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1.
选择性激光熔炼(SLM)建立在激光熔覆/沉积基础上,能够由粉末直接制备或修复近成形高性能部件。选择性激光熔炼部件优异的力学性能是保证其用于航空发动机产品的先决条件。镍基高温合金IN718广泛用于制备航空发动机中的高性能部件。在过去的研究中,利用预合金化IN718合金粉末,通过选择性激光熔炼制备出增材制造部件。通过优化激光沉积过程试验参数,以最大限度地降低气孔率。对沉积态、直接时效态、固溶时效态、均匀化后固溶时效态四种状态激光沉积IN718合金的显微组织和力学性能进行了对比分析。拉伸试验结果显示,直接时效态合金强度最高,均匀化后固溶时效态合金塑性最好。综合考虑三种热处理状态的室温和高温拉伸试验结果,均匀化后固溶时效态试样不仅具有优于锻态AMS标准的强度,而且有很好的塑性。因此,选择均匀化后固溶时效处理作为选择性激光熔炼IN718合金的热处理方式。考察了该种热处理状态合金的650oC/700MPa和725MPa持久性能和455oC低周疲劳性能,并与锻态IN718进行了对比。 相似文献
2.
A quantum chemical molecular dynamics method was used in order to understand the oxide film degradation mechanism at metal/metal-oxide interfaces. The present study shows that oxygen diffusivity in the metal is significantly higher at a Fe-Cr/Fe2O3 interface compared to a Fe-Cr/Cr2O3 interface. This indicates that Cr2O3 enables protection of the surface for a longer period of time than Fe2O3 in a high temperature environment. Applied tensile strain enhances the oxygen mobility towards the metal surface. This process helps to increase the oxidation of the metal surface by forming metal oxygen bonds. Atomic charge analysis reveals that the oxygen atoms are negatively charged and the chromium atoms are more highly positively charged than iron ones. The negatively charged oxygen atoms are able to make covalent bonds with the positive metal atoms. This charge transfer process facilitates the formation of metal-oxygen bonds and weakens the metallic bonds. 相似文献
3.
A case of severe hot corrosion of wrought IN 657 has been reported in an industrial furnace burning a fuel containing a high proportion of sodium sulphate. The sequence of events appears to have been (i) a coarsening of the fine eutectic structure of the alloy, to form a coarse mixture of γ (Ni, Fe, Cr) in ∝ (Cr) matrix; (ii) oxidation of the ∝ to form initially internal Cr2O3, and eventually a mixture of γ particles in a Cr2O3 matrix (sulphidation ahead of the oxide front may possibly have some significance in this step); (iii) fracture or exfoliation of the mixed oxide/metal scale from the alloy, allowing the ingress of molten salt to a locally highly reducing environment; (iv) the reduced salt (acid) rapidly fluxing the metal. A high chromium content, although protective against basic fluxing processes, may well be less effective against acid fluxing.The key to the attack thus appears to be the coarsening of the structure, which must have been caused by the inward diffusion of some component of the environment: the most likely species is thought to be sulphur, but no evidence of this has been obtained. 相似文献
4.
The oxidation behavior of the Ni-base alloys IN 617, IN 713 LC, Ni20Cr, and Ni20Cr+Si has been investigated in the temperature range from 850°C to 1000°C in air and at low-oxygen partial pressure p(O2) (10–19 to 10–16 bar). With the exception of alloy IN 713 LC, the materials show no influence of p(O2) on the oxidation mechanisms and the kinetics. This result can be explained by the formation of a dense Cr2O3 layer, the growth rate of which is controlled by the Cr ion interstitial concentration in Cr2O3 at the phase boundary oxide/alloy and the mobility of Cr ions in Cr2O3. For the alloy IN 713 LC which develops a dense Al2O3 layer in air, a modified transition mechanism at low p(O2) leads to the formation of Cr2O3 at the surface and a strong internal oxidation of Al. 相似文献
5.
