Analysis of the Chemistry of Ni-Base Turbine Disk Superalloys Using An Alloys-By-Design Modeling Approach

The chemistry of the Ni-base superalloys used for turbine disks is critiqued by making use of the recently developed Alloys-By-Design computer-based tools. Compositions within the Ni-Cr-Co-Al-Ti-Mo-W-Ta(-Zr-C-B) design space are evaluated virtually. The assessment is made on the basis of sub-models for yield strength, creep behavior, oxidation resistance, and density; microstructural factors such as $\gamma^{\prime}$ volume fraction and $\gamma^{\prime}$ solvus temperature are considered where needed. The trade-offs between the different factors are studied in a quantitative sense. Diagrams are developed for the different alloy properties to highlight the limitations and challenges that one encounters when designing new grades of alloy or when optimizing existing grades. Composition-property maps are constructed that allow for an informed approach when defining an alloy composition. Specifically, the impact of chromium, molybdenum, and tungsten additions when mechanical behavior and lifing considerations are of concern is demonstrated.     

Alloy Composition Screening for Ni-Base Turbine Disc Superalloys Using the Creep Property of Single Crystal

This paper proposes a method for alloy composition screening using the creep property of a single crystal (SC) for designing new Ni-base powder metallurgy (P/M) turbine disc superalloys. A commercial Ni-base disc alloy, U720Li®, a Ni-Co-base disc alloy, TMW-4M3, and a Ni-base conventionally cast alloy, TM-47, were selected for investigation. Their SC and P/M samples were prepared such that their γ/γ′ structures were similar. Moreover, tensile creep tests were performed on SC samples, and compressive creep tests were performed on SC and P/M samples. The tensile creep test results of SC samples at 1073 K (800 °C) and 735 MPa indicate that 0.2 and 1 pct creep times, as well as rupture life, are long in the order of TM-47 SC, TMW-4M3 SC, and U720Li SC. These results simulate the intragranular creep resistances of the corresponding P/M alloys. Furthermore, there is no significant difference in 0.2 and 1 pct compressive creep times between the SC and P/M samples of each alloy. Additionally, the 0.2 and 1 pct creep times of tensile and compressive creep tests of every alloy had an identical order. Therefore, alloy composition screening using SC creep property enables the design of new disc alloys with excellent creep resistance.

     

铁水预处理同时脱硫和脱磷反应模型及其应用

通过对在5kg的感应炉上，对3种硅含量不同的铁水，模拟喷水熔剂进行铁水预处理试验，建立了铁水同时脱硫，脱磷的动力学反应模型，并通过计算机编程求解，其结果可用来指导优化铁水预处理的生产工艺。     

Quantitative Precipitate Classification and Grain Boundary Property Control in Co/Ni-Base Superalloys

A correlative approach is employed to simultaneously assess structure and chemistry of (carbide and boride) precipitates in a set of novel Co/Ni-base superalloys. Structure is derived from electron backscatter diffraction (EBSD) with pattern template matching, and chemistry obtained with energy dispersive X-ray spectroscopy (EDS). It is found that the principal carbide in these alloys is Mo and W rich with the M₆C structure. An M₂B boride also exhibiting Mo and W segregation is observed at B levels above approximately 0.085 at. pct. These phases are challenging to distinguish in an SEM with chemical information (EDS or backscatter Z-contrast) alone, without the structural information provided by EBSD. Only correlative chemical and structural fingerprinting is necessary and sufficient to fully define a phase. The identified phases are dissimilar to those predicted using ThermoCalc. We additionally perform an assessment of the grain boundary serratability in these alloys, and observe that significant amplitude is only obtained in the absence of pinning intergranular precipitates.

