混合稀土对Cu-Al合金薄板内氧化组织和性能的影响

采用内氧化工艺,以工业N2中余氧为氧源,在950℃使Cu-Al-RE合金薄板内氧化成功制备了Al2O3/Cu复合材料,并对其显微硬度、电导率进行测试,用透射电子显微镜(TEM)对内氧化生成相和微观亚结构进行了分析.结果表明,与未添加混合稀土相比,Cu-Al-0.05(Ce+Y)合金950℃×2h内氧化层深度增加了22.8%,表现出明显的稀土催渗作用;TEM分析表明,在铜基体上弥散分布着大量细小均匀的γ-Al2O3颗粒;适晕添加混合稀土改善了合金的导电性,提高了合金的显微硬度,添加0.05%(Ce+Y)的Cu-Al-RE内氧化后综合性能最优.     

添加Ni对Cu-25Co合金在600,700℃纯氧气中氧化行为的影响(英文)

研究了三元双相Cu-20Ni-25Co合金在600,700℃、0.1 MPa纯氧气中的氧化行为.结果表明:合金的氧化动力学不规则且偏离抛物线规律,氧化动力学曲线由3段抛物线段组成.前期研究的二元双相Cu-25Co合金经过了较长时间的氧化后合金表面未能形成活泼组元Co的选择性外氧化,而本研究的Cu-20Ni-25Co合金表面氧化膜外层主要是由CuO组成.紧接着是Co的氧化物层.可见,向Cu-25Co合金中加入Ni后,降低了合金表面形成活泼组元Co外氧化膜所需的临界浓度,促使合金表面在较低Co含量下能形成活泼组元Co的外氧化膜.     

Internal Oxidation Thermodynamics and Isothermal Oxidation Behavior of AgSnO2 Electrical Contact Materials

研究了Ag-Sn合金内氧化热力学与恒温氧化行为。热力学计算结果表明,Ag-Sn合金内氧化在热力学上是可行的,并绘制了合金氧化热力学区位图。经氧化实验获得Ag-Sn合金恒温氧化行为曲线。Ag-Sn合金快速氧化的温度区间为550℃至800℃。随内氧化温度的升高,合金的氧化更为彻底并逐步趋于平稳。实验所得AgSnO2材料中,SnO2颗粒弥散分布于Ag基体中。在内氧化过程中,氧的扩散使合金内部发生氧化,并生成呈网状排布的氧化物。     

合金上氧化物的体积比的分析

氧化物与形成该氧化物消耗的金属的体积比（Ｐｉｌｌｉｎｇ－Ｂｅｄｗｏｒｔｈ Ｒａｔｉｏ简称ＰＢＲ）是判断氧化膜完整性的一个重要判据,也是氧化膜内产生生长应力的主要因素之一,已发发表的关于ＰＢＲ的数据都是针对纯金属的,本文基于合金的氧化行为建立了一个简化的模型,给出了合金上形成的氧化物的ＰＢＲ的人体估算了Ａｌ２Ｏ３、ＮｉＯ及Ｃｒ２Ｏ３等几种氧化物膜以及它们的混合膜ＰＢＲ值,合金上氧化物的ＰＢＲ值与合金　成分有关,并与纯金属上形成的同种氧化物的PBR有显著差别.     

The transition from the formation of mixed scales to the selective oxidation of the most-reactive component in the corrosion of single and two-phase binary alloys

The conditions for the transition from the formation of mixed scales to the exclusive oxidation of the component B, forming the most stable oxide, are examined for both single-phase and two-phase binary A-B alloys by taking into account the displacement of the alloy-scale interface due to the growth of the protective oxide. This procedure eliminates the inconsistencies arising from Wagner's classical treatment for single-phase alloys when the interdiffusion coefficient in the alloy is small with respect to the parabolic rate constant for outer-scale growth; but the same procedure leads to a significantly-improved treatment also for two-phase alloys. For the latter systems, the transition is shown to depend also on the solubility of B in the A-rich phase.Moreover, the exclusive growth of the most-stable oxide is more difficult than for single-phase alloys because it requires higher average concentrations of B in the alloy and may even become impossible if the parabolic rate constant of oxidation is large with respect to the interdiffusion coefficient in the alloy.     

Oxidation Behavior of Tribaloy T-800 Alloy at 800 and 1,000 °C

The oxidation behavior of Co-based Tribaloy T-800 alloy has been studied isothermally in air at 800 and 1,000 °C, respectively. The results showed that the oxidation mechanism was dependent on the exposure temperature. The oxidation of the alloy followed subparabolic oxidation kinetics at 800 °C. The oxide scale at this temperature exhibited a multi-layered structure including an outer layer of Co oxide, a layer composed of complex oxide and spinel, a nonuniform Mo-rich oxide layer, an intermediate mixed oxides layer and an internal attacked layer with different protrusions into Laves phase. During 1,000 °C exposure, it followed linear kinetics. The oxidation rendered a relatively uniform external Cr-rich oxide layer coupled with a thin layer of spinel on the top surface and voids at local scale/alloy interface and intergranular region together with internal Si oxide at 1,000 °C.     

