Phase equilibria in the Fe–Rh–Ti system I. Experimental results

Two isothermal sections of the ternary system Fe–Rh–Ti were determined experimentally at 1000 °C and 800 °C using annealed alloys and diffusion couples. No ternary compound was found in this system. The B2 ordered phase is stable in all three binary subsystems of the Fe–Rh–Ti system and forms a range continuous solid solution at both temperatures. At 800 °C the B2-phase exhibits a tetragonal structure at certain ranges of composition. The same structure was observed in the binary Ti–Rh system. Within the B2 phase domain pseudo-interfaces were observed when the diffusion path crosses equiatomic compositions. A large miscibility gap between A2 and B2 was observed in the Fe-rich part of the Fe–Rh–Ti system.     

弥散强化Pt－5Rh合金（制造大型玻纤漏板新材料）

作者采用内氧化－复合工艺研制成功弥散强化Ｐｔ－５Ｒｈ合金（ＭＱＰｔＲｈ５）。其高温强度及抗蠕变性能明显地好于普通的Ｐｔ－Ｒｈ合金。它广泛地用作玻璃纤维漏板底板的结构材料。本文叙述了此材料的物理及力学性能以及在玻纤工业的应用例子。     

高温下Pt-13Rh/Pt热电偶的热电动势衰减机理研究

模拟1400℃富含Pt-Rh的使用环境,研究R型热电偶(Pt-13Rh/Pt)在高温下的衰减机理。分析竹节状缩颈现象的形成原因,讨论引起热电动势衰减的因素。结果表明,在富含气相Pt-Rh的高温环境下,热电偶外瓷珠表面沉积了固态的Pt、Rh,导致绝缘电阻的降低以及实际测温点向低温区转移,最终导致热电动势衰减。     

Pt合金氨氧化催化剂的结构和性能

采用平行比较法研究了Pt-10Rh、Pt-4Pd-3.5Rh和Pt-12Pd-3.5Rh-RE合金以及其氨氧化催化剂的结构与性能.与传统的Pt-10Rh和Pt-4Pd-3.5Rh合金及其催化剂比较,以稀土改性的合金,即Pt-12Pd-3.5Rh-RE合金及其催化剂,具有更高的力学性能(包括室温和高温拉伸强度、持久强度和...     

Effects of alloy microstructure on the high temperature oxidation of an Fe-10% Cr alloy

The oxidation resistance of an Fe-10% Cr alloy at 600°C in air increased with increasing amounts of cold work in the alloy. Breakaway oxidation could be prevented for at least 2000 h at 600°C by severe cold rolling or by pretreatment to produce 3–7 μm diameter grains. These treatments increased the mass of Cr passing into the oxide and also reduced the mechanical stress. The improvement in oxidation resistance could not have been due entirely to the increased oxidation of Cr. It is suggested that the microstructure produced by pretreatment strengthened the alloy so that it resisted the deformation normally produced by growth stresses. This allowed time for diffusion of Cr into the outer layer of the oxide, leading to a permanent reduction of stress.Shot blasting and mechanical abrasion also significantly improved oxidation resistance at 600°C, but very little improvement could be achieved at 800°C using the treatments discussed in this paper.     

Activity coefficients and partial molar volumes of boron in platinum-rhodium alloys

Activity coefficients of B in the phase of Pt and of three Pt---Rh alloys with 3, 6, and 10 wt.% Rh were obtained by equilibration of B₂O₃ with H₂-H₂O mixtures between 750 and 1000 °C and subsequent determination of the B mole fraction x_B 0.06 by the mass gain of the samples or by photometric analysis. Additions of Rh to Pt have rather large but opposing effects on the partial molar enthalpies and entropies of B, resulting in partial molar excess Gibbs energies within the modest range between −40 and −55 kJ mol⁻¹. The change in the lattice contraction from −13.5 to −3.2 pm/x_B in the phase of Pt and of Pt-10Rh can be fully described in terms of a substitutional solution model with strictly constant partial molar volumes of 9.09 cm³ mol⁻¹ and 8.28 cm³ mol⁻¹ for Pt and Rh respectively and a partial molar volume for B that increases linearly from 8.2 to 8.9 cm³ mol⁻¹ between pure Pt and Pt-10Rh.     