     

预熔铝酸钙钢水脱硫实验研究

使用预熔铝酸钙在MoSi2电阻炉内进行了钢水的脱硫实验研究。结果表明,使用预熔铝酸钙后,钢水平均脱硫率达到82.1%,钢水中Si、Mn、P含量变化较小,C、Ti含量增加。为避免钢水增C、Ti,应采用低C、低Ti型预熔铝酸钙或尽量使钢中C、Ti含量控制在钢种允许的下限区域。     

Determination of the Lithium Content of Molten Aluminum Using a Solid Electrolyte

A lithium probe has been used for the determination of the lithium content of molten aluminum alloys. The electrolyte is a two-phase mixture of Li₃PO₄ and Li₄Si0₄ to give an overall composition of Li_3.6Si_0.6P_0.4O₄. This electrolyte was found to be slightly attacked by pure liquid lithium, but no attack was detected in the aluminum-lithium melts. However, exposure to high humidity caused the electrolyte to degrade. A satisfactory reference electrode was found to be decomposed Li₂Ti₃0₇ consisting of Li₄Ti₅O₁₂ and TiO₂. An activityvs composition plot showed that Henry’s law was obeyed, and the activity coefficient was 0.17 at 984 K and 0.26 at 1050 K. P. C. YAO, formerly Research Student in the Department of Metallurgy and Materials Science, University of Cambridge     

Agglomeration of Solid Inclusions in Molten Steel

Metallurgical and Materials Transactions B - Agglomeration of alumina inclusions in the molten steel is investigated through the free energy analysis of the cavitation between inclusions. The...     

太钢铁水脱硫处理工艺研究分析

分析了太钢铁水预处理脱硫生产工艺中,粉剂、铁水与脱硫率的相关关系,及脱硫处理过程中对铁水温度、成份的影响,并通过计算机进行数据处理,得出了粉剂加入量、铁水原始硫含量与脱硫率的回归方程。     

氧化钙对熔盐法制备片状氧化铝的影响

以氢氧化铝为原料,氯化钠-氯化钾为熔盐,在1 000℃保温4 h,熔盐加入量为70%时,得到了结晶完整的片状α-Al2O3,片的边长为5～10μm,厚度为0.6～1.4μm;研究了氧化钙对试样物相和形貌的影响。结果表明:氧化钙的加入阻碍了氧化铝向α相转变,阻碍片状氧化铝的生成。     

Quenching Differential Thermal Analysis and Thermodynamic Calculation to Determine Partition Coefficients of Solute Elements in Simplified Ni-Base Superalloys

In this article, a profile-fitting methodology was developed to measure the partition coefficients of solute elements during the solidification of Ni-base alloys. Better agreement with the theoretically calculated values is expected if the accuracy of the composition and the homogeneity of the model alloys are enhanced. Regular differential thermal analysis (DTA) measurements were consistently higher than the theoretical transition temperatures, and the differences were smaller when compared to the predictions performed with the thermodynamical database developed by Du et al. The better agreement between the experimental results and the theoretical predictions made with the newly developed database suggests that improvements in the accuracy of the theoretical predictions can still be obtained and are necessary for accurate freckling prediction. Quenching modified DTA (MDTA) experiments were proven to be appropriate for directly measuring the average partition coefficients of the solute elements. Regarding the cooling rate of the first stage of the quenching experiments, it was assumed successfully that the cooling rate prior to the quenching step of 0.083 Ks⁻¹ was sufficiently slow to permit easy quenching, while being fast enough for the primary solidification reaction to depart from the equilibrium model and being closer to the Scheil model of segregation. The minimization of the error function defined from the Scheil equation was found to be an appropriate method for describing the segregation profiles of the quenched samples and permitted good estimations of the partition coefficients of the solute elements. The reliability of the methodology was found to be satisfactory given that the magnitudes calculated for the partition coefficients of the solutes in the multicomponent alloy 718 were found to be very close to the values reported in the literature.     

Change of Nitrogen Content in the Molten Steel during CaO Powder Blowing

The rates of nitrogen desorption from molten steel were measured with the blow of CaO powder or argon gas onto the melts under reduced pressure. 15kg of electrolytic iron was melted in a MgO crucible by a high frequency induction furnace and the temperature of the melt was held at 1873 K. A mathematical model was developed with the consideration of the chemical reaction between sulphur in molten steel and CaO powder and the desorption of nitrogen at gas‐metal interface. The calculated results were in good agreement with the measured ones. The apparent rate constant of nitrogen desorption and the rate controlling step were examined.     

