Ti-re-n Ve Cr-re-n Kaplamalarda Aşınma Deneyi Sırasında Oluşan Katı Yağlayıcı Filmlerin Araştırılması

Abstract

Malzemeler kullanım koşullarında çeşitli etkilere maruz kalmaktadır. Bu etkileri gidermek ve daha uzun ömürlü malzeme dayanımı sağlamak amacıyla yeni malzemeler ve kaplamalar geliştirilmektedir. Aşınma ve sürtünme etkilerinden dolayı geleneksel kaplamalar değişen çevre koşullarında yetersiz kalmaktadır. Geleneksel kaplamalara eklenen bazı elementlerle elde edilen yeni kaplamalar üstün sürtünme ve aşınma özellikleri sergiledikleri yapılan araştırmalarla belirlenmiştir. Geleneksel kaplamalara eklenen metalik elementlerin kaplamaların aşınma ve sürtünme özellikleri geliştirmesi kaplamanın yağlayıcılık özelliklerinin gelişmesi ile ilgilidir. Aşınma esnasında oluşan tribokimyasal reaksiyonlarla oluşan yağlayıcı filmlerin araştırılması ve geliştirilmesi çok önemlidir. 2010 yılında Dr. Zafer KAHRAMAN’ ın doktora çalışması olan ve “Tribolojik Amaçlı, Üstün Özellikli Renyum Esaslı Sert Nanokompozit Yapılı Kaplamaların Geliştirilmesi” isimli 105M146 nolu TÜBİTAK projesi kapsamında desteklenen “Renyum Nitrür ve Renyum Katkılı Nanokompozit Yapılı Sert Seramik Kaplamaların Üretimi ve Karakterizasyonu” konulu tez çalışması kapsamında Ti-Re-N ve Cr-Re-N kaplamalar üretilmiştir. Kaplamaların oda sıcaklığından 2000C ye kadar karşılıklı aşınma deneyi yapılmış ve tribokimyasal reaksiyonlar neticesinde oluşan oksitlerin incelenmesi Mikro Raman Spektroskobu ile yapılmıştır Bu çalışmanın amacı; Dr. Kahraman’ın doktora tez çalışmasından farklı olarak Ti-Re-N ve Cr-Re-N kaplamalarda karşılıklı aşınma deneyleri sırasında meydana gelen tribokimyasal reaksiyonlar sonucu oluşan katı yağlayıcı filmlerin XPS ile detaylı bir şekilde araştırılmasıdır. Bu amaçla CrN ve TiN kaplamalar Katodik ark FBB, Ti-Re-N ve Cr-Re-N kaplamalar Hibrit kaplama (katodik ark+manyetik alanda sıçratma) yöntemleri ile üretilmiş, karşılaştırmalı XRD analizleri ile Ti-Re-N ve Cr-Re-N kaplamalardaki fazlar belirlenmiş, kalotest yöntemi ile kaplama kalınlıkları belirlenmiş, Kaplamalardaki atomik % Renyum oranları EDS ile belirlenmiş, kaplama morfolojileri SEM ile belirlenmiş, kaplamaların oda sıcaklığı aşınma deneyleri ve 1500C de 1 saat ön ısıtmalı aşınma deneyleri yapılmış ve aşınma deneyleri sırasında yüzeyde oluşan katı yağlayıcı oksitlerin tesbiti için XPS analizi yapılmıştır. Son olarak aşınma bölgelerinin optik profilometre incelemeleri yapılarak çalışma tamamlanmıştır. Yapılan çalışma neticesinde renyum katkısının kaplama mikroyapısını kolonsaldan eş eksenliye dönüştürdüğü, kaplama sertliklerinde belirgin bir azalmaya neden olmadığı, Cr-Re-N kaplamada at. %5.3 Re ve Ti-Re-N kaplamada at. % 7.6 Re olmasından dolayı XRD analizlerinde ReN’ lerin bariz bir şekilde görülmediği fakat CrN ve TiN piklerinin tane boyutunun düşmesiyle genişlediği, karşılıklı aşınma deneylerinden Ti-Re-N kaplamalardaki sürtünme katsayısının renyum katkısı sayesinde dramatik bir şekilde düştüğü ve Cr-Re-N deki at. %5.3 lük renyum katkısının sürtünme katsayısı üzerinde olumlu etkisi olmakla beraber CrN e göre çok düşürmediği, tribokimyasal reaksiyonlar sonucu oluşan oksitlerin Re2O7, ReO3, ReO2, TiO2 ve CrO2 olduğu belirlenmiştir.

