Oxidation of Fe–Si,Fe–Al and Fe–Si–Al alloys in CO2–H2O gas at 800 °C

Binary Fe–(1, 2, 3)Si and Fe–(2, 4, 6)Al, and ternary Fe–(2, 3)Si–(4, 6)Al alloys (all in wt%) were oxidised in Ar–20% CO₂, with and without H₂O, at 800 °C. All binary alloys except Fe–6Al, in all gases, formed a thin outer layer of Fe₃O₄, an intermediate Fe₃O₄ + FeO layer, an inner FeO + Fe₂SiO₄ (or FeAl₂O₄) layer and internally precipitated SiO₂ (or FeAl₂O₄). Ternary alloys and Fe–6Al developed a protective Al₂O₃ layer beneath Fe₂O₃ in Ar–20% CO₂. Water vapour affected ternary alloy oxidation only slightly, but Fe–6Al oxidized internally in high H₂O-content gas, and its scale was non-protective.     

Coking and Dusting of Fe–Ni Alloys in CO–H2–H2O Gas Mixtures

Metal dusting of Fe–Ni alloys was investigated in a CO–H₂–H₂O–Ar gas corresponding to a _C = 19.6 at 650 °C. Thermogravimetric analysis showed that increasing the nickel content in the alloy decreased the initial rate of carbon uptake. A uniform Fe₃C scale formed on pure iron, a layer with mixed structures of Fe₃C, γ and α-Fe developed on ferritic Fe–5Ni, and small amounts of Fe₃C developed at the surface of an austenite layer grown on two-phase (α + γ) Fe–10Ni. At nickel levels above 10%, no carbide appeared. These observations are shown to be broadly consistent with local equilibrium according to the Fe–Ni–C phase diagram. However, the failure of higher nickel austenitic alloys to form the (Fe,Ni)₃C expected at high carbon activities indicates a barrier to nucleation and growth of this phase. Graphite deposition was catalysed by (Fe,Ni)₃C on ferritics and by the metal itself on austenitics. The rates of carbon deposition on Fe–60Ni corresponded to the existence of three parallel and independent paths: the synthesis gas, the Boudouard and the carbon methanation reactions.     

Corrosion Behavior of Y–Al Alloys in a H2/H2S/H2O Gas Mixture at 800–950°C

The corrosion behavior of pure Y and two Y–Al alloys containing 5 and 10 wt.% Al was studied over the temperature range 800–950°C in a H₂/H₂S/H₂O gas mixture. Both alloys had the two-phase structure of Y+Y₂Al. With the exception of Y–10Al, for which a kinetics inversion was observed between 800°C and higher temperatures (T 850°C), the parabolic rate constants generally increased with increasing temperature, but decreased with increasing Al content. The scales formed on pure Y and the Y–Al alloys were single but heterophasic, consisting of mostly Y₂O₃ and minor Y₂O₂S. XRD results showed no evidence of Al₂O₃ and pure sulfides. The formation of Y₂O₃ and Y₂O₂S on Y–10Al at 800°C resulted in a subsurface phase transformation from Y+Y₂Al to YAl₂ and broke the structural integrity of the scale, being responsible for the fast corrosion rate.     

The Corrosion of Titanium Aluminides in H2/H2S/H2O Atmospheres at 800–1000°C

The corrosion behavior of three Ti–Al intermetallics containing 20, 30, and 40 wt.% Al was studied over the temperature range 800–1000°C in a H₂/H₂S/H₂O gas mixture. Ti–20Al and Ti–40Al alloys had the single-phase structure of Ti₃Al and TiAl, respectively, while Ti–30Al was a two-phase mixture of Ti₃Al+TiAl. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants increased with increasing temperature, but decreased with increasing Al content. The Ti–40Al alloy exhibited the best corrosion resistance among all alloys studied. The scales formed on Ti–Al intermetallics were heterophasic and duplex, consisting of an outer-scale layer of pure -TiO₂ and an inner layer of -TiO₂ with minor amounts of -Al₂O₃ and Ti_l-xS. The amount of -Al₂O₃, which increased with increasing Al content, is responsible for the reduction of the corrosion rates as compared with those of pure Ti oxides.     

