铌合金表面渗镀复合涂层及其抗氧化研究

利用包埋渗结合化学镀技术在铌合金表面制备了复合涂层,研究了涂层在退火过程中的元素扩散行为及涂层的高温抗氧化性能。结果表明:复合涂层以晶态Ni和Al_3Nb相为主;退火过程中渗层中的Al元素向外扩散,涂层转变为晶态,形成了Ni Al_3、Al_3Nb、Ni Al相。对退火前后的涂层进行1000℃恒温氧化实验,20 h后沉积态涂层的增重为7.7 mg/cm~2,表面主要含Ni O、Al_2O_3、Ni Al相;退火态涂层样品的增重为4.9 mg/cm~2,表面生成了Al_2O_3、NiNb_2O_6、NiAl_2O_4等相。氧化后涂层与基体结合良好。退火态涂层表面由于富Al元素,氧化后形成较多的Al_2O_3,比沉积态的涂层能更有效地减缓氧化进程,提高铌合金的抗氧化性。     

一种新型钴基高温合金在900℃熔融NaCl中的热腐蚀行为

采用浸盐法研究一种新型钴基高温合金在900℃熔融NaCl中的热腐蚀行为。结果表明:腐蚀初期合金发生选择性氧化,在表面生成Al_2O_3,Cr_2O_3和少量的TiO_2。随着腐蚀时间的延长,熔融NaCl开始侵蚀表面保护性Cr_2O_3和Al_2O_3,使腐蚀性介质与基体逐渐接触,加速合金腐蚀。随着腐蚀的进行,合金内腐蚀层生成棒状Al_2O_3。由于基体中Al的消耗,棒状Al_2O_3周围易生成Co3W。Co3W与棒状Al_2O_3的相界面形成氧扩散的快速通道,导致80h后合金热腐蚀加剧。     

水蒸气温度对700℃先进超超临界锅炉候选合金GH2984氧化行为的影响

采用X射线衍射仪、扫描电子显微镜对比研究GH2984合金在750℃和850℃纯水蒸气中的氧化行为。结果表明:GH2984合金的氧化动力学遵循抛物线规律;温度升高,Cr挥发加速,外氧化和内氧化的速率急剧增加,氧化膜的组成结构发生明显的变化。750℃时,合金表面形成单层致密的(Cr,Mn)_2O_3膜;温度升至850℃,氧化膜中空洞的数量大幅增加,氧化膜转变为由薄的外层Fe_2TiO_5和厚的次外层(Cr,Mn)_2O_3及薄的内层(Nb,Mo)_2O_5组成的三层结构。Ti,Al优先于晶界处发生内氧化,分别形成TiO_2和Al_2O_3;两种内氧化产物的尺寸和数量均随温度升高而增加。     

Ti_2AlNb合金表面渗镀Al层的抗热腐蚀性能

目前,鲜见对Ti_2AlNb合金表面渗镀Al层在高温熔盐环境中耐腐蚀性能的报道。采用加弧辉光等离子渗镀技术在Ti_2AlNb合金表面渗镀Al层。采用扫描电镜、X射线衍射仪分析了渗镀Al层的形貌、结构及相组成;采用涂盐热腐蚀试验研究了渗镀Al层在750℃的Na_2SO_4熔盐中的热腐蚀行为。结果表明:渗镀Al层由外层纯Al沉积层和内层Al-Ti-Nb扩散层组成,其组织均匀致密,与基体结合良好;在750℃的Na_2SO_4熔盐中,Ti_2AlNb合金基体腐蚀增重显著,腐蚀产物出现明显的层状剥落现象,耐热腐蚀性较差,而渗镀Al层试样仅发生微小的增重,腐蚀100 h后,内部扩散层还比较完整,未出现氧化和硫化的现象,仍拥有足够的Al源来抵抗接下来的腐蚀进程。     

一种新型Ni-Fe-Cr基合金在模拟锅炉烟气中的腐蚀行为研究

应用X射线衍射仪、扫描电子显微镜、能谱仪等分析方法研究一种新型Ni-Fe-Cr基高温合金在700℃/750℃煤灰/烟气中的腐蚀行为。结果表明:750℃的腐蚀速率明显高于700℃,其腐蚀层的厚度由700℃的3μm增加到20μm。腐蚀1 000h后,SEM观察到Ni-Fe-Cr高温合金在700℃下表面有少量"瘤状"凸起产物,XRD结合EDS表明其腐蚀产物由表向里依次是结构疏松的NiO、Fe_2O_3和Fe3O4,内层为相对致密的Cr_2O_3、Al_2O_3和TiO2,基体和腐蚀层界面靠近基体一侧是多孔的硫化物。提高腐蚀温度到750℃表面出现更多凸起,并且出现了破裂。Cr_2O_3保护性氧化膜局部开裂或者剥落而形成"瘤状"凸起产物。氧化膜生长过程中的内应力以及温度降低产生的热应力共同作用,导致氧化膜开裂甚至与基体剥离。温度升高同样加剧熔融盐破坏氧化膜从而加快腐蚀进程。     

