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1.
三相Cu—Ni—30Cr合金高温氧化行为研究   总被引:1,自引:0,他引:1  
研究了Cr含量相对较高的Cu—Ni—30Cr合金在700℃-800℃,0.1MPa纯氧气中的氧化行为。结果表明:合金氧化动力学较复杂,其瞬时抛物线速率常数随时间而降低,氧化动力学曲线通常不是由单一的抛物线或直线组成而是由几段组成。Cu—Ni—Cr为三相合金,3相的存在增加了合金表面形成Cr2O3氧化膜所需临界浓度,但30at%Cr足以使合金表面形成连续的Cr2O3外氧化膜。氧化膜内层是合金和氧化物相共存的混合区,被氧化的岛状物是由Cr2O3和Cu,Ni组成。这种混合内氧化机制与经典内氧化明显不同。  相似文献   

2.
Microstructures and oxidation behaviors of four Dy-doped Nb–Si-based alloys at 1250℃ were investigated. The nominal compositions of the four alloys are Nb–15Si–24Ti–4Cr–2Al–2Hf–xDy(at.%), where x = 0, 0.05, 0.10 and 0.15,respectively. Results showed that the four alloys all consisted of Nbss, αNb_5Si_3 and γNb_5Si_3, and the addition of Dy produced no obvious effect on the phase constitution and the microstructures of Nb–Si-based alloys. After oxidation at 1250℃ for 58 h, it was found that the addition of Dy accelerated the oxidation rate of Nb–Si-based alloys and caused a larger weight gain, accompanied by the formation of a more porous and less protective oxide scale. The oxides of Nb_2O_5,Ti_2Nb_(10)O_(29), TiNb_2O_7, Ti_(0.4)Cr_(0.3)Nb_(0.3)O_2 and glassy SiO_2 were formed on Dy-doped Nb–Si-based alloys. The hightemperature oxidation mechanism of Dy-doped Nb–Si-based alloys was discussed.  相似文献   

3.
The isothermal and cyclic-oxidation behavior of three different batches of commercial chromium (purity >99.9%) at 900 and 1000°C has been investigated by means of conventional thermogravimetry and thin-layer activation. Two batches with a similar microstructure and one, with a five times larger average grain size, were used. Isothermal-oxidation experiments were performed in synthetic air for 150 hr. Cyclic-oxidation experiments were executed in static laboratory air with each cycle corresponding to a period of 1 hr at test temperature and 12 min at ambient temperature up to a maximum of 3000 cycles. Results showed significant differences between the oxidation behavior of chromium derived from the three different batches. This was found under isothermal as well as under cyclic-oxidation conditions, especially at 1000°C. The mass-loss rates during cyclic oxidation for the different batches differed up to more than 30 times at 1000°C. In addition, the complementary nature of the different specimen-evaluation techniques, i.e., conventional thermogravimetry and thin-layer activation in cyclic oxidation is shown.  相似文献   

4.
Pint  B.A.  Tortorelli  P.F.  Wright  I.G. 《Oxidation of Metals》2002,58(1-2):73-101
Cycle frequency affects both high-temperature oxidation behavior and the method in which the cyclic test is conducted. Several issues are discussed using examples taken from results for Ni-base and Fe-base, alumina-forming alloys. For alloys that form adherent scales, cycle frequency has little effect on results over extended test times ( 500 hr). When an alloy forms a less adherent scale, reducing the cycle time often has the expected effect of increasing the mass loss per unit exposure time; however, the opposite effect is observed in other cases. Low-frequency cycle experiments can be conducted with specimens contained in alumina crucibles. This has the important benefit of collecting the spalled oxide and measuring the total mass gain, equivalent to the metal wastage. However, higher-frequency-cyclic tests cannot be performed with crucibles because of the large thermal mass and thermal-shock problems of alumina crucibles. The test method and cycle frequency ultimately have a strong effect on lifetime predictions.  相似文献   

