From Powder Metallurgy Technology

3.1. 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. In the present chapter, various characteristics of the powder, some interrelated, are considered. Table 3.1 gives a brief summary of principles involved in the characterization of various powder properties which shall be described in subsequent sections.

Table 3.1: Powder properties and methods of mesuring them

Particle size and size distribution

Sieve analysis: Permeability: Sedimentation electrical resistance; Light obscuration; Light scattering; Microscopy; Surface area.

Particle shape [external]

SEM; Shape parameters; Morphological analysis; Fractals.

Particle shape [external and internal]

Stereology; Mercury Porosimetry; Gas absorption.

Particle density

Pycnometry; Mercury porosimetry.

Specific surface area

Gas absorption; Permeametry.

Surface chemistry

X-ray photoelectron spectroscopy (ESCA); Auger electron spectroscopy; Secondary ion mass spectroscopy; Ion scattering spectroscopy.

Alloy phases and phase distribution

Optical metallography; Stereology; Electron microscopy; EDAX; X-ray diffraction.

Quality of mixing [segregation]

Macroregion:Variability coefficient (by chem.anal.); Microregion: Variability coefficient (2 nd comp. >5%); Homogeneity coefficient (2 nd comp. <5%); by metallography

3.2 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...

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