Effect of Ca2+ and Mg2+ ions on the sintering and spectroscopic properties of cr-doped yttrium aluminum garnet ceramics

In this work, we investigated the effects of Ca²⁺ and Mg²⁺ ions and annealing temperature on the spectroscopic parameters of chromium-doped yttrium aluminum garnet ceramics (Cr:YAG). Samples were obtained with either a separate or a simultaneous addition of calcium and magnesium oxides. To achieve this, aqueous suspensions were prepared using Y₂O₃, Al₂O₃, Cr₂O₃, MgO, and CaO high-purity powders as raw materials. The obtained suspensions were freeze-granulated, pressed into pellets, debinded, and subjected to reactive sintering in vacuum at 1715°C for 6 h. Each material was annealed in air with temperatures between 1300 and 1700°C. Samples were also compared to Cr:YAG ceramics with the addition of silica as a sintering aid. All the materials obtained were then exposed to 445 nm excitation, and emission spectra in the visible and infrared wavelengths were recorded. The results showed that the emission spectra of Cr:YAG ceramics varied according to the annealing conditions: as-sintered samples exhibited strong emissions of around 680 nm and, after air annealing, of around 1400 nm. This phenomenon is attributed to the Cr³⁺→Cr⁴⁺ transition. Samples doped solely with MgO exhibited the highest emission intensity in the infrared region. Thus, Mg²⁺ ions provided the best conversion efficiency of chromium ions.     

25Cr2Ni4MoV钢转子轴颈损伤修复工艺研究

汽轮发电机运行过程中,转子轴颈磨损拉伤的情况较为普遍,采用微弧冷焊技术可以实现对损伤部位的修复。针对25Cr2Ni4MoV材料转子,通过焊接工艺试验和试样性能检测,得到一种可靠的微弧冷焊工艺;并通过对焊缝无损检测标准和焊后尺寸恢复工艺的研究,形成了一套完善的轴颈损伤修复工艺方案。     

1Cr18Ni9Ti不锈钢氮离子注入层超显微硬度的研究

应用超显微硬度计测定１Ｃｒ１８Ｎｉ９Ｔｉ奥氏体不锈钢氮离子注入层的硬度，并用Ａｕｇｅｒ电子能谱仪（ＡＥＳ）及高精度轮廓仪测定氮离子注入层氮浓度分布及深度．结果表明：在９０ｋｅＶ，３ｘ１０~１７Ｎ＋／ｃｍ~２注入时．共注入层深度为０．１８μｍ、用１ｍＮ载荷侧得本征硬度ＨＶ为３．４７ＧＰａ，比非注入态表面硬度提高三倍之多，合理的试验载荷应≤ｌｍＮ（０．１ｇ）．     

Microstructural evidence for short-circuit oxygen diffusion paths in the oxidation of a dilute Ni-Cr alloy

A comparative study of high-temperature oxidation of Ni containing 1 at.% Cr and pure Ni was carried out. Instead of the conventional kinetics study using thermogravimetry, a microlithographic marker experiment was designed. Observation of the markers using cross-sectional TEM and SEM has revealed striking differences in the scale morphology, microstructures, and oxidation mechanisms between pure Ni and the Cr-doped Ni substrates. In particular, the results suggest that a small addition of Cr promotes significant inward transport of oxygen. Marker experiments revealed that NiO grown on pure Ni is wholly attributable to outward-cation diffusion. In contrast, NiO grown on Ni–1 at.% Cr exhibited formation of a substantial inner layer having a submicron grain size, established by the markers to have formed from oxygen ingress. For pure Ni, voids were observed to be distributed only within oxide grains. In contrast, for Ni containing 1 at.% Cr, elongated pores formed extensively along oxide-grain boundaries. Formation of new fine-grain oxide in these pores was observed to have sometimes completely resealed the void. It is, therefore, proposed that the transport of oxygen in the case of oxide scale grown on Ni–1 at.% Cr occurs via voids (pores) formed by vacancy coalescence at the grain boundaries.     

