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Oxidation Behavior of (W, Re)-Bearing Single Crystal Nickel-Base Superalloys
Junhee Hahn,Dongyi Seo,Sunghun Lee,Eungseon Byon,Dong Bok Lee 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8
Four kinds of single-crystal Ni-base superalloys (12Ta–7.5Cr–5Co–4.8Al–1.9Mo–1Ti, balance Ni in wt%) containing (0–3)wt%W and (1–4) wt%Re were cast, and oxidized at 1000 °C for up to 275 h in air. In the as-cast condition, the microsegregations of (Cr, Co, Mo, W, Re) in the dendrites and (Al, Ti, Ta) in the interdendritic regions were observed. The γ/γ′ eutecticphases formed in the interdendritic regions. The oxidation rate of the cast alloys was comparable to that of the 2nd generation alloys, displaying relatively good oxidation resistance due primarily to the formation of stable alumina and chromia onthe surface. Especially, the alloy with 2 wt% W and 2 wt% Re showed the best oxidation resistance among the four alloys. Uniform oxidation occurred in the dendrite area, whereas nodular oxidation occurred in the interdendrite region.
Corrosion of Multilayered TiAlSiN Films at 800–1000 °C in N2/0.1%H2S Gas
Junhee Hahn,Muhammad Ali Abro,Xiao Xiao,Dong Bok Lee 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9
A multilayered TiAlSiN thin film consisting of alternating nanocrystalline Ti(Si)N and Al(Si)N nanolayers was deposited onsteel by arc ion plating. The film composition was 26Ti–16.3Al–1.2Si–56.50N in at%. The film was corroded at 800–1000 °Cfor 4–100 h in N2/0.1%H2S gas to study its corrosion behavior in hostile (H, S)-containing environments. The corrosion wasprimarily governed by oxidation, because oxides of Ti and Al were much more stable than the corresponding sulfides. Theoxygen source for oxidation was impurity oxygen in N2/0.1%H2S gas. Initially, a superficial Al2O3scale formed. Soon, thescale developed into the outer TiO2-rich layer and the inner Al2O3-rich layer, beneath which formed an oxygen affected zone. As corrosion progressed, Si tended to accumulate in the lower part of the inner Al2O3-rich layer owing to its thermodynamicnobility. Preferential oxidation of Al to Al2O3,formation of fine, dense Al2O3and TiO2grains in the oxide scale, and strongTi–Si, Al–N and Ti–N bonds in the TiAlSiN film caused the scale to grow quite slowly and suppressed fast inward diffusionof sulfur and hydrogen as well as fast outward diffusion of Ti, Al, and Si. Therefore, the film displayed good corrosionresistance at 800–900 °C for up to 100 h. However, it corroded completely, with partial scale spallation and whisker growthat 1000 °C for 50 h.
High Temperature Oxidation of Hot-Dip Aluminized T92 Steels
Muhammad Ali Abro,Junhee Hahn,Dong Bok Lee 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.3
The T92 steel plate was hot-dip aluminized, and oxidized in order to characterize the high-temperature oxidation behaviorof hot-dip aluminized T92 steel. The coating consisted of Al-rich topcoat with scattered Al 3 Fe grains, Al 3 Fe-rich upperalloy layer with scattered (Al, Al 5 Fe 2 , AlFe)-grains, and Al 5 Fe 2 –rich lower alloy layer with scattered (Al 5 Fe 2 , AlFe)-grains. Oxidation at 800 °C for 20 h formed (α-Al 2 O 3 scale)/(AlFe layer)/(AlFe 3 layer)/(α-Fe(Al) layer), while oxidation at 900 °Cfor 20 h formed (α-Al 2 O 3 scale plus some Fe 2 O 3 )/(AlFe layer)/(AlFe 3 layer)/(α-Fe(Al) layer) from the surface. During oxidation,outward migration of all substrate elements, inward diff usion of oxygen, and back and forth diff usion of Al occurredaccording to concentration gradients. Also, diff usion transformed and broadened AlFe and AlFe 3 layers dissolved with someoxygen and substrate alloying elements. Hot-dip aluminizing improved the high-temperature oxidation resistance of T92steel through preferential oxidation of Al at the surface.
Yeom, Bongjun,Kim, Suhan,Cho, Jinhan,Hahn, Junhee,Char, Kookheon Gordon and Breach [etc.] 2006 The Journal of adhesion Vol.82 No.5
<P> Two different kinds of organic polyelectrolyte (PE)/inorganic silicate nanolaminates carrying dissimilar interfacial adhesion between the organic and the inorganic layers were prepared using the layer-by-layer self-assembly. To investigate the mechanical behavior of the prepared hybrid films, apparent modulus (E'), hardness (H), and crack length were measured by depth-sensing nanoindentation as well as a microVickers experiment. The fracture toughness of the hybrid films was then calculated based on the measured mechanical values. In the case of forming strong interfacial adhesion between the organic and the inorganic layers (A series), the fracture toughness and the crack resistance of hybrid multilayer films were significantly improved as a result of the redistribution of stress concentration and the dissipation of fracture energy by the plasticity of organic PE layers. On the other hand, samples with relatively low interfacial adhesion between the organic and the inorganic layers (T series) had little effect on the improvement of fracture toughness of the hybrid films.</P>
Oxidation of Titanium Matrix Composites Reinforced with (TiB + TiC) Particulates
Young‑Jig Kim,Poonam Yadav,Junhee Hahn,Xiao Xiao,Dong Bok Lee 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3
Titanium matrix composites reinforced with (5, 10, 20) vol% (TiB + TiC) particulates were in situ synthesized using melting-investment casting method by reacting Ti with B4Cpowder. Their oxidation behavior was studied at 800–1000 °C inair. Formed scales consisted of transient TiO3and stable rutile-TiO2. More dispersed (TiB + TiC) particulates had higheroxidation resistance due to strong Ti–B and Ti–C bonding which required higher activation energy for oxidation comparedto Ti–Ti bonding in the matrix. However, such increment in oxidation resistance was limited by the formation of semiprotectivetitanium oxides, volatile B2O3,and CO2gas. With increment of (TiB + TiC), scales progressively became thinner,thus improving scale adherence.