Ti-n Ve Cr-n Esaslı Pvd Kaplamaların Oksidasyon Davranışları

Abstract

İhtiyaçların artması ve gelişmesi, teknolojik gelişmeyi de beraberinde getirmektedir. Bunun sonucu olarak, endüstriyel malzemelerin kullanım ve üretimlerinde bir takım alternatif arayışlara gidilmiştir. Bunların başında gelen konulardan bir tanesi seramik esaslı kaplamalardır. Sert seramik esaslı kaplamaların metal işleme endüstrisinde kullanımının sağladığı başlıca faydalar; daha uzun takım ömrü, üretim hızında artış, takım stok maliyetinin azalması, daha iyi işleme yüzey kalitesi... bazılarıdır. 1980'li yılların başından itibaren yüksek oranda takımların kaplanmasına başlanmıştır. Endüstriyel uygulamalarda yüzey kaplama teknolojileri, 1- Optik amaçlı 2- Elektrik- elektronik sanayinde kullanım amaçlı 3- Dekoratif amaçlı 4- Korozyondan korunma amaçlı 5- Tribolojik amaçlı, olarak yaygın şekilde kullanılmaktadır. Bu çalışmada TİN ve ON esaslı seramik kaplamaların statik hava şartlarındaki oksitlenme davranışları incelenmiştir. Burada katodik ark PVD yöntemi kullanılarak alümina plakalar kaplanarak yatay tüp fırında oksitlenme işlemine tabi tutulmuştur. Toplam 18 adet numune oksitlenmiştir. Oksitlenen numuneler daha sonra x-ışını analiz yöntemiyle oluşan oksit yapıları incelenmiştir. Yapılan X-ışınlan analiz neticesinde TİN ve CrN kaplamaların belirlenen deney sıcaklık ve sürelerinde oksitlendikleri fakat, tamamen kararlı oksit yapısına ulaşamadıktan tesbit edilmiştir.

High Temperature Behaviours of the Ti-N and Cr-N based PVD Coatings. In the metalworking and plastic working industry many different operations are used: Cutting, forming, punching, plastic injection moulding... For each of these operations some predominant tool failure mechanisms can be derived. Due to the thermal shock resistance, high temperature stability, corrosion resistance, resistance to chemicals... ceramics and their coatings have been grate interest and successfully used in industry. Coatings of hard materials such as TiC, TiN and other carbides, nitrides, or oxides are applied to the surfaces of industrial materials. Wear and corrosion of materials is one of the larger technical problems in todays industry resulting in high economical losses. Surface treatment can yield here better surface properties to reduce the deleterious effects of this wear and corrosion. Since the beginning of the 80's PVD ceramic coatings are used for many applications. Nowadays, 4 types of coatings are frequently used : TİN, Ti(C,N), (Ti,Al)N, and CrN. The PVD technology has reached a degree of maturity so that in general a constant coating quality can be guaranteed by several jobcoaters. However, only about 5% of the tools that could be coated are indeed coated nowadays. In the past decade, substitution of uncoated tools by tools coated in titanium nitride has taken place to a significant extent in one of the following two ways: 1- Changes in the machining conditions have been accompanied by changes in tool manufacturing and preparation methods. In most cases these changes have xn included: tool material, cutting edge geometry, surface finishing methods and tool resharpening procedures. 2- New manufacturing steps have been introduced based on entirely new types of tools which can only function when coated. It was only some rare instances that tools were coated simpiy to increase their lifetimes. Initially, the industrial use of phsical vapor deposition methods for the coating of tools was limited to tools made of high speed steels. It took many years for manufacturing engineers and tool producers to realize that PVD coatings have particular mechanical properties which aiso make them useful for carbide tools, and make possible the design of high performance carbide tools with sharp edges. Ironically, this was the first application for hard PVD coatings which university researchers investigated in the mid-seventies. Vapour deposited coatings are not oniy used in cutting industry but aiso in other fields including optical, electrical, electronic, chemical and decorative applications. These coatings are extensively used on giass frame for optical and decorative functions, on watches and automotive parts for decorative function, on capacitors for electronically function, on cutting tools for mechanical function and manufacturing corrosion resistant parts. PVD processes permit the deposition of fiims whose phases are usually not in equilibrium. This is made possible by the nature of the process, in which the components forming the fiim are charged with high energies and/or deposited on a substrate with certain structural and thermal states. PVD is therefore able to produce differently formed phases, modifying not oniy the composition but aiso he structure of the film. PVD processes mainly can be divided into two groups a) evaporation b) sputtering Xill Evaporation is the oldest and well-known PVD method. The basic evaporation process involves the transfer of material to form a coating by vapourization. PVD by cathodic arc evaporation is often preferred for its low substrate coating temperature, good target economy, high deposition rate and high degree of ionization. One of the main characteristics of arc evaporation is macro particles, which are generated by the action of the cathode spots. Coatings that include significant macro particles have a surface roughness and matt appearance. Applications where macro particle would clearly be detrimental include optical and microelectronic coatings. In order to reduce the generation of macro particle it is necessary to reduce the cathode temperature or to use steered arc deposition technique and to filter macro particles from plasma by using low angle collectors and increasing substrate bias voltage. Under most conditions of use metals are thermodinamically unstable with respect to ambient gases, and-depending on their composition and the reaction conditions- will react to form oxides, sulphides, carbides, nitrides etc. or mixtures of reaction products The extent of the oxygen solubility varies greatly for different metals. The solubility may qualitatively be correlated with the position of the metals in the periodic table. All metals may occlude gases. The gases may be present in metals as intersitially dissolved atoms, as molecular gas in micro cracks or voids, or in the form of separate phases such as oxides, nitrides or hybrides. Oxygen is readily soluable in the transition metals belonging to groups IV and VA. However, the solubility in group VIA metals is extremely small. As a measure of the solubility it may be mentioned that the solubility in the alpha- phase of titanium, zirconium and hafnium amounts to about 30 at. % 28.5 at. % and 20 at. %, respectively. xiv In this study, the PVD method of arc evaporation is used for deposition. The coating substrate was alumina plates. Alumina was used as the substrate material since the coating is not affected by alumina and the qualities of coating could be determined without the influence of substrate materials. The alumina samples have been coated with mainly TiN and CrN ceramic films. Coating Was obtained with cathodic arc PVD method at 450 - 500°C and under partial pressure nitrogen 4-5x1 0"3 Torr. The study was conducted in order to determine the oxidation behaviour of TiN and CrN ceramic coatings. The coated samples (TiN and CrN) were oxidized under the static atmosphere pressure conditions. The horizontal tube oven was used to oxidize. The oxidation parameters for TiN and CrN as follows; 450 °C, 30min., 45min. 60min. 500 °C 30min. 45min. 60min. 550 °C 30min. 45min. 60min., for TiN. 700 °C 30min. 60min. 90m 800 °C 30min. 60min. 90min. 900 °V 30min. 60min. 90min., for CrN. 18 TiN and CrN coated samples, which oxidized were analysed with a X-ray difractometer. xv As a conclusion, it was found out that, two type of coated samples were oxidized mainly in form of Tİ203 and Cr203/Cr304, respectively. However, it was also found out that oxidation times were too short to exactly form oxide