Investigations On Material Transfer Behavior Of AgSnO₂ And AgTiB₂ Contact Materials

To clarify the effect of the characteristics of strengthening phase,current and voltage on the arc characteristics and material transfer behaviors of silver base contact materials,the Ag-4wt.%TiB₂ and Ag-4wt.%SnO₂ contact materials were prepared with different sized TiB₂ and SnO₂ powders by powder metallurgy.Furthermore,the effect of WO₃ addition on the arc characteristics and material transfer behaviors was investigated as well.The arc duration and arc energy were analyzed,and the surface morphologies and chemical compositions of eroded anode and cathode were characterized by a scanning electron microscope（SEM）equipped with energy disperse spectroscopy（EDS）,and a confocal laser canning microscope（CLSM）.The following conclusions can be drawn from above investigations.（1）Ag-4wt.%TiB₂ contact material presents relative smooth erosion surface at 12 V DC and5-24 A,whereas an apparent protrusion occurs at the anode and a large crater exists at the cathode for the Ag-4wt.%SnO₂ contact material.Furthermore,the material transfer mode for the Ag-4wt.%TiB₂ contact material is closely related to the current level.At small currents,the material transfer is from cathode to anode,whereas it has an opposite mode at large currents.The critical currents for the Ag-4wt.%TiB₂ contact material prepared with 500 nm and 60 nm TiB₂ powders are 16 A and 24 A,respectively.However,for the Ag-4wt.%SnO₂ contact material,the material transfer always occurs from cathode to anode in the range of 5-24 A.Moreover,the Ag-4wt.%SnO₂ contact material has a larger relative transfer mass in comparison with Ag-4wt.%TiB₂ contact material.（2）Voltage has a significant effect on make arc and break arc.The make-arc-energy and break-arc-energy for the Ag-4wt%TiB₂ and Ag-4wt% SnO₂ contact materials have different increments at 12-24 V and 24-36 V.Furthermore,the material transfer modes change two times with increase of voltage.The material transfer from cathode to anode changes from anode to cathode,followed by transferring from cathode to anode.（3）WO₃ addition changes the material transfer mode.The material transfer is from cathode to anode for the Ag-4wt.%TiB₂ contact material without WO₃ addition,whereas it has a reverse change for the Ag-4wt.%TiB₂ contact material with WO₃ addition.Furthermore,WO₃ addition can eliminate the generation of cracks on the eroded surface.（4）Fine strengthening particles are beneficial for reducing erosion area and splash,thus improving the arc erosion resistance for the Ag base contact materials.Moreover,the Ag base contact materials prepared with fine strengthening particles have small mass loss and relative transfer mass.