The effects of Sn addition on the internal oxidation of Ag-Cd alloys

摘要

The effects of Sn addition on the internal oxidationof Ag-Cd alloys were studied. Four types of Ag-15Cd alloys with0.3, 0.5, 0.8 and 1.5 wt%Sn were prepared by induction melting inAr atmosphere. Alloys were internally oxidized at 677, 735 and782C with 1.0-3.0×10 5 Pa oxygen partial pressure. Internaloxidation increased the hardness of all alloys by 65-100%. Alloyswith higher Sn content showed higher hardness. Oxidationcondition proved to have significant influence on the oxidationmicrostructure and wear resistance. The oxides observed afterinternal oxidation were identified as SnO2, Cd2SnO4 and CdO.Cd2SnO4 particles were embedded within CdO particles. Themechanism of oxidation is considered as follows. First, Sn isoxidized to form SnO2, then it transforms to Cd2SnO4 by furtherreaction with Cd and O. Finally CdO grows around the Cd2SnO4particles. Because Cd2SnO4 particles act as nuclei for CdOprecipitation, finer dispersion of oxides occurs in higher Sncontent alloys resulting in higher hardness and improved wearresistance of the alloy.