Study of thermal ageing effects on Rh coating's mechanical performance upon CuCrZr substrate through modeling and experimental methods

Rhodium (Rh) coating on CuCrZr substrate is a promising material option for optical, structural and electrical applications on nuclear fusion reactors. For these applications, Rh coated CuCrZr components subject to long time of thermal ageing due to pre-treatment or normal operation condition. In this paper, both finite element method (FEM) and experimental method were applied to investigate the effects of thermal ageing on mechanical performance of Rh coating after 250 °C, 500 h baking in vacuum. Based on FEM analysis, thermal stresses which concentrate at Rh coating interface is the main source of cracking, and such stresses can be minimized efficiently by introducing a 0.5 μm Au interlayer into the coating layer structure. According to thermal ageing experiments, through-thickness cracking in the Rh coating due to thermal stress releasing and voids generated at the Rh bonding interface caused by Kirkendall effect were the main micro-structure changes in the coating system. The solid-solution hardening caused by significant Cu diffusion into Rh is the dominant factor that affected the Rh coating's hardness. The existing of large amount of cracks in the Rh coating and voids at the Rh coating interface deteriorated the adhesion performance of Rh on CuCrZr substrate by 30%

Multi-physics modeling and Au-Ni/Rh coating assessment for ITER ion cyclotron resonance heating radio-frequency sliding contacts

ITER is a large scale fusion experimental device under construction in Cadarache (France) intended to prove the viability of fusion as an energy source. Ion Cyclotron Resonance Heating (ICRH) system is one of the three heating systems which will supply total heating power of 20 MW (40-55 MHz) up to one hour of operation. Radio-Frequency (RF) contacts are integrated within the antennas for assembly and operation considerations, which will face extremely harsh service conditions, including neutron irradiation, heavy electrical loads (RF current reaches up to 2 kA with a linear current density of 4.8 kA/m) and high thermal loads. Based on the thermal analysis, the contact resistance is expected to be lower than 7 mΩ to keep the maximum temperature on the louvers lower than 250°C. Few weeks of vacuum (~10 -5 Pa) baking at 250°C for outgassing is expected before each plasma experimental campaign, under which the RF contact materials' mechanical properties change and diffusion phenomena between different materials are inevitable. CuCrZr and 316L are proper base materials for ITER RF contact louvers and conductors respectively. In order to improve the RF contact's wear and corrosion resistivity as well as to reduce the contact resistance, Au-Ni and Rh functional layers could be electroplated on CuCrZr and 316L accordingly. The application of the Au-Ni/Rh coating pairs is assessed through the thermal ageing and diffusion tests. Wear and electrical contact performances of the Au-Ni/Rh pairs are deeply studied on a dedicated tribometer operated at ITER relevant conditions

Radiofrequency and mechanical tests of silver coated CuCrZr contacts for the ITER ion cyclotron antenna

The ITER Ion Cyclotron Resonance Heating (ICRH) system is designed to couple to the plasma 20 MW of RF power from two antennas in the 40–55 MHz frequency range during long pulses of up to 3600 s and under various plasma conditions with Edge Localized Modes. Radio-Frequency (RF) contacts are integrated within the ITER ICRH launcher in order to ensure the RF current continuity and ease the mechanical assembly by allowing the free thermal expansion of the Removable Vacuum Transmission Line coaxial conductors during RF operations or during 250 °C baking phases. A material study has been carried out to determine which materials and associated coatings are relevant for RF contacts application in ITER. In parallel, RF tests have been performed with a new prototype of Multi-Contact® LA-CUT/0,25/0 contacts made of silver-coated CuCrZr louvers. During these tests on a RF vacuum resonator, currents between 1.2 kA and 1.3 kA peak have been reached a few tens of times in steady-state conditions without any visible damage on the louvers. A final 62 MHz pulse ending in a 300 s flat top at 1.9 kA resulted in severe damage to the contact. In addition, a test bed which performs sliding test cycles has been built in order to reproduce the wear of the contact prototype after 30 000 sliding cycles on a 3 mm stroke at 175 °C under vacuum. The silver coating of the louvers is removed after approximately a hundred cycles whilst, to the contrary, damage to the CuCrZr louvers is relatively low

Evaluating the Performance of Aluminum Sacrificial Anodes with Different Concentration of Gallium in Artificial Sea Water

