Metallographic Preparation Procedures - Powder Metallurgy

Sintered Iron

The metallographic specimen preparation of Powder Metallurgy samples is affected by the specimens composition, packing and sintering conditions. Microstructural features of interest include: porosity, grain size, inclusions and orientation of voids. Proper metallurgical preparation takes into account that the microstructure may be porous and perhaps somewhat brittle because of inadequate sintering conditions. To fill in the void, mounting with epoxies or acrylics is recommended. the use of a vacuum impregnator and / or pressure device is also recommended to better fill in the voids and positiy. Initial grinding is recommended with 30 um or 45 um diamond suspension on a metal mesh cloth. This step is very important to minimize damaging or pulling out the grains of a poorly sintered material. The metal mesh cloth provides a trough for the diamond particle to become semi-fixed, thus providing high grinding rates, as well as an opportunity for the diamond to become dislodged under high shear conditions, the result is a planar grinding process which has high removal rates and minimizes deformation and damage to the specimen. A commonly used procedure which helps to open up smeared pores is to etch the solution for approximately 2 minutes. For ferrous materials such as sintered iron an etch with 2% nital by immersion is recommended. The next rough polishing stage is required to eliminate any remaining surface and subsurface deformation to the specimen surface. Polycrystalline diamond suspensions used in conjunction low napped polishing pads result in minimal edge rounding and relief for the rough polishing stage. For a final finish, 0.05 um polycrystalline alumina provides an excellent surface finish.

SECTIONING
MAXCUT Abrasive blade (Cat. No. MAX-E or MAX-I series)

MOUNTING
Castable mounting with epoxies or acrylics using vacuum impregnation

POLISHING

Sintered Iron, Mag. 100x (B.F.), as polished