Improvement in the load-bearing capacity and adhesion of TiC coatings on TiAl6V4 by duplex treatment

Abstract

It is shown that the use of nitrogen or carbon as alloying elements in plasma diffusion treatment of TiAl6V4 is beneficial for the load-supporting properties of the base material. The plasma diffusion treatment produces a compound layer consisting of nitrides or carbides and an inner diffusion zone, essentially characterized by the presence of nitrogen- or carbon-rich α-Ti crystals which are embedded in the metal matrix. This results in a hardness gradient from the interior to the surface. To avoid hydrogen embrittlement, plasma nitriding is performed in a pure nitrogen atmosphere. The formation of soot by carburizing could be avoided by optimizing the carbon flow during plasma carburizing. The influence of plasma nitriding and carburizing on the adhesion of the TiC coating depends on the plasma diffusion pretreatment and the conditions of the TiC coating. Plasma-nitrocarburizing pretreatment leads to the best adhesion of the TiC coating; the critical load of failure is 80% higher than in the case of TiC on base material. A critical load of approximately 33 N was found under the optimum parameters. We conclude that the combination of plasma diffusion treatment and TiC coating extends the tribological applicability of TiAl6V4 in many industrial sectors. Fretting fatigue and wear could be increased by a duplex plasma treatment combined with shot peening.