NITROGEN IN SPRAY FORMED SUPERALLOYS

Spray forming is of considerable interest for potential commercial production of superalloy forging and rolling preforms. The low degree of macrosegregation and the relatively small grain size (25-40 mu m) make this process look attractive for compositionally complex modern day nickel based superalloys. Both argon and nitrogen have been used successfully as the atomising gas. Argon atomisation has been used when little or no oxygen or nitrogen pickup is desired and when a small amount of argon filled porosity (similar to 1 vol.-%) can be tolerated. Nitrogen atomisation has been used when a decrease in porosity is desired and when a small amount of nitrogen pickup can be tolerated. In this case, rather than staying in the pores, the nitrogen gas dissolves into the alloy and precipitates as submicrometre titanium and niobium carbonitrides. These precipitates have been observed to have little effect on creep, and fatigue). PM/0649