5.
郭万根  刘越 《物理测试》2011,29(5):15-19
观察分析了不同稀土添加量高铬铸铁的铸态微观组织;通过对不同氧化温度和保温时间下不同稀土添加量的高铬铸铁高温氧化过程的对比,探讨了含稀土高铬铸铁抗高温氧化机制。研究结果表明:随着稀土元素的加入,高铬铸铁组织中晶粒得到了明显细化,碳化物形状发生了变化;高铬铸铁单位面积上氧化增重随时间变化遵循抛物线规律;稀土质量分数为0%~...  相似文献   

6.
Two simple cast nickel alloys Ni–30Cr–0.2C and Ni–30Cr–0.8C were oxidized at 1,000, 1,100 and 1,200°C. Their behaviors were characterized using thermogravimetry techniques and their parabolic and chromia volatilization constants were determined by analyzing the versus −m curves. The constants obtained were generally in good agreement with experimental mass-gain kinetics and chromium-balance aspects. A higher carbon content i.e., a higher carbides density leads to higher values of the transient linear-oxidation constant K l , of the parabolic constant K p , and obviously also of the volatilization constant K v . Chromium diffusion coefficients through the zone affected by oxidation were calculated from the oxidation kinetics and chromium gradients. They increase when the carbide density increases.  相似文献   

7.
Al含量变化对CoNiCrAlYRe合金氧化行为的影响   总被引:1,自引:0,他引:1  
利用X射线衍射仪、扫描电镜和能谱分析研究不同铝含量的CoNiCrAlYRe合金在1000℃空气中的恒温氧化行为。结果表明:铝含量的增加促进了合金中富Cr相在γ、β相界面处的析出;铝含量的增加显著抑制了尖晶石氧化物的形成;高铝含量合金中存在的富Cr层有利于致密氧化膜的形成,从而降低了氧化速率,提高了合金的抗氧化性能。  相似文献   

8.
Oxidation of Metals - The high-temperature oxidation kinetics at 800 to 1200 °C of as-cast heat-resistant HP40NbTi alloys produced by either static or centrifugal casting were studied...  相似文献   

9.
The high-temperature oxidation behavior of a new family of refractory high-entropy alloys (HEAs) with compositions of W–Mo–Cr–Ti–Al, Nb–Mo–Cr–Ti–Al and Ta–Mo–Cr–Ti–Al was studied at 1000 and 1100 °C. Based on these equimolar starting compositions, the main incentive of this study was to select the most promising alloy system whose properties may then be successively improved. Despite the high amount of refractory elements, Ta–Mo–Cr–Ti–Al showed good oxidation resistance at 1000 and 1100 °C. Moderate values of mass gain and complex oxidation kinetics were observed for the W- and Nb-containing HEAs. These alloys formed inhomogeneous oxide scales possessing regions with thick and porous layers as well as areas revealing quite thin oxide scales due to the formation of discontinuous Cr- and Al-rich scales. The most promising behavior was shown by the alloy Ta–Mo–Cr–Ti–Al which followed the parabolic rate law for oxide growth due to the formation of a thin and compact Al-rich layer.  相似文献   

10.
Al含量对二元Ti—Al合金高温氧化行为的影响   总被引:7,自引:0,他引:7  
研究了Al含量为33.3at%~52at%Al的5种二元Ti-Al合金在800℃和900℃空气中的恒温氧化行为,用X射线衍射仪和扫描电子显微镜对其氧化产物,氧化物表面形貌和氧化层剖面结构进行了分析,研究发现:在该Al含量范围内,二元Ti-Al合金的氧化层均由具有典型形貌特征的一系列氧化薄层组成,而且在氧化层中均未形成连续致密分布的Al2O3;Al含量对氧化层中Al2O3的形态,分布以及恒温氧化反应  相似文献   

