Boron-doped molybdenum silicides for structural applications

The addition of as little as 1 wt.% (= 3 at.%) boron improved the oxidation resistance of Mo,Si, by as much as five orders of magnitude over a tempera ture range of 800-1500 degrees C. The mechanism of oxidation protection is the formation of a borosilicate glass scale that flows to form a passivatin g layer over the base intermetallic. The compositional homogeneity range fo r T1 (Mo5Si3Bx) phase was determined to be much smaller than that reported previously by Nowotny. Compressive creep measurements show that materials b ased on the phase assemblage of T1-T2 (Mo5SiB2)-Mo3Si have high creep stren gths similar to single phase Mo,Si,. Electrical resistivity of selected com positions was also measured and varied from approximate to 0.06 m Omega-cm at room temperature to 0.14 m Omega-cm at 1500 degrees C. Temperature coeff icient of resistivity (TCR) was estimated to be on the order of 1 x 10(-4) C-1 for most compositions. (C) 1999 Elsevier Science S.A. All rights reserv ed.