The Corrosion Behavior of Sulfidation-Resistant Fe–Mo–Al Alloys in H2/H2S Atmospheres at 900°C

The corrosion behavior of Fe–22Mo–10Al (a/o, atom %),Fe–20.5Mo–15.7Al, and Fe–10Mo–19Al was examined inflowing H₂/H₂S gases of 4 Pa sulfur partial pressureat 900°C. Al₂O₃ was stable on all the alloys inthe atmospheres investigated. Fe–22Mo–10Al andFe–20.5Mo–15.7Al reacted slowly, following the parabolic ratelaw. Multilayered reaction products were formed on these alloys and it isuncertain which layer(s) provided the protection. Fe–10Mo–19Alreacted even more slowly, exhibiting two-stage parabolic kinetics. Duringthe early stage of this alloy's reaction, a preferential reaction zone,consisting of an oxide mixture, possibly Al₂O₃+FeAl₂O₄,and nonreacting Fe₃Mo₂, provided the protection. Duringthe later reaction stage, the formation of a continuous, externalAl₂O₃ layer further decreased the alloy reaction rate.     

The corrosion behavior of Fe-Al alloys in H2/H2S/H2O atmospheres at 700–900°C

The corrosion behavior of five Fe-Al binary alloys containing up to 40 at. % Al was studied over the temperature range of 700–900°C in a H₂/H₂S/H₂O mixture with varying sulfur partial pressures of 10^–7–10^–5 atm. and oxygen partial pressures of 10^–24–10^–2° atm. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants decreased with increasing Al content. The scales formed on Fe-5 and –10 at.% Al were duplex, consisting of an outer layer of iron sulfide (FeS or Fe_1–xS) and an inner complex scale of FeAl₂S₄ and FeS. Alloys having intermediate Al contents (Fe-18 and –28 at.% Al) formed scales that consisted of mostly iron sulfide and Al₂O₃ as well as minor a amount of FeAl₂S₄. The amount of Al₂O₃ increased with increasing Al content. The Fe 40 at.% Al formed only Al₂O₃ at 700°C, while most Al₂O₃ and some FeS were detected at T800°C. The formation of Al₂O₃ was responsible for the reduction of the corrosion rates.     

The Influence of H,W, H/E,H 3/E 2, Structure and Chemical Composition on the Resistance of Ti–B–(N), Mo–B–(N), Cr–B–(N), and Zr–B–(N) Coatings to Cyclic Impact Loading

Protection of Metals and Physical Chemistry of Surfaces - Coatings based on transition metal borides (Ti, Mo, Cr, Zr) were obtained by magnetron sputtering of ceramic targets in Ar and Ar–15%...     

Sulfidation Properties of Ni–20Cr and Ni–13.5Co–20Cr Alloys at 873 K under Low Sulfur Pressures in H2S-H2 Atmospheres

The sulfidation properties of Ni–20Cr and Ni–13.5Co–20Cralloys as well as a nickel-base superalloy AISI685 were investigated at873 K in H₂S–H₂ gas mixtures with sulfur partial pressures of10^–4, 10^–5.5, and 10^–7Pa by mass-gain measurements,electron-probe microanalysis (EPMA), and X-ray diffraction (XRD)analysis. Sulfidation obeyed the parabolic rate law, and the parabolic rateconstants decreased in the order Ni–20Cr, Ni–13.5Co–20Cr,and AISI685 at each sulfur pressure. With decreasing sulfur pressure, therate constants first decreased slowly and then rapidly at a 10–7 Pasulfur pressure. At both 10^–4 and 10^–5.5 Pa sulfur pressures,Ni–20Cr formed a surface scale with a duplex structure of inner(Cr₃S₄) and outer (Ni₃S₂) layers, while Ni–13.5Co–20Cr formeda triplex structure of inner (Cr₃S₄), intermediate(Ni,Co)Cr₂S₄, and outer[Ni₃S₂+(Co,Ni)₉S₈] layers. Thesurface scale formed on AISI685 was verycomplex, comprising at least four layers, a fibrous (Co,Ni)₉S₈ top surface,outer [Ni₃S₂+(Co,Ni)₉S₈], and intermediate [(Cr,Ti)₃S₄] layers, as well asan inner layer containing Cr, Ti, Mo, Al, and S. At the 10^–7 Pa sulfurpressure, which is lower than the dissociation pressure of Ni₃S₂, bothNi–20Cr and Ni–13.5Co–20Cr formed a surface scale ofCr₃S₄ covered by a thin NiCr₂S₄ layer, accompanied by copious internalsulfidation of Cr₃S₄ and/or CrS. On AISI685 there was a surface scale of(Cr,Ti)₃S₄ accompanied by the usual internal sulfidation. It is discussedthat diffusion of cations in the inner Cr₃S₄ layer is the rate-determiningstep for the growth of the multilayer structures. At the 10^–7 Pasulfur pressure, diffusion of Cr and S contribute to form a thin surfacescale and internal sulfidation, respectively.     

