scholarly journals Microstructure and Tensile Properties of Diffusion Bonded Austenitic Fe-Base Alloys—Before and After Exposure to High Temperature Supercritical-CO2

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 480 ◽  
Author(s):  
Sung Hwan Kim ◽  
Ji-Hwan Cha ◽  
Changheui Jang ◽  
Injin Sah
Keyword(s):  
High Temperature ◽  
Tensile Properties ◽  
Heat Exchangers ◽  
Boundary Migration ◽  
Bond Line ◽  
Grain Boundary Migration ◽  
Compact Type ◽  
Before And After ◽  
Temperature Exposure ◽  
Co2 Environment

Austenitic Fe-base alloys, SS 316H and Alloy 800HT, were diffusion bonded for use in compact-type heat exchangers in supercritical-carbon dioxide (S-CO2) Brayton cycles. For diffusion bonded 316H, grain boundary migration across the bond-line was observed despite the formation of some Cr-rich carbide, and its tensile properties were similar to those of as-received 316H. However, diffusion bonded Alloy 800HT exhibited severely degraded elongation compared to as-received 800HT due to the formation of continuous Ti-rich carbides along the bond-line. Post-bond heat treatment (PBHT) was found to improve elongation at fracture for diffusion bonded alloys. However, a subsequent corrosion test in S-CO2 at 600 °C (20 MPa) for 1000 h resulted in a loss of elongation. This was much more severe for PBHT-ed 800HT due to the formation of Cr-rich carbides at the bond-line. Meanwhile, it was found that the effect of ageing on loss of elongation during high temperature exposure was greater than that of S-CO2 environment.

scholarly journals Novel Multilayer SAW Temperature Sensor for Ultra-High Temperature Environments

Micromachines ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 643
Author(s):  
Xuhang Zhou ◽  
Qiulin Tan ◽  
Xiaorui Liang ◽  
Baimao Lin ◽  
Tao Guo ◽  
...  
Keyword(s):  
High Temperature ◽  
Temperature Sensor ◽  
X Ray Diffraction ◽  
Aero Engine ◽  
Before And After ◽  
Application Potential ◽  
Passive Sensors ◽  
Temperature Exposure ◽  
Engine Systems

Performing high-temperature measurements on the rotating parts of aero-engine systems requires wireless passive sensors. Surface acoustic wave (SAW) sensors can measure high temperatures wirelessly, making them ideal for extreme situations where wired sensors are not applicable. This study reports a new SAW temperature sensor based on a langasite (LGS) substrate that can perform measurements in environments with temperatures as high as 1300 °C. The Pt electrode and LGS substrate were protected by an AlN passivation layer deposited via a pulsed laser, thereby improving the crystallization quality of the Pt film, with the function and stability of the SAW device guaranteed at 1100 °C. The linear relationship between the resonant frequency and temperature is verified by various high-temperature radio-frequency (RF) tests. Changes in sample microstructure before and after high-temperature exposure are analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The analysis confirms that the proposed AlN/Pt/Cr thin-film electrode has great application potential in high-temperature SAW sensors.

Increased Thermal Stability of Co-silicide Using Co-Ta Alloy Films

2001 ◽  
Vol 670 ◽  
Author(s):  
Min-Joo Kim ◽  
Hyo-Jick Choi ◽  
Dae-Hong Ko ◽  
Ja-Hum Ku ◽  
Siyoung Choi ◽  
...  
Keyword(s):  
Thermal Stability ◽  
High Temperature ◽  
Grain Boundary ◽  
Reaction Rate ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Alloy Films ◽  
Post Annealing ◽  
Alloy Process ◽  
Thermal Stability Of

ABSTRACTThe silicidation reactions and thermal stability of Co silicide formed from Co-Ta/Si systems have been investigated. In case of Co-Ta alloy process, the formation of low resistive CoSi2phase is delayed to about 660°C, as compared to conventional Co/Si system. Moreover, the presence of Ta in Co-Ta alloy films reduces the silicidation reaction rate, resulting in the strong preferential orientation in CoSi2 films. Upon high temperature post annealing in the furnace, the sheet resistance of Co-silicide formed from Co/Si systems increases significantly, while that of Co-Ta/Si systems maintains low. This is due to the formation of TaSi2 at the grain boundaries and surface of Co-silicide films, which prevents the grain boundary migration thereby slowing the agglomeration. Therefore, from our research, increased thermal stability of Co-silicide films was successfully obtained from Co-Ta alloy process.

High-temperature high-resolution in-situ microscopy of grain boundary migration and structure change

1990 ◽  
Vol 48 (4) ◽  
pp. 514-515
Author(s):  
Hideki Ichinose ◽  
Tokuji Kizuka ◽  
Yoichi Ishida
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
Grain Boundary ◽  
High Stability ◽  
Boundary Migration ◽  
Structure Change ◽  
Objective Lens ◽  
Video Tape ◽  
Grain Boundary Migration

A high resolution high temperature specimen stage of 200kV HRTEM was newly designed and produced in order to investigate the physical and mechanical nature of materials at high temperature.The atomic process of silicon grain boundary migration and the structure change was successfully observed in-situ at 1000K by the new specimen stage.The high temperature specimen stage consists of a heating specimen holder, a high stability power supply and a high stability current controller. Heat is provided by an induction free double spiral coil heater which is made of tungsten. Excellent current stability, better than 10−6 , prevents the objective lens from the magnetic disturbance which is caused by heating current. The highest temperature of the specimen is designed to be 1100K. The accuracy of the temperature measurement is checked by the melting test of tin. In order to keep the high resolution of the microscope(JEM-200CX) at such high temperature as 1100K an objective lens is also newly designed and produced. Aberration constants of the new lens are respectively Cs=0.7mm and Cc=1.2mm. Resulted resolution at high temperature is as same level as the that of the original JEM-200CX at room temperature. Images are recorded by a video tape recorder.

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