Effect of Specimen Thickness on the Oxidation Rate of High Chromium Ferritic Steels: The Significance of Intrinsic Alloy Creep Strength

Previous studies revealed that initial sample thickness affects the growth rate of oxide scales formed during 800 or 900 °C air exposure. The effect is partially related to differences in depletion of minor alloying additions such as Mn, Ti, La in thick and thin specimens. However, it has previously been proposed that the specimen thickness dependence is partially governed by differences in creep strength of thick and thin substrates. To investigate this hypothesis, discontinuous air oxidation experiments were carried out with the Laves phase strengthened ferritic steel Crofer 22 H at 800 °C. Comparing the data for solution annealed and pre-aged (500 h, 900 °C) materials it could be shown that intrinsic creep strength of the alloy substantially affects oxidation rates. The observations can qualitatively be explained by assuming the relaxation of oxide growth stresses by plastic deformation of the metallic substrate to be an important parameter affecting the kinetics of oxide scale growth.     

AlCoCrFeNiTi_(0.5)高熵合金的高温氧化行为

采用水冷铜坩埚真空感应悬浮熔炼法制备AlCoCrFeNiTi_(0.5)多主元高熵合金,研究合金在800、900、1000和1100℃下的高温氧化行为,采用XRD,SEM及EDS对氧化膜的成分及形貌进行了分析,探索了合金的氧化机制。结果表明,合金的氧化动力学曲线在800和900℃时近似遵循六次方抛物线规律,在1000和1100℃时近似遵循四次方抛物线规律。合金具有优异的抗氧化性,在800、900和1100℃下为抗氧化级别,而在1000℃下为完全抗氧化级别。合金的氧化主要发生在枝晶间和共晶区,呈岛状团聚堆叠生长,1100℃氧化时该区域的氧化物发生明显剥落,氧化产物主要是TiO_2、Fe_2TiO_5和FeCr_2O_4等;而枝晶相的氧化产物较单一,1000℃及以下温度氧化时为弥散分布的Al_2O_3颗粒,1100℃氧化时为致密的Al_2O_3氧化层。高温氧化后,合金基体相结构稳定,未出现软化现象。     

Effect of Chromium Content on the Oxidation Behaviour of Ferritic Steels for Applications in Steam Atmospheres at High Temperatures

Environments containing water vapour are common in many industrial processes, such as power generation systems. Hence, long-term oxidation (1000 h) of P-91 and AISI 430 was studied at 650 and 800 °C, in 100% H₂O atmosphere. The oxidation resistance of the AISI 430 is better than that of the P-91, due to the formation of protective phases on the surface. At 650 °C, a scale composed of Fe₃O₄, Fe₂O₃ and (Fe,Cr)₃O₄ is formed on P-91, although at 800 °C the scale is mainly composed of Fe₃O₄ and (Fe,Cr)₃O₄. On the other hand, on AISI 430 the scale is composed mainly of (Fe,Cr)₂O₃ at 650 °C, and at 800 °C a layer of Cr₂O₃ is formed and remains owing to the higher diffusion rate of Cr at this temperature than at 650 °C, the latter of which compensates the Cr depletion by the degradation of the chromia scale.     

High-Temperature Erosion of HVOF Sprayed Cr3C2-NiCr Coating and Mild Steel for Boiler Tubes

The comparison of the high-temperature erosion behavior of a High-velocity oxyfuel (HVOF) sprayed Cr₃C₂-NiCr coating with mild steel for circulating fluidized bed boiler tubes was investigated. Results showed that the erosion rate of the mild steel at 800 °C was four times that at 300 °C at an erosion angle of 30°. However, the erosion rate of the HVOF sprayed Cr₃C₂-NiCr coating was not influenced by the temperature in the range of 300-800 °C. It was found that the erosion resistance of HVOF sprayed Cr₃C₂-NiCr coating was more than three times higher than that of the mild steel at 700-800 °C. In addition to the ploughing on the coating surface, the cracking along splat interfaces in the coating was clearly observed on the cross-sectional microstructure. The results indicate that the erosion performance of the HVOF sprayed Cr₃C₂-NiCr coating is controlled by the cohesion between splats and can be further enhanced by improving splat cohesion.     

Characterization of High-Temperature Abrasive Wear of Cold-Sprayed FeAl Intermetallic Compound Coating

FeAl intermetallic compound coating was prepared by cold spraying using a mechanically alloyed Fe(Al) alloy powder followed by post-spray annealing at 950 °C. The high-temperature abrasive wear test was carried out for the FeAl coating at a temperature range from room temperature to 800 °C. The high-temperature abrasive wear of a heat-resistant stainless steel 2520 was performed for comparison. It was observed that the abrasive wear weight loss of FeAl coating was proportional to wear cycles in terms of sample revolutions at the tested temperatures. It was found that with the increase of the test temperature higher than 400 °C, the wear rate of cold-sprayed FeAl coating decreased with the increase of test temperature, while the wear rate of the heat-resistant steel increased significantly. The results indicate that the high-temperature abrasive wear resistance of the cold-sprayed FeAl intermetallic coating increased with the increase of the wear temperature in a temperature range from 400 to 800 °C. The wear resistance of cold-sprayed FeAl coating was higher than that of heat-resistant 2520 stainless steel under 800 °C by a factor of 3.     