11.
Oxidation of two low-Cr (Cr content 1.5 wt% and 2.25 wt%) and three high-Cr (Cr content 9 wt%, 12 wt% and 18 wt%) boiler steels was investigated at temperatures between 550 °C and 830 °C in laboratory air. Thermogravimetry (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied for evaluation of the oxidation kinetics, oxides phase identification and scale structure analysis. Particular attention was paid to the phenomenon of inward oxidation and its relationship with the Cr content of the steels under investigation. The results showed that the inward oxidation of the Cr steels is governed by grain boundary diffusion. Two different Cr-depending tendencies concerning the effect of alloy grain size on the inward oxidation were observed. For low-Cr steels (less than 2.25 wt% Cr), an increase in the grain size improved the oxidation resistance, while steels with high Cr content (18 wt% Cr) can form a thin and protective chromia scale on the surface more easily at finer grain size. In the latter case an increase in grain size deteriorates the oxidation resistance by the formation of a thicker scale composed of both an outer and an inner Fe-oxide-based layer.  相似文献   

12.
On the High-Temperature Oxidation of Cu-Rich Cu-Ni Alloys   总被引:9,自引:0,他引:9  
Haugsrud  Reidar  Kofstad  Per 《Oxidation of Metals》1998,50(3-4):189-213
Cu-2 wt.%Ni and Cu-5wt.%Ni were oxidized at 800to 1050°C and oxygen pressures from from 5 ×10-4 to 1 atm. The oxidation, as measured bythermogravimetry, was approximately parabolic. The oxidescales could be divided in two main regions: An outerregion consisting of copper oxides and an inner porousregion, which consists of Cu2O with dispersedNiO particles. NiO particles exists as internal-oxide particles. The interface between the two layersreflects the original surface, which shows that theouter part grows by outward Cu diffusion via vacancies.The inner part grows by outward diffusion of copper and inward transport of gaseous oxygen by thedissociative-transport mechanism. The amount ofporosity, the relative thickness of the inner layercompared to the total thickness of the scale, and theoxidation rate as a function of Ni content was dependenton the reaction conditions.  相似文献   

13.
The purpose of the present study was to examine the oxidation of Mg–Al alloys in the atmosphere of oxygen at various temperatures. The basic examination methods used were differential scanning calorimetry (DSC) and thermogravimetry (TG). The results show that the oxide layer can either protect the material against progressive oxidation or it can cause complete disintegration of material. The nature of the oxide layer formed depends on the external conditions, i.e. on the atmosphere, temperature, and type of alloy. A model of the Mg–Al alloy oxidation was calculated from the TG curves.  相似文献   

14.
The aim of the study was to investigate the impact of the Al and Cr content on the oxidation behaviour of the commercial spun cast Ni-base alloy Centralloy® 60 HT R, an Al2O3 former. State-of-the-art Ni-base alloys intended for service temperatures above 1,000 °C rely on secondary carbide or γ′ formation in order to obtain sufficient creep strength and formation of either Cr2O3 or Al2O3 for corrosion protection. Decreased Cr and increased Al contents promote γ′-formation. The oxidation resistance suffers with decreased Cr and the ductility and thermal shock resistance becomes catastrophic with increased Al. 60 HT R has Cr and Al contents that result in a good compromise between oxidation and creep resistance. Samples from a cast of 60 HT R with modified Al content have been exposed in artificial air for up to 500 h at 1,200 °C. The Cr2O3 former G4879 has been co-exposed as a reference. The exposed samples were evaluated using gravimetry, optical microscopy and SEM/EDX. The results showed that too much Al, 10 % (even though the oxidation properties were passable but worse than the for 60 HT R), destabilizes the austenitic matrix, resulting in a non-controllable multiphase structure.  相似文献   

