محاضرة رقم 10

METAL POWDER CHARACTERISTICS
1. Introduction
The success of any powder metallurgical process depends to a great extent on the complete characterization and control of the metal powders. The method of powder production influences particle chemistry and structure, apart from the precise nature of particle size distribution. These properties also influence the behaviour of the powder during compaction and sintering, and the composition, structure and properties of the sintered material.
2 Chemical Composition and Structure
The levels of impurity elements in metal powders can be very significant to both the processing and properties of the final product. It is necessary to know whether such elements are present in their elemental form or whether they are present in the form of a chemical compound. Details of procedures for determining these parameters can be had from the standards of Metal Powder Industries Federation (MPIF) and the American Society for Testing and Materials (ASTM).
3 Particle Size and Shape
The shape of the powder is characterised by the dimensionality of the particle and its contour surface. An ideal system of shape characterisation is given in Fig.3.1, together with the major manufacturing techniques which produce such shapes. Most powder particles are three-dimensional in nature and they may be considered as being somewhat equiaxed. Spherical particles represent the simplest and ideal example of this shape.