The effects of reactive gas partial pressure on droplet formation, deposition rate and change of preferred orientation of CrN and Cr2O3 coatings were studied. For CrN coatings, as nitrogen partial pressure increases, the number and size of droplets increases, the deposition rate initially increases obviously and then slowly, and the preferred orientation of CrN changes from high-index plane to low-index one. For Cr2O3 coatings, with the increase of oxygen partial pressure, the number and size of droplets decreases, the deposition rate decreases and the (300) becomes the preferred orientation. These differences are ascribed to the formation of CrN (with a lower melting point) and Cr2O3 (with a higher melting point) on the surface of Cr target during the deposition of CrN and Cr2O3. Complete coatings CrN or Cr2O3 film can be formed when reactive gas partial pressure gets up to 0. l Pa. The optimized N2 partial pressure for CrN deposition is about 0.1-0.2 Pa in order to suppress the formation of droplets and the suitable 02 partial pressure for Cr2O3 deposition is approximately 0.1 Pa for the attempt to prevent the peel of the coating. 相似文献
6.
Soo-Haeng Cho Il-Je Cho Gil-Sung You Ji-Sup Yoon Seong-Won Park 《Metals and Materials International》2007,13(4):303-309
The electrolytic reduction of a spent oxide fuel involves the liberation of the oxygen in molten LiCl electrolyte, which is a chemically aggressive environment that is excessively corrosive for typical structural materials. Accordingly, it is essential to choose the optimum material for the processing equipment that handles the molten salt. In this study, the corrosion behaviors of Haynes 263, Haynes 75, Inconel 718 and Inconel X-750 in a molten LiCl?Li2O salt under an oxidizing atmosphere were investigated at 650°C for 72 to 216 hrs. The Haynes 263 alloy showed the best corrosion resistance among the examined alloys. The corrosion products of Haynes 263 were Li(Ni,Co)O2 and LiTiO2; those of Haynes 75 were Cr2O3, NiFe2O4, LiNiO2 and Li2FiFe2O4; while Cr2O3, NiFe2O4 and CrNbO4 were identified as the corrosion products of Inconel 718. Inconel X-750 produced Cr2O3, NiFe2O4 and (Cr, Nb, Ti)O2 as its corrosion products. Haynes 263 showed a localized corrosion behavior while Haynes 75, Inconel 718 and Inconel X-750 showed a uniform corrosion behavior. 相似文献
7.
The nature of the first-formed oxide on 20% Cr/25% Ni/Nb stabilized steel during exposure to CO2 at high and low temperatures has been determined by surface analytical techniques. These results together with a consideration of gas/solid interactions show that the oxide produced may be determined by kinetics or thermodynamic factors, and a diagram is presented to show that rhombohedral Cr2O3 or spinel may be the oxide first formed. Under most standard conditions, a mixed spinel oxide is formed initially, and the subsequent growth of a duplex oxide is analyzed in terms of a solid-state reaction in which the spinel oxide is reduced to Cr2O3 at the metal/oxide interface. Diffusion control of growth by either spinel or Cr2O3 is incorporated in new equations describing the kinetics of oxidation, and weight-gain predictions are tested against experimental observations. 相似文献
8.
Ni-base superalloy IN 718 was cyclically oxidized in laboratory air at temperatures ranging from 750 to 950 °C for up to 12 cycles (14 h/cycle). The kinetic behaviour as well as the surface morphology, and the oxide phases of the scales were characterized by means of weight gain measurements, cyclic oxidation kinetics, scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) analysis techniques. The results showed that as the oxidation temperature increased, the oxidation rate, the external scale thickness, and internal oxidation zone increased. It was suggested that the oxidation rate was controlled by the diffusion of substrate elements in the alloy and the inward diffusion of oxygen through the oxide scale. The oxidation kinetics followed a sub-parabolic rate law and, the activation energy of oxidation was 249 ± 20 kJ mol?1. The scaling process was controlled mainly by the diffusion of chromium, titanium, manganese, and oxygen ions through the chromia scale. IN 718 showed low weight gain and very slow reaction rates of substrate elements at 750 °C. At 850 °C, a continuous and very thin oxide scale was formed. At 950 °C, XRD and EDS-elemental mapping analysis revealed that a complex oxide scale had formed. It consisted of an outermost layer of TiO2?CMnCr2O4 spinels, inner layer of Cr2O3, and the inner most layer composed of Ni3Nb enriched with Nb, Ti and Al oxides underneath the chromia layer. The oxide scale at this temperature seemed to be thicker layer, significant spallation and volatilization had apparently occurred, and greater internal corrosion was identified. The doping effect of titanium was observed, where it was found to be diffused through the chromia scale to form TiO2 at the oxide-gas interface as well as internally and at the oxide alloy interface. The amount of rutile (TiO2) at the oxide surface increased with temperature. In view of Mn contents in the alloy, the manganese?Cchromium spinel oxide was inferred to have played an important role in cyclic oxidation behaviour of IN 718, where the change in oxidation kinetic was noted. The Al contents would cause internal Al-rich oxide formation at grain boundaries. 相似文献
9.