Oxidation behavior of sulfidation processed TiAl–2 at.%X (X=Si,Mn, Ni,Ge, Y,Zr, La,and Ta) alloys at 1173 K in air

The oxidation behavior of sulfidation processed TiAl–2 at.%X (X=Si, Mn, Ni, Ge, Y, Zr, La, and Ta) alloys was investigated at 1173 K in air for up to 630 ks under a heat-cycle condition between 1173 K and room temperature. During the sulfidation processing the TiAl–2 at.%Ta alloy formed Ta-aluminides on the TiAl₃ layer, while the alloys containing Mn, Ni, Y, and Zr formed a TiAl₃ (TiAl₂ included) layer including a small amount of the third element, like the TiAl binary alloy. The cross-sectional microstructure of the TiAl–2 at.%Ta alloy shows the sequence: oxide scale/TiAlTa/TiAl₂/alloy substrate; and the cross sections of the alloys containing Mn, Ni, Y, and Zr are: oxide scale/Ti₃Al/alloy substrate. The TiAl–2 at.%Ta alloy showed some scale exfoliation at the initial stage of oxidation, but very little exfoliation after long oxidation times, whereas alloys containing other third elements such as Si and Ge showed little exfoliation at the first several cycles and then tended to exfoliate significantly, resulting in very rapid oxidation. The TiAlTa/TiAl₂ layers formed by the reaction between the Ta-aluminide and TiAl₃ improve the oxidation properties of the TiAl–2 at.%Ta alloy.     

Corrosion of Fe-(4.8, 9.2, 14.3) Wt%Al alloys at 700 and 800 °C in N2/H2O/H2S gases

Fe-(4.8, 9.2, 14.3)wt%Al alloys were corroded at 700 and 800 °C for up to 70 h in 1 atm of N₂/H₂O and N₂/H₂O/H₂S gases. Oxidation prevailed in N₂/H₂O gases. Fe-(4.8, 9.2)Al alloys formed a duplex scale that consisted of an outer iron oxide layer and an inner (Fe, Al, O)-mixed layer. The Fe-14.3Al alloy formed a thin layer consisting of α-Al₂O₃. Sulfidation dominated in N₂/H₂O/H₂S gases, resulting in rapid corrosion. Fe-(4.8, 9.2)Al alloys formed a duplex scale that consisted of an outer FeS layer and an inner (Fe, Al, S, O)-mixed layer. The high growth rate of FeS impeded the formation of a continuous, protective aluminium-rich oxide. The Fe-14.3Al alloy formed a thin layer consisting of α-Al₂O₃ that was incorporated with a bit of sulfur.     

Structural Stability,Electronic Structure and Mechanical Properties of Li–N–H System

Ab initio calculations are performed to investigate the ground state properties, structural phase transition,electronic structure and mechanical properties of lithium nitride(Li3N), lithium imide(Li2NH) and lithium amide(LiNH2).The computed ground state properties like equilibrium lattice constant, cell volume, valence electron density, cohesive energy, bulk modulus and its derivatives are in good agreement with available experimental data. The structural phase transitions from a-P6/mmm to b-P63/mmc phase at a pressure of 17.5 GPa in Li3N and cubic(Fm3m) to hexagonal(P63/mmc) phase at a pressure of 102 GPa in lithium imide(Li2NH) are observed. A new high pressure hexagonal(P63/mmc)phase is predicted for Li2NH. Electronic structure reveals that Li3N and LiNH2 are semiconductors, whereas Li2 NH is an insulator. The calculated elastic constants indicate that these materials are mechanically stable at ambient condition.     

