Material science
Maedeh sadat Zoei; S. Javid Mirahmadi; Mojtaba Forghani; mohammad chiani; Saeed Asghari
Abstract
Thermal barrier coatings (TBCs), advanced ceramic systems, are usually applied to the surface of hot industrial parts to improve equipment performance at higher temperatures. During each thermal cycle, the layers of the TBC system expand and contract unevenly due to the mismatch in the coefficients of ...
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Thermal barrier coatings (TBCs), advanced ceramic systems, are usually applied to the surface of hot industrial parts to improve equipment performance at higher temperatures. During each thermal cycle, the layers of the TBC system expand and contract unevenly due to the mismatch in the coefficients of thermal expansion of the TBC layers. The resulting thermal stresses cause the nucleation and growth of microcracks in the TBC system. After a few hundred thermal cycles, the microcracks eventually combine and form a relatively large crack that causes spallation and separation of coating, exposing parts to high temperature and ultimately leading to catastrophic failure of the entire equipment. The creation of self-healing capability provides the ability to repair cracks spontaneously. In this article, various technologies for achieving self-healing in YSZ thermal barrier coatings and the structure and properties of the resulting coatings have been introduced and reviewed. After extracting the technologies of applying self-healing thermal barrier coating and comparing them with each other, it is possible to obtain coatings with self-healing properties according to the needs of each industry and then determined the proper composition of the self-healing coating, the proper thickness of the self-healing coating layer, the proper arrangement of the self-healing coating layer and the parameters of the coating process.
Structure
S. Javid Mirahmadi; Mohsen Hamedi; Maedeh sadat Zoei
Abstract
Ti-6Al-4V is one of the most common materials in the aerospace industry. For example, satellite fuel tanks are made of this alloy. Among manufacturing processes, forming processes is one of the most widely used areas in the manufacture of Ti-6Al-4V components. Due to the importance of determining the ...
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Ti-6Al-4V is one of the most common materials in the aerospace industry. For example, satellite fuel tanks are made of this alloy. Among manufacturing processes, forming processes is one of the most widely used areas in the manufacture of Ti-6Al-4V components. Due to the importance of determining the allowable deformation limit in the successful design of the Ti-6Al-4V forming process, in this paper, the amount of critical damage was studied. For this purpose, parts with double-cone geometry with grooves on the maximum diameter with two initial microstructure, lamellar and equiaxed, were fabricated and subjected to hot compression testing. The results showed that the initial equiaxed microstructure provides good accumulated damage tolerance. Up to 2.38, 2.67, and 5.89 accumulated damage values, according to Cockcroft-Latham, Brozo, and McClintock criteria, respectively, no crack was observed on the samples. However, with an initial lamellar microstructure, the damage tolerance was significantly reduced. The critical damage value based on Cockcroft-Latham, Brozzo and McClintock criteria was 1.05±0.02, 1.03±0.02, and 2.56±0.05, respectively.
Structure
Maedeh sadat Zoei; hadi gorabi; mohammadreza asharf khorasani; saeed asghari; S. Javid Mirahmadi
Abstract
Space systems in Low Earth Orbit (LEO) are exposed to the destructive parameter of atomic oxygen. In long-term missions, the rate of degradation of the material resulting from the reaction with atomic oxygen is significant and reduces the performance of the structure. Due to the harmful effects of atomic ...
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Space systems in Low Earth Orbit (LEO) are exposed to the destructive parameter of atomic oxygen. In long-term missions, the rate of degradation of the material resulting from the reaction with atomic oxygen is significant and reduces the performance of the structure. Due to the harmful effects of atomic oxygen on materials, the choice of atomic oxygen resistant materials or the use of durable surface coatings is very common. In this study, the corrosion resistance of atomic oxygen of an interconnector part of a solar cell was studied by applying a silicone base coating. In order to investigate the corrosion behavior of atomic oxygen, ground test method with equivalent conditions of LEO orbit was used by DC plasma equipment. Initially, the parameters of the atomic oxygen corrosion ground test were determined under the equivalent conditions of the LEO orbit. The results of atomic oxygen application in this study showed that the amount of atomic oxygen erosion yield of silicon coating is significantly lower than the amount of atomic oxygen erosion yield of silver substrate. Also, the study of the coating surface after applying atomic oxygen by SEM images led to the determination of the optimal coating thickness. EDX results showed that after applying atomic oxygen, no significant change in the chemical composition of the coating was achieved.
