Damage initiation in hard-coated hard metal substrates under normal and tangential loads at elevated temperature

Lukas Walch

Research output: ThesisMaster's Thesis

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Abstract

In the manufacturing industry, WC-Co hard metals are among the most important tool materials. They are used for machining applications like the milling of high-strength materials. Their lifespan is often limited by defects in the hard metal substrate. Among the main causes for defect initiation and growth are the significant multi-axial loads and high temperatures present e.g. at the cutting edge of milling inserts. Presently there is a lack of testing methods capable of reproducing such conditions in controlled environments. In the current work a novel ball-in-cone test setup utilizes a spherical indenter and an inclined sample surface to introduce cyclic multi-axial loads into the specimen substrate in isothermal conditions. The setup is used to study the contact fatigue behavior of TiN-TiB2 hard-coated WC-12 wt.% Co hard metal specimens with a mean grain size of 2 µm. Cyclic loads of a level comparable to that seen at the cutting edge of milling tools were applied to tested specimens at a temperature of 700 °C induced via eddy current heating in a vacuum. The specimens’ microstructures were documented using scanning electron microscopy on sections exposed via focused ion beam milling. The stress situation in the specimen substrate was studied with a finite element simulation using an experimentally parameterized materials model also considering creep. The simulation showed stresses ranging from mainly compressive to tensile-compressive. Defect formation trends at up to 10,000 load cycles could be correlated with the applied stress ratio. Positions subjected to a combination of tensile and compressive stresses showed a significantly higher defect formation rate than positions with mainly compressive stresses. The defect initiation behavior in specimens under multi-axial loads at elevated temperature can be studied using the ball-in-cone test method.
Translated title of the contributionSchadensinitiierung in beschichteten Hartmetallsubstraten mit normaler und tangentialer Last
Original languageEnglish
QualificationDipl.-Ing.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Ebner, Reinhold, Supervisor (internal)
Award date25 Jun 2021
Publication statusPublished - 2021

Bibliographical note

embargoed until null

Keywords

  • WC-Co
  • hard metal
  • hard-coated
  • Ball-in-Cone
  • high temperature
  • damage initiation
  • defect initiation
  • multi-axial loads
  • tangential loads
  • normal loads

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