Effect of Powder Morphology (Semi-Spherical vs. Flake Shape) on the Compress-ability and Hardness of Sintered Bronze Samples

Flake powder metallurgy is a relatively new technique that utilizes flake shaped metallic powders instead of common powder particles. These powders are stacked in the mold cavity insuch a way that their largest surfaces are in touch with each other and therefore the consolidated material exhibits non-isotropic properties. In addition, the relatively large surfaces of powders are suitable locations for Nano-sized and micron-sized ceramic particles and therefore this techniquecan be utilized for processing of metal matrix composites with controlled distribution of reinforcingparticles. The metallic flakes are usually produced via milling which is time consuming and expensive. In the present study, for the first time, cold rolling was utilized to make bronze flakes with an average diameter of 1200 μm and thickness of 55 μm from 390 μm sized semi-spherical powders. The size and morphology of powders were characterized via light microscopy and Scanning Electron Microscopy (SEM) and their micro-hardness values were compared with thatof the as-received powders. The results revealed that the number of rolling passes did not haveconsiderable effect on the dimensions of the rolled powders. In the second stage, the cavity of a steel die was filled with aligned powder flakes and cylindrical bronze compacts were prepared byusing a hydraulic press. The resultant samples were sintered using optimized time and temperature. The density values of samples were quantified using Archimedes principle and their hardness were obtained via a Brinell hardness tester. Reference samples were prepared from as-received bronzepowders and characterized at identical conditions for comparison. The results revealed nonisotropicmicrostructure and properties for samples made from flake shaped powders. In addition, powder rolling resulted in decreased powder compress-ability and increased hardness ofconsolidated samples. These results were attributed to different arrangement of flake shaped andsemi-spherical powders in the mold cavity before pressing (due to their different size and morphology) as well as different plastic deformation of powders during pressing (due to strain hardening throughout rolling).

کلیدواژه ها:

Flake powder metallurgy ، Bronze powder ، Powder rolling ، Powder morphology ، Compress-ability ، Hardness