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1.
The effect of temperature on oxidation behavior of ternary Fe-15Cu-5Al (mole fraction, %) alloy in pure oxygen was studied. Fe-15Cu-5Al alloy presents an irregular high-temperature oxidation behavior between 700-1 000 ℃, though the kinetic curve at each temperature can be approximately considered as being composed of two quasi-parabolic stages. At 700 ℃ the alloy forms bulky stratified scales. On the contrary, at 800℃ the alloy forms an external protective Al2O3 layer. The trend of decrease of oxidation rate does not continue at elevated temperatures. Due to the high stress-growth effect at 900℃, the thin Al2O3 layer cannot completely prevent further oxidation of the alloy underneath. When the temperature rises to 1 000℃, the high stress-growth effect is more obvious and the alloy forms overgrown large nodules. Compared with the Fe-10Al binary alloy, the presence of 15 % Cu tends to greatly increase the flaw of the formed Al2O3 layer at elevated temperatures, resulting in a peculiar oxidation pattern of Fe- 15Cu-5Al alloy.  相似文献   

2.
The effect of 5%Cr(mole fraction) on the scaling behavior of Ni-10Al was investigated at 900 ℃ and 1 000 ℃ with the aim to discuss the third element effect(TEE). The oxidation rate of the ternary alloy containing Cr is much slower than the corresponding binary alloys at both temperatures. A dense external scale of NiO overlying a zone of internal oxide precipitates forms on Ni-10Al, while Ni-5Cr-10Al develops a protective layer. So the addition of Cr promotes the formation of alumina scale. The possible mechanism of Cr on the oxidation of Ni-Al alloy is discussed.  相似文献   

3.
The oxidation of two two-phase ternary Fe-Cu-Al alloys containing about 5%(mole fraction) aluminium, one Fe-rich and one Cu-rich, has been studied at 900 ℃ in 1~105 Pa pure oxygen. The Fe-rich Fe-15Cu-5Al alloy presents two quasi-parabolic stages, with a large decrease of the parabolic rate constant after about 50min. The presence of 5% Al greatly reduces the oxidation rate of this alloy with respect to a binary Fe-Cu alloy of similar composition by forming an external protective Al203 layer, which is present near the scale/alloy interface. Due to the high stress-growth effect, this thin Al203 layer cannot completely prevent further oxidation of the alloy underneath. On the contrary, the Cu-rich Fe-85Cu-5Al alloy presents a single parabolic stage and forms a thick and porous external scale, coupled to the internal oxidation of Fe and Al. As a result, the oxidation of Cu-rich alloy at 900 ℃ is much faster than that of the Fe-rich alloy.  相似文献   

4.
Formation mechanism of amorphous Ni-Fe-P alloys by electrodeposition   总被引:2,自引:0,他引:2  
The formation mechanism of the amorphous Ni-Fe-P coating was studied by analysis of the forming thermodynamics, dynamics, and crystallography of the amorphous alloy. The results show that, in the initial stage of deposition a thin “crystal epitaxial growth” layer first forms, and then transforms to amorphous gradually. The cross section in Ni-Fe-P coatings by electrolytic etching exhibits a banded structure of alternate dark and light bands. It is proposed that the banded structure is caused by a change in the P content with thickness,which is due to alternated depletion and enrichment of [OH^-] in the diffusion layer resulting from the generation and evolution of hydrogen gas. The amorphous Ni-Fe-P coating will be formed in proper composition, high nucleation rate and strongly hindered growth of the crystal nucleus. Amorphous Ni-Fe-P alloys form as islands, and grow up by layer.  相似文献   

5.
The electrochemical corrosion behavior of the two Cu-40Ni-20Cr alloys prepared by conventional casting(CA) and mechanical alloying(MA) with the different grain sizes was studied by using open-circuit potential(OCP), potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) methods in solutions containing chloride ions. The results show that the free corrosion potentials of the two alloys move towards negative values, corrosion currents increase and therefore corrosion rates become faster with the increase of chloride ion concentrations. EIS plots of CACu-40Ni-20Cr alloy are composed of single capacitive loop, while EIS plots of MACu-40Ni-20Cr alloy are composed of double capacitive loops in solution containing lower chloride ion concentrations. EIS plots of the two alloys have Warburg impedance with the increase of chloride ion concentrations. Corrosion rates of MACu-40Ni-20Cr alloy become faster than those of CACu-40Ni-20Cr alloy obviously in solutions containing the same chloride ion concentrations because MACu-40Ni-20Cr alloy is able to produce large concentrations of grain boundaries in the course of reduction in grain size by mechanical alloying.  相似文献   