Materials are exposed various harmful effects according to using conditions. Especially, wear and friction leads to materials, performance and energy losts. In the practice, solid lubricants are frequently used to overcome friction and wear problems. The designing of the suitable solid lubricants for using conditions is an important issue. A crystal chemical approach is presented by Erdemir to account for the low friction behavior of oxides that form on sliding surfaces of the films. According to this approach, oxides or oxide mixtures with higher ionic potential provide low friction when present at sliding surfaces. For binary oxide systems, the crystal chemical approach considers the difference in the ionic potentials of the two oxides. The larger difference of ionic potatials means the lower the friction coefficients. Rhenium oxides have the highest ionic potantial according to the crystal chemistry approach. The using of rhenium as a dopant is more suitable because of its costs. In phD study of Dr. Kahraman Ti-Re-N (at. % 8 Re) and Cr-Re-N (at. % 6.3 Re) coatings were produced by using hybrid coating method. Reciprocating wear tests of the coatings were carried between 25-2000C. To determine tribofilms formed during wear tests, micro Raman spectroscopy analysis were done. Production and Characterization of Rhenium nitride and Rhenium doped nanocomposite structure Hard Ceramic Coatings named phD study of Dr. Zafer Kahraman was supported by TUBITAK 105M146 project (Development of High Performance Rhenium Based Hard Nanocomposite Coatings for Tribolojical Application). The aim of this thesis is to investigate the solid lubricant films formed during reciprocating wear tests of Cr-Re-N and Ti-Re-N coatings. X- ray Photo Electron Spectroscopy analyses was used to determine solid lubricant films. In the experimental study, CrN and TiN coatings were produced by reactive Physical Vapor Deposition technique. Cr-Re-N and Ti-Re-N coatings were produced by Hybrid Coating System (Cathodic ark PVD+Magnetron PVD). For all coatings, hardened high-speed seel was used as a subtrate material and same cathode current (80A) was used. Before coating process of all coatings, ion etching and heating were done. During coating, -150V bias voltage was applied for all coatings. The thickness of the coatings was determined by using a ball cratering technique (Calotest). Hardness measurements were carried out with an ultra micro-hardness test machine. The structural analysis of the coatings were done by using a glancing angle X-ray diffractometer with a thin film attachment. The film morphology of the coatings were observed with Scanning Electron Microscope, and elemental analyses were conducted using energy dispersive spectroscopy method. Tribological investigations of the coatings were performed by using a reciprocating test system. The reciprocating wear tests of the coatings were carried at room temperature and 1500C (samples heated for one hour at 1500C). Worn samples of all the coatings were kept in vacuum conditions to prevent deteriation. For XPS investigations, AlKα radiation was used. EDS analyses showed that the hard coatings produced on High Speed Steel substrates contained 5.3–7.6 at% rhenium (Ti-Re-N with at. % 7.6 Re, Cr-Re-N with at. % 5.3 Re). The thickness of the coatings varied between 1.61 and 2.86 µm. These thickness values were verified by cross section SEM investigations. The cross-sectional SEM images showed that the film morphology of the coatings changed from a columnar one to a nearly featureless sutructure with the addition of rhenium. The XRD analyses of the coatings showed that the presence of rhenium in the structure did not create a change in the crystal structure of the coatings. No diffraction peaks are found for rhenium and/or rhenium nitride in the coatings because of the quantitiy of the rhenium in the coatings was so few to observe with XRD. Peak broadening was observed for Ti-Re-N and Cr-Re-N coatings because of grain size refinement. This is a typical result for nanocomposite structures. In reciprocating tests, the TiN coatings exhibited the worst tribological performance. In addition to this, TiN coating exhibited the highest friction among all the coatings tested, they were also worn out even after sliding for only a few meters distances. A few amount of rhenium (with at. %7.6) in the Ti-Re-N (at room temperature, CoF: 0.22) caused a dramatic decrease in friction coefficient. Ti-Re-N sample (heated for one hour at 150oC) exhibited a slight lower friction according to room temperature Ti-Re-N wear sample. In reciprocating wear test conducted at room temperature. CrN coating a CoF value of 0.3. It is clear that the presence of Re in the Cr-Re-N film slightly reduced its friction coefficient according to CrN films. Cr-Re-N (heated for one hour at 150oC) exhibited a slightly lower friction then Cr-Re-N room temperature wear sample. Ti-Re-N worn sample O 1s spectrum was decomposed to four peaks. These peaks associated with the presence of Re2O7 (533.4 eV), ReO3 (531.6 eV), ReO2 (530.4 eV) and TiO2 (529.2 eV). Cr-Re-N worn sample O 1s spectra was decomposed to four peaks. These peaks associated with the presence of Re2O7 (532.9 eV), ReO3 (531.5 eV), ReO2 (529.3 eV) and CrO2 (529.3 eV).