连铸大方坯夹渣缺陷的改进措施

对用户处夹渣缺陷异议进行分类,连铸坯夹渣分布进行调查,发现夹渣主要发生在开浇头坯。通过对浸入式水口结构型式由单孔型改为双孔型的改进,以及对切头控制长度的计算,认为现行工况条件下切头长度按1 m控制较为合适。从改进前后头坯低倍夹渣数量看,发生比例由改进前17%下降至0;同时从用户质量异议反馈看,夹渣类缺陷也得到显著下降。     

邯钢CSP连铸机浸入式水口的优化及改进

针对CSP连铸机浸入式水口穿孔及侵蚀较快等现象,邯钢连铸连轧厂从水口材质、制造工艺、分离环形状等多方面进行改进;同时为了进一步提高连铸机拉速,在数学模拟的基础上,优化了浸入式水口的形状,使结晶器内流场更趋合理,大大提高了浸入式水口的使用寿命,促进了CSP连铸机拉速及铸坯质量的提高。     

含钛超低碳钢连铸浸入式水口结瘤机理的研究

通过对含钛超低碳钢连铸浸入式水口结瘤物的物相及钢中夹杂物的类型进行分析,研究了浸入式水口的结瘤机理,并提出了改进措施。结果表明,浸入式水口的主要结瘤物为Al2O3和Fe Al2O4夹杂;钢中夹杂物主要为Al2O3-Ca S类、纯Al2O3类以及复杂的Al2O3-Mg O-Ca S-Mn S夹杂物,与水口结瘤物的物相一致。为了改进水口结瘤,其根本方法是降低钢液中Al2O3夹杂的含量。     

防止浸入式水口结瘤和堵塞的新技术

从水口堵塞物的来源、微观结构、分布状况以及堵塞物的形成等方面,分析了浸入式水口结瘤和堵塞的机理,介绍了国内外防止浸入式水口结瘤和堵塞的新技术,并针对水口堵塞问题,提出了具体解决措施.     

中薄板坯连铸机板间漏钢的原因分析及控制措施

对中薄板坯连铸机板间漏钢的原因进行了分析.结果 表明,造成板间漏钢的主要原因是水口面氧化.通过优化水口面材质、提高水口面精度、改进水口烘烤工艺,确保上下水口对中、氩气压力在0.01 MPa以上,提高快换机构液压缸速度、保证快换机构的精度和冷却效果,规范快换浸入式水口操作等措施,可以使中薄板坯连铸机无板间漏钢.     

浸入式水口壁厚影响坯壳粘结的原因分析

对济钢中薄板坯连铸机增加浸入式水口壁厚频繁造成粘结的原因行了分析,主要原因是由于流场的不同分布,在水口周围形成死区,影响了传热,并通过数模进行了验证,提出了改进方案。     

矩形坯结晶器凝固坯壳分析与流场的优化

针对某公司350 mm×150 mm断面连铸铸坯生产中易发生卷渣等一系列的质量问题,采用物理模拟和fluent凝固融化模型的方法 ,对结晶器钢液的表面流速、波高、凝固坯壳厚度等进行系统研究。结果表明:当倾角为15°、20°、25°时,倾角每增加5°,表面流速平均下降20%左右;浸入式水口的出口和中孔面积比由2.37变化到2.63,结晶器出口的坯壳平均厚度由18 mm减少为15 mm;出口面积比为2.63时坯壳有明显的变薄区域,最小的坯壳厚度区坯壳厚度为11 mm左右。通过一系列分析最终指出断面为350 mm×150 mm的结晶器,应当使用倾角为25°,出口与中孔面积比为2.42的水口进行生产。     