Zr、Y元素对Pt-10Rh合金性能的影响研究

在Pt-10Rh合金中添加少量的Zr、Y元素,利用真空充氩电弧熔炼方法制备了Pt-10Rh-0.5Zr合金及Pt-10Rh-0.5Zr-0.2Y合金。研究了合金的相结构、室温与高温力学性能以及高温抗氧化性能,观察分析了合金高温氧化及高温断口的形貌组织结构。结果表明,合金形成了由铂铑固溶体基体相与少量的金属间化合物相构成的组织结构;添加少量的Zr、Y元素大幅提高了Pt-10Rh合金的力学性能,同时Y元素还显著改善了Pt-10Rh-0.5Zr合金的高温塑性和抗氧化性能。     

Development of Creep-Resistant and Oxidation-Resistant Austenitic Stainless Steels for High Temperature Applications

Austenitic stainless steels are cost-effective materials for high-temperature applications if they have the oxidation and creep resistance to withstand prolonged exposure at such conditions. Since 1990, Oak Ridge National Laboratory (ORNL) has developed advanced austenitic stainless steels with creep resistance comparable to Ni-based superalloy 617 at 800–900°C based on specially designed “engineered microstructures” utilizing a microstructure/composition database derived from about 20 years of radiation effect data on steels. The wrought high temperature-ultrafine precipitate strengthened (HT-UPS) steels with outstanding creep resistance at 700–800°C were developed for supercritical boiler and superheater tubing for fossil power plants in the early 1990s, the cast CF8C-Plus steels were developed in 1999–2001 for land-based gas turbine casing and diesel engine exhaust manifold and turbocharger applications at 700–900°C, and, in 2015–2017, new Al-modified cast stainless steels with oxidation and creep resistance capabilities up to 950–1000°C were developed for automotive exhaust manifold and turbocharger applications. This article reviews and summarizes their development and their properties and applications.     

The Binary Bi-Rh Phase Diagram: Stable and Metastable Phases

The binary bismuth-rhodium (Bi-Rh) phase diagram was reinvestigated from 23 to 60 at.% Rh with focus on the BiRh phase, applying powder-x-ray diffraction (XRD), high temperature powder-XRD, differential thermal analyses and scanning electron microscopy. The phase boundaries of the BiRh phase at 750 °C and the temperature of its peritectic decomposition were refined. In addition, the existence of the two phases Bi₄Rh and Bi₂Rh (in two modifications depending on temperature) could be confirmed. Most of the reaction temperatures reported in the literature could be verified within a range of about ± 10 °C. Nevertheless, a few temperatures had to be revised, such as those of the peritectic reactions L + Rh \(\rightleftharpoons\) BiRh at 979 °C and L + BiRh \(\rightleftharpoons\) β-Bi₂Rh at 785 °C. No evidence could be found for the presence of a stable Bi₃Rh phase in well annealed samples; from the present results it must be concluded that Bi₃Rh is actually metastable. On the other hand, a new orthorhombic phase BiRh_0.81 was discovered which crystallizes in the MnP structure type (Pmna). It was found that the temperatures of the transition between the low-temperature modification α-Bi₂Rh and its high-temperature form β-Bi₂Rh depend considerably on the presence or absence of metastable Bi₃Rh and stable BiRh_0.81, respectively.     

Ni-Al-Sn三元系相平衡的实验研究

采用电子探针显微分析和X-ray衍射分析方法实验研究了Ni-Al-Sn三元体系在800°C和1000°C时的相平衡。结果表明：(1) Ni-Al-Sn三元体系在800°C和1000°C时均未发现三元化合物;(2) Ni-Al侧包含NiAl、Ni3Al、Al3Ni和Al3Ni2四个化合物,其中800°C时,Sn在NiAl和Ni3Al中的固溶度在分别为3.1和14.7 at.%,在1000°C时分别为3.0和8.0 at.%。而Sn在Al3Ni和Al3Ni2相中几乎没有固溶度;(3) Ni-Sn侧包含Ni3Sn(r)、Ni3Sn(h)和Ni3Sn2(h)三个化合物相。800°C时,Ni3Sn(r)相的固溶度为4.2 at.%,1000°C时,Ni3Sn(r)相转变为Ni3Sn(h)相,拥有5.5 at.% 的固溶度。另外,800°C时,Al在Ni3Sn2(h)相中的固溶度为8.4 at.%,1000°C时为12.1 at.%;(4) Ni-Al-Sn三元体系Al-Sn侧为相互贯通的液相区域,实验测得的Ni在Al-Sn侧的溶解度约为1 at.%。     

