Stress-Induced Heat Generation and Strain Localization in Polycrystalline and Nanocrystalline Nicke

Commercially available polycrystalline Ni (Ni200; grain size: 32 mum) and electrodeposited nanocrystalline Ni (grain size: 57 nm), Ni-2.6%Fe (grain size: 25 nm) and Ni-8.5%Fe (grain size: 20 nm) were analyzed for the phenomena of stress-induced heat generation and strain localization during plastic deformation at room temperature (i.e. 25°C). Tensile specimens according to ASTM E8 standard dimensions were tested at strain rates of 10 -2/s and 10-1/s, respectively, to record the amount of heat dissipated and the change of localized strain using a high resolution infrared (IR) detector and digital image correlation (DIC) camera, respectively. Results have shown that the maximum temperatures that were recorded in nanocrystalline Ni and Ni-Fe alloys were at least 30°C lower than the onset temperatures for subgrain coalescence previously measured through differential scanning calorimetry. It can be concluded that thermally activated grain growth during tensile testing of nanocrystalline Ni and Ni-Fe alloys is not likely to occur.