Orkun Tunçkan 1 , and Servet Turan 2

1. A.R 900 oC Orkun Tunçkan1 , and Servet Turan2 Microanalysis at the Reaction Layers Formed Between TiCN Coated Si3N4 and Ti Foil After Heat Treatment TiCN TiCN TiCN Ti Si3N4 Si3N4 Si3N4 Si3N4 Point WDX Analysis 1Anadolu University, School of Civil Aviation, Iki Eylül Campus, 26555 Eskisehir, TURKEY 2Anadolu University,Dept. of Materials Science & Eng., Iki Eylul Campus, Eskisehir, 26555 TURKEY Ti CAPACITOR DISCHARGE JOINING PURPOSE OF THE STUDY Use of ceramic joining techniques enable the production of more complex shapes than can presently be achieved in monolithic ceramics. Several techniques are available for joining ceramics such as mechanical joining,active-metal brazing, diffusion bonding and ceramic adhesives. However, the use of ceramic adhesives gives relatively low mechanical strength, while diffusion bonding and brazing both necessitate heating the ceramic parts for relatively long periods of time, which is not only expensive but also can alter the properties of the ceramic. Therefore, a new ceramics joining technique, namely capacitor-discharge joining, has been developed in Russia. Silicon nitride (Si3N4) based materials are widely used as cutting tools in the machining of cast iron, where excellent resistance to wear, corrosion and erosion in operation at high temperature are required, whereas in the field of stainless