Verformungsinduzierte Ausscheidungsbildung von Hafniumkarbiden in der Molybdänbasislegierung MHC (Mo-Hf-C)

Translated title of the contribution: Strain induced precipitation of hafnium carbide particles in the molybdenum based alloy MHC (Mo-Hf-C)

Roland Dallinger

Research output: ThesisDiploma Thesis

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Abstract

The excellent high temperature properties of molybdenum can be remarkably enhanced by precipitation hardening. During thermo-mechanical processing of the powder metallurgically produced molybdenum based alloy MHC, with a nominal content of 0.65 at% Hf and 0.65 at% C, strain induced hafnium carbide particles with a size of 10 nm to 100 nm are formed. These particles interact with dislocations, which increases the strength and the recrystallisation temperature. The aim of this work was to study the kinetics of the precipitation of hafnium carbides in order to gain knowledge for further improvement of the thermo-mechanical processing route. Therefore, the evolution of the micro- (HV 0,1) and macrohardness (HV 10) in comparison to the strength, determined via two stage deformation experiments, was studied for different aging times at aging temperatures of 1100°C, 1350°C and 1600°C. The obtained sample conditions were preliminary characterized with a scanning electron microscope. Additionally, the size of the precipitated particles was determined with a transmission electron microscope for selected sample conditions. Furthermore, the material was fully chemically analyzed and the bulk composition of the molybdenum matrix was determined with atom probe tomography. At an aging temperature of 1100°C no precipitation of hafnium carbides occurred. At 1350°C and 1600°C, however, precipitates have already been formed after 1 min and the peak hardness was detected after aging for 30 min respectively 1 min. With increasing aging time a drop in hardness occurs. The reason for this are ongoing recovery and overaging processes and at 1600°C also recrystallisation. For both aging temperatures, 1350°C and 1600°C, the particle size was about 10 nm at the peak hardness.
Translated title of the contributionStrain induced precipitation of hafnium carbide particles in the molybdenum based alloy MHC (Mo-Hf-C)
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Primig, Sophie, Co-Supervisor (internal)
  • Schatte, Jürgen, Supervisor (external), External person
  • Clemens, Helmut, Supervisor (internal)
Award date26 Jun 2015
Publication statusPublished - 2015

Bibliographical note

embargoed until 16-06-2020

Keywords

  • molybdenum-hafnium-carbon alloy (MHC)
  • strain-induced precipitation
  • particle hardening
  • precipitation kinetics
  • two stage deformation
  • transmission electron microscopy

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