For the Aw sample, a “white” area corresponding to a heat affected zone is also observed immediately below the surface, the width of this UK-5099 layer is about 10 μm. Careful SEM inspection of the sub-surface does not evidence the presence of a mechanical affected zone.
3.2.3. Microstructure within the substrate under both the abusive and gentle conditions
Fig. 7. a) Micro-hardness profiles (HV0.5) for the Gw and Gd samples.b) Micro-hardness profiles (HV0.5) for the Aw and Ad samples.c) Optical cross-section after Nital etching for the Aw and Ad samples.Figure optionsDownload full-size imageDownload high-quality image (164 K)Download as PowerPoint slide
For the Aw sample, only an over-tempering area is observed and the width of this layer is about 15 μm.
These optical observations are completed by micro-hardness profiles presented Fig. 7a and b. For Gw and Gd samples (Fig. 7a), the micro-hardness appears to be constant over the measured depth. On the other hand, grinding under abusive condition drastically changes the micro-hardness profiles within the substrate for Aw and Ad samples (Fig. 7b). Grinding under dry condition (sample Ad) leads to a slight increase in the micro-hardness close to the interface followed by a decrease corresponding to measurements in the over-tempered area. Optically, the width of this last one is not well defined but, taking into account the micro-hardness profile, oils is larger than 300 μm. The heat affected zone (HAZ) within the substrate is then larger than 600 μm. For the Aw sample, the micro-hardness is lowered close to the interface and reaches the initial hardness value 400 μm below the interface.