Influence of Hydrogenation on the Character of Fracture of Nitinol Alloy in Tension

Materials Science - We establish the macro- and microfractographic features of the tensile fracture of cylindrical specimens made of nitinol (Ni–Ti alloy) at room temperature and at 0°C...     

Diagnostics of the Engineering State of Steam Pipelines of Thermal Power Plants by the Hardness and Crack Resistance of Steel

Materials Science - We propose a nondestructive method for the diagnostics of the current state of heat-resistant steels after long-term operation in the steam pipelines of thermal power plants...     

西班牙电信跨国经营的经验及启示

西班牙电信(Telefonica)是西班牙和葡萄牙语国家主要的电信运营商，并在资本运作方面是欧洲地区第二大电信运营商．同时它还是全世界具有最大海外市场的电信运营商。其跨国经营的经验包括：与世界上大型电信运营商结成战略联盟，以发展跨国经营业务；强化在关键业务和核心市场的竞争地位；以收购、合资等多种方式进入国际市场；实现融资渠道多样化；适时进行业务重组以适应不斯变化的市场；遵循审慎的财务管理原则等。     

双旋Y切石英振子“T”模分析及SC切双模同时振荡的研究

本文推导了石英晶体基本物理参数的双旋变换关系,并利用克里斯托费尔方程,对其厚度模式的a、b、c三个模作了分析。文中也论证了SC切中b、c模的正交性,并用一块SC切晶体同时激励了b、c模振荡,给出了双模振荡器的测试结果,它表明利用b模频率信息来对C模实行最佳温度补偿是可能的。     

The kinetics of the internal nitriding of Fe-2 at. pct Al alloy

The kinetics of the precipitation of aluminum nitride on internal nitriding the Fe-2 at. pct Al alloy was investigated for cold-rolled and recrystallized specimens exhibiting “ideally weak” interaction behavior of the solutes Al and N. The kinetic analysis was performed using mass-increase data obtained for thin foils (thickness ⪯0.1 mm) upon nitriding in a NH₃/H₂ gas mixture at temperatures in the range 803 to 853 K. Activation-energy analysis revealed that precipitation of AlN in the recrystallized specimens is associated with a Gibbs free energy barrier for the formation of a precipitate of critical size; the precipitation rate is controlled by both nucleation and growth. On the other hand, precipitation of AlN in the cold-rolled specimens occurs without a Gibbs free energy barrier for formation of a precipitate of critical size; the precipitation rate is controlled by growth with kinetics governed by volume diffusion of alu-minum. Analysis of the total Gibbs free energy of formation of AlN in the α-Fe matrix showed that in the case of the recrystallized specimens, the formation of incoherent AlN precipitates with a hexagonal crystal structure is favored. In the case of the cold-rolled specimens, containing a high dislocation density, the formation of coherent AlN precipitates with cubic crystal structure is favored, at least in the beginning of precipitation.     

Critical analysis of alloy 600 stress corrosion cracking mechanisms in primary water

In order to study the mechanisms involved in the stress-corrosion cracking (SCC) of Alloy 600 in primary water, the influence of the relevance of physicochemical and metallurgical parameters was assessed: hydrogen and oxygen overpressures, microstructure, and local chemical com-position. The obtained results show that, even if the dissolution/oxidation seems to be the first and necessary step responsible for crack initiation and if hydrogen effects can also be involved in cracking, neither a dissolution/oxidation model nor a hydrogen model appears sufficient to account for cracking. Moreover, fractographic examinations performed on specimens’ fracture surfaces lead to the fact that attention should be paid to a cleavagelike microcracking mechanism involving interactions between corrosion and plasticity at the vicinity of grain boundaries. A corrosion-enhanced plasticity model is proposed to describe the intergranular and transgranular cracking in Alloy 600.     

Mechanisms of inclusion formation in Al−Ti−Si−Mn deoxidized steel weld metals

The present investigation is concerned with basic studies of the mechanisms of inclusion formation in submerged arc (SA), gas metal arc (GMA), and flux cored arc (FCA) steel weld metals. Theoretical models of deoxidation have been developed to establish a basis for quantitative predictions of important inclusion characteristics, such as volume fraction, size, and chemical composition from knowledge of weld metal chemistry and operating parameters. The relevance of these models has been tested against extensive inclusion data obtained from scanning electron microscope (SEM) and scanning transmission electron microscope (STEM) examinations of a large number of experimental welds containing various contents of aluminum, titanium, silicon, manganese, and oxygen.     

High-temperature low-cycle fatigue of an iron-base oxide-dispersion strengthened alloy: Grain structure effects and lifetime correlations

The high-temperature low-cycle fatigue (LCF) behavior of the new oxide-dispersion strengthened (ODS) alloy PM 2000 is investigated at 1050 °C using symmetrical and asymmetrical wave shapes. The grain structures range from “single crystals” (grain size of several centimeters) to polycrystals with an average grain size of less than 30 μm. It is found that the grain structure determines the fracture path but cannot be correlated with cyclic lifetimes. Instead, lifetime can be predicted on the basis of the different Young’s moduli of the grain structures and correlates with the reciprocal of Young’s modulus. A normalization is proposed that condenses all lifetime data, which span two orders of magnitude, into a narrow scatterband.