W. Fang T.Y. Cho J.H. Yoon K.O. Song S.K. Hur S.J. Youn H.G. Chun 《Journal of Materials Processing Technology》2009,209(7):3561-3567
In this work, the optimal coating process (OCP) designed by Taguchi program for high velocity oxy-fuel (HVOF) thermal spraying WC–CrC–Ni powder on Inconel 718 substrate (IN 718) is obtained by optimizing hardness (38 FMR oxygen flow rate, 53 FMR hydrogen flow rate, 25 g/min powder feed rate and 7 in. spray distance). Oxygen flow rate affects hardness mostly. The surface properties such as microstructure, crystalline phase, hardness, and porosity of WC–CrC–Ni coating have been investigated. The phase of coating has been changed during the OCP spraying because a portion of carbides, such as WC, Cr7C3, Ni3C decomposes to W2C, Cr, Ni and free carbon. Hardness (1150 ± 50 Hv) and porosity (1.2 ± 0.2%) of the OCP coating have been improved by optimization. The friction and wear behaviors of the WC–CrC–Ni coating, electrolytic hard chrome (EHC) plating and IN 718 have been studied comparatively. The lubrication due to free carbon and metal oxide debris results in a decrease of friction coefficients of the WC–CrC–Ni, compared to EHC and IN 718 at both 25 and 450 °C. It is concluded that HVOF WC–CrC–Ni coating performs more excellent anti-wear than others at both temperatures. 相似文献
10.
The initial oxide was CoO which formed very rapidly by outward cation diffusion. A chromium-enriched substrate layer subsequently reacted via internal oxidation to form a continuous film of Cr2O3. The formation of CoCr2O4 occurred rapidly by the reaction of CoO and Cr2O3. The presence of CoCr2O4 spinel in the oxide scale was found to offer less oxidation resistance than a layer of Cr2O3 in Co-20Cr. The large mass of CoO that existed, as well as the much more rapid rate of spinel formation compared to the rate of Cr2O3 growth, resulted in the Cr2O3 being used up faster than new Cr2O3 could form. This behavior was opposite that observed in Ni-Cr alloys. Manganese additions slightly reduced the oxidation rate as well as the solid-state growth rate of spinel. However, the spinel still formed faster than new Cr2O3, and hence the protective layer was used up. Silicon additions reduced the oxidation rate, but the layers were highly susceptible to spalling upon cooling as well as during isothermal oxidation. The scales contained both spinel and Co2SiO4. The ortho-silicate was present as isolated particles and did not form a continuous protective film per se. The reduced oxidation rate was associated with a thin inner film of Cr2O3.This work was performed at Stanford Research Institute, Menlo Park, California and was supported by the National Aeronautics and Space Administration, Contract NAS 3-11165. 相似文献
11.
以AZ31B变形镁合金为材料,采用五种单一氧化物MgO,Cr2O3,CaO,TiO2,MnO2进行混合配制得到复合配方.比较了无活性剂、涂敷单一TiO2活性剂和复合活性剂的焊缝熔深、接头金相组织、相组成及力学性能.结果表明,熔深达到最大的复合活性剂比常规TIG焊增加2.5倍左右,也比单一活性剂的熔深增加效果明显,同时其焊缝中晶粒比单一TiO2活性剂的晶粒细小,焊缝的抗拉强度比单一TiO2活性剂的高.经XRD分析复合配方中活性元素的加入改善了焊缝的相组成,避免了接头低熔点镁铝化合物脆性相的形成. 相似文献
12.
