ULTRASONIC DETERMINATION OF DENSITY VARIATIONS IN GREEN AND SINTERED POWDER METALLURGY COMPONENTS.

In this paper, frequency analysis is introduced as a procedure for evaluation density variations in powder metallurgy materials. The method of ultrasonic spectroscopy can often be used to evaluate ultrasonic signals when standard pulse echo or through transmission methods fail because of poor resolution or lack of basic understanding and interpretation. The frequency signature approach represents an alternative approach to ultrasonic signal analysis that provides feature extraction and dimensional reduction. Utilizing spectrum analysis from ultrasonic back wall echoes and through transmission pulses, systematic changes in the ultrasonic frequency spectra have been measured and correlated with density variations. By means of this technique the magnitude of density, as well as density variations may be determined in green as well as sintered P/M components. In addition, a comparison of the ultrasonic back wall echo amplitudes in as-sintered and repressed ferrous P/M specimens demonstrates systematic variations in the frequency spectra and amplitude which are dependent on pore morphology as well as density.