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1.
TiAl alloys incorporated in (0,3,5,10) wt.% TiB2 dispersoids were manufactured via mechanical alloyingspark plasma sintering (MA-SPS), and their cyclic oxidation characteristics were studied at 800, 900 and 1000°C in air. The cyclic oxidation resistance of the prepared TiAl-TiB2 composites effectively increased with increases in TiB2 content. The oxide scale formed consisted of an outer TiO2 layer, an intermediate Al2O3 layer, and an inner (Al2O3+TiO2) mixed layer. The scale adherence was relatively good, and much thinner oxide scales, when compared to TiB2-free TiAl alloys, were formed on the prepared composites. The incorporated TiB2 dispersoids oxidized to TiO2 and B2O3 which evaporated during oxidation.  相似文献   

2.
The Oxidation of TiB2 Particle-Reinforced TiAl Intermetallic Composites   总被引:3,自引:0,他引:3  
Lee  D. B.  Kim  M. H.  Yang  C. W.  Lee  S. H.  Yang  M. H.  Kim  Y. J. 《Oxidation of Metals》2001,56(3-4):215-229
The oxidation kinetics of TiAl alloys with and without (3, 5, 10 wt.%) TiB2 dispersoids were studied between 1073 and 1273 K in atmospheric air. The inert TiB2 dispersoids effectively increased the oxidation resistance of TiAl alloys. The higher the TiB2 dispersoids content, the more pronounced the effect. The oxide scale formed on TiAl–TiB2 composites was triple-layered, consisting mainly of an outer TiO2 layer, an intermediate Al2O3 layer, and an inner (TiO2+Al2O3) mixed layer. No B2O3 was observed within the oxide scale because of its high vapor pressure. A thin Ti3Al sublayer and discrete TiN particles were found at the oxide–substrate interface. During the oxidation of TiAl alloys with and without TiB2 dispersoids, titanium ions diffused outwardly to form the outer TiO2 layer, while oxygen ions transported inwardly to form the inner (TiO2+Al2O3) mixed layer. The increased oxidation resistance by the addition of TiB2 was attributed to the enhanced alumina-forming tendency and thin and dense scale formation.  相似文献   

3.
The oxidation behavior of TiAl alloys containing dispersed particles of (5, 10, 15 wt.%) SiC, (3,5 wt.%) Si3N4 or (3, 5, 10 wt.%) TiB2 was studied between 800 and 1200°C in atmospheric air. The TiAl−(SiC, Si3N4) alloys oxidized to TiO2, Al2O3, and SiO2. The TiAl−TiB2 alloys oxidized to TiO2, Al2O3, and B2O3 which evaporated during oxidation. Improvement in oxidation resistance accompanied by thin, dense scale formation due to the addition of dispersoids originated primarily from the enhanced alumina-forming tendency, improved scale adhesion by oxide grain refinement owing to the beneficial effect of dispersoids, and the incorporation of SiO2 within the oxide scale in the case of TiAl−(SiC, Si3N4) alloys.  相似文献   

4.
Titanium oxide (TiO2) and boron carbide (B4C) were added to TiB2 raw powders to prepare porous TiB2 ceramics by reactive spark plasma sintering, and the gas escape (such as CO and B2O3) resulted in higher porosity. X-ray Diffraction results indicated that the reduction reaction was completed after the reactive spark plasma sintering process. The porosity could be controlled by changing the ratio of synthesized TiB2 to raw TiB2 powders. The porosity of porous TiB2 ceramics with 20 wt.% and 40 wt.% synthsized TiB2 ceramics are 18.5% and 22.2%, respectively. The thermal diffusivity of the porous TiB2 ceramics decreased with the porosity due to the low diffusivity behavior of gas and vacuum in pores, and the thermal conductivity for porous TiB2 ceramics decreased as the temperature increased throughout the measured temperature range. The results here pointed to a potential method for fabricating porous TiB2 ceramics with controllable thermophysical properties.  相似文献   

