Book Description

Chromium alloys were coated with silicon, aluminum, and boron by pack cementation. None of these simple coatings provided adequate nitridation-oxidation protection for a chromium +0.17 wt % yttrium alloy substrate as shown by a substantial increase in the ductile-brittle transition temperature after air exposure for 100 hr at 2100 degrees F (1420 K). Iron modified silicides coatings afforded good protection, holding the transition temperature of air exposed specimens to 3500 F (450 K) compared to 200 degrees F (370 K) for recrystallized uncoated specimens. Additional attractive modifying elements included iron-molybdenum, iron-molybdenum-tungsten, iron-molybdenum-tungsten-titanium and vanadium-molybdenum-tungsten-titantum.