Characteristics of High-Temperature Deformation Behavior of Ti-45Al-2Cr-3Ta-0.5W Alloy

High-temperature deformation behavior tests of as-cast Ti-45Al-2Cr-3Ta-0.5W alloy were conducted over a wide range of strain rates (0.001-1.0 s^?1) and temperatures (1150-1300 °C). The flow curves for the current alloy exhibited sharp peaks at low strain levels, followed by pronounced work hardening and flow localization at high strain levels. Phenomenological analysis of the strain rate and temperature dependence of peak stress data yielded an average value of the strain rate sensitivity equal to 0.25 and an apparent activation energy of ~420 kJ/mol. Processing maps were established under different deformation conditions, and the optimal condition for hot work on this material was determined to be 1250 °C/0.001 s^?1. The stable deformation region was also found to decrease with increasing strain. Dynamic recrystallization (DRX) was the major softening mechanism controlling the growth of grains at the grain boundary. Meanwhile, local globularization and dynamic recovery (DR) were the main softening mechanisms in the lamellar colony. When deformed at higher temperatures (~1300 °C), the cyclic DRX and DR appeared to dominate the deformation. Moreover, the evolution of the β phase during hot deformation played an important role in the dynamic softening of the alloy.     

Oxidation and sulfidation behavior of Fe-20Cr-16Ni-4Al-1Y2O3 oxide-dispersion-strengthened alloy

High-temperature oxidation and sulfidation studies were conducted on an oxide-dispersion-strengthened alloy of composition Fe-20Cr-16Ni-4Al-1Y₂O₃. The oxidation studies were conducted in air and low-PO₂ environments over a temperature range of 650–1200°C. Results are also reported on the sulfidation resistance of preformed oxide scales and the influence of reoxidation of preformed sulfide scales. Detailed microstructural results and x-ray diffraction analysis data are presented to substantiate the corrosion behavior of the alloy over the wide range of conditions anticipated in fossil-energy systems. Data are also presented on the corrosion behavior of the alloy in oxygen/sulfur mixed gas atmospheres, and the results are used to compare the corrosion behavior of the present alloy with other chromia- and alumina-forming alloys.     

溅射Ni-16Co-26Cr-10Al纳米晶涂层的熔盐热腐蚀性能

利用磁控溅射技术在铸造Ni-16Co-26Cr-10Al合金上溅射了相同成分的纳米晶涂层,并进行900℃热腐蚀实验,结果表明:溅射Ni-16Co-26Cr-10Al纳米晶涂层由于晶粒尺寸细小,促进了保护性氧化物形成元素Al沿原"短路扩散通道-晶界"向氧化前沿的扩散,从而促进了保护性Al2O3的快速形成,使得溅射Ni-16Co-26Cr-10Al纳米晶涂层表现出比M38合金更优异的抗热腐蚀性能。     

纳米晶化对Ni-25 Cr-5Al-1S合金热生长氧化膜粘附性的影响

比较研究了高S铸态合金Ni-25Cr-5Al-1S(mass%)及其溅射纳米涂层在1000℃的氧化行为,结果表明:铸态合金在20小时恒温氧化中生长的氧化膜在冷却时发生严重剥落,氧化膜/基体界面局部区域S含量较高;而溅射纳米涂层没有发生氧化膜剥落现象,涂层/氧化膜界面上明显无S的存在.这说明Ni-25Cr-5Al-1S合金纳米化可以有效抑制S对氧化膜/合金界面结合的毒化效应,提高了氧化膜的粘附性.     

Thermophysical properties of Ti-5Al-5V-5Mo-3Cr-1Zr titanium alloy

The thermophysical properties of the Ti-5Al-5V-5Mo-3Cr-1Zr titanium alloy in a wide range of temperatures from room temperature to 1000°C have been studied by the methods of differential scanning calorimetry, the laser flash method, and dilatometry. The obtained data on heat capacity, thermal diffusivity, and thermal expansion have been used for calculating coefficient of thermal conductivity. The sequence and temperatures of structural transformations during heating of the alloy have been established. It has been shown that the studied alloy possesses a coefficient of thermal conductivity that is 3.5–4 times smaller than that of pure titanium.     

Effect of nanocrystallization on hot corrosion resistance of Ti-48Al-8Cr-2Ag alloy in molten salts

1 Introduction There was considerable interest in the use of γ-TiAl alloys within advanced gas turbines where they offered greater high temperature capability over conventional titanium at reduced mass. These factors would enable engines with greater th…     