The Effect of Cr on the Oxidation of Ni–10 at% Al in 1 atm O2 at 900–1000°C

The oxidation of three Ni–xCr–10Al alloys with a constant Al content of 10 at% and containing 3, 5, and 10 at% Cr was investigated at 900–1000°C in 1 atm of pure oxygen and compared to the behavior of Ni–10Al. At both temperatures, an external NiO scale overlying a zone of internal-oxide precipitates formed on Ni–10Al and Ni–3Cr–10Al: in addition, a discontinuous Al₂O₃ layer formed at the front of the internal oxidation for Ni–3Cr–10Al. An exclusive external scale of Al₂O₃ formed at most places on Ni–5Cr–10Al at 900°C, while, at some sites, the same alloy formed an outer NiO layer overlying an internal oxidation zone. The scales formed on Ni–5Cr–10Al at 1000°C were complex, but eventually a protective Al₂O₃ layer developed either at the alloy surface or beneath a region containing a mixture of different oxides. Finally, an exclusive external Al₂O₃ layer formed on Ni–10Cr–10Al at both temperatures. Thus, the addition of sufficient chromium to Ni–10Al produced a classical third-element effect, inducing the transition between internal and external oxidation of aluminum under a constant Al content. A possible mechanism for the effect of chromium on the oxidation of Ni–10Al is discussed on the basis of an extension to ternary alloys of a criterion first proposed by Wagner for the transition between internal and external oxidation of the most-reactive component in binary alloys.     

晶粒尺寸对Cu-60Ni合金高温氧化行为的影响

研究了铸态Cu-60at%Ni(CACu-60Ni)和机械合金化制 备的纳米晶Cu-60at%Ni(MACu-60Ni)合金在800℃空气中的氧化行为.结果表明：CACu-60Ni 合金的氧化动力学偏离抛物线规律,形成外层为CuO,内层为疏松、多孔的Cu2O和NiO混合 氧化物层,同时沿合金基体发生了Ni的内氧化;MACu-60Ni合金的氧化动力学近似遵循抛物 线规律,合金表面氧化膜外层为很薄一层CuO,内层为较厚,且均匀致密的NiO层.晶粒细化 明显促进了由Cu2O和NiO混合氧化膜向单一连续NiO膜的转变.讨论了合金的氧化机制.     

Oxidation behavior of three-phase Cu-25Ni-30Cr alloy at 700- 800℃ under high oxygen pressures

The thermogravimetric analysis of a ternary Cu-25Ni-30Cr alloy prepared by conventional casting was performed in 0.1 MPa pure O2 at 700 - 800 ℃. The results show that the alloy is composed of three phases,where the phase with the largest copper and lowest chromium content forms the matrix, while the other two,much richer in chromium, form a dispersion of isolated particles. At variance with another three-phase Cu-20Ni-20Cr alloy, which forms complex scales containing the oxides of the various components and double oxides plus an irregular region composed of alloy and oxides, the present alloy can form a very irregular but continuous chromia layer at the base of the mixed internal region, producing a gradual decrease of the oxidation rate down to very low values. A larger chromium content needed to form chromia layer for a ternary three-phase alloy is attributed to the limitations to the diffusion of the alloy components in the metal substrate imposed by their multiphase nature.     

The Oxidation of a Directionally Solidified Ni-Al-Cr3C2 Alloy at 1100 and 1200°C in Oxygen

The oxidation behavior of a directionallysolidified Ni-Al-Cr₃C₂ alloy ofover all composition Ni-12.3Cr-6.9Al-1.8C (wt.%) hasbeen investigated at 1100 and 1200°C under 1 atmoxygen. Experiments have also been carried out on specimens having the samecomposition but with a nonaligned structure. At1100°C, in both cases and unlike conventionalnickel-base superalloys with the same chromium andaluminum contents, aluminium was found to oxidize internallybeneath an external Cr₂O₃ scale.Although the volume fraction of the internalprecipitates was significant, they showed no tendency tocoalesce into a compact subsurface layer, but formed randomly distributed clustersin the alloy matrix. The kinetics of oxidation andmorphologies of the oxide scales were not substantiallyaffected either by thermal cycling or by the alloy microstructure. At the higher temperature,continuous Al₂O₃ scales formedbeneath thick layers of transient nickel andnickel-chromium-rich oxides; no internal precipitationof aluminum-rich oxides was observed. However, internal degradation of thedirectionally solidified specimens at 1200°C wasquite significant, due to in situ oxidation of primarycarbides. The multilayered scales formed at 1200°C spalled extensively on cooling as a consequenceof loss of contact, starting preferentially at theintersections of the Cr₂C₃ fiberswith the alloy-scale interface. The observed behaviorcan be attributed to a reduction in the availability of chromiumbecause of the multiphase structure of the alloy; this,in turn, resulted in an increase in the flux of oxygeninward, leading to internal oxidation of aluminum at 1100°C. The almost exclusive externaloxidation of aluminum becomes possible at 1200°C,probably because of an increase in the diffusivity ofaluminum in the alloy matrix.     