42CrMoA曲轴钢中CaO-SiO2-Al2O3系夹杂物的塑性化控制

为了减少42CrMoA曲轴钢精炼过程中CaO-SiO2-Al2O3系夹杂物对其基体损伤的影响,利用Factsage软件计算了42CrMoA曲轴钢中CaO-SiO2-Al2O3系低熔点夹杂物的成分,并根据钢液-夹杂物,钢液-精炼渣之间的平衡,计算分析了CaO-SiO2-Al2O3系夹杂物控制在塑性区域内所需的钢液成分及对精炼渣的要求.结果表明:CaO-SiO2-Al2O3系夹杂物存在两个变形良好的控制区域.区域1对应的精炼渣成分由于碱度过低在生产中受到极大限制,区域2要求的精炼渣成分往往会发生偏离.建议向精炼渣中配加适量的CaF2和MgO,以将CaO-SiO2-Al2O3三元系夹杂物转变为四元或多元系夹杂物.     

电磁旋流水口对圆坯结晶器液面波动的控制

在大圆连铸坯生产过程中,过强的结晶器电磁搅拌会造成结晶器液面波动,影响连铸坯的表面和内部质量。将电磁旋流水口技术与结晶器电磁搅拌配合使用,通过调整电磁旋流装置的搅拌方向和电流强度来弱化结晶器电磁搅拌引起的二次流,从而使结晶器液面波动控制在一个较小的范围内。结果显示,当两个电磁装置的搅拌方向相反,电流强度为400 A时,大于±2 mm的液面波动比例由单用结晶器电磁搅拌时的0.62%降至0.13%,在±1 mm～±2 mm范围内的液面波动比例由单用结晶器电磁搅拌时的5.90%降至3.56%。当搅拌方向相同时,对大于±2 mm的液面波动的控制效果不佳。因此,使用与结晶器电磁搅拌方向相反的水口旋流可实现对结晶器液面波动的有效控制。     

42CrMoA曲轴钢中SiO2-Al2O3-MnO系夹杂物的塑性化控制

为预测42CrMoA曲轴钢中SiO2-Al2O3-MnO系夹杂物具有良好塑性变形能力的成分控制范围,利用热力学计算软件Factsage对1873 K下42CrMoA曲轴钢钢液与SiO2-Al2O3-MnO系夹杂物间的平衡进行计算.结果表明:为得到塑性变形良好的SiO2-Al2O3-MnO系夹杂物,应控制SiO2-Al2O3-MnO三元系夹杂物中15wt％～60wt％SiO2,17wt％～75wt％MnO,Al2O3＜30％,ω(MnO)/ω(SiO2)值为0.28～5.与之平衡时钢液中酸溶铝[Al]s含量应小于2.50×10-4,溶解氧含量小于3×10-5.     

Formation of zirconium diboride (ZrB2) by room temperature mechanochemical reaction between ZrO2, B2O3 and Mg

A mixture of magnesium, boric oxide and zirconium dioxide were mechanically milled under argon for up to 15 h in a laboratory scale ball mill. X-ray diffraction showed that there was an increasing conversion of ZrO₂ to ZrB₂ with milling time with >98% reaction after 15 h. Differential thermal analysis revealed there were multiple, overlapping reactions all of which seemed to be formation of ZrB₂. The energy evolved decreased with milling time and the sample after 15 h milling showed no thermal reaction. After milling, separation of the ZrB₂ from the coproduct MgO was easily achieved by a mild acid leaching leaving essentially pure ZrB₂ with a crystallite size of 75 nm.     