5.
The beneficial effect of dispersions of reactive-metal oxide particles on the adhesion of Cr2O3 and Al2O3 scales formed on heat-resisting alloys is wellknown. It has been shown that an Al2O3 dispersion in an alloy can improve the adhesion of a Cr2O3 scale, and it is of particular interest in assessing the various theoretical proposals for the effect to determine whether such a dispersion can affect the adhesion of an Al2O3 scale. In this investigation, a Co–10% Cr–1 % Al alloy was first internally oxidized to form an Al2O3 dispersion. This alloy was then aluminized so that on subsequent oxidation an Al2O3 scale developed. It was shown that the dispersion did indeed improve the scale adhesion. The implications of this result are discussed.  相似文献   

6.
Thin Y2O3 films were deposited by the electrochemical deposition-pyrolysis process on Fe–25Cr and Fe–25Cr–10Al alloys. The influence of the films on the oxidation behavior of the alloys was studied at 850°C and 1000°C. The results showed that Y2O3 films remarkably decreased the oxidation rate of Cr2O3-forming alloys and spallation of the scales, but they did not decrease the oxidation rate of the Al2O3-forming alloys, although they do reduce the spallation of Al2O3 scales. Y2O3 films remarkably change the morphology of the scales on both alloys, depending on the oxidation temperatures. These results show that the reactive-element effects of Y2O3 films on the Cr2O3 formers and Al2O3 formers are different.  相似文献   

7.
The corrosion behavior of 11 Fe-Mo-Al ternary alloys was studied over the temperature range 700–980°C in H2/H2O/H2S mixed-gas environments. With the exception of Fe-10Mo-7Al, for which breakaway kinetics were observed at higher temperatures, all alloys followed the parabolic rate law, despite two-stage kinetics which were observed in some cases. A kinetics inversion was observed for alloys containing 7 wt.% Al between 700–800°C. The corrosion rates of Fe-20Mo and Fe-30Mo were found to be reduced by five orders of magnitude at all temperatures by the addition of 9.1 or higher wt.% aluminum. The scales formed on low-Al alloys (5 wt.% Al) were duplex, consisting of an outer layer of iron sulfide (with some dissolved Al) and a complex inner of Al0.55Mo2S4, FeMo2S4, Fe1.25Mo6S7.7, FeS, and uncorroded FeAl and Fe3Mo2. Platinum markers were always located at the interface between the inner and outer scales for the low-Al alloys, indicating that outer-scale growth was due mainly to outward diffusion of cations (Fe and Al), while the inner scale was formed primarily by the inward flux of sulfur anions. Alloys having intermediate Al contents (7 wt.%) formed scales that consisted of FeS and Al2O3. The amount of Al2O3 increased with increasing reaction temperature. The high-Al-content alloys (9.1 and 10 wt.%) formed only Al2O3 which was responsible for the reduction of the corrosion rates.  相似文献   

8.
Boron carbide (B4C) ceramics, with a relative density up to 98.4% and limited grain growth, were prepared at 1600-1800 °C by spark plasma sintering (SPS) technique. The effects of powder milling medium (water and 2-propanol) on the powders' surface characteristics and TiB2 addition on the sintering densification were investigated. The ball milling processing of B4C powders in water can promote the sintering of B4C ceramics. A B2O3 layer on B4C particle surface is concluded to promote the densification of the B4C ceramics at an early sintering stage. This B2O3 layer, which normally inhibits the densification process at the final stage of the sintering, can be reduced through reaction with TiB2 particles, resulting in further densification of the B4C ceramics.  相似文献   

