The Corrosion Performance of Nickel-Based Alloys containing group II-V elements in a gas turbine material test rig

The corrosion of eight Ni-based ternary alloys (15 w/o Cr plus 1 w/o X, where X = Mg, La, Ce, Gd, Th, U, Zr or V), and a binary control alloy (15 w/o Cr) has been assessed in a rig designed to simulate combustion conditions in gas turbines operating on a contaminated Diesel fuel. Performance has been evaluated in terms of metal loss (radius measurements), scale thicknesses and depths of internal corrosion after 10 and 200 h exposure: the morphology and composition of corrosion products have also been examined. Although the pattern of oxide scale formation was broadly similar from alloy to alloy, considerable differences in the type and depth of the internal corrosion taking place were apparent. The possibility of the use of some of these addition elements in future turbine materials, particularly coatings, is considered in the light of these observations.     

A comparison of the effects of small additions of various second elements on the oxidation of nickel at 1200°C

The oxidation behaviour of Ni-4.2% Mo, Ni-4.0% W, Ni-2.5% Al, Ni-4.2% V and Ni-5.0% Cr (all wt. %) at 1200 °C in flowing oxygen at 1 atm. pressure has been studied using various techniques. In particular, the solubility of the second element in NiO, its distribution across the NiO scale and the effects of these on the oxidation rates and scale morphologies have been examined. The oxidation rates of all the alloys are greater than that of nickel, although for Ni-4.2% Mo, where incorporation of internal oxide into the scale does not occur and molybdenum does not dope the oxide, the small increase in weight gain during oxidation Compared with that for nickel is due to internal oxide formation only. As the internal oxide particles pileup at the alloy/oxide interface, they exert a blocking effect to outward diffusion of Ni²⁺ ions, especially in the later stages of oxidation. Ni-4.0% W behaves similarly, although a few internal oxide particles are incorporated into the scale and a small amount of doping of the oxide ensures that it thickens at a slightly faster rate than the scale on nickel and for Ni-4.2% Mo. The oxidation rates of the other alloys are significantly faster than that of nickel and increase in the order Ni-2.5% Al, Ni-4.2% V, Ni-5.0% Cr. These increased rates are largely caused by increases in the total cation vacancy concentrations in the scales, although internal oxide formation can make a significant contribution to the oxidation kinetics. The influence on the oxidation behaviour of a number of factors, namely doping of the scale, internal oxidation, dissociation of NiO and transport of gaseous oxygen within the scale, blocking effects in the oxide and at the alloy/oxide interface, and grain growth of the oxide, are considered in detail.     

Corrosion of Ni-Ti alloys in the molten (Li,K)2CO3 eutectic mixture

The corrosion of pure Ni and of binary Ni-Ti alloys containing 5, 10, and 15 wt.% Ti respectively in molten (0.62Li,0.38K)₂CO₃ at 650°C under air has been studied. The corrosion of the single-phase Ni-5Ti alloy was slower than that of pure Ni, forming an external scale composed of NiO and TiO₂. The two-phase Ni-10Ti and Ni-15Ti alloys underwent much faster corrosion than pure Ni, producing an external scale containing NiO and TiO₂, and a thick internal oxidation zone of titanium mainly involving the intermetallic compound TiNi₃ in the original alloys. The rates of growth of the external scales for the Ni-Ti alloys were reduced with the increase of their titanium content, while the internal oxidation was significantly enhanced. The corrosion mechanism of the alloys is also discussed.     

Electrochemical corrosion behavior of Cu-40Ni-20Cr alloys with different grain sizes in solutions containing chloride ions

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.     

Some interactions in the erosion-oxidation of alloys

The modes of interaction of erosion and high-temperature oxidation, occurring simultaneously on an alloy surface, have been studied using Ni-30Cr, MA754, Ni-20Al, and Co-22Cr-11Al-0.2Y alloys to examine the influence of chromia and alumina scale formation on the erosion of nickel and cobalt base alloys. The results have shown that, in the presence of a rapidly flowing oxidizing gas stream, the evaporation of volatile metal oxides becomes important at lower temperatures where normally it can be ignored. Otherwise, the erosion and oxidation of alloys parallels the behavior of pure metals but also introduces additional factors derived from lengthening of the period of transient oxidation and modification of concentration profiles in the alloy adjacent to the alloy/scale interface. Higher erosion intensities extend the transient oxidation behavior which adversely affects the formation of protective scales. As with pure metals, the presence of erosion and oxidation together always produced increased rates of degradation.     

