Abstract
Because of the importance, from the engineering point of view of evaluating brittleness, a study was undertaken on critical stress (Pf) and critical strain (df) in the relation between load (stress) and the size of the pyramidal hole (strain) under microplastic deformation of brittle Ni-S alloys. Deformation energy (Ef) on fracture was also evaluated. Brittle Ni-S alloys were prepared by electroplating on Cu sheet (current density=60A/m2, distance between electrodes=40mm, pH=6.0, bath temperature=303K). The concentration of the water solutions were 100g/L for NiSO4(NH4)2SO4·6H2O, 15g/L for Na3C6H5O7·2H2O, and 1∼30g/L for Na2S2O3·5H2O. Ni-S alloy composition was varied by controlling the concentration of Na2S2O3. Precise evaluations of fractures were preformed with a Vickers microhardness tester. The addition of sulfur was found to decrease resistance to microplastic deformation (Po), however the higher the sulfer concentration, the lower were the values of Ef, df, and Pf become. Comparing values of Ef, the brittleness of Ni-S alloys was found to approximate the values obtained for Al2O3 and slide glasses.
