Lokales Verformungsverhalten von gehipptem Molybdän

Translated title of the contribution: Local deformation behaviour of hipped molybdenum

Christopher Heim

Research output: ThesisMaster's Thesis

Abstract

Nanoindentation is a depth-registering hardness testing method which is not only limited to measuring hardness. With suitable methodology it is possible to measure the Young¿s modulus, strain rate sensitivity and local microplasticity of a material. Due to the simple sample preparation nanoindentation is an excellent choice as a screening method for production processes, for material development and for validating modelling approaches. This thesis describes the local deformation behaviour of a molybdenum alloy and focuses on the development of a new nanoindentation method to determine the local fatigue behaviour. The material investigated is called DUMOMET from Plansee SE, which is a micro doped molybdenum alloy. Three manufacturing states were investigated: sintered, HIP and rolled and recrystallised. A comprehensive microstructural analysis was carried out using SEM, EBSD measurements and an optical microscope to ensure the comparability of the production states. Using nanoindentation, tests were carried out with a Berkovich tip at a constant strain rate to determine the hardness and modulus of elasticity, strain rate cycling tests to determine the strain rate dependence and creep tests with a constant load to determine time-dependent local microplasticity. In order to draw possible comparisons, the macro and micro hardness was determined according to Vickers. In addition, local flow curves of the material were recorded using ball indentations. The developed nanoindentation fatigue method is based on controlling the load cycles via the global indentation depth signal. Previous tests using the superimposed CSM signal as loading cycles did not lead to fatigue of the material, therefore the switch to global indentation depth-controlled measurements followed, as this enables greater amplitude changes as well as partial unloading. The evaluation of the developed method is carried out by Python scripts, which determine the stiffness of the material and the development of the width at half maximum (WHM)of the loading hysteresis for each fatigue cycle. This way, the development of the stiffness and hysteresis WHM can be analysed with the number of loading cycles respectively over time. The effect of the unloading height and measuring frequency on the automated evaluation was analysed to determine differences and optimise test parameters. The nanoindentation measurements were carried out at room temperature, 100 °C and 300 °C, except for the ball indentations (RT only), to analyse the development of the material properties with increasing temperature. Macroscopic fatigue tests were carried out in the HCF and fatigue strength regime at room temperature in order to be able to draw possible comparisons. This work demonstrates again the flexibility and wide range of applications of nanoindentation measurements and provides a newly developed nanoindentation fatigue measurement method which is a solid foundation for further research.
Translated title of the contributionLocal deformation behaviour of hipped molybdenum
Original languageGerman
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Maier-Kiener, Verena, Supervisor (internal)
Award date22 Mar 2024
Publication statusPublished - 2024

Bibliographical note

no embargo

Keywords

  • Nanoindentation
  • Molybdenum
  • local deformation behaviour
  • CSM
  • local creep
  • strain rate jump test
  • fatigue
  • local fatigue
  • ball indents
  • microplasticity

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