Corrosion-Electrochemical behavior of 13% chromium (Cr) martensitic stainless steel in hydrochloric acid (HCl) solutions

Corrosion-Electrochemical behavior of a commercial API5CT grade L80 type 13Cr tubing enriched with microalloying elements is studied in 6, 7.5, 9, 12 and 15% HCl solutions by electrochemical methods. The objective is to contribute to the comprehension of corrosion phenomena caused by HCl of similar concentrations, generally used in acidizing job. The corrosion morphology is examined by scanning electron microscopy (SEM) coupled with EDAX. The soluble corrosion products are analyzed by atomic absorption spectroscopy and colorimetric methods. General, as well as localized, corrosion is present. The severest general corrosion with a maximum rate of 26 mm/year is obtained at 15% HCl. The localized corrosion which morphologically differs as function of HCl concentrations is revealed by SEM investigation. In all the above HCl solutions, the commercial 13% Cr martensitic stainless steel tubing shows no passive state. Above 6% HCl, the microalloying elements promote forming a discontinuous film of the corrosion products. The corrosion rate slightly decreases in 15% HCl compared to the published data on a conventional 13% Cr martensitic stainless steel tubing. This is due to both the chemical composition (silicon, manganese and vanadium) and microstructural properties. Copper seems to additionally accelerate the corrosion of the alloy. Published in Russian in Zashchita Metallov, 2007, Vol. 43, No. 4, pp. 372–380. The article was translated by the authors in English.     

Thermal stability behaviors of Cr(N,O)/CrN double-layered coatings by TGA/DTA analysis

In this study, Cr(N,O)/CrN double-layered coatings were synthesized using the cathodic arc deposition (CAD) process. CrN film was first deposited onto a substrate as an interlayer to ensure better adhesion, and Cr(N,O) film was subsequently deposited on top of the CrN layer as the surface layer. Variation in the Cr(N,O) coating composition was achieved through changing the O₂/N₂ flow ratio during the last stage of processing. Phase structure, chemical composition, and morphology of the resulting coatings were analyzed and observed using the X-ray diffractometer, Auger electron spectrometer and SEM. In addition, oxidation behavior of the coatings was investigated using TGA/DTA methods. The tests were carried out by increasing temperature up to 1000 °C in ambient air. With the introduction of oxygen gas during the CAD process, a superficial layer was produced in the Cr(N,O) constituent containing CrN and Cr₂O₃ phases. The formation of the oxide phase attributed to the reaction of chromium and oxygen was more favorable than that of chromium and nitrogen. The results also showed that Cr(N,O)/CrN double-layered coatings exhibited superior oxidation resistance at elevated temperature than that of CrN single-layer coated specimen (870 °C vs. 750 °C).     

3Cr2W8V钢锻件表面裂纹的成因及预防措施

通过对难变形钢3Cr2W8V进行实验,证明了合理地选择锻造工艺参数,也是解决表面裂纹的重要途径之一。     

金属型铸造高铬白口铸铁磨球的复合变质处理研究

研究了复合变质处理对金属型铸造的高铬格白口铸铁磨球组织及性能的影响。结果表明，采用ＲＥ、Ｂ、Ｖ、Ｔｉ元素复合变质处理，可有效细化磨球结晶组织，改善碳化物的形态与分布，并显著提高冲击韧性和耐磨性能。     

利用"正火液"作为高铬铸铁磨球淬火介质的生产实践

高铬铸铁件在没有添加贵重元素的条件下,利用"正火液"配入适量的水作为淬火介质进行了试验和生产.实践证明,产品在热处理淬火时从未发生炸裂现象,同时完全达到了要求的力学性能指标.生产的锤头其使用寿命为高锰钢的6～8倍,为低铬白口铸铁的4～6倍.     

00Cr17Ni14Mo2不锈钢的性能及应用研究

研究了00Crl7Nil4M02不锈钢材料的机械性能、焊接性能和耐腐蚀性能，从用户和研究开发的角度探讨了其在压力容器、化工装置、化肥装置、海洋装置和建筑业等领域的应用。