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

It is shown that the use of nitrogen or carbon as alloying elements in plas ma diffusion treatment of TiAl6V4 is beneficial for the load-supporting pro perties of the base material. The plasma diffusion treatment produces a com pound layer consisting of nitrides or carbides and an inner diffusion zone, essentially characterized by the presence of nitrogen- or carbon-rich alph a -Ti crystals which are embedded in the metal matrix. This results in a ha rdness gradient from the interior to the surface. To avoid hydrogen embritt lement, plasma nitriding is performed in a pure nitrogen atmosphere. The fo rmation of soot by carburizing could be avoided by optimizing the carbon fl ow during plasma carburizing. The influence of plasma nitriding and carburi zing on the adhesion of the TiC coating depends on the plasma diffusion pre treatment and the conditions of the TiC coating. Plasma-nitrocarburizing pr etreatment 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 criti cal load of approximately 33 N was found under the optimum parameters. We c onclude that the combination of plasma diffusion treatment and TiC coating extends the tribological applicability of TiAl6V4 in many industrial sector s. Fretting fatigue and wear could be increased by a duplex plasma treatmen t combined with shot peening. (C) 2001 Elsevier Science B.V. All rights res erved.