固溶态和挤压态Mg-xLi-3Al-2Zn-0.5Y(x=4,8,12)合金的显微组织和腐蚀行为

研究固溶态和挤压态Mg-xLi-3Al-2Zn-0.5Y(x=4,8,12,质量分数,%)合金的显微组织和腐蚀行为。结果表明,当锂含量从4%增加到12%,合金基体由α-Mg单相转变为α-Mg+β-Li双相,再转变为β-Li单相。Mg-4Li-3Al-2Zn-0.5Y和Mg-12Li-3Al-2Zn-0.5Y合金具有晶间腐蚀和点蚀的混合腐蚀特征,前者与沿晶界析出的AlLi相有关,后者与第二相与基体之间的高电位差有关。挤压态合金的耐蚀性优于固溶态合金。挤压态Mg-8Li-3Al-2Zn-0.5Y合金具有最低腐蚀速率(P_W=(0.63±0.26)mm/a),主要归因于该合金的第二相分布更均匀、通过牺牲β-Li相形成的保护性α-Mg相和相对完整的更均匀分布的氧化膜。     

The spalling modes and degradation mechanism of ZrO2-8 wt.% Y2O3/CVD-Al2O3/Ni-22Cr-10Al-1Y thermal-barrier coatings

State-of-the-art conventional thermal-barrier coatings consist of a thermalinsulating, partially-stabilized ZrO₂ top coat and a bond coat. In this study, a continuous alumina-diffusion-barrier layer was deposited and interposed between the top coat and bond coat by chemical-vapor deposition (CVD). Both the conventional and the experimental TBC systems were cyclically tested at 1000°C, 1050°C, 1100°C, and 1150°C to evaluate and compare oxidation, performance, and fracture behavior. Introduction of the intermediate CVD-Al₂O₃ layer effectively suppressed the oxidation rate of the bond coat and sufficiently altered its oxidation behavior. The thermal-cyclic life of TBCs was improved by the new system. The failure of the ZrO₂-8 wt.% Y₂O₃/CVD-Al₂O₃/Ni-22Cr-10Al-1Y TBC specimens was observed to propagate mainly along the lamellar splats of the top coat, and secondarily along the top coat/CVD-Al₂O₃ interface.     

The influence of yttrium on the Oxidation behaviour of Ni-23Co-19Cr-12Al alloy at high temperatures

The effect of 0.6 wt.% yttrium addition on the oxidation behaviour of the coating material Ni-23Co-19Cr-12Al was studied under isothermal and thermal cycling conditions in air at 1373 and 1473 K. The reaction was followed thermogravimetrically while the SEM, EDX, EPMA and X-ray diffraction techniques were used to characterise the starting materials and the oxidized samples. Intensive spalling and the formation of a deep internal oxidation zone were observed in the case of the yttrium-free alloy. Yttrium strongly improved the oxidation resistance by substantial suppression of scale spalling and considerable reduction of internal oxidation.     

5GPa超高压凝固Al-1Ni-3Y合金的凝固组织及相分析

利用X射线衍射分析方法分析了高压下凝固的Al-Ni-Y合金的相组成;利用光学显微镜对在不同条件下制备的高压凝固合金的显微组织形貌和共晶组织形貌进行研究;通过显微硬度测试方法,确定出冷却速度与显微硬度之间的关系。实验结果表明,高压条件下凝固的合金共晶点发生偏移,使得常压共晶成分的合金在高压下变成亚共晶成分合金。在5 GPa超高压力、不同冷速(50、100、200 K/min)条件下凝固的合金的显微组织形貌发生了很大的改变,但是合金的相组成没有发生变化。随着冷却速率的不断提高,合金组织逐渐细化,二次枝晶间距也随之减小,共晶团尺寸也更加细小,显微硬度提高,Al3Y相的各向异性逐渐减弱。     

Properties of TIMETAL 555 (Ti-5Al-5Mo-5V-3Cr-0.6Fe)

TIMETAL 555 is a high-strength near-β titanium alloy that was designed for improved producibility and excellent mechanical property combinations, including deep hardenability. The nominal chemical composition of TIMETAL 555 is Ti-5wt.%Al-5wt.%Mo-5wt.%V-3wt.%Cr. This article provides a summary of the available data for this relatively new alloy. This paper was presented at the Beta Titanium Alloys of the 00’s Symposium sponsored by the Titanium Committee of TMS, held during the 2005 TMS Annual Meeting & Exhibition, February 13–16, 2005 in San Francisco, CA.     

铸造Ti-45Al-8.5Nb-0.5(W,B,Y)合金组织均匀化处理

采用水冷铜坩埚感应熔炼制备了Ti-45Al-8.5Nb-0.5(W,B,Y)(at%)合金铸锭,研究了铸造合金组织特点及均匀化处理温度对显微组织的影响规律。结果表明,铸锭组织呈全层片,有大量β相网,富Al相等成分偏析;调整热处理温度使合金偏析区域处于α单相区,充分保温后缓慢冷却可消除偏析形成全层片组织;经过1420℃×12 h炉冷,β相与富Al相偏析均得以消除,获得平均尺寸约为320μm,层片间距约为0.8μm的均匀全层片组织。     

Effects of bond coat preoxidation on the properties of ZrO2-8wt.% Y2O3/Ni-22Cr-10Al-1Y thermal-barrier coatings