熔盐中CaO浓度对O~(2-)放电过程的影响

为研究熔盐中CaO浓度对O~(2-)在石墨阳极放电过程的影响,以钛铁矿为电解阴极、石墨为阳极,以添加有摩尔百分数0～2%CaO的CaCl_2-NaCl熔盐为电解质,采用气相色谱法测试阳极气体成分。结果表明,当采用石墨为电解阳极时,阳极气体为CO和CO_2混合气。改变CaO的浓度对O~(2-)的放电路径影响显著,当CaO浓度为0～0.5%时,O~(2-)放电主要生成CO;当CaO浓度增加至1%时,O~(2-)放电主要生成CO_2;当继续增加CaO浓度至1.5%～2%时,O~(2-)放电主要生成CO。     

用炼钢废渣作铁水脱硫扒渣板涂层材料的实践

文章主要介绍了将精炼炉白渣中间含有的胶凝性材料作为和扒渣板相粘结的粘结剂,添加了一些中间包弃渣成分的抗渣性材料,作为扒渣板的隔离膜材料。以及主要实施过程及其产生的工艺效益。     

铁水包喷吹Mg+CaO粉剂脱硫技术

分析了宝山钢铁股份有限公司采用TDS(Torpedo Car Desulphurization)、PTC(Hot Metal Pre-treatment Center)和铁水包单枪、双枪喷Mg+CaO脱硫模式的生产情况.结果表明,采用铁水包喷吹Mg+CaO脱硫在喷吹时间、脱硫效果、粉剂消耗、生产组织及经济效益等方面明显优于混铁车喷吹脱硫.脱硫时间可缩短50%以上,终点硫质量分数可达到0.001%～0.003%,粉剂总耗量仅为CaC2基粉剂耗量的50%、CaO基粉剂耗量的20%,综合成本比TDS或PTC混铁车脱硫低18%～30%.铁水罐双枪喷Mg+CaO脱硫模式的效果最好.     

Oxidation of Silicon and Boron in Boron Containing Molten Iron

 A new process of directly smelting boron steel from boron containing pig iron has been established. The starting material boron containing pig iron was obtained from ludwigite ore, which is very abundant in the eastern area of Liaoning Province of China. The experiment was performed in a medium frequency induction furnace, and Fe2O3 powder was used as the oxidizing agent. The effects of temperature, addition of Fe2O3, basicity, stirring, and composition of melt on the oxidation of silicon and boron were investigated respectively. The results showed that silicon and boron were oxidized simultaneously and their oxidation ratio exceeded 90% at 1 400 ℃. The favorable oxidation temperature of silicon was about 1 300-1 350 ℃. High oxygen potential of slag and strong stirring enhanced the oxidation of silicon and boron.     

Effect of Al on the NiAl-Type B2 Precipitates in Ferritic Superalloys

Ultra-small-angle X-ray scattering (USAXS) is employed to quantify the average size, interparticle spacing, and volume fraction of the primary B2 precipitates in Fe-based superalloys with varying Al concentration. The results are analyzed with a model incorporating polydispersity and interference effects and verified by transmission electron microscopy (TEM) characterizations. As the Al amount increases from 4 to 10?mass pct, there is an approximately 40?pct decrease in the average interparticle spacing and?~30?pct reduction in the average particle diameter.     

Electrochemical Deoxidation of Solid Zirconium Dioxide in Molten Calcium Chloride

The reduction of zirconium dioxide pellets by electro-deoxidation in molten calcium chloride-calcium oxide (900 °C) has been studied. In this technique, the solid oxide is cathodically polarized against a graphite counter electrode under a constant applied potential. Unlike other metal oxides that have been reduced by this technique, only a small area around the cathodic current-collector wire was reduced to zirconium metal with zirconia pellets sintered at ~1100 °C; the rest of the sample was largely calcium zirconate. Pellets sintered above 1200 °C showed better reduction near the cathode wire and the reduction extended to the entire surface of the pellet with the passage of time. However, reduction of the inner core was found to be increasingly difficult, because the surface metal layer thickened on continuous electro-deoxidation. An analysis of the experimental results showed that the poor electrical conductivity of the intermediate compound, CaZrO₃ and its blocky morphology inhibited the electro-deoxidation process. The increase in the sintering temperature of the pellet made it better conducting. However, the pores formed in the thick zirconium metal layer in such samples were too small for an ideal contact between the inner core and the molten electrolyte and hence the reduction of the inner core remained incomplete. Within the scope of this study, it is concluded that preforms with good grain growth and porosity are necessary for the electro-deoxidation of solid zirconium oxide.