AgSn合金粉末非抛物线性内氧化研究

采用逐步氧化增重法,研究了AgSn合金粉末中低温内氧化的动力学行为,结果表明其内氧化动力学曲线明显不同于高温氧化的抛物线定律,中低温氧化的各个不同阶段的内氧化机制符合不同的规律,区别于高温氧化,本实验合金粉末的中低温内氧化过程动力学由化学反应和产物层扩散相互作用控制.     

Oxidation of a quaternary three-phase Cu-20Ni-20Cr-5Fe alloy at 700-900 °C in 1 atm of pure O2

The oxidation of a quaternary Cu-Ni-Cr-Fe alloy containing approximately 20 at.% Ni, 20 at.% Cr and 5 at.% Fe, balance Cu (Cu-20Ni-20Cr-5Fe), was studied at 700-900 °C in 1 atm of pure oxygen. The alloy is composed of a mixture of three phases, where the lightest α phase with the largest Cu content forms the matrix, while the other two, much richer in Cr, form a dispersion of isolated particles. At variance with the ternary three-phase Cu-20Ni-20Cr alloy examined previously, which was unable to form protective chromia scales over the alloy surface even after an extended period of oxidation, the present alloy formed complex external scales containing mixtures of the oxides of the various components plus a deep internal region containing a mixture of alloy and oxide phases. With time, a very irregular and thin but essentially continuous chromia layer formed at the bottom of the mixed internal oxidation region, producing a gradual decrease of the oxidation rate. Thus, the addition of 5 at.% Fe to Cu-20Ni-20Cr alloy is able to decrease the critical Cr content required to form the most stable oxide and promotes the formation of a continuous chromia scale under a lower Cr content in spite of the simultaneous presence of three different phases.     

Internal oxidation in heat-resisting stainless steels caused by presence of halides

When Ni-20 Cr alloys or stainless steels are heated in air in contact with liquid sodium halides, massive internal oxidation can occur, but only when the surface of the alloy is not well shielded from the air by the salt film. Thus, internal oxidation can occur during intermittent exposure to an aqueous salt solution, and to high temperature oxidation. On the contrary, if the alloy is completely submerged in molten NaCl-KCl and oxidized by bubbling oxygen into the fused salt, the effective oxygen concentration at the alloy surface is too low to allow internal oxidation; only surface porosity results, as previously shown. Different morphologies of internal oxidation were observed for oxidation in the presence of NaBr, NaI, NaCl, and NaF.     

Effect of high-temperature annealings and creep on structure and properties of single- and double-layer heat-resistant coatings

The evolution of the structure, phase, and chemical composition in the double-layer refractory heat-resistant plasma coatings and surface layers of ZhS6U alloy [Ni-(8–9)Cr-2,4Ti-5,3Al-(9–10)Co-(1,2-2,4)Mo-10,5W-1,0Nb–0,02B-(0,18–0,2)C] under a coating was investigated during high-temperature annealings and creep. The internal oxidation was observed in ZhS6U alloy under a single-layer coating of Ni-Cr-Al-Y alloy after high-temperature annealings and creep in air. The possibilities of inhibiting internal oxidation by the application of an additional barrier layer for oxygen diffusion were considered. It was shown that ion implantation does not lead to the suppression of internal oxidation in the alloy under a coating and does not significantly affect the long-term strength during creep at 1273 K. An additional ceramic layer delays the internal oxidation of ZhS6U alloy by 50–60 h, which leads to an increase in the time until destruction at a stress of 170 MPa from 100 h for an alloy with a single-layer coating to 120 h. The application of a sublayer of refractory alloys completely suppresses internal oxidation. A refractory alloy with a double-layer coating has the same long-term strength for 100 h both in air and under a vacuum.     

