An Overview on the Properties and Testing of Metal Powders

April 23, 2020

The main purpose of powder testing is to ensure that the powder is suitable for subsequent processing. The basic properties or characteristics of powder are chemical composition and purity, particle size and its distribution, particle shape, particle porosity and particle microstructure. The secondary properties or characteristics are specific surface, apparent density, tap density, flow rate, compacting characteristic and sintering characteristic. The important secondary properties such as apparent density and flow rate are most widely used in specification and control routine. Below is an overview on the properties and testing of metal powders.

Basic Characteristics of Metal Powders

Chemical composition

The chemical composition of powders is the outstanding characteristic. It usually reveals the type and percentage of impurity and determines the particle hardness and compressibility. The term impurity refers to some elements or compounds which has an undesirable effect. Impurities influence not only the mechanical properties of the powder compacts, but also their chemical – electrical and magnetic properties. It may also exert a decisive effect on pressing, sintering and other post – sintering operation which are essential for the production of finished product from powders.

The chemical composition of a powder is determined by the well established standard techniques of chemical analysis. Oxygen content is determined either by wet analysis or by loss of weight in hydrogen. Some oxides may not be reduced at all or there may be error due to incomplete reduction of oxides, therefore it is desirable for both processing and optimum properties of the final product to have a low oxygen content.

Particle size

The particle size has a great important in properties and testing because it affects most of the properties such as mould strength, density of compact, porosity, expulsion of trapped (occluded) gases, dimensional stability, agglomeration and flow and mixing characteristics. Particle size is expressed by the diameter for spherical shaped particles and by the average diameter for non – spherical particles. Average employed is defined in different ways according to the method employed for size distribution. When the method involves sizing, the particle size is measured as the opening of a slandered screen which just retains or passes the particle. When determined by micro count method, the diameter is measured by averaging several dimensions.

According to the sedimentation method the particle size is defined as the diameter of the spherical particle having the same specific gravity and setting velocity as the non – spherical particle under test.  The average diameter in the case of large particle sizes can be determined by counting and weighing at the cube root of the volume.

Practical properties and testing metal powders are divided into three distinct classes – the sieve, sub sieve and sub – micron or ultrafine. The screen with the opening of finest standard mesh – sieve for production purposes is the 325 mesh screen having the aperture of 44 micron.

Metal powders has a lot of advantages that make it suitable for a lot of metal forming applications. If you want to learn more about its properties and testing, contact us now at PM Distributors so that we can readily provide you with more information about this process.

 

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