9.
A new composite of TiB2 with CrSi2 has been prepared with excellent oxidation resistance. Dense composite pellets were fabricated by hot pressing of powder mixtures. Microstructural characterization was carried out by XRD and SEM with EDAX. Mechanical and physical properties were evaluated. Extensive oxidation studies were also carried out. A near theoretical density (99.9% TD) was obtained with a small addition of 2.5 wt.% CrSi2 by hot pressing at 1700 °C under a pressure of 28 MPa for 1 h. The microstructure of the composite revealed three distinct phases, (a) dark grey matrix of TiB2, (b) black phase – rich in Si and (c) white phase – Cr laden TiB2. Hardness and fracture toughness were measured as 29 ± 2 GPa and 5.97 ± 0.61 MPa m1/2, respectively. Crack branching, deflection and bridging mechanisms were responsible for the higher fracture toughness. With increase in CrSi2 content, density, hardness and fracture toughness values of the composite decreased. Thermo gravimetric studies revealed the start of oxidation of the composite at 600 °C in O2 atmosphere. Isothermal oxidation of these composites showed better oxidation resistance by formation of a protective oxide layer. TiO2, Cr2O3 and SiO2 phases were identified on the oxidized surface. Effects of CrSi2 content, temperature and duration of oxidation on the oxide layer formation are reported. Activation energy of the composite was calculated as ∼110 kJ/mol using Arrhenius equation. Diffusion controlled mechanism of oxidation was observed in all the composites.  相似文献   

10.
Ul-Hamid  A. 《Oxidation of Metals》2002,58(1-2):23-40
This study was undertaken to investigate and compare the effects of a yttrium addition on the oxide scale development of -Cr2O3- and -Al2O3-forming alloys under isothermal oxidation conditions. The alloys had a nominal composition (in wt.%) of Ni–30Cr, Ni–30Cr–0.5Y, Ni–30Cr–5Al, and Ni–30Cr– 5–Al–0.5Y. They were oxidized in air for 50 hr at 1000°C. The scale microstructures were characterized using cross-sectional transmission-electron microscopy combined with energy-dispersive X-ray spectroscopy. It was observed that the scale thickness decreases and the scale adherence increases due to the Y addition. The growth direction of -Cr2O3 scale changes from predominately outward to inward while countercurrent diffusion within -Al2O3 is replaced by inward diffusion due to Y modification. It is considered that the ability of Y to scavenge sulfur from the alloy and its segregation to the oxide grain boundaries primarily account for most of its beneficial effects.  相似文献   

11.
Oxide scale adhesion and impurity segregation at the scale/metal interface   总被引:3,自引:0,他引:3  
The chemistry at scale/metal interfaces was studied using scanning Auger microscopy after removal of the scale in ultra-high vacuum using an in situ scratching technique. Al2O3 and Cr2O3 scales formed between 900°C and 1100°C on Fe-18 wt.% Cr-5 wt.% Al and on Ni-25 wt.% Cr alloys, respectively, were investigated. The adhesion of these scales was determined qualitatively by way of micro-indentation and scratching on the surface oxide. All of the alumina scales fractured to the same degree to expose the metal surface, regardless of the oxidation temperature. The chromia-forming alloy on the other hand, developed more adherent scales at lower oxidation temperatures. About 20 at.% sulfur was found at the metal surface in all cases, and its presence was not only detected on interfacial voids, but also on areas where the scale was in contact with the alloy at temperature. Results from this study clearly demonstrated that sulfur as an alloying impurity does segregate to the scale/alloy interface. However, for alumina scales and chromia scales, the effect of this segregation on oxide adhesion is noticeably different.  相似文献   

12.
Huang  Jinfeng  Fang  Hongsheng  Fu  Xiaorong  Huang  Fuxiang  Wan  Hong  Zhang  Qianfa  Deng  Shiping  Zu  Jishseng 《Oxidation of Metals》2000,53(3-4):273-287
The oxidation behavior of a new type of wrought Ni–Fe–Cr–Alsuperalloy has been investigated systematically in the temperature range of1100 to 1300°C. Results are compared with those of alloy 214, Inconel600, and GH 3030. It is shown that the oxidation resistance of the newsuperalloy is excellent and much better than that of the comparisonalloys. Scanning electron microscopy (SEM), electron probe microanalysis(EPMA), and X-ray diffraction (XRD) experiments reveal that the excellentoxidation resistance of the new superalloy is due to the formation of adense, stable and continuous Al2O3 and Cr2O3 oxide layer at hightemperatures. Differential thermal analysis (DTA) shows that the formationof Cr2O3 and Al2O3 oxide layers on the new superalloy reaches a maximum at1060 and 1356°C, respectively. The Cr2O3 layer peels off easily, and thesingle dense Al2O3 layer remains, giving good oxidation resistance attemperatures higher than 1150°C. In addition, the new superalloypossesses high mechanical strength at high temperatures. On-site testsshowed that the new superalloy has ideal oxidation resistance and can beused at high temperatures up to 1300°C in various oxidizing andcorrosion atmospheres, such as those containing SO2, CO2 etc., for longperiods.  相似文献   

