Development of Novel Coating Technology by Vacuum Arc with Rotating Cathodes for Industrial Production of nc-(Al1−xTix)N/a-Si3N4 Superhard Nanocomposite Coatings for Dry, Hard Machining 79602

The development of  novel  superhard  nanocomposite,  nano-layered  coatings  and of the coating technology based on vacuum arc evaporation from  rotating elec- trodes is summarized。 The nc-(Al1−x Tix )N/a-Si3N4   coatings in which the nano-

crystals of the Al-rich solid solution with the fcc crystal structure of TiN are

imbedded into a thin matrix of amorphous silicon nitride show high thermal stability, oxidation resistance and excellent performance in dry, fast machining that is superior to the state-of-the-art (Ti1−x Alx )N    coatings。

KEY WORDS: Superhard nanocomposites; industrial applications; (AlTi)N/Si3N4;  Al–Ti–Si–N;  vacuum arc。

1。INTRODUCTION

The demand for the improvement of machining technology in terms of higher cutting speed, better quality of the machined surface, lower con- sumption of lubricants and coolants calls for the development of new wear resistant coatings for machining tools。 Because the costs  of environmen- tally friendly recycling and disposal of the  coolants  represent  a signifi- cant part of the total machining costs, the ultimate goal is dry, high speed machining。 Under such conditions, the temperature of the cutting tool and of the coatings can reach 800◦C or more。 This poses strong requirements on  the  quality  of  the  coatings,  such  as  a  high  hardness  combined with

1SHM  Ltd。,  CZ-78803  Novy  Malin  266,  Czech Republic。

2PLATIT  AG,  Moosstr。  68,  CH-2540  Grenchen,  Switzerland。

3Institute for Chemistry of Inorganic Materials, Technical  University  Munich,  Lich- tenbergstr。  4,  D-85747  Garching/Munich,  Germany。

4To whom correspondence should be addressed。 Telephone: +49 89 289 136 24; fax: +49

89  289  136  26;  e-mail:   veprek@ch。tum。de

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0272-4324/04/1200-0493/0  © 2004 Plenum Publishing  Corporation

a high resistance against crack formation and adherence to the substrate, high temperature stability and oxidation resistance, low coefficient of fric- tion, absence of reaction with the material being machined and others。 For

(1, 2)

these reasons, the earlier developed (Ti1−x Alx )N    coatings

and more

recent (Tix Aly Yz )N, (Tix Aly Yz Crc )N coatings with a high oxidation resis-

tance(3, 4) and similar coatings alloyed with Hf, Zr, V and other elements in order to improve the cutting performance are  progressively replacing TiN。

Also superlattice coatings (“heterostructures”), that show enhanced hardness when the superlattice period decreases to 5–8 nm,(5, 6) are receiv- ing increasing attention as protection coatings of machining tools at industrial scale。(7) Much work is also devoted to the development of self-lubricant hard coatings, low friction coatings  for  bearings  and others。(8)

In the present paper  we  shall  concentrate  on  the  recently  devel- oped superhard nanocomposites that are formed according to the generic design principle(9, 10) by self-organization due to thermodynamically driven spinodal phase segregation。 It will be shown that the superhard nano- composites nc-(Al1−x Tix )N/a-Si3N4 with hardness of ≥40GPa posses a high thermal stability and meet the requirements for a new generation of

advanced wear resistant and tribological coatings。 In order to achieve the formation of the stable nanostructure during the deposition a new coating technology based on rotating vacuum arc cathode was developed。