15.
Grit blasting (corundum) of an austenitic AISI 304 stainless steel (18Cr-8Ni) and of a low-alloy SA213 T22 ferritic steel (2.25Cr-1Mo) followed by annealing in argon resulted in enhanced outward diffusion of Cr, Mn, and Fe. Whereas 3 bar of blasting pressure allowed to grow more Cr2O3 and Mn x Cr3?x O4 spinel-rich scales, higher pressures gave rise to Fe2O3-enriched layers and were therefore disregarded. The effect of annealing pre-oxidation treatment on the isothermal oxidation resistance was subsequently evaluated for 48 h for both steels and the results were compared with their polished counterparts. The change of oxidation kinetics of the pre-oxidized 18Cr-8Ni samples at 850 °C was ascribed to the growth of a duplex Cr2O3/Mn x Cr3?x O4 scale that remained adherent to the substrate. Such a positive effect was less marked when considering the oxidation kinetics of the 2.25Cr-1Mo steel but a more compact and thinner Fe x Cr3?x O4 subscale grew at 650 °C compared to that of the polished samples. It appeared that the beneficial effect is very sensitive to the experimental blasting conditions. The input of Raman micro-spectroscopy was shown to be of ground importance in the precise identification of multiple oxide phases grown under the different conditions investigated in this study.  相似文献   

16.
Kim  Sung Hwan  Kim  Chaewon  Cha  Ji-Hwan  Jang  Changheui  Yoo  Young Soo 《Oxidation of Metals》2019,92(5-6):505-523
Oxidation of Metals - Model alloys based on Alloy 617 were fabricated with modified minor alloying elements for improvement in oxidation resistance in high-temperature steam environments. Model...  相似文献   

17.
18.
研究了Ti2Al Nb基合金Ti-22Al-(27-x)Nb-x Zr(x=0,1,6,at%)在650~800℃的氧化行为。采用XRD和SEM等测试技术对此温度区间形成的氧化层特征进行了分析。结果表明,相比Ti-22Al-27Nb,含锆合金具有较好的抗氧化性能。Ti-22Al-(27-x)Nb-x Zr合金在650℃氧化100 h,主要氧化产物为Ti O2,而在800℃氧化100 h,Ti O2,Al2O3和Al Nb O4为主要产物,但是在Ti-22Al-21Nb-6Zr合金中还有Zr O2生成。Ti-22Al-26Nb-1Zr合金具有优异抗氧化性能,归因于氧化产物细化形成了致密的氧化层,而Ti-22Al-21Nb-6Zr合金,虽然在800℃也形成了较多Al2O3,但是氧化层中的Zr O2为氧的快速扩散提供通道,进而导致该合金氧化增重明显。  相似文献   

19.
在45钢基体上用激光熔覆方法制备FeCoCr_xNiB(x=0.5~3)高熵合金涂层。不同Cr含量(原子数分数)的FeCoCr_xNiB高熵合金涂层在900℃下进行高温氧化实验,测定其氧化动力曲线,并采用XRD、SEM和EDS等方法分析氧化层结构和形貌。结果表明,不同Cr含量的FeCoCr_xNiB涂层氧化动力学曲线基本都符合抛物线规律。随着Cr含量的增加,FeCoCr_xNiB涂层的氧化膜由富Fe的氧化物逐渐向富Cr氧化物转变,并最终生成稳定、连续的Cr2O3氧化膜。富Fe的氧化物表面形貌为针状且较为疏松,而富Cr的氧化物则为较为致密颗粒状。涂层的抗氧化性能随Cr含量的增加而增强。当Cr含量超过x=2后,FeCoCr_xNiB涂层获得了较好的抗氧化性能。  相似文献   

20.
镍基高温合金在恶劣环境下具有优异的力学性能和耐高温性能。镍基高温合金的氧化行为高度依赖于材料的固有性能和氧化膜性能,而氧化膜性能主要取决于合金元素的种类和含量。大气成分、温度、应力、熔融盐等各种环境参数是直接影响材料氧化行为的基本因素。综述了合金元素和服役环境对镍基高温合金氧化行为的影响。铝、铬和钴是有利元素,可以形成致密、结合力强的氧化膜,以保护基体。钛、钼、铌、钨、钽的添加一般被认为会削弱抗氧化性能,但最近的研究有不同的观点。讨论了镍基高温合金的氧化机理,并对镍基高温合金的未来发展进行了展望。  相似文献   

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