Volume 8, Issue 4 (April 2011)
Modification of NiAl Intermetallic Coatings Processed by PTA with Chromium Carbides
Equipment that operates under high-temperatures can be protected with NiAl intermetallic coatings because of their metallurgical stability. This study evaluates the effect of chromium carbides added to Ni–Al intermetallic coatings processed by plasma transferred arc (PTA). Mixtures of Ni and Al powders with and without different Cr23C6 fractions (15, 30, and 45 wt %) were deposited by PTA on an AISI 304 stainless steel plate, using two different currents (100 and 150 A). Coatings were evaluated for the presence of welding defects, and the developed microstructures were characterized by X-ray diffraction and scanning electron microscopy. Vickers microhardness and semiquantitative energy dispersive spectroscopy chemical composition were also determined. NiAl and Cr7C3 development was confirmed by X-ray diffraction analysis. A combination of NiAl/Cr–Fe–Ni phases was identified. The hardness was strongly related to the formed phases and volume fractions. The present study shows that PTA hardfacing can be used to produce reinforced intermetallic coatings for high-temperature applications, showing significant advances toward the development of coatings that can withstand severe operation conditions.