Characterisation of oxide films formed on Co–29Cr–6Mo alloy used in die-casting moulds for aluminium
Oxide films formed at 700 °C on Co–29Cr–6Mo alloy were characterised extensively to improve the corrosion resistance of the alloy to liquid Al, enabling its use in Al die-casting moulds. Film of duplex layer consisting of an outer CoO-rich layer and an inner Cr2O3-rich layer was observed in samples subjected to oxidation for 4 h. With an increase in duration of oxidation, CoO was gradually replaced by Cr2O3, resulting in a single-layered oxide film dominantly composed of Cr2O3. The oxide film evolved with duration of oxidation treatment indicating the possibility of optimising films for Al die-casting moulds. 相似文献
13.
S. W. Shyu H. Y. Huang K. H. Tseng C.P. Chou 《Journal of Materials Engineering and Performance》2008,17(2):193-201
The purpose of the present work was to investigate the effect of oxide fluxes on weld morphology, arc voltage, mechanical
properties, angular distortion and hot cracking susceptibility obtained with TIG welding, which applied to the welding of
5 mm thick austenitic stainless steel plates. A novel variant of the autogenous TIG welding process, oxide powders (Al2O3, Cr2O3, TiO2, SiO2 and CaO) was applied on a type 304 stainless steel through a thin layer of the flux to produce a bead on plate welds. The
experimental results indicated that the increase in the penetration is significant with the use of Cr2O3, TiO2, and SiO2. A-TIG welding can increase the weld depth to bead-width ratio, and tends to reduce the angular distortion of the weldment.
It was also found that A-TIG welding can increase the retained delta-ferrite content of stainless steel 304 welds and, in
consequence, the hot-cracking susceptibility of as-welded is reduced. Physically constricting the plasma column and reducing
the anode spot are the possible mechanism for the effect of certain flux on A-TIG penetration. 相似文献
14.
针对铝合金,提出了一种气体输送活性钨极氩弧焊,即GTFA-TIG焊(gas transfer flux activating TIG welding).该方法改变了活性元素的引入方式,通过自动送粉装置将活性剂输送到保护气体中,由保护气体将其引入电弧-熔池系统进行施焊,使得电弧收缩,熔池金属流态改变,熔深增加,同时省却了涂覆活性剂工序,实现了焊接过程自动化.进行了普通交流TIG焊和8种单组元活性剂的GTFA-TIG表面熔焊,分析了不同活性剂对焊缝成形、拉伸性能以及缺陷的影响.结果表明,大多数卤化物和氧化物活性剂都能使熔深增加到传统TIG焊的2.5~3倍以上,单质碲增加熔深效果较差.采用V2O5的焊缝抗拉强度接近母材金属,而采用MnCl2和AlF3的焊缝有一定程度降低.焊缝X射线探伤结果表明,采用V2O5,MnCl2和AlF3的焊缝评片结果均为Ⅰ级,而采用碲的焊缝为Ⅲ级. 相似文献
15.
The surface oxidation of Incoloy 800 was studied using dilute O2 gas at temperatures of 300 °C. Samples with two differing grain sizes were studied using time-of flight secondary ion mass spectrometry (ToF–SIMS) and X-ray photoelectron spectroscopy (XPS) as primary analysis tools. A multi-layered oxide film was detected and was composed of an exterior gamma-Fe2O3 with a Cr2O3 layer at the oxide–metal interface also containing significant concentrations of NiCr2O4. Minor concentrations of another spinel oxide, NiFe2O4 were distributed throughout the film. The kinetics of oxidation growth was found to follow a direct logarithmic relationship for both grain sizes, suggesting that the oxide would be a suitably protective. Very small oxide nodules formed at later stages, particularly for the small grained samples. A protocol for assessment of XPS spectral envelopes is advanced. The method measures the percent residual intensities remaining after spectral subtraction of reference spectra and appears to be an effective means for screening of possible components. 相似文献
16.
Cr was oxidized in 1 aim O2 at 980, 1090, and 1200°C. ElectropolishedCr and some orientations of etched Cr oxidize rapidly and develop compressive stress in the growing Cr2O3; other orientations oxidize slowly, apparently free of stress. SEM examination of fracture sections shows that the thick oxide is polycrystalline whereas the thin oxide on etched Cr is monocrystalline. It is deduced that the monocrystalline oxide grows by lattice diffusion of cations outward, and the polycrystalline layer by the two-way transport of cation diffusion outward and anion diffusion inward along oxide grain boundaries. The consequent formation of oxide within the body of the polycrystalline layer generates compressive stress and leads to wrinkling by plastic deformation. The activation energy for oxidation of Cr by cation lattice transport is 58 kcal/mole. Polycrystalline Cr2O3 forms on Fe-26Cr alloy, whether electropolished or etched; oxidation is accordingly rapid and accompanied by compressive stress. 相似文献
17.
