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Enhancement of metal creep lifetime by graphene coating
Fahim Ahmed Ibupoto,임장균,이동목,백승현,김문기 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5
An advancement can be seen in ultra-thin coatings used for the enhancement of material durability and lifespan. Among candidate materials, copper is used in various applications, such as micro sensors, nuclear fuel waste deposition canisters, and International Thermonuclear Experimental Reactor first walls. However, it is easily susceptible to metal creep, due to its exposure to harsh environments. In this study, graphene, a promising ultra-thin material, is tested as a single-layer coating substance used to enhance the creep property of copper. For measuring creep life, the small punch creep test methodology is adopted. Results show that, remarkably, the creep lifetime of copper increases by up to 19 % with the use of the graphene coating. In testing, the heat-treated copper specimen without graphene was fractured at 45 hours, while the graphene-coated copper specimen was fractured at 55.4 hours. The finite element method also supports the experimental results obtained.
Inconel 617 alloy creep life augmentation by graphene transfer coating
Fahim Ahmed Ibupoto,임장균,김성균,김범준,백승현,김문기 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.12
Presently, countries are trying to increase their energy efficiency. Therefore, the operating temperatures of very high temperature reactor (VHTR) and high temperature gas-cooled reactor (HTGR) are increasing in order to increase overall efficiency. A metallic material’s intrinsic creep property is a limitation in this scenario. Inconel 617 alloy is a candidate material used in the intermediate heat exchangers of the VHTR and HTGR. Therefore, in this work, graphene, which is a promising ultra-thin material, is utilized as an efficient coating to augment the creep property of the Inconel 617 alloy substrate. The Inconel 617 alloy substrate is coated with graphene via a transfer methodology. The small punch creep test methodology is applied in order to measure the creep lifetime of the specimens. From the experimental results it can clearly be seen that the creep lifetime of the Inconel 617 alloy substrate specimen increases by a significant 5~20 % with the transferred graphene coating compared to the as-received Inconel 617 alloy specimen.
Small punch test and simulation of HR3C steel
이택상,이후민,강석준,Fahim Ahmed Ibupoto,이정민,이종훈,김범준,최재붕,배시연,김문기 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.7
As the traditional uniaxial test requires substantial amount of cost and material usage for specimen, it is hardly applied to the direct diagnosis of structural integrity of in-service facilities. Small punch (SP) test has been, alternatively, introduced to procure material properties because SP test just needs a slice of material (10 ´ 10 ´ 0.5 mm) which can be easily obtained from real components without loss of integrity. In this study, for HR3C steel, SP tests were carried out and its three-dimensional finite element (FE) model was also developed to cross-validate the test results. Scanning electron microscope images for SP specimens were taken and compared with crack propagation simulation results generated by the extended finite element method. Furthermore, the minimum thickness change of specimen during the test was measured by several interruption tests. Configuration of SP test specimen was intensively observed with respect to punch displacement by both experiment and FE analysis, respectively.