The effect of aluminum as an alloying addition or as an implant on the high-temperature oxidation of Ni-25Cr

The oxidation behavior of aluminum-implanted Ni-25Cr and Ni-25Cr containing 1 wt.% Al has been studied at 1000°C and 1100°C in oxygen. As did Y alloying addition or Y-implantation, 1 wt.% Al added to Ni-25Cr prevented nodular formation of Ni-containing oxides, improved spalling resistance of the scale upon cooling to a similar degree, and eliminated the formation of large voids between the alloy and the scale at the oxidation temperature. However, the Al addition did not alter the rate of growth of the Cr₂O₃ scale, nor did it change the growth direction. Al-implantation produced no effect even when the maximum concentration and depth of penetration were adjusted to be identical with those of the yttrium in the Y-implanted alloy. The implications of these results concerning the reactive element effect are discussed.     

Grain size effects on the oxidation of two ternary Cu-Ni-20wt.% Cr alloys at 700-800 °C in 1 atm O2

Two nanocrystalline two-phase Cu-Ni-Cr alloys, both prepared by mechanical alloying and containing about 20 at.% Cr but with different Ni contents (40 and 20 wt.%, respectively), have been oxidized in 1 atm O₂ at 700-800 °C. Their oxidation behavior has been compared with that of two cast alloys of the same composition, already studied previously, to examine the effects of a large reduction of the size of the individual phase grains and particles. The nanophase alloy with 40 wt.% Ni formed a flat external layer of chromia of regular thickness, while the corresponding cast alloy produced a very irregular chromia layer, often protruding deeply into the alloy, only after an initial stage of rather fast corrosion involving also copper and nickel, associated with some degree of internal oxidation. By oxidation at 700 °C the nanophase alloy with 20 wt.% Ni formed an irregular chromia layer associated with low corrosion rates. The corresponding cast alloy formed complex scales containing Cu, Ni and Cr oxides, extending into the alloy in the form of large pegs, even though a very irregular and discontinuous innermost chromia layer was still able to produce low corrosion rates. On the contrary, at 800 °C both alloys formed complex scales containing mixtures of the oxides of the three metal components. However, the scales grown on the cast alloy were much more irregular in thickness and formed large protrusions into the alloy. In spite of this, the corrosion kinetics of the nanophase 20 wt.% Ni alloy at 800 °C were more irregular and, except for an initial stage, less protective than that of the cast alloy with the same composition.     

The effect of gas composition and contaminants on the lifetime of surface‐treated FeCrAlRE alloys

The degradation of a variety of alumina‐forming Fe20Cr5Al based alloys has been investigated at temperatures ranging from 1100°C to 1300°C for up to 4000 h (100 h/cycle) in different oxidising environments such as laboratory air, air + 10 vol% H₂O, air + 60 vol% H₂O and simulated automotive exhaust gas. Seven model alloys with controlled levels of impurities such as P, S and C and carefully controlled levels of additional elements (Y, Zr, Ti, Hf, Si, La, etc.) and two different commercial alloys (Aluchrom YHfAl and Kanthal APMT) were chosen for this study. The investigation showed that the model alloys containing La, Y + Si and Y with added C, and the commercial alloy APMT usually had the lowest initial oxidation growth rates, whereas model alloys containing Y plus Zr, and the commercial alloy YHfAl had the higher oxidation rates regardless of the different oxidising environments. Scale spallation was more prevalent in the case of alloys with low oxide growth rates but changing the levels of water vapour in the oxidising atmospheres had only a minor influence on the degree of spallation or the oxide morphology. The scales formed on the alloys containing La, Y + Si and high C spalled in an adhesive manner (at the scale/metal interface), whereas scales formed on alloys containing Y plus Hf, Zr or Ti cracked and spalled in a cohesive manner (within the scale). Inhomogeneities in the distribution of the alloying additions led to greater changes in the oxide morphologies than any difference in oxidising atmosphere, but the crystallographic textures of all the oxides were similar. This pilot study enabled us to rank the alloys according to their resistance to spallation and also to determine the influence of minor elements when added as tightly controlled single or multiple element additions. Some of these alloys were then used as mechanically weak PVD coatings on a strong (APMT) substrate, and further oxidation experiments confirmed that the coatings then oxidised in a similar way to the bulk alloys.     

Relation between impurities and oxide-scale growth mechanisms on Ni-34Cr and Ni-20Cr alloys. I. Influence of C,Mn, and Si

The oxidation behavior of Ni-Cr alloys (34 and 20 wt.% Cr) was investigated between 850 and 1200°C in oxygen for a maximum duration of about 70 hr. The oxide-growth mechanism is a diffusion process controlled by either outward diffusion of chromium in Cr₂O₃ (Ni-34Cr alloy) or by an increase in grain size (Ni-20Cr alloy). In the case of the Ni-34Cr alloy, low values of chromium diffusion were found for the growth of Cr₂O₃ by taking into account the general equation of Wagner. The influence of impurities (Si, C, Mn, Ni) diffusing from the underlying alloy is analyzed because of their doping effect in the outer oxide scales.     

