental techniques. The experimental results were supported by ab initio and thermodynamic calculations. [ABSTRACT FROM AUTHOR]

The hot ductility and high-temperature oxidation behavior of 20CrMnTi steel with 0.02% Cu and x% Sn (0.004 ⩽ x ⩽ 0.049) were investigated. The results show that tin has no significant effect on tensile strength of sample with less than 0.049% Sn. The critical temperature where the hot ductility reduces dramatically rises with the increase of tin content while the hot ductility decreases with its increase. The average tin content at austenite grain boundaries (GB) and substrate is 0.108% and 0.045% respectively in the specimen containing 0.049% tin quenched after heated to 1223 K and held for 600 s. Sn-segregation at the GB deteriorates the hot ductility. There is no direct relationship between the cause of the ductility trough and tin. However, Sn-segregation at the GB causes it to deepen a lot. The tin content should be controlled below 0.021%, which would not deteriorate the hot ductility significantly. There is no tin-enrichment at the scale/substrate interface when tin content is less than 0.049%. Moreover, although Sn is enriched under the steel surface, any liquid Sn-enrichment wasn't observed at the oxide/steel interface even in as high as 0.45% Sn-bearing steel with 0.02% Cu.

The effect of VC addition on microstructure, mechanical properties and high-temperature oxidation behavior of the TiC steel-bonded carbides, fabricated by two-step sintering, were examined by SEM, EDS, and XRD. The results show that an appropriate amount of VC enables the TiC steel-bonded carbide to further refine the hard phase particles while maintaining high density. When the VC addition amount is not higher than 0.8 wt%, the hard phase particles are gradually refined with the increase of VC content. The added VC is mainly distributed in the rim phase around the hard phase particles, which inhibits the dissolution and precipitation of TiC and thus refines the grains. When the VC addition amount reaches 1.2 wt%, the excess VC raises the possibility of particle agglomeration or segregation, which will coarsen the rim phase and degrade the mechanical properties. Overall, TiC steel-bonded carbides with 0.8 wt% VC possesses superior comprehensive mechanical properties. Moreover, when TiC steel-bonded carbides are oxidized at a constant temperature of 750 °C, their high-temperature oxidation behavior follows a parabolic law. The oxidation rate is mainly controlled by the surface chemical reaction rate in the early stage and the oxygen ion diffusion rate in the later stage. • Series of TiC steel-bonded carbides with different VC content were firstly fabricated by two-step sintering technology. • Microstructures, mechanical properties and high-temperature oxidation behavior were firstly studied. • An appropriate amount of VC refines the hard phase particles while maintaining a high density of TiC steel-bonded carbides. • The as-prepared TiC steel-bonded carbides show excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Electron beam remelting of composites can effectively improve the strength and hardness of the material surface via regulating the geometry and microstructure of grains and reinforcements. In the present work, the microstructure and high-temperature oxidation behavior of the remelted layer of TiBw/TC4 composites with different heat inputs are systematically investigated. During the whole remelting process, the preferentially precipitated TiBw acts as heterogeneous nucleation site to accelerate the nucleation and growth of TC4 alloy, and are finally pushed to the grain boundary on account of the interfacial energy. Compared with untreated samples, many stacking faults are observed in the remelted nanoscale TiB whisker with the crystal structures of B 27 and B f. It follow as that the surface hardness increases by nearly 40% under the line energy of 96 J/mm (4 mA) because of the smaller network structure TiBw than the parent material, as well as a moderate thickness remelting layer without coarse dendrites. After electron beam remelting treatment, the oxidation resistance of the composite was significantly improved due to the segregation of aluminum on the surface of the remelting layer during oxidation. • The electron beam remelting is used to modify the surface of TiB/TC4 composites. • Comparison between the microstructure of remelted material and the parent material. • Research on cooling process of molten pool after electron beam remelting. • Research on hardness of materials by electron beam remelting. • Research on high-temperature oxidation behavior of the remelted material and the parent material. [ABSTRACT FROM AUTHOR]

(Ti, Cr)N coatings were deposited on 4Cr13 stainless steel by multi-arc ion plating. High-temperature oxidation behaviors of (Ti 1- x Cr x )N ( x =0.28, 0.56, 0.73) coatings with different chrome contents were investigated at 700 °C. And surface morphologies and surface compositions of oxidized coatings were also studied. Thermal analysis experiments of (Ti,Cr)N coatings were conducted by thermogravimetry (TG) and differential scanning calorimetry (DSC), and the results were compared with TiN coating. The results show that Cr content in the (Ti 1- x Cr x )N coating increases with the elevation of the arc current of Cr target, and a linear relation exists between Cr content and the ratio of arc current of Cr target and Ti target ( I Cr / I Ti for short). The higher the Cr content is, the better the high-temperature oxidation resistance of (Ti 1- x Cr x )N coating is, and the oxidation thermodynamics temperatures of (Ti 1- x Cr x )N coating are higher than that of TiN coating, which indicates that the oxidation thermodynamic equilibrium temperature of the coating elevates observably with the addition of Cr. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation behavior of the DED repaired IC10 DS superalloy is studied by selecting five representative zones, i.e., substrate, HAZ, and the bottom, middle, and top zones of the deposition layers. Results show that the substrate has the best oxidation resistance, while the oxidation resistance of the HAZ is the worst. For the deposit, the oxidation resistance decreases from the bottom to the top zones. The oxidation films consist of the internal continuous film of Al 2 O 3 and the external granular Cr 2 O 3 and TaO 2. The high-temperature oxidation resistance is mainly dominated by the fraction of γ′ phases. • The high-temperature oxidation resistance in HAZ is weaker than that in the substrate, and decreases along the BD. • The oxidation films consist of an internal continuous Al 2 O 3 film and external Cr 2 O 3 and TaO 2 particles. • The high-temperature oxidation resistance is more sensitive to fraction of γ′ phases than to the size of γ′ phases. [ABSTRACT FROM AUTHOR]

Abstract: Dense molybdenum disilicide with a nano-organized microstructure was synthesized by mechanical activation, by producing nanostructured agglomerates of a 1:2 mixture of Mo and Si, followed by the synthesis/consolidation in one step using SPS technology. In order to synthesize a dense molybdenum disilicide with a perfectly controlled microstructure, an investigation of the influence of Spark Plasma Sintering processing parameters (temperature, heating rate, mechanical pressure and holding time) on the chemical composition and the microstructure characteristics has been performed. The present work shows also that the so-obtained materials present better oxidation resistance in comparison to a dense microstructured MoSi2, due to the silica scale formation under high-temperature oxidizing atmosphere. The most interesting results are obtained at “low” temperature (673–873K). [Copyright &y& Elsevier]