The corrosion behavior of several heat resistant materials in air + 2% Cl2 at 300 to 800 °C. Part 3 – Alumina formers and intermetallics

The corrosion behavior of Alloy 214 and the intermetallics Fe₃Al, TiAl and MoSi₂ was investigated in dry air and air with 2% Cl₂ at temperatures of 300 to 800 °C. The results show that corrosion resistance of Alloy 214 and the two aluminides very much depend on the test temperature. For TiAl massive corrosion starts at 500 °C. Alloy 214 shows corrosion rates similar to chromia formers at temperatures of 650 and 800 °C while the best corrosion resistance of all alumina formers tested is revealed by Fe₃Al. For MoSi₂ only some little (“internal”) oxidation is observed even at 800 °C.     

Optical spectroscopic and electrochemical characterization of oxide films on a ferritic stainless steel

Colored oxide films that form on ferritic stainless steel in a high-temperature, oxidizing environment and correspond to different chemical compositions can cause a deterioration of pitting resistance and corrosion performance. Herein, optical spectroscopic and electrochemical techniques have been used to reveal the relationship between color, chemical composition, and corrosion resistance of oxide films formed in the temperature range from 400°C to 800°C for 30 min and at 800°C for 10, 20, 30, and 60 min. The substrate with a thin and dense passivation film leads to a low pitting potential but high corrosion resistance. Oxide films of yellowish or brownish color formed below 600°C are mainly iron oxides, which correspond to low corrosion resistance. No passivation characteristics can be observed for polarization curves of oxide films formed at 500°C and 600°C. The color of oxide films varies from blue to dark gray with the increase of oxidation time at 800°C. Corrosion resistance changes with different proportions of Fe₃O₄, Cr₂O₃, and FeCr₂O₄. The gray oxide films formed at 800°C for 30 min exhibit the lowest pitting susceptibility and the highest corrosion resistance.     

The mechanism of oxidation of dilute NiAl alloys at 800–1200°C

The oxidation behaviour of dilute NiAl alloys at 800–1200°C in flowing oxygen at 1 atm pressure has been studied using kinetic measurements, optical and scanning electron microscopy and electron probe micro-analysis. The oxidation rates of Ni0.5 to 4%Al alloys are greater than the corresponding values for nickel at 1000 and 1200°C, but less at 800°C. The increased rates at the higher temperatures are largely due to increases in the total cation vacancy concentration in the scale, although internal oxide formation can make a significant contribution to the oxidation rate. The decreased rates at 800°C are almost certainly due to a build-up of Al₂O₃ particles at the oxide/alloy interface. The roles played in the oxidation processes by doping, internal oxidation, blocking effects in the oxide, dissociation of NiO and gaseous transport of oxygen within the scale are considered in detail and related to the oxidation rates of the various alloys.     

The Precipitation Behavior and Hot Deformation Characteristics of Electron Beam Smelted Inconel 740 Superalloy

The Inconel 740 superalloy was prepared by the electron beam smelting (EBS) technology, the precipitation behavior and strengthening mechanism were studied, and the hot deformation characteristics of EBS 740 superalloy were investigated. The results indicate that the EBS 740 superalloy is mainly strengthened by the mechanism of weakly coupled dislocation shearing, and the resulting critical shear stress is calculated to be 234.6 MPa. The deformation parameters show a great influence on the flow behavior of EBS 740 superalloy. The strain rate sensitivity exponent increases with the increasing of deformation temperature, and the strain hardening exponent shows a decreasing trend with the increasing of strain. The activation energy of EBS 740 above 800 °C is measured to be 408.43 kJ/mol, which is higher than the 740H superalloy. A hyperbolic-sine-type relationship can be observed between the peak stress and Zener–Hollomon parameter. Nevertheless, the influence of deformation parameters is found to be considerably different at temperatures below and above 800 °C. The size of dynamic recrystallization (DRX) grains decreases with the increasing of strain rate when the strain rate is lower than 1/s, and reverse law can be found at higher strain rate. As a result, a piecewise function is established between the DRX grain size and hot working parameters.     

High-Temperature Corrosion Behaviour of Aluminized-Coated and Uncoated Alloy 718 Under Cyclic Oxidation and Corrosion in NaCl Vapour at 750 °C

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.