Dislocation and Structural Studies at Metal–Metallic Glass Interface at Low Temperature

In this paper, molecular dynamics (MD) simulation deformation studies on the Al (metal)–Cu₅₀Zr₅₀ (metallic glass) model interface is carried out based on cohesive zone model. The interface is subjected to mode-I loading at a strain rate of 10⁹ s^?1 and temperature of 100 K. The dislocations reactions and evolution of dislocation densities during the deformation have been investigated. Atomic interactions between Al, Cu and Zr atoms are modeled using EAM (embedded atom method) potential, and a timestep of 0.002 ps is used for performing the MD simulations. A circular crack and rectangular notch are introduced at the interface to investigate the effect on the deformation behavior and fracture. Further, scale size effect is also investigated. The structural changes and evolution of dislocation density are also examined. It is found that the dominant deformation mechanism is by Shockley partial dislocation nucleation. Amorphization is observed in the Al regions close to the interface and occurs at a lower strain in the presence of a crack. The total dislocation density is found to be maximum after the first yield in both the perfect and defect interface models and is highest in the case of perfect interface with a density of 6.31 × 10¹⁷ m^?2. In the perfect and circular crack defect interface models, it is observed that the fraction of Shockley partial dislocation density decreases, whereas that of strain rod dislocations increases with increase in strain.     

Oxidation of Minor Elements from an Iron–Nickel–Chromium–Cobalt–Phosphorus Alloy in 17.3% CO2–H2 Gas Mixtures at 700–1000 °C

Fe–Ni–Cr–Co–P alloys were exposed to 17.3% CO₂–H₂ gas mixtures to investigate the oxidation of minor elements in metallic alloys in the early solar system. Reaction temperatures varied between 700 and 1000 °C. Gas-phase equilibrium was attained at 800, 900, and 1000 °C, yielding H₂–H₂O–CO–CO₂ gas mixtures. Experiments at 700 and 750 °C did not achieve gas-phase equilibrium and were performed in H₂–CO₂ gas mixtures. Reaction timescales varied from 1 to 742 h. The experimental samples were characterized using optical microscopy, electron microprobe analysis, wavelength-dispersive-spectroscopy X-ray elemental mapping, and X-ray diffraction. In all experiments Cr experiences internal oxidation to produce inclusions of chromite (FeCr₂O₄) and eskolaite (Cr₂O₃) and surface layers of Cr-bearing magnetite [(Fe,Cr)₃O₄]. At 900 and 1000 °C, P is lost from the alloy via diffusion and sublimation from the metal surface. Analysis of P zoning profiles in the remnant metal cores allows for the determination of the P diffusion coefficient in the bulk metal, which is constant, and the internally oxidized layer, which is shown to vary linearly with distance from the metal surface. At 800 and 900 °C, P oxidizes to form a surface layer of graftonite [Fe₃(PO₄)₂] while at 700 and 750 °C P forms inclusions of the phosphide-mineral schreibersite [(Fe,Ni)₃P].     

Microstructure and Oxidation Behavior of Ni–TiO2 Composite Coating at High Temperature

Oxidation of Metals - Ni-based composite coatings are considered to improve the oxidation resistance of stainless steel. In this study, Ni–TiO2 composite coatings were electrodeposited onto...     

