Understanding the strength of hot-pressed nanostructured powder compacts

Attrition-milled nanostructured powders were hot pressed, and macroscopic p roperties of density, hardness, grain size, and strength were measured. No correlation was found between processing conditions (temperature and time) used in this study and compact properties, nor was a correlation found betw een the tensile (or failure) stress and density, hardness, or grain size. V ariations of compact properties of unmilled powder were similar to that of milled powders. Tensile data were not well fitted to a Gaussian distributio n but were well fitted to a two-parameter Weibull distribution, Thus, altho ugh the milled powder compacts had an average tensile strength greater than the unmilled powder compacts, all sample compositions fit a distribution w ith zero as a possible minimal stress level. Weibull analysis suggests that the tensile and compression strength is controlled by the presence of fine cracks, which may limit future engineering applications. Efforts to elimin ate these cracks during hot pressing were unsuccessful.