Beneficial and detrimental Effects of Nitrogen on the oxidation behaviour of TiAl-based intermetallics

The isothermal oxidation of binary and ternary, Nh-containing titanium aluminides was studied at 900°C in air and Ar/O₂. It was found that the presence of nitrogen in the atmosphere is in some cases beneficial, in others detrimental. For an interpretation of the effects of nitrogen it is necessary to consider the various oxidation stages in which the mechanisms of titanium aluminide oxidation fundamentally differ. For High-Al alloys, which tend to form protective alumina based scales in the early oxidation stages, nitrogen always scenes to he detrimental because it promotes the formation of a more rapidly growing mixed alumina/titania scale. After this shift to mixed oxide scales, nitrogen can be detrimental as well as beneficial. It is proposed that the last mentioned case prevails if a near-continuous Ti-rich nitride layer is stable at the oxide/alloy interface, thereby preventing internal oxidation of aluminium. This beneficial effect, of nitrogen was found under all studied conditions for the Nb-containing alloys but only in some cases for the binary alloys.     

Kinetics of internal oxidation in Ag-6Sn-2In-1Te-0.2Ni and Ag-6Sn-0.6Cu-1Bi-0.2Ni type alloys

Internal oxidation process was followed in Ag-6Sn-2In-1Te-0.2Ni and Ag-6Sn-0.6Cu-1Bi-0.2Ni alloy types in free air and oxygen at 650 °C and 680 °C. It was found that the Cu and Bi bearing alloy had a higher rates of internal oxidation in all of the tested conditions, whish was due to Bi effect accelerating the internal oxidation. In the early stage of internal oxidation of the Ag-6Sn-2In-1Te-0.2Ni alloy, an inhomogeneous structure revealed, which changed to a homogenous pattern after longer oxidation times. Such a structure was suppressed in the Bi bearing alloy. The applied 6 bar oxygen atmosphere brought on a 5–6 times higher rate of internal oxidation, with a homogenous structure compared to the free air oxidation. In free air after long time oxidation (200 h–250 h), the rate of internal oxidation was found to have almost doubled in both alloys.     

Investigation of Internal Oxidation on Pt-Ir-Zr High-Temperature Alloy

An internal oxidation method was applied to investigate the dispersion-strengthening of Pt-Ir-Zr alloy, and the thermodynamic condition was explored for this alloy. Scanning electron microscopy (SEM) was employed to analyze the internal oxidation morphologies. Combining with tensile strength, the optimal internal oxidation time was determined. The results show that oxidation of Ir and Zr will occur under the experimental condition, and the oxygen pressure of Zr is lower than that of Ir. The grain size of the alloy increases with the prolonging of time and remains stable when the oxidation time is up to 40 h. The tensile strength decreases exponentially with the increase of oxidation time. The time for optimal internal oxidation is 40 h at 1100 °C.     

Selective Internal Oxidation of the Noble Metal-Rich Intermetallic Compound,BaAg5

Although the internal oxidation of noble metal-base solid solutions (particularly Ag-base alloys) has been examined extensively, no detailed studies have been reported on the exclusive internal oxidation of noble metal-rich intermetallic compounds. In this paper, the internal oxidation of a silver-rich compound, BaAg₅, has been examined at 400°C in pure O₂. Under these conditions, the BaAg₅ was converted into a mixture of submicron barium-oxide particles in a silver matrix. Image analysis of the oxide content, and chemical analysis with an electron microprobe, revealed the absence of preferential barium segregation to the oxidized zone. Silver nodules were detected on the specimen surface, which was consistent with outward silver migration to relieve the stress associated with internal-oxide formation. Although the oxidation zone thickened at a parabolic rate, the measured rate was higher than expected from the Wagner model. The internal oxidation of BaAg₅ is demonstrated to be a relatively simple means of synthesizing an intimate mixture of BaO₂ and Ag for potential use in gas-phase catalysis.     

显微组织对Cu—Cr—Ni合金高温氧化行为的影响

研究了两种单／双相Cu-Cr-Ni合金的高温氧化行为。结果表明,合金氧化动力学偏离抛物线规律,其瞬时抛物线速率常数随时间延长而降低。两种合金表面氧化膜的结构差别较大,单相合金表面形成－连续的Cr2O3层,双相合金表面氧化膜外层是一边疆的CuO层,Ni和Cr的氧化发生在合金内部,这种合金与氧化物共存的混合内氧化与经典的内氧化明显不同,氧化层最里面形成了一连续的CrO3膜,抑制了合金的进一步氧化。     

铁在双相Fe—Cu合金中的内—外氧化

三处Ｆｅ－Ｃｕ合金在氧分压低于氧化铜平衡分解压条件下的高温氧化结果表明,合金中同时发生了活泼组元铁的内氧化和外氧化,外氧化膜为单一铁的氧化物,内氧化区中氧化铁和金属铜继承了原始合金中两相的分布。内氧化区前沿的合金中未发现铁的贫化。这种氧化膜结构的单相合金中罕见而在双相合金中较为普遍,被认为是双相合金中两组元间有限地互溶度使得氧在合金中的过饱和程度比在固溶体合金中更强烈的结果。