Low-pressure-plasma-deposited coatings formed from mechanically alloyed powders

A limiting feature of the low-pressure-plasma-coating process at the present state of the art is the need for −400 mesh (−37 μm) feed powder for the gun. In this study we demonstrated that mechanically alloyed M Cr Al type (where M is cobalt, nickel or iron) powders suitable for low pressure plasma spraying can be prepared using the attritor process. A two-step attriting process was developed which yields a large fraction of −400 mesh powders. A study of the effects of attritor processing parameters was made on Co 29Cr 6Al 1Y powder that was mechanically alloyed from a blend of cobalt, chromium, Co Al and Co Y powders. Coatings deposited onto IN-738 pin specimens by low pressure plasma spraying were hot corrosion tested; these compare favorably with Co 29Cr 6Al 1Y coatings deposited using atomized powders. A three-step attriting process also was developed which is particularly useful in forming M Cr Al-type powders using elemental aluminum as a starting ingredient.