13.
NiAl-TiB2 composite coatings with 0, 10 and 20 wt.% TiB2 were synthesized on the Ni-based superalloy substrate using electro-thermal explosion ultrahigh speed spraying technology. The microstructure analysis shows that the coatings consist of submicron grains. The bond between coatings and substrate is metallic cohesion. TiB2 as a powerful reinforcement is doped in NiAl for increasing its hardness. The isothermal oxidation test is carried out for the composite coatings at 1100 °C in air. The result shows that the oxidation resistance of NiAl coating is higher than that of NiAl-10TiB2 and NiAl-20TiB2 coatings. The phases of oxides on the coatings during the process at high temperature have been analyzed by X-ray diffraction. The results show that Al2O3 and Cr2O3 coexistence on surface of NiAl coating, while Al2O3, Cr2O3, TiO2 and a small amount of NiO form on surface of NiAl-10TiB2 and NiAl-20TiB2 coatings after oxidation for 4 h.  相似文献   

14.
The effects of BaCu(B2O5) additives on the sintering temperature and microwave dielectric properties of (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics were investigated. The (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics were not able to be sintered below 1000 °C. However, when BaCu(B2O5) were added, they were sintered below 1000 °C and had the good microwave dielectric properties. It was suggested that a liquid phase with the composition of BaCu(B2O5) was formed during the sintering and assisted the densification of the (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics at low temperature. BaCu(B2O5) powders were produced and used to reduce the sintering temperature of the (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics. Good microwave dielectric properties of Q × f = 35,000 GHz, ?r = 18.5.0 and τf = −51 ppm/°C were obtained for the (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics containing 7 wt.% mol% BaCu(B2O5) sintered at 950 °C for 4 h.  相似文献   

15.
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 Fe1–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.  相似文献   

16.
PbO–Sb2O3–B2O3 glasses mixed with different concentrations of TiO2 (ranging from 0 to 1.5 mol.%) were synthesized. The samples are characterized by X-ray diffraction, scanning electron microscopy and DSC techniques. A variety of properties, i.e. optical absorption, photoluminescence, infrared, ESR spectra, magnetic susceptibility, photo-induced birefringence (PIB) and dielectric properties (constant ′, loss tan δ, a.c. conductivity σac over a wide range of frequency and temperature) of these glass–ceramics have been explored. The analysis of these results indicated that Ti ion surrounding ligands play principal role in the observed PIB and the sample crystallized with 0.8 mol.% of TiO2 is the most suitable for the applications in non-linear optical devices.  相似文献   

17.
The high-temperature oxidation behavior of vanadium-aluminum alloys   总被引:1,自引:0,他引:1  
The oxidation behavior in air of pure vanadium, V-30Al, V-30Al-10Cr, and V-30Al-10Ti (weight percent) was investigated over the temperature range of 700–1000° C. The oxidation of pure vanadium was characterized by linear kinetics due to the formation of liquid V2O5 which dripped from the sample. The oxidation behavior of the alloys was characterized by linear and parabolic kinetics which combined to give an overall time dependence of 0.6–0.8. An empirical relationship of the form: W/A=Bt + Ct1/2 + D was found to fit the data well, with the linear contribution suspected to be from V2O5 formation for V-30Al and V-30Al-10Cr, and a semi-liquid mixture of V2O5 and Al2O3 for V-30Al-10Ti. The parabolic term is presumed related to the formation of a solid mixture of V2O5 and Al2O3 for V-30Al and V-30Al-10Cr, and TiO2 for V-30Al-10TiThe addition of aluminum was found to reduce the oxidation rate of vanadium, but not to the extent predicted by the theory of competing oxide phases proposed by Wang, Gleeson, and Douglass. This was attributed to the formation of a liquid-oxide phase in the initial stages of exposure from which the alloys could not recover. Ternary additions of chromium and titanium were found to decrease the oxidation rate further, with chromium being the most effective. The oxide scales of the alloys were found to be highly porous at 900° C and 1000° C, due to the high vapor pressure of V2O5 above 800° C.  相似文献   

