Details

Autor(en) / Beteiligte

• Maier, Kathrin
• Klünsner, Thomas
• Pichler, Philip
• Marsoner, Stefan
• Ecker, Werner
• Czettl, Christoph
• Schäfer, Jonathan
• Ebner, Reinhold

Titel

Damage indicators for early fatigue damage assessment in WC-Co hardmetals under uniaxial cyclic loads at a stress ratio of R = −1 at elevated temperatures

Ist Teil von

• International journal of refractory metals & hard materials, 2022-02, Vol.103, p.105749, Article 105749

Ort / Verlag

Shrewsbury: Elsevier Ltd

Erscheinungsjahr

2022

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• WC-Co hardmetals are utilized as tool materials in metal cutting applications in which they are exposed to high mechanical cyclic loads and elevated temperatures. A better understanding of the failure mechanisms of WC-Co hardmetals under these application conditions and the ability to diagnose the damage evolution state are key factors to understand the limits of endurable cyclic load at a certain temperature. The aim of the current work was the experimental determination of stress-strain-hysteresis loops for the investigation of damage indicators in uniaxial cyclic tests at a stress ratio of R = σmin/σmax = −1 for two WC-10 wt% Co hardmetals at 700 °C and 800 °C in vacuum. An increase in the stress-strain-hysteresis loop area and tension-compression-strain asymmetry was recorded with increasing number of load cycles at 800 °C, with earlier failure than at 700 °C. The relationship between the stress-strain-hysteresis loop parameters and the damage evolution state at the microstructure level, as well as the deformation behavior of WC- and Co-phases with increasing number of load cycles, were analyzed. To this end, the microstructure for one WC-Co hardmetal grade was analyzed by scanning electron microscopy and electron backscatter diffraction after cyclic testing up to defined numbers of load cycles at 800 °C. It was observed that the hysteresis loop area and strain asymmetry coincide with the formation of nanopores at WC/WC interfaces and WC/Co phase boundaries, which enlarge to form larger cavities with increasing number of load cycles. Additionally, electron backscatter diffraction data showed that the fcc Co-phase partially transformed into hcp Co under cyclic loading. All specimens, in which an increase in the stress-strain hysteresis loop area or strain asymmetry was observed, ultimately failed when a sufficiently high number of load cycles was applied. Thus, these results indicate that the investigated parameters are reliable indicators for bulk material damage. •Results of uniaxial cyclic tests for two WC-Co hardmetal grades at R = σmin/σmax = −1 at 700 °C & 800 °C.•The selected loads correspond to application-relevant stress amplitudes for cutting edges of milling insert plates.•Identification of material damage indicators from cyclic stress-strain-hysteresis loops.•Loop area & strain asymmetry increase with increasing load cycles are indicative of progressive formation of microdefects.