Oxidation behavior of Nb–24Ti–18Si–2Al–2Hf–4Cr and Nb–24Ti–18Si–2Al–2Hf–8Cr hypereutectic alloys at 1250°C

Nb-24Ti-18Si-2Al-2Hf-4Cr and Nb-24Ti-18Si-2Al-2Hf-8Cr alloys were prepared by arc melting in a water-cooled crucible under argon atmosphere.Microstructural characteristics and oxidation resistance of the alloys at 1250 ℃ were investigated.The results show that,when the Cr content is 4 at%,the microstructures consist of(Nb,Ti)_(ss) and Nb_5Si_3;as Cr content increases to8 at%,C14 Laves phase Cr_2Nb is formed.The isothermal oxidation tests show that the oxidation kinetics of the two alloys follow similar features.The weight gains of the two alloys after oxidation at 1250℃ for 100 h are 235.61 and198.50 mg·cm~(-2),respectively.During oxidation,SiO_2,TiO_2,Nb_2O_5 and CrNbO_4 are formed at first.Then,Ti_2Nb_(10)O_(29) is formed after oxidation for 20 min and begins to change into TiNb_2O_7 as the oxidation proceeds.SiO_2 is formed as solid state at first but later evolves into glassy state to improve the cohesion of the scale.After oxidation for 100 h,oxidation products consist of SiO_2,TiNb_2O_7,Nb_2O_5 and CrNbO_4.     

Constitution of the Mn–H system at high hydrogen pressures

The structure of Mn–H alloys was determined by X-ray diffraction under high hydrogen pressures and high temperatures, and a phase diagram was established over a wide range of p(H₂), T conditions. A new phase having a dhcp structure was found, and the stability of various phases was examined in particular relation to superabundant vacancy formation.     

Structure and Properties of Coatings in the Cr–B–C–N System Obtained Using a CrB2 Cathode by the Method of Pulsed Cathode-Arc Evaporation P-CAE in Ar,N2, and C2H4 Media

Protection of Metals and Physical Chemistry of Surfaces - The technology of pulsed cathode-arc evaporation (P-CAE) has been successfully applied for coating deposition in the...     

Chemical and physical sputtering of aluminium and gold samples using Ar–H2 DC-glow discharges

We present a series of sputtering experiments on aluminium samples performed with an Ar–H₂ DC-glow discharge at varying Ar–H₂ gas-composition, driven at a discharge voltage of –300 V and a pressure of 0.2 mbar, in conjunction with measurements of the corresponding ion-energy distributions of the ions bombarding the discharge cathode (Ar⁺, Ar²⁺, ArH⁺, H₂⁺ and H₃⁺). Similar measurements on gold samples, which have been published, have shown that the Au-sputtering efficiency of an Ar–H₂ glow discharge as a function of gas-composition could be adequately described by the corresponding change in the measured ion-energy distributions, under the assumption of a purely physical sputtering process. The experiments presented here show that this is not the case for aluminium (effectively Al₂O₃). In this case, a measured optimal gas-composition of 80% H₂ was found for Al-sputtering, while the energy-distributions suggest an optimum at 20% (as for gold). This clearly suggests that hydrogen-enhanced chemical sputtering is taking place.     

ZrNi–H2: microstructural analysis of the thermodynamically controlled hydride phase growth,and electronic properties

The ZrNi–H₂ phase diagram indicates the presence of two stable hydrides: a triclinic monohydride ZrNiH and an orthorhombic trihydride ZrNiH₃ [1]. In this paper, we present the results of some thermodynamic, microstructural and electronic properties of the ZrNi–H₂ system. A strict control of the thermodynamic variables (P, T) during the hydride phase growth allowed us to prepare two samples of overall composition ZrNiH_0.70 and ZrNiH_2.5. In a first step, the microstructure evolutions induced by hydrogen absorption are investigated during the activation process. The intermetallic and hydrided compounds are studied by energy dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) methods. The nature of defects generated in ZrNi and its hydrides compounds are observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Ab-initio electronic structure calculations have been performed. They clearly show the importance of chemical effects besides geometrical factors in explaining the preferential site occupancy of hydrogen atoms in the ZrNiH phase.     

X18H9和X19H25C2耐热鋼的焊接

我厂热处理工部貫通式渗碳炉,是拖拉机零件进行渗碳处理的重要設备,炉內分加热、渗碳、扩散、預冷四个溫度区,其中最低溫度也达840℃,利用噴咀将噴出的煤气在炉罐外进行燃燒,使炉罐及罐内零件达到預定溫度。炉罐內流动着雾化的煤油,每隔30～50分钟送进托着零件的料盘,經11～18小时,雾化的煤油使零件表面