6.
The oxidation of the Ni-10Cr-xAl(x=7%, 10%, molar fraction) alloys was studied at 1 100℃ under 0.1 MPa 02 and compared with that of the binary Ni-7Al and Ni-10Al alloys. The results show that the binary alloys form NiO external scales associated with an internal oxidation of Al. On the contrary, the ternary Ni-10Cr-7Al and Ni-10Cr-10Al form external alumina scale in contact with the alloy substrate. An addition of 10%Cr(molar fraction) into Ni-7Al and Ni-10A1 inhibits the internal oxidation of aluminum and considerably reduces the critical content of A1 needed to form exclusive alumina scales with respect to binary Ni-Al alloy, providing an example of third-element effect.  相似文献   

7.
The oxides formed on the surface of the alloy 690 in hydrogenated supercritical water at 400℃ for 1000 h were investigated using scanning electron microscopy,transmission electron microscopy,scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy.The oxides on me surface of the alloy 690 exhibited multi-layer structure:an outer layer consisted of granular crystallites(NiO and NiFe_2O_4) and a compact inner layer(spinel and Cr_2O_3).Chemical analysis indicated that the outer layer was enriched in nickel but depleted in chromium,whereas the inner layer was enriched in chromium and iron but depleted in nickel.The inner layer was also characterized as layered structure by Fe-rich spinel on top of continuous Cr_2O_3 layer.Besides,Cr_2O_3 nodules were readily observed at the oxides/alloy interface.  相似文献   

8.
To promote the solution of chromium in copper and the purity of copper-chromium (Cu-Cr) alloy, vacuum continuous casting (VCC) process was employed to fabricate the Cu-Cr alloy required for electrode material. Cu-0.6Cr (containing 0.6%(mass fraction) chromium) alloy bar with a diameter of 12 mm was cast with a constant rate of 250 mm/min. The microstructure, mechanical properties, and physical properties were discussed. After solid solution strengthening and aging treatments, Cu-0.6Cr alloy fabricated by VCC process has higher tensile strength (σ≥314 MPa), elongation rate (δ≥34%), conductivity (≥80.5% IACS), and hardness (80 HRB) compared to the as-cast alloy.  相似文献   

9.
To downsize and lighten automatic transmission components, the gears installed must be strengthened in terms of pitting endurance and/or wear resistance. The most important metallurgical factor affecting fractures is well known to be resistance to softening when steel is tempered at approximately 573 K. Carbonitriding with a high amount of nitrogen is a very effective production technique because nitrogen increases the resistance during tempering. However, structural anomalies begin to appear in the surface layer when the nitrogen content exceeds 0.6 mass% in the chromium steel generally used. To address this, we have developed new high-strength chromium steel with an optimized chemical composition that effectively inhibits anomalies even when carbonitriding with a nitrogen content of more than 0.6 mass%.We performed a drivetrain durability test on an automatic transmission component designed to have excellent contact fatigue strength and a tooth root bending impact and fatigue strength. We found that the developed steel that was carbonitrided with a content of about 0.9 mass%, and then shot peened hard, has a pitting life of roughly 4.5 times that of conventionally manufactured steel.  相似文献   

10.
This paper reports TiC–(Ni–Cr) metal ceramic alloy(ratio of components 50:50) with nanoscaled components formed in the surface layer and smoothly transformed into the initial inner structure throughout the material under pulsed electron irradiation of the alloy surface. Principal changes in the surface layer are ascribed to the formation of gradient structure leading to the increase in wear resistance of the surface layer, drop of friction coefficient and improvement of specimen bending resistance when stressing on the irradiated surface side. The above changes of tribological and strength properties in the surface layer under pulsed electron irradiation become more apparent with increasing atomic mass of a plasma-forming inert gas.  相似文献   

