Double-pore structure porous Mo–Si–B intermetallics fabricated by elemental powder metallurgy method using NH4HCO3 as pore-forming agent

The multiphase porous intermetallic compounds Mo 3 Si-Mo 5 Si 3 -Mo 5 SiB 2 of a double-pore structure has been successfully fabricated by combining the in situ reaction 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 × 10 −7 l/(min · cm 2  · Pa) to 1.74 × 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 μ m to 230 μ m, the parameters of this porous intermetallics changed slightly except to the significant increase of big pores diameter. An exponential equation of σ c  =  σ s (1- ρ ) 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.