Effects of carbamide shape and content on processing and properties of steel foams

Spherical and irregular carbamide particles covered with Fe-1.5% Mo steel powder have been employed to produce foams using space holder-water leaching technique in powder metallurgy. Foams having porosities between 49.2% and 71.0% were produced after sintering at 1200 degrees C for 60 min. The effect of carbamide shape and content on the foams' processing, microstructure and mechanical properties has been evaluated. Using irregular carbamide particles and increasing its content decreased leaching time. The extents of specimens' volumetric expansion after carbamide leaching and volumetric shrinkage after sintering also depended on volume fraction and carbamide shape. Final porosity was directly related to the added fraction of carbamide. Pore shape was similar to initial carbamide particle shape. Foams having irregular pore shape were observed to have compressive yield strengths between 20 MPa and 92 MPa and Young's moduli between 0.45 GPa and 2.69 GPa. The corresponding values for foams having spherical pore shape varied between 25 MPa and 112 MPa and between 0.71 GPa and 2.91 GPa, respectively. The foams' strength increased with increasing relative density. Microstructure having spherical pores resulted in better compressive behavior. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.