Toughened ZrO2 ceramics sintered with a La2O3-rich glass as additive

In this study, the influence of the glass addition and sintering parameters on the densification and mechanical properties of tetragonal zirconia polycrystals (3Y-TZP) ceramics were evaluated. High-purity tetragonal ZrO₂ powder and La₂O₃-rich glass were used as starting powders. Two compositions based on ZrO₂ and containing 5 wt.% and 10 wt.% of La₂O₃-rich glass were studied in this work. The starting powders were mixed/milled by planetary milling, dried at 90 °C for 24 h, sieved through a 60 mesh screen and uniaxially cold pressed under 80 MPa. The samples were sintered in air at 1200 °C, 1300 °C, 1400 °C for 60 min and at 1450 °C for 120 min, with heating and cooling rates of 10 °C/min. Sintered samples were characterized by relative density, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Hardness and fracture toughness were obtained by Vickers indentation method. Dense sintered samples were obtained for all conditions. Furthermore, only tetragonal-ZrO₂ was identified as crystalline phase in sintered samples, independently of the conditions studied. Samples sintered at 1300 °C for 60 min presented the optimal mechanical properties with hardness and fracture toughness values near to 12 GPa and 8.5 MPa m^1/2, respectively.     

Properties of ZrO2–Al2O3 composite as a function of isothermal holding time

Zirconia and alumina based ceramics present interesting properties for their application as implants, such as biocompatibility, good fracture resistance, as well as high fracture toughness and hardness. In this work the influence of sintering time on the properties of a ZrO₂–Al₂O₃ composite material, containing 20 wt% of Al₂O₃, has been investigated. The ceramic composites were obtained by sintering, in air, at 1600 °C for sintering times between 0 and 1440 min. Sintered samples were characterized by microstructure and crystalline phases, as well as by mechanical properties. The grain growth exponents, n, for the ZrO₂ and Al₂O₃ were 2.8 and 4.1, respectively, indicating that different mechanisms are responsible for grain growth of each phase. After sintering at 1600 °C, the material exhibited a dependency of hardness as function of sintering time, with hardness values between 1500 HV (120 min) and 1310 HV (1440 min) and a fracture toughness of 8 MPa m^1/2, which makes it suitable for bioapplications, such as dental implants.     

激光悬浮区熔定向凝固Al2O3/YAG/ZrO2三元过共晶合金的微观组织

利用自行研制的激光悬浮区熔设备制备了Al₂O₃/YAG/ZrO₂三元过共晶自生复合材料.在过共晶成分下获得了不含初生相的全共晶层片状组织.详细分析了固/液界面形貌形成原因,并由界面形貌出发阐述了Al₂O₃/YAG/ZrO₂三元过共晶组织织构化趋势.结果表明,低凝固速率下,三元过共晶成分下层片间距大于三元共晶成分下层片间距,而在高凝固速率下则相反,这主要是由于ZrO₂的加入影响了体系的传热及传质条件,通过经典非规则共晶模型综合分析了传输条件对层片间距的影响.过共晶平均层片间距(λ_av)与凝固速率（V）满足λ_avV^0.5=14.7μm^1.5·s^-0.5,符合JH模型.对于激光加工中经常出现的带状组织形成机理也进行了讨论.     

Thermoelectric properties of Fe0.98Co0.02Si2 with ZrO2 and rare-earth oxide dispersion by mechanical alloying

The n-type Co-doped β-FeSi₂ (Fe_0.98Co_0.02Si₂) with dispersion of several oxides, such as ZrO₂ or several rare-earth oxides (Y₂O₃, Nd₂O₃, Sm₂O₃ and Gd₂O₃), was synthesized by mechanical alloying and subsequent hot pressing. The effects of these oxide dispersions on the thermoelectric properties of Fe_0.98Co_0.02Si₂ were investigated. ZrO₂ was decomposed in the β phase, and the ZrSi and -FeSi phases, which are metallic phases, were formed in the samples with ZrO₂ addition. The Seebeck coefficient and the electrical resistivity were significantly decreased with increasing amount of ZrO₂, indicating that a part of the Zr atoms was substituted for Fe atoms in the β phase. In the case of the samples with rare-earth oxide addition, a decomposition of a large amount of these added oxides did not occur. However, the rare-earth oxide addition caused a slight increase in the amount of the phase. The Seebeck coefficient was significantly enhanced by the rare-earth oxide addition especially in the low temperature range. These facts indicated that a small amount of rare-earth oxides was decomposed in the β phase, and rare-earth elements were substituted for Fe atoms as a p-type dopant, resulting in the decrease in the carrier concentration. The rare-earth oxide addition was also effective in reducing the thermal conductivity.     

纳米ZrO2激光重熔涂层组织与性能分析

采用金相试验、扫描电镜试验、热震试验和显微硬度试验对不同激光重熔工艺下的Y2O3部分稳定ZrO2纳米陶瓷涂层组织与性能进行研究.重点分析了涂层重熔宽度与深度、表面形貌、显微硬度和热震性能随激光比能量的变化规律.结果表明,ZrO2纳米陶瓷涂层的重熔深度和宽度随着激光比能量的增大而增加;涂层的表面成形与激光比能量密切相关;涂层的显微硬度随激光比能量的增大而升高;激光比能量对涂层热震性能的影响十分明显,当激光比能量为37.2 J/mm2时重熔涂层的热震性能最好.     

ZrO_2陶瓷与Kovar合金钎焊接头的组织与性能

在钎焊温度825~960℃,保温时间1~60 min的条件下,采用自行设计制备的Ag-Cu-TiH2活性粉末钎料实现了ZrO2陶瓷和4J33 Kovar合金的钎焊.利用扫描电镜、能谱分析及X射线衍射分析的方法对接头的界面组织进行了分析.结果表明,接头典型界面结构为Kovar/Ag（s.s）＋Cu（s.s）＋TiFe2/...     

Effects of particle size of 8 mol% Y2O3 stabilized ZrO2 (YSZ) and additive Ta2O5 on the phase composition and the microstructure of sintered YSZ electrolyte

The chemical stability and sinterability of nano- and micro-sized yttria stabilized zirconia (YSZ) powders were investigated, and the effect of Ta₂O₅ additive on the sinterability of YSZ electrolyte was also studied. Addition of Ta₂O₅ easily causes phase transformation of YSZ from cubic to monoclinic, and thus unfavorable for the improvement of ionic conductivity of YSZ electrolyte. Nano-sized YSZ easily causes abnormal grain growth and hence readily results in inhomogeneous microstructure of YSZ matrix, while micro-sized YSZ displays relatively low sinterability. Comparatively, mixture with 50 wt.% nano-sized and 50 wt.% micro-sized YSZ powders exhibits high sinterability and could be sintered to homogeneous microstructure, which can be used as starting materials to prepare dense YSZ electrolyte at low temperatures.     

Stress analysis of high temperature ZrO2 insulation coatings on Ag using finite element method

The aim of this study is to investigate residual stresses occurred during cooling procedure of ZrO₂ insulation coating on Ag substrate for magnet technologies. ZrO₂ coatings were produced on Ag tape substrate by using a reel-to-reel sol–gel technique. SEM inspection showed that ZrO₂ coatings had mosaic structures. ANSYS finite element software was used to calculate the temperature and stress distribution of the ZrO₂/Ag structure. The effect of coating thickness on residual stresses was also examined. The results obtained showed that thermal stresses in ZrO₂ coating and Ag substrate were considerably affected by the cooling time and coating thickness. It is concluded the thermal stresses increase with increase of film thickness.     

Corrosion Electrochemical Behavior of the NiCoCrA1Y/ZrO2 Coating in Natural Seawater

NiCoCrAlY/ZrO2 coatings were obtained by cold spraying.Nitrogen gas was used as processing gas(750℃,3.8 MPa).The corrosion electrochemical behavior of the coating on 907A steel in seawater was studied using open circuit potential monitoring,potentio-dynamic polarization and electrochemical impedance spectroscopy.Results showed that the as-deposited NiCoCrAlY/ZrO2 coatings,which were formed through significantly plastic deformed particles during impact,presented a dense microstructure and a high hardness.Results indicated that the formation of the stable and consecutive oxidation film,which has an outstanding anti-corrosion performance,was contributed to the compact structure of cold spray coatings.The pervasion of seawater was held back resulting from the cooperation of the oxidation film and the scale-like structure.