A sputtered nanocrystalline coating of IN 738 alloy was obtained by means of magnetron sputtering. The isothermal oxidation behavior at 800, 900, and 1000°C and the cyclic oxidation behavior at 950°C of the coating were studied in comparison with IN 738 cast alloy. The results indicated that a double external oxide scale was formed on the nanocrystalline coating at 900, 950, and 1000°C without internal oxide and nitride. The scale consisted in an outer mixture of Cr2O3, TiO2, and NiCr2O4 and an inner, continuous Al2O3 layer, which offered good adhesive and protectiveness. However, at 800°C a continuous Al2O3 scale could not be formed during oxidation of nanocrystalline coating and aluminum was still oxidized internally. 相似文献
18.
To evaluate the suitability of HR3C and 22Cr–25Ni–2.5Al AFA steels as the heat-resistant alloys, the oxidation behavior of them was investigated in air at 700, 800, 900 and 1000 °C. The evolution of oxide layer on the surface and subsurface was investigated using a combination of compositional/elemental (SEM, EDS) and structural (XRD, GDOES) techniques. A dense and continuous Cr2O3 healing layer on the HR3C was formed at the temperature of 700 or 800 °C, but the Cr2O3 oxide film on HR3C was unstable and partly converted into a less protective MnCr2O4 with the increase in temperature to 900 or 1000 °C. The composition and structure of oxide film of 22Cr–25Ni–2.5Al AFA steels are significantly different to the HR3C alloys. The outer layer oxides transformed from Cr2O3 to Al-containing oxides, leading to a better oxidation resistance at 700 or 800 °C compared to HR3C. Further, the oxide films consist of internal Al2O3 and AlN underneath the outer loose layer after 22Cr–25Ni–2.5Al AFA oxidized at 900 or 1000 °C. It can be proved that the internal oxidation and nitrogen would make 22Cr–25Ni–2.5Al AFA steels have worse oxidation resistance than HR3C alloys at 900 or 1000 °C. 相似文献
19.
The formation and breakdown of a protective layer of Cr2O3 on L-605 during oxidation at 1100° C was investigated. The effects of surface deformation, pressure, and water vapor on the breakdown time were evaluated. It was found that increasing surface deformation, increased the time to breakdown. Decreasing pressure below 1 atm to 0.13 N/m2 increased time of breakdown as did decreasing water content from 25,000 to 2.5 ppm. By metallographic and microprobe examinations of samples during breakdown a model was deduced. Surface deformation promotes Cr2O3 formation, while increasing pressure and moisture increases the volatility of Cr2O3. Thus, the Cr2O3 grows for a time determined by these three factors. At the end of this time the growth stresses cause the oxide to crack, exposing a chromium-depleted metal surface to the oxidizing gas. The resultant rapid oxidation of this surface lifts the remaining Cr2O3, exposing more depleted metal. When the depletion zone is consumed and a very thick oxide has formed, the rate of oxidation slows and no further disruption is noted. 相似文献
20.
The microstructure and mechanical properties of the laser welded joint of DZ125L and IN718 nickel base superalloys were investigated. The results show that the fusion zone (FZ) mainly consists of fine dendrite structure with fine γ′, Laves phases and MC carbides inhomogeneously distributed. The high welding temperature induces the partial dissolution of γ′ in the heat-affected zone (HAZ) of DZ125L and liquation of grain boundaries in both of the HAZs. After post-weld heat treatment (PWHT), fine γ″ and γ′ phases precipitate in the FZ, IN718 HAZ and IN718 base metal (BM), and fine γ′ precipitate in the γ channel of the HAZ and BM of DZ125L. With tensile testing, the joints after PWHT show higher strengths than that of the weaker DZ125L alloy. Plastic deformation mainly concentrates in the weaker DZ125L and the joint finally fails in the DZ125L BM. 相似文献