In this manuscript, the influence of gallium content additions of Al-Zn-In-Mg alloy was investigated through electrochemical techniques and microstructure observation in 3.5 wt% NaCl solution. The results indicated that Al-Zn-In-Mg-0.03Ga alloy has the best discharge performance among all alloys. We propose that this is due to the fact that gallium addition to the Al-4Zn-In-Mg alloy improves the discharge activity of the alloy as well as elevating its anodic efficiency. In particular, the effect of gallium addition to improve discharge activity tends to be a parabolic curve, in which there is an increase when the gallium is first added that rises to the maximum anode current efficiency of about 98.25% whenever gallium content is 0.03 wt%

Psychological Research of College Students Based on Online Education under COVID-19

As a socially sensitive group, college students have a higher risk of mental health problems. However, because of the COVID-19 pandemic, many nonlocal college students were isolated locally and were not able to attend classes as usual. This series of protective measures to avoid the spread of the disease may bring an additional mental impact on college students’ lives. As an important aspect of the sustainable development goals of quality education, education plays a central role in shaping personal and social change towards sustainability. The COVID-19 environment poses a great challenge to the education of university students. The purpose of this study is to propose a strategy to use an intelligent online learning system based on content recommendation and electronic questionnaires in the field of education. We invited 3000 isolated college students (47.6% male and 52.4% female) to participate in an internet trial. It proved to be effective in helping us intervene quickly, objectively, effectively, and in real-time in students’ psychological problems. In addition, according to the data analysis collected by the intelligent online learning system, we found that the degree of isolation regarding college students’ psychological problems was closely related to their grade, family background, professional category, and computer proficiency. This study shows that, during the period of isolation, the mental health of college students should be well monitored. Targeted psychosocial guidance is more needed for students with higher grades, those with low-income families, liberal arts majors, and those with weak computer skills in order to reduce the emotional impact of isolation on students

A Visual Measurement of Decision Consensus -An Idea Derived from GAE

It is widely known that the knowledge era has arrived that is changing our work and life styles. New network technology provides us valuable ways to solve the difficult and ambiguous problems. Design In GSS pattern, GAE integrates the frameworks of HWMSE and knowledge creating model to facilitate idea generation process, and it is regarded as a convergent process-idea generation which is the first step of MSA (meta-synthesis system approach) to complex problem solving. To enlarge the use of GAE, the evaluation values of experts’ keywords are added to illustrate both arguments and evaluation values on three-dimension snapshots, and based on the three-dimension snapshot, a two-dimension focuses snapshot is proposed to facilitate the decision process by focusing the discussing on the differences of the opinions, which may enhance the efficiency and effectiveness of decision. A measurement of decision consensus derived from GAE is also provided. At last, system realization will be expected later.The original publication is available at JAIST Press http://www.jaist.ac.jp/library/jaist-press/index.htmlIFSR 2005 : Proceedings of the First World Congress of the International Federation for Systems Research : The New Roles of Systems Sciences For a Knowledge-based Society : Nov. 14-17, 2112, Kobe, JapanSymposium 4, Session 5 : Meta-synthesis and Complex Systems Knowledge Creation and Transfe

The distinctive effects of dual-level leadership behaviors on employees' trust in leadership: An empirical study from China

The loss of trust within and between organizations has become serious worldwide, especially in China. In this study, we seek to explain why as well as how leaders at two different levels (i.e., the top management and the supervisory levels) affect employees' trust in leadership at the two levels distinctively, especially in the context of China as an emerging economy. Adopting the perspective of multi-level social exchanges within organizations, we develop a dual-level model with perceived organizational support and leader-member exchange as two major mediating mechanisms for the distinctive effects of transformational leadership behaviors on employees' trust in leadership at both top management and supervisory levels, respectively. The empirical evidence based on a sample of 357 Chinese employees and their supervisors supports the proposed model. Both theoretical and practical implications of our findings are discussed

The Contextual Antecedents of Organizational Trust: A Multidimensional Cross-level Analysis

In this article we seek to explore the contextual antecedents of organizational trust. In light of the complex links between organizational contexts and organizational behaviours, we focus on the effects of the three most critical contextual antecedents, i.e., leadership role, structural rule, and cultural norm at the organizational level, on organizational trust directly, and their behavioural outcomes at the individual level indirectly, using organizational trust as a cross-level mediator. The empirical results, based on a hierarchical linear model with a sample of 444 employees from 82 firms in China, lent support for our multidimensional cross-level model of contexttrustbehaviour link. We extend the research on organizational trust by treating it as a cross-level phenomenon and by specifying its core contextual antecedents and behavioural consequences