A study of the strain rate microstructural response and wear of metals |
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Authors: | Satish V Kailas |
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Affiliation: | (1) Department of Mechanical Engineering, Indian Institute of Science, 560 012 Bangalore |
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Abstract: | Titanium (Ti) and copper (Cu) pins were slid against alumina in a pin-on-disk machine at a load of 50 N and sliding speeds
varying from 0.1 to 4 ms−1. The evolution of the microstructure in the subsurface of the material and the wear rate was co-related to the strain rate
microstructural response of the material in uniaxial compression, at different strain rates (0.1–100 s−1) and temperatures (298–673 K). The strain rates and temperatures in the plastically deforming zone near the surface of the
pins were determined using noniterative methods. The strain rates were found to be in the region of 100 s−1 near the surface and decreases as one moves into the sub-surface of the pin. The temperatures increased as the speed increased.
These estimated strain rates and temperatures were superimposed on the strain rate microstructural response maps of these
materials. The uniaxial compression test results of Ti showed adiabatic shear banding as a microstructural mechanism that
evolves at high strain rates (≥10 s−1) and lower temperatures (<575 K). Adiabatic shear bands are sites of easy crack nucleation and propagation. When Ti is slid
at low speeds the near surface region of the pins deform in the adiabatic shear banding regions in the strain rate microstructural
response map. At such speeds the wear rate is found to be high and reduces as the sliding speed is increased, when the material
undergoes a more homogeneous deformation. The microstructural response of Cu under uniaxial compression showed that the material
undergoes flow banding at intermediate strain rates (1 s−1) and temperatures of up to 473 K. The subsurface microstructure of the pins slid at low speeds showed subsurface cracking
and sheet like debris formation. This happen at lower speeds because the flow banding and crack nucleation is expected in
the subsurface where the strain rates and temperatures are lower. The present test results show a clear relation to exist
between the strain rate response of the material in uniaxial compression and its subsurface microstructural evolution and
wear rate. |
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Keywords: | adiabatic shear banding flow banding homogeneous deformation microstructural response strain rate wear |
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