Plasma-sprayed thermal barrier coatings (TBCs) consist of an intermediate MCrAlY bond coat to protect the substrate superalloy from oxidation/hot corrosion and a thermal insulating zirconia-based ceramic top coat. This system is developed for advanced turbine-engine, hot-section components. In this study the as-sprayed Ni-22Cr-10Al-1Y bond coat was subjected to preoxidation treatment at 1000° C for 1, 50, 100, and 200 hr, also at 1100°C, 1200°C and 1300°C for 1 hr to form an oxide scale before subsequent deposition of a ZrO₂-8wt.% Y₂O₃ top coat. The oxidation kinetics were measured, and the phase constitution and morphology of pregrown oxides on the Ni-22Cr-1Y bond coat were analyzed by x-ray diffractometer and SEM/EDS to elucidate the improvement and degradation mechanisms of the new system. The results of the experiments in this study showed that the tentative ZrO₂-8wt.% Y₂O₃ TBC specimens with preoxidized Ni-22Cr-10Al-1Y bond coat, when properly processed, exhibited lower oxidation rates and generally longer lifetime compared with traditional TBC specimens.     

Effectiveness of hot deformation and subsequent annealing for grain refinement of Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy

High strength titanium alloys suffer from a limited combination of strength and ductility.Considering their microstructure,the coarse β grain is a detrimental f...     

Oxidation study of Fe-8Cr-10Ni-(0-3)Si-(0-6)Mo alloys

Mechanisms are proposed to explain the oxidation rate behavior of Fe-8Cr-10Ni alloys to which varying amounts of either Si (0–3%) or Mo (0–6%), or both have been added. The formation and breakdown of a silica sublayer cause significant changes in the oxidation mechanism. The formation of the silica depends on preformation of a Cr₂O₃ outer layer. The addition of Mo enhances the oxidation protection of Fe-Si alloys by producing an Fe-Mo-Si precipitate in the base metal.     

Cellular automaton simulation of dynamic recrystallization behavior in V-10Cr-5Ti alloy under hot deformation conditions

The deformation behavior of V-10Cr-5Ti alloy was studied on the Gleeble-1500 thermomechanical simulator at the temperatures of 950-1350 °C, and the strain rates of 0.01-10 s^?1. Based on the Arrhenius model, dislocation density model, nucleation model and grain growth model, a numerical cellular automaton (CA) model coupling simulation of hot deformation is established to simulate and characterize the microstructural evolution during DRX. The results show that the flow stress is fairly sensitive to the strain rate and deformation temperature. The error between the predicted stress by the Arrhenius model and the actual measured value is less than 8%. The initial average grain size calculated by the CA model is 86.25 μm, which is close to the experimental result (85.63 μm). The simulations show that the effect of initial grain size on the dynamic recrystallization microstructure evolution is not significant, while increasing the strain rate or reducing the temperature can refine the recrystallized grains.     

Effect of pre-aluminization on the properties of ZrO2-8wt.% Y2O3/Co-29Cr-6Al-1Y thermal-barrier coatings

Specimens of investment-cast Mar-M247 superalloy were vacuum-plasma sprayed with Co-29Cr-6Al-1Y bond coat, and part of the specimens were further pre-aluminized at 980°C for 2, 4, 6, 8, and 10 hours. All the specimens were then deposited with ZrO₂-8 wt.% Y₂O₃ thermal-barrier coatings (TBCs) and thermally cycled at 1050°C to evaluate the effect of time of the prealuminizing treatment on the performance and failure mechanism of the modified system. Results showed that TBC specimens with pre-aluminized bond coatings exhibited lower oxidation rates and significantly higher cyclic life when compared with unaluminized specimens. The failure of bond-coat pre-aluminized TBC specimens was observed to propagate mainly along the lamellar splats of the top coat, whereas the failure of conventional TBC specimens occurred mainly along the top-coat/spinel oxides interface.     

Fe-25Cr-12Co-1Si合金分级回火过程中的组织、磁性能及M(o)ssbauer谱研究

本文应用TEM和M(o)ssbauer谱系统研究了Fe-25Cr-12Co-1Si合金在分级回火过程中磁性能与微观组织以及超精细结构变化的相互关系.结果表明,随分级回火进行,合金磁性能不断提高主要是源于其微观组织中调幅分解产生的α1和α2两相的饱和磁化强度差别的增加,这种差别是由两相成分差别导致的.调幅分解生成的单畴粒子的形状各向异性不是Fe-Cr-Co合金在分级回火过程中磁性能提高的决定性因素.     

挤压对Mg-5Li-5Al-0.6Y合金组织、力学性能和腐蚀行为的影响

对铸态Mg-5Li-5Al-0.6Y合金进行了热挤压,采用光学显微镜(OM)、扫描电镜(SEM)和X射线衍射仪(XRD)研究了挤压对铸态合金物相和微观组织的影响.通过对挤压前后的合金进行室温拉伸试验和断口形貌分析,研究了挤压对合金力学性能的影响.通过析氢、质量减少、动电位极化曲线和电化学阻抗分析了挤压对合金腐蚀行为的影...