Zirkonyum Nitrür (ZrN) kaplamalar endüstriyel alanda yaygın uygulaması olan diğer fiziksel buhar biriktirme (FBB) kaplamalar ile kıyaslandığında, düşük yüzey sürtünme katsayısına, az sayıda metalik damlacık dağılımına ve düşük yüzey pürüzlülüğüne sahip olmasına rağmen, görece düşük sertliği ve kötü yapışma mukavemeti sebebiyle yaygın uygulama alanına sahip değildir. Genel kullanım alanı sadece demir dışı yumuşak metal ve alaşımların (alüminyum, bakır, pirinç vb.) talaşlı şekillendirilmesi prosesleriyle kısıtlıdır. Bazı özel üretim proseslerinin kullanımıyla, ZrN’in sürtünme katsayısı arttırılmaksızın, kaplama sertliği ve yapışma mukavemeti arttırılabilirse, ZrN kaplamalara yeni kullanım alanları oluşturmak mümkün olabilecektir. Özetle, eğer hem yüksek sertliğe ve yapışma mukavemetine, hem de düşük sürtünme katsayısına sahip bir kaplama üretilebilirse bu ideal bir kaplama olur ve endüstriyel uygulamada yaygın olarak kullanılabilir. Böyle bir kaplama geliştirmek amacıyla FBB kaplama proses parametrelerinin etkilerinin incelendiği bu çalışmada, öncelikle ZrN kaplamaların üretiminde azot kısmi basıncının optimizasyonu yapılmış, sonra belirlenen azot kısmi basıncı değerinde doğru akım bias, tek kutuplu değişken bias ve asimetrik çift kutuplu değişken bias voltajları uygulanarak elde edilen kaplamaların yapısı ve kalınlık, sertlik ve yapışma mukavemeti gibi mekanik özelliklerindeki değişimler incelenmiştir. Deneysel çalışmalar sonucunda, 8 mtorr azot kısmi basıncında, -200 volt asimetrik çift kutuplu değişken bias voltajıyla üretilen FBB ZrN kaplamanın en iyi mekanik özelliklere sahip olduğu tespit edilmiştir. Anahtar Kelimeler: FBB kaplamalar, ZrN, doğru akım bias, tek kutuplu değişken, asimetrik çift kutuplu. When compared to the other Physical Vapor Deposition (PVD) coatings which are extensively used in industrial applications, Zirconium Nitride (ZrN) coating does not have a wide application in industry because of its relatively low hardness and low adhesion strength despite its low friction coefficient. Its common application field is restricted by machining soft and ductile non-ferrous metals and alloys like aluminium, copper, brass etc. under well-cooled machining conditions. Although surface friction coefficient of a material changes due to its surface roughness, ambient temperature and lubrication regime; when all the simulation conditions are fixed, it would be a physical material property that is variable characteristically for each material surface. The low friction coefficient of the polished surface of ZrN coating at room temperature and non-lubricated conditions enhances adhesive wear resistance of ZrN coated tools and considerably reduces the built-up edge formation and the material loss during machining and forming processes. Therefore ZrN coating has a significant effect to improve the wear resistance of the tools especially used in adhesive wear conditions. Furthermore, ZrN coating has lower surface roughness and less droplet (macroparticle) distribution than Titanium Nitride (TiN) and Chromium Nitride (CrN) coatings which are widely used in the industry; and this is also an important effect on reducing friction. However, ZrN coating has some unfavorable properties such as relatively low hardness and low adhesion strength. If the coating hardness and adhesion strength of ZrN coating could be improved without altering its friction properties by performing some special processes, it would be possible to extend its usage in the new applications. Briefly, if a coating which has both a high hardness and low friction coefficient and also a high adhesion strength can be produced; it would be an ideal coating which would have both adhesive and abrasive wear resistances and can be extensively used at all processes in industrial applications. ZrN might be an ideal coating for such a study because of its low friction coefficient and low droplet size and distribution. Furthermore, since zirconium metal has higher melting temperature and lower vapor pressure than the other cathode metals like titanium, aluminium and chromium; droplet transfer from the cathode to the coating would be at a minimum degree, so ZrN coatings contain much fewer and smaller droplets. In such a way, as a result of droplet decrease, the durability and homogenity of the coating increases and the surface roughness decreases. The aim of this study is to enhance the properties of ZrN coating through the optimization of PVD process parameters and to expand its market usage. In the first step of the experimental studies, the reactive gas (nitrogen) partial pressure used at the PVD ZrN coating was optimized. The basic mechanical properties such as coating hardness, coating thickness and adhesion strength of ZrN films deposited in various nitrogen partial pressures were determined and compared. Coating hardnesses were measured by using a Micro Vickers test device, coating thicknesses were measured by using Calotest ball cratering method and coating adhesion strengths were measured by using a scratch tester. Furthermore a standard Rockwell-C hardness measurement method was used for determining coating adhesions comparatively. As the result, the coating produced under 8 mtorr nitrogen partial pressure exhibited the best mechanical properties. In the next step of the experimental studies, 8 mtorr was kept constant as the nitrogen partial pressure and a bias voltage scan was performed by applying various d.c., unipolar pulse and asymmetric bipolar pulse bias voltages. The pulse frequency was kept constant as 50 kHz for all the coatings deposited by pulse bias voltages. Related to the ion energy improvement in asymmetric bipolar pulse bias mode, a grain orientation close to single crystal structure, dense film structures, enhancement in nitrogen content and improvement on the mechanical properties such as hardness, adhesion, thickness etc. compared to d.c. and unipolar pulse bias modes were achieved. As the result of experimental studies, the coating hardness equivalent to TiN coatings and friction and adhesion properties equivalent to CrN coatings were achieved in a single coating. The best results were achieved in ZrN coatings deposited by applying 8 mtorr nitrogen partial pressure and -200 volt asymmetric bipolar pulse bias voltage value. Keywords: PVD coatings, ZrN, d.c. bias, unipolar pulse, asymmetric bipolar