18.
Li  M. H.  Zhang  Z. Y.  Sun  X. F.  Guan  H. R.  Hu  W. Y.  Hu  Z. Q. 《Oxidation of Metals》2002,58(5-6):499-512
Thermal–barrier coatings (TBCs) consist of a magnetron-sputtered Ni–30Cr–12Al–0.3Y (wt.%) bond coat to protect the substrate superalloy from oxidation/hot corrosion and an electron-beam physical-vapor deposited (EB–PVD) 7 wt.% yttria partially stabilized zirconia (YPSZ) top coat. The thermal cyclic life of the TBC system was assessed by furnace cycling at 1050°C. The oxidation kinetics were evaluated by thermogravimetric analysis (TGA) at 900, 1000, and 1100°C for up to 100 hr. The results showed that the weight gain of the specimens at 1100°C was the smallest in the initial 20 hr, and the oxide scale formed on the sputtered Ni–Cr–Al–Y bond coat is only Al2O3 at the early stage of oxidation. With aluminum depletion in the bond coat, NiO, Ni(Cr,Al)2O4, and other spinel formed near the bond coat. During thermal cycling, microcracks were initiated preferentially in the YPSZ top coat along columnar grain boundaries and then extended through and along the top coat. The growth stress of TGO added to the thermal stress imposed by cycling, lead to the separation at the bond coat–TGO interface. The ceramic top coat spalled with the oxide scale still adhering to the YPSZ after specimens had been cycled at 1050°C for 300 cycles. The failure mode of the EB–PVD ZrO2–7 wt.% Y2O3 sputtered Ni–Cr–Al–Y thermal-barrier coating was spallation at the bond coat–TGO interface.  相似文献   

19.
Haugsrud  R.  Gunnaes  A.E.  Nilsen  O. 《Oxidation of Metals》2003,59(3-4):215-232
The effects of superficial (30–100 nm) La2O3 surface coatings on the oxidation kinetics of Ni from 700 to 1100°C in air and the oxide morphology of the NiO scales have been investigated. The parabolic rate constant is lower than for uncoated Ni by a factor of 5 to 10. The oxide morphology changes with the La2O3 coatings: The oxide scale consists of an outer fine-grain layer with an inner region of coarser, but still equiaxed, grains. SIMS shows that the majority of the La remains at the surface where a highly oxygen-defective spinel, La2Ni4O7, was found by TEM. Two-stage oxidation followed by SIMS profiling reveals that the oxide growth occurs inside the scales.  相似文献   

20.
Nano-particles of homogeneous solid solution between TiO2 and Fe2O3 (up to 10 mol%) have been prepared by mechanochemical milling of TiO2 and yellow Fe2O3/red Fe2O3/precipitated Fe (OH)3 using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO2/Fe2O3) on photo-oxidation of different organic dyes like Rhodamine B (RB), Methyl orange (MO), Thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm) showed that TiO2 having 5 mol% of Fe2O3 (YFT1) is 3-5 times higher photoactive than that of P25 TiO2. The XRD result did not show the peaks assigned to the Fe components (for example Fe2O3, Fe3O4, FeO3, and Fe metal) on the external surface of the anatase structure in the Fe2O3/TiO2 attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO2 anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe2O3/TiO2 particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO2 anatase structure. EPR and magnetic susceptibility show that Fe3+ is in low spin state corresponding to μB = 1.8 BM. The temperature variation of μB shows that Fe3+ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe3+ in TiO2/Fe2O3 alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.  相似文献   

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