11.
ZH1 technique was used to form a corrosion resistant layer on LC4 alloy. The composition of the layer was studied by X-ray photoelectron spectroscopy (XPS). It is found that the layer is composed of oxides of metals on the substrate, such as A12O3, ZnO, MgO2, CuO, and MnO2. The electrochemical impedance spectrums (EIS) of LC4 aluminum alloy specimen were measured in NaCl solutions to study the mechanism of the corrosion resistance of the alloy treated with ZHI technique. The results show that in NaCl solutions the capacitance of the Helmholtz layer and space charge layer of the oxide coating formed on the surface of LC4 alloy is less than that of a normal metal electrode while its ohmic resistance is relatively greater. At the same time, the thickness of the Helmholtz layer is 1-3 exponentially greater than that of a normal metal electrode. Compared with a normal metal electrode, all these characteristics make it more difficult for charges to transfer between the solution and the surface of the electrode. That is why the polarized current density of LC4 alloy treated with ZHI technique kept small in 3.5% NaCl solution within a wide range of potential, and why the polarized curves of LC4 alloy treated with ZH1 technique changed a little in 3.5% NaCl solution of different pH values.Moreover, according to the capacitance of the space charge layer (Csc) obtained at different potentials in 3.5% NaCI solution, I/Csc^2-E curve was laid out. It is found that there does not exist a simple linear relation between I/Csc^2 and the potential. Therefore, the oxide coating formed on LC4 alloy with ZH1 technique is not a semiconductor at room temperature.  相似文献   

12.
The surface layer of Ni_(68)P_(18)Cr_(14) amorphous alloy was studied by AES and XPS associated with ion beam sputtering. It was found that great differences existed between the surface layer and the bulk both in composition and chemical states. The dominant component elements Ni and P were of lower content in the surface laver, while Cr was enriched. Cr was drastically oxidized in the surface layer, but Ni underwent no oxidation. There was a P enriched region just helow the surface oxide layer, which was supposed to enhance the surface segregation of Cr. Ni underwent no oxidation in Ni_(68)P_(18)Cr_(14) amorphous alloy.  相似文献   

13.
The influence of cerium addition on the isothermal oxidation behavior of 00Cr17 NbTi ferritic stainless steel was studied at temperature up to 1,000 °C for 100 h in air. The results show that cerium additions can reduce the grain size of this ferritic stainless steel, improve the diffusion of chromium and decrease the critical concentration of chromium to form protective Cr2O3 layer. With the increasing of cerium addition, the oxide particles become smaller and this can increase the rupture strength and spalling resistance of oxide layers. The transport mechanism through the oxide layer is varied from metal transport outward from steel to principally oxygen transport inward with the increase of cerium content,which leads to the lower oxidation rate and the better scale adherence of 00Cr17 NbTi ferritic stainless steel.  相似文献   

14.
The corrosion behavior of nickel-based 718 alloy at seven partial pressures of H_2 S(P_(H_2 S))was investigated using electrochemical impedance spectroscopy(EIS)and polarization methods in 25 wt% NaCl solution at150℃ for 168 h.The tested results show that anodic reactions are controlled alternately by the diffusion mostly,then both charge transfer and diffusion and finally charge transfer mainly with the increment of P_(H_2 S).The corrosive products are composed of sulfides and oxides of Ni,Cr and Fe with double layers for P_(H_2 S) of 5.1 and 13.0 MPa and three layers for P_(H_2 S) of 10.4 MPa according to microstructures and compositions of corrosion products characterized by the scanning electron microscope(SEM)and electron probe microanalysis(EPMA)methods.The inner oxides layer plays a critical role in anti-corrosion in a wet H_2 S environment at high temperature and pressure.  相似文献   

15.
Effect of small content of chromium(Cr) on wet–dry acid corrosion behavior of low alloy steels has been investigated.The results show that the corrosion resistance of the steels increased with increasing Cr content from 0.10 to0.50 wt%.Higher content of Cr promotes initial corrosion and accelerates the formation of dense and protective rust in long-term corrosion.The enhanced protectiveness of the rust is closely related to its composition.High content of Cr increases the content of amorphous phases and decreases the content of c-Fe OOH in the rust,resulting in the high compactness of the rust and low electrochemical activity in acid condition.Cr dopes in rust and depresses the transformation from amorphous phases to a-Fe OOH,as well as the growth process of Fe OOH particles,which is responsible for the enhanced compactness of rust in long-term corrosion.  相似文献   