The oxidation of Ni-20 wt. % Cr-2ThO2

The oxidation of TD NiCr (Ni-20 wt. % Cr-2ThO₂) has been investigated between 900 and 1200°C, and the oxidation behavior is compared with Ni-30 wt. % Cr and Co-35 wt. % Cr alloys. All alloys develop Cr₂O₃ scales but the weight changes obtained for the NiCr and CoCr alloys show an increase with time whereas above 1000° C the TD NiC shows a progressive loss in weight from the evaporation of CrO₃ from the scale, and the reaction products appear to be formed mainly at the alloy-scale interface. However, no mechanism for its formation has been established.     

The Effects of Reactive-Element,Ion-Implantation-Induced Amorphous Layers on the Oxidation of Co-12Cr and Ni-12Cr Alloys

Nickel-chromium (Ni-12Cr, wt.%) andcobalt-chromium (Co-12Cr, wt.%) alloys were ionimplanted with 150 keV yttrium to fluences that rangedbetween 2 × 10¹⁶ and 1 ×10¹⁷ ions/cm². The influence ofthe implantation on the microstructure of the alloy wasdetermined. The effect of the highest dose implantationon the alloys' oxidation response at 1000°C, 48 hrwas measured. Both alloys contained an amorphous surface phase as a result of this fluence and one ofthe effects of oxidation was to recrystallize theamorphized alloy in the first few minutes of oxidation.The lower doses of 2 × 10¹⁶ions/cm² were sufficient to cause amorphization of both the Ni-12Cr andthe Co-12Cr. The implantation reduced the isothermalmass gain by a factor of 25% for the Ni-12Cr, but had anegligible effect on the Co-12Cr alloy. Short-term oxidation experiments at 600°C showed viatransmission electron microscopy that, in the absence ofthe yttrium implant, the Ni-12Cr alloy forms NiO in thefirst minute of oxidation and the Co-12Cr alloy forms CoO and CoCr₂O₄.The implanted Ni-12Cr, on the other hand (1 ×10¹⁷Y⁺/cm²), formsrecrystallized Ni-Cr, Y₂O₃, andNiO in the near-surface region, while the implantedCo-12Cr alloy forms CoO, CoCr₂O₄, and a recrystallized intermetallic alloy fromthe amorphized region.     

The corrosion behavior of Ni-Nb alloys in a mixed gas of H2-H2O-H2S

The corrosion behavior of Ni-Nb alloys containing up to 40 wt.% Nb was studied over the temperature range of 550–800°C in a mixed H₂/H₂O/H₂S gas. The scales formed on all alloys were multilayered. The outer scale was single-phase Ni₃S₂, while the structure and constitution of the inner scale depended on alloy composition and reaction conditions. Internal oxidation has been found in Ni-20Nb and Ni-30Nb, external oxidation has been observed on Ni-34Nb. Platinum markers were located at the interface between the outer scale and inner scale. The decrease in corrosion rate with increasing Nb content may be attributed to the presence of increasing amounts of Ni-Nb double sulfides as well as to the presence of Nb₂O₅ in the inner region of the scale.     

稀土元素Ce和La合金化对AM60镁合金腐蚀行为的影响

采用电子探针-能谱分析,场发射扫描电镜X射线衍射等方法研究了稀土元素Ce和La合金化对AM60镁合金结构和耐蚀性能的影响.结果表明,Ce和La的加入可在AM60镁合金中形成了富含稀土元素的γ相（MgAlRE）;能有效抑制析氢,提高镁合金的耐蚀性能;改善镁合金在含Cl-溶液中的耐蚀性能;腐蚀产物膜的晶态主要成分为铝和锰的氧化物,并含有少量的稀土氧化物和氢氧化物.     

Effect of internal oxidation pretreatments and Si contamination on oxide-scale growth and spalling

Internal oxidation pretreatments carried out in quartz capsule with a Rhines pack were found to have a profound effect on the subsequent oxidation behavior of alloys. Specimens of Co-15 wt.% Cr, Co-25 wt.% Cr, Ni-25 wt.% Cr, and Ni-25 wt.% Cr-1 wt.% Al were tested at 1100°C after pre-oxidation treatments. Even without the development of internal oxide particles, pretreated binary CoCr and NiCr alloys oxidized with significantly lower rates. Selective oxidation of chromium was observed on the non-Cr₂O₃-forming Co-base alloys, whereas on the Cr₂O₃-forming Ni-base alloys, elimination of base-metal oxide, reduction in the Cr₂O₃ growth rate, and better scale adhesion were found. These effects were more apparent with pre-oxidation temperatures greater than 1000°C and with longer pretreatment times. Contaimination of Si from the quartz is believed to be the cause.     

