Double-pore structure porous Mo-Si-B intermetallics fabricated by elemental powder metallurgy method using NH4HCO3as pore-forming agent

The multiphase porous intermetallic compounds Mo3Si-Mo5Si3-Mo(5)SiB(2)of a double-pore structure has been successfully fabricated by combining thein situreaction synthesis with the pore-forming agent method. The effects of NH(4)HCO(3)content and size on porosity, pore diameter distribution, permeability, and compressive strength were investigated systematically. The results show that: with the NH(4)HCO(3)increasing from 0 to 60 vol%, the total porosity increases from 46.6% to 73.2%, the big pores volume increases from 2.3% to 69.4%, the gas permeability increases from 5.34 x 10(-7)l/(min cm(2) Pa) to 1.74 x 10(-4)l/(min cm(2) Pa), and the compressive strength decreases from 392 MPa to 14.8 MPa; on the other side, with the NH(4)HCO(3)size increased from 48 mu m to 230 mu m, the parameters of this porous intermetallics changed slightly except to the significant increase of big pores diameter. An exponential equation of sigma(c) = sigma(s)(1-rho)(1/0.254)based on generalized mixture rule (GMR) has been put forward to quantitatively describe porosity-compressive strength behaviors. Results from this study indicate the potential applications in various filtration environments by tailoring the shape, contents, and size of the pore-forming agent.