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Quantitative overview and clarification of hot hardness
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
2018 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Hardness measurement at high temperatures is of increasing interest in many sections within research and material development. The hardness of materials used for applications at, or manufactured at, elevated temperature conditions shows a high dependence on the temperature. Technical development has made instrumented indentation possible which allows indentation of individual grains or precipitates down to the nanometer scale. With increasing temperature and decreasing loads, many challenges arise such as temperature drift, chemical reactions, size effects and degradation of indenters. From an engineering perspective it is important to understand these challenges to draw valid conclusions from the measured data. In this work, the methodology for accurate high temperature hardness measurements is investigated. The current market is evaluated to give a foundation for future investments. The development of hot hardness is explained as well as some background of the standard room temperature measurements on the different scales: nano-, micro- and macroindentation.

 

To demonstrate the possibilities of hot hardness, measurements are performed on various samples from the industry. The tested samples include a broad range of materials including aluminium from Gränges, hydrides in zircaloy-2 from Studsvik, Al-Si ceramic coated steel from Gestamp, stainless steel from Outokumpu, high alloyed steels from Uddeholm, low alloyed steels from SSAB and 3D-printed steel from VBN Components. The evaluated equipments include Micro Materials Vantage, Bruker Triboindenter 980, Picoindenter 88, Bofors HT macroindenter as well as the reference systems KB Prüftechnik universal hardness tester, Qness Q10A+ microindenter and Picoindenter 87. The equipments are located in Sweden, the United Kingdom and USA.

 

Indentation was successfully conduced up to 700°C ex-situ and 800°C in-situ. It was found that all tested materials show a decrease in hardness except for one duplex stainless steel which is harder at 400-500°C depending on the thermal history of the sample. It could be concluded that the main challenge of high temperature measurements is the tip material since diamond suffers from transformation into graphite and carbides. An operator is needed for extensive lengths of time during testing, especially for in-situ systems where the indenter and sample temperature have to be perfectly matched due to the lack of convective heating. Therefore, it is argued that it might be best to invest in an ex-situ system to decrease the operator-time and thus the cost for the customer.

Place, publisher, year, edition, pages
2018. , p. 91
Series
UPTEC Q, ISSN 1401-5773 ; 18027
Keywords [en]
Hot hardness, high temperature hardness, high temperature indentation, nanoindentation, microindentation, macroindentation, instrumented indentation
Keywords [sv]
Varmhårdhet, hårdhetsmätning vid hög temperatur
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:uu:diva-371285OAI: oai:DiVA.org:uu-371285DiVA, id: diva2:1273002
External cooperation
Swerim / Swerea KIMAB
Educational program
Master Programme in Materials Engineering
Supervisors
Examiners
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2018-12-20Bibliographically approved

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