Microstructural Analysis of a Silver-Plated Trombone

Abstract

The joint was sectioned, mounted, and polished with standard metallographic procedures. Due to the fact that several different materials were used in this joint, it was not possible to reveal all microstructures simultaneously with a single etchant. The metallographic sample, shown in Fig. 3, prepared from the location shown in Fig. 2, was initially etched with a potassium dichromate solution: 2 g K2Cr2O7, 8 mL H2SO4, 4 drops HCl, 125 mL H2O. The sample was viewed under crossed polars to reveal the brass microstructure (Regions 1, 3, and 5 in Fig. 4). The lead–tin solder of the brace joint was severely attacked by the potassium dichromate. The sample was re-polished and imaged in the as-polished condition, Fig. 5. To reveal the microstructure of the silver braze (Region 6, Fig. 4), the specimen was etched with a modified Stewart’s reagent: A solution of 50 mL 3% hydrogen peroxide and 50 mL ammonium hydroxide diluted with 25 mL of water. The as-prepared samples were examined under a light microscope (LM), and a scanning electron microscope (SEM) using energy dispersive spectroscopy (EDS) to qualitatively identify composition of the various components.