Abstract
Pressureless consolidation of metallic powders is achieved by sintering, in a nonoxidizing atmosphere, a blend of the metallic powder with a small amount of finely divided lithium tetraborate. For example, a tool steel powder of 80-mesh particle size or finer, consisting of mo 4.9, W 6.3, Cr 4, V 2, mn 0.26, C 1 pct, the balance Fe, was blended with 0.5 Wt pct Li2B4O7, of about minus 100- mesh particle size by ball-milling for 1/2 h in a jar mill containing agate balls. Blended powder was loaded into an open ceramic-lined graphite mold, and the mold was vibrated to achieve a tap density of approximately 40 pct. The blended powder and mold then were heated to about 760 deg C for 1/2 h in either a helium atmosphere or in a vacuum of less than 5 x 10-2 torr, then the temperature was raised to about 1,225 deg C and held there for approximately 1 h per inch of starting powder thickness. The resulting product was found to have a sintered density of 94 pct of the theoretical density with the helium atmosphere and 92 pct with the vacuum.
