An application of universal hardness test to metal powder

Artikel i vetenskaplig tidskrift, 2009

Powder metallurgy is a “net shape” components producing technology from metal powders by compaction with following sintering processes. For today actual trends of powder metallurgy are associated with modern powder grades, alloyed by elements with high affinity to oxygen (Cr, Mn, Si, etc.). Contamination of powder particles by oxides and/or other secondary phases have a negative effect on their compressibility and sinterability. The geometry properties of powders give integral information about powder quality. Evaluation of yield strength and/or rather the strain hardening exponent, characterizing the mechanical properties on the level of individual particles, really is not possible. One of available approaches could be measurement of the microhardness of particles. The contribution deals with the evaluation of the microhardness of powder particles and specification of the factors affecting measured values. Using standard Vickers microhardness HV0.01 measurements for two different powders the results obtained showed large scattering from the average. This gave no possibility to identify the influence of alloying and particle matrix purity on microhardness. Problem was solved utilizing instrumented indentation test using NanoIndenter XP. This is usable technique for estimation of microhardness of powder particle matrix and gives possibility to recognize differences between different size fractions of particles. Based on the obtained results it was concluded, that absolute results of indentation hardness and indentation modulus are strongly affected by mounting resin type. Utilizing DSI method and mounting resin of proper hardness enabled to evaluate the microhardness of powders with different alloying element content. Influence of particles purity/size on powder microhardness was established as well. Indentation hardness and indentation modulus for sintered materials are in good agreement with the data for corresponding bulk materials. Obtained results confirm that universal hardness test is valuable instrument for evaluating of sintered materials properties.