Corrosion behaviour of experimental alloys in simulated HTGR helium at temperatures in the 750–1050°C

A series of experimental alloys (basically Ni-20 Cr, with addition of one of more of the elements Al, Ti, Si, Nb and Y) has been examined after exposure to controlled purity helium for periods of 1000–6000 hours at 750–1050 °C. This environment was intended to simulate the primary coolant of a high temperature gas-cooled reactor. Alloys containing aluminum were found to be particularly susceptible to internal oxidation at the lower temperatures, but at 950 °C and above carburization became the dominant corrosion mechanism. The most corrosion resistant alloys were Ni-20Cr and Ni-20 Cr containing small amounts of silicon, titanium and niobium. The presence of 1% yttrium dramatically increased the incidence of carburization, even at temperatures as low at 850°C.     

新型银稀土合金的制备工艺及性能研究

采用石膏模精密浇注工艺技术,成功制备了银稀土合金铸锭,并确定了合理的浇注工艺技术参数,分析了稀土元素的作用机理。结果表明,在银中添加多元稀土元素(La、Ce、Sm、Y),改善了银合金的物理、力学、焊接性能、抗氧化和耐腐蚀性能。研发的新型银多元稀土合金具有良好的抗氧化、耐腐蚀性能及可铸性能,在银饰品材料领域具有明显的应用市场前景。     

Effect of presulfidation on the oxidation behavior of Co-based alloys. Part I. Presulfidation at sulfur partial pressures above the dissociation pressure of cobalt sulfide

The effects of presulfidation in H₂-H₂S atmospheres of sulfur activity sufficient to form cobalt and chromium sulfides on the oxidation rates of Co-Cr binary alloys containing 0–25 wt.% Cr and Co-25 wt.% Cr alloys containing 0–2 wt.% C have been investigated. Presulfidation increases the oxidation rate, but the effect is not very dramatic. Carbon additions to the Co-25 wt.% Cr alloy progressively increase the oxidation rate, but not to as great an extent as a simple model based on the reduction of the chromium activity in the alloy. Sulfur released from the preformed sulfides by oxidation diffuses into the alloy precipitating fresh sulfides, there appears to be no outward diffusion of sulfur through the oxide scale. These internal sulfides have a liquid-like morphology in cobalt-base alloys when the oxidation is carried out at 1000°C, as compared to 800°C in corresponding nickel-base alloys. When the sulfide layer produced during the presulfidation is thin, so that oxidation destroys the continuous sulfide layer, the subsequent scale morphologies after oxidation exhibit many features similar to samples subjected to hot corrosion in environments containing sodium sulfate.     

Relationship between phase composition and corrosion resistanceof Ni-Ti-Nb based shape memory alloys

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INTERNAL OXIDATION BEHAVIOR OF Pd-40Ag-1M(M=Zr,Y)ALLOYS

The internal oxidation behavior of Pd-40Ag-1M(M=Zr,Y)alloy wires has been studied inair at 800—1200℃.The relationship between the internal oxidation depth ξ and the reactiontime t can be expressed as ξ= Kt~n,where n=0.5—0.75.The higher the temperature,thelarger the value of n is.The active elements Zr and Y show different internal oxidationcharacters.For the alloys eontaining Zr,the oxidation rate along the grain boundaries isabout twice as high as that in grains,and“lateral oxidation”exists along the grainboundaries.For the alloys containing Y,the oxidation rates in grains and along the grainboundaries are roughly the same,and there is no“lateral oxidation”along the grain bounda-ries.The activation energies of both alloys are in the range of 120—150kJ/mol.Some prop-erties for oxidized alloys were studied.The mechanisms of the internal oxidation were dis-cussed.     

A TEM study of the oxide scale development in Ni-Cr-Al alloys

In the present study the isothermal oxidation behaviours of Ni-10Cr-5Al, Ni-20Cr-5Al and Ni-30Cr-5Al alloys were investigated. The alloys were oxidised in air for 50 h at 1000 °C. Analytical transmission electron microscopy was used to characterize the morphology, structure and composition of the oxide scale. The oxide formed adjacent to the alloy was α-Al₂O₃ such that the higher was the Cr content of the alloy the easier was its formation. The Ni-30Cr-5Al alloy formed a complete layer of α-Al₂O₃ in the initial stages of oxidation through ‘oxygen gettering’ by Cr. A decrease in scale thickness and an increase in scale adherence were observed with an increase in Cr content from 10 to 30 wt.%.