16.
The corrosion behaviors and mechanism of Ni-14%Cr alloys in molten salt with Na2SO4 at 1000℃ was investigated by means of XRD analysis and SEM observation. Results show that the alloys were subjected to the accelerated corrosion in molten salt and the corrosion kinetic of the alloy obeys the parabolic law. On the other hand, the corrosion-resistance of the alloy could be improved significantly by increasing of chromium content. Corrosion products may be divided into three layers, i. e. NiCr2O4, CoCr2O4, CoN...  相似文献   

17.
Tungsten heavy alloys(WHAs) produced by powder technology are widely used for the mechanical manufacturing, electronic and defense components, etc.Tribological properties of these alloys need to be improved to meet the severe service conditions demanded. Carburization is a promising way to resolve this problem. In this work, microstructure and tribological properties of the carburized 95W–3.5Ni–1.0Fe–0.5Co heavy alloy were investigated in comparison with those of the untreated alloy. Results show that the carburized layer consists of a porous, outer WC layer and a modified W grain layer surrounded by Fe_6W_6C and Co_6W_6C at 970℃, regardless of the carburizing time. The depth of the carburized layer linearly increases in a relatively short time and slightly increases during the subsequent period. Surface roughness increases with carburizing time. Carburization can stabilize friction coefficient and effectively improve the wear resistance of the tungsten heavy alloy due to its significantly increased hardness and non-deformability, but the porous structure in the WC layer has a negative influence on its wear resistance. The carburized layer is damaged in the porous WC layer in the form of the spalling of WC particles where there are some microcracks and micropores, accompanied with peeling due to the solid tribofilm being pushed away.  相似文献   

18.
An additive of Y to Ni_3Al based alloy may form a phase YNi_5 which increases in amount withthe increase of Y content.It was found that the YNi_5 phase in Ni_3Al alloy could remarkablymake its grains finer and its grain boundaries more crooked other than straight.If the Y con-tent≥0.1 wt-%,it occurs as solid solution state and is favorable to high temperaturecompressive properties and oxidation resistance of the alloy.While Y≥0.3 wt-%,the forma-tion of YNi_5 is predominant in the shape of irregular strips inside Ni_3Al grains and alongtheir grain boundaries.This seems to be quite harmful to high temperature strength,ductilityand oxidation resistance of the alloy.  相似文献   

19.
The composite metastable (Ti0.5Al0.5)N, (Ti0.45Al0.45Cr0.1)N and (Ti0.35Al0.35Cr0.3)N coatings were respectively deposited on a wrought martensite steel 1Crl 1 Ni2W2MoV for aero-engine compressor blades by arc ion plating technique with pulse substrate bias. All the coatings have B1NaCl phase with a (200) preferred orientation and dense structures. The results show that the introduction of Cr into (Ti,Al)N gives rise to a minute shrinkage of crystal lattice. The incorporation of chromium into the coatings dramastically improves the oxidation-resistance of the coatings. For (Ti0.5Al0.5)N, a layered oxide scale forms after 100 h oxidation and the outer layer is the blend oxide of TiO2 and Al2O3, and the middle layer is rich in AI and the inner layer is rich in Ti. For (Ti0.45Al0.45Cr0.1)N, the oxide scale possesses a double-layered structure and the outer layer is rich in Ti. For (Ti0.35Al0.35Cr0.3)N, a Cr-rich compound oxide scale of Ti, AI and Cr forms, and a out-diffusion of Fe from steel to the nitride coating and oxide film during the oxidation takes place.  相似文献   

20.
Interaction behaviors between Al-Si, Zn-Al alloys and Al2O3p/6061Al composite at different heating temperatures were investigated. It is found that Al2O3p/6061Al composite can be wetted well by AlSi-1, AlSi-4 and Zn-Al alloys and an interaction layer forms between the alloy and composite during interaction. Little Al-Si alloys remain on the surface when they fully wet the composite and Si element in Al-Si alloy diffuses into composite entirely and assembles in the composite near the interface of Al-Si alloy/composite to form a Si-rich zone. The mierostrueture in interaction layer with Si penetration is still dense. Much more residual Zn-Al alloy exists on the surface of composite when it wets the composite, and porosities appear at the interface of Zn-Al alloy/composite. The penetration of elements Zn, Cu of Zn-Al alloy into composite leads to the generation of shrinkage cavities in the interaction layer and makes the microstructure of Al2O3p/6061Al composite loose.  相似文献   

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