EXPERIENCE OF IMPROVING STANDARDS AND METHODS FOR STUDYING THE PROPERTIES OF METAL POWDERS AND SINTERED ARTICLES

摘要

Reasons are considered for improving standards in the following methods for testing powder materials: tensile, transverse bending, gas and liquid permeability, and determination of powder compact dimensions after compaction pressure removal and during sintering. Calculated data for representative specimen dimensions (cross section and thickness) for these and other test methods for sintered articles (materials) prepared from mono - and polyfraction iron powder of different sizes are confirmed by experiment. It is shown that the representative specimen dimensions prepared from monofraction powder are more than an order of magnitude less than for those prepared from polyfraction powder. The reason for this difference is considered to be the special role of individual particles for monofraction powder) or assemblies of these particles for polyfraction powder) in forming elementary fragments within the structure of compacts and sintered articles. Data are provided for the improved ISO 4492-1985 standard and a new GOST 29012-91 standard developed on the basis of it for precise determination of changes in the dimensions of powder compacts during pressing and sintering. Use of this method makes it possible to reveal the existence of different structural states within narrow porosity limits for powder materials. It is shown by experiment that the pulsed ultrasonic method for monitoring these structural states based on measuring the propagation rate and (or) the elastic wave damping factor, exhibits high sensitivity, it is rapid, and it may be recommended for extensive introduction and standardization in powder metallurgy.