Ni-Cr-Co-Mo-W-Ta-Al合金在900℃和1000℃的高温氧化行为

采用X射线衍射(XRD),扫描电镜(SEM)及能谱(EDAX)等方法,研究了Ni-4.66Cr-5.87Co-7.54Mo-2.90W-4.97Ta-6.32Al合金在900℃和1000℃的高温氧化行为。结果表明,合金氧化动力学曲线遵循氧化初期氧化增重速率较快,氧化期间氧化动力学曲线呈波浪式变化,且呈现氧化温度越高波浪式越明显的特征;氧化300h后合金表面氧化物膜分为2层,外层氧化物为NiO、Ni_2Cr_2O_4、Ni_2CoO_4和CoTa_2O_6,分布在外层的CoTa_2O_6抑制基体中元素Al向外扩散,形成内层氧化物Al_2O_3。在氧化期间,合金内部生成了内氮化物AlN,且在合金内部AlN与Al_2O_3成规律性分布,与外氧化膜相邻的为元素Al的内氧化物Al_2O_3区域,远离外氧化膜的基体内部为元素Al的内氮化物AlN区域,随氧化温度升高,内氧化区和内氮化区的深度增加,内氧化物和内氮化物的尺寸增大。     

Nb掺杂对Ti-Al合金化层抗高温氧化性能的影响

为提高钛合金TC4的抗高温氧化性能,采用激光表面合金化技术在钛合金表面制备不同Nb掺杂量的Ti-Al合金化层。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)、箱式电阻炉等对合金化层的组织结构和高温氧化行为进行分析测试。结果表明,合金化层主要组成物相为TiAl以及少量的Ti_3Al相。Nb主要以置换溶质原子的形式固溶于合金化层中。合金化层组织均匀,与基体呈典型的冶金结合,在不含Nb的Ti-Al合金化层中发现大量的表层裂纹及少量的贯穿性裂纹,而在Nb掺杂的合金化层中未发现明显的宏观裂纹。合金化层在800℃保温1000h的氧化增重显著低于基体,表现出优异的抗高温氧化性能。相比而言,随着Al含量和Nb掺杂量的提高,合金化层的抗高温氧化能力也随之提高。Nb掺杂提高Ti-Al合金化层抗高温氧化性能的作用机理包括减少TiO_2中的空位缺陷、细化氧化物颗粒及促进Al_2O_3的形成。     

强流脉冲电子束作用下Ti2AlNb微观结构状态与耐腐蚀性能研究北大核心CSCD

利用强流脉冲电子束(HCPEB)对Ti2AlNb合金进行辐照处理,利用X射线衍射仪(XRD),场发射扫描电子显微镜(SEM),透射电子显微镜(TEM)对辐照后合金的显微组织结构进行分析,结果表明,辐照后表面形成大量火山状熔坑,随着辐照次数的增加,熔坑的密度显著减少,辐照后合金发生α+β→O相变,β和O相显著细化;辐照后表层形成了一层厚度约为4μm的重熔层,重熔层中Al发生过饱和固溶而富Al;辐照在亚表层产生高幅值的应力和温度梯度,造成亚表层发生强烈塑性变形,生成高密度的位错,孪晶和层错等缺陷结构。辐照后试样的耐腐蚀性能得到了提高,这主要归因于辐照后产生的表面净化效应和成分均匀化,表面富Al生成致密的Al_(2)O_(3)保护膜以及Al的增强扩散修复腐蚀过程中损耗的Al_(2)O_(3)膜,提高了Ti2AlNb合金的耐腐蚀性能。     

溅射Ni11Co26Cr6Al0.5Y涂层对镍基合金在1000 ℃氧化行为的影响

通过对有/无Ni11Co26Cr6Al0.5Y涂层镍基合金在1000℃进行氧化动力学曲线测定,及组织结构观察,研究了Ni11Co26Cr6Al0.5Y涂层对镍基合金高温氧化行为的影响。结果表明:高温氧化期间,合金发生外氧化和内氧化,外氧化层由NiO、NiCrO_4、CoWO_4构成,中间氧化物由TiO_2、Al_2O_3、NiWO_4构成,中间层氧化物层抑制了基体中Al元素向外扩散,形成平直连续的Al_2O_3内氧化物层;合金氧化动力学曲线呈现起伏波动的特征。镍基合金经溅射Ni11Co26Cr6Al0.5Y涂层,可有效改善合金的抗氧化性能;涂层的氧化动力学曲线仅在氧化初期有轻微增重而后趋于平稳,遵循抛物线规律,其形成的Al_2O_3氧化膜未发生明显剥落,仅在涂层内及近涂层/基体界面区域存在少量Al_2O_3内氧化物。     

溅射CoCrAlY涂层对Ni3Al金属间化合物热腐蚀抗力的影响

采用电化学方法并结合物相分析技术研究了溅射CoCrAlY涂层对Ni_3Al金属间化合物热腐蚀抗力的影响。结果表明,Ni_3Al金属间化合物的耐蚀性能极差,合金表面没有形成Al_2O_3保护膜。CoCrAlY涂层表面形成了富铝氧化膜,明显改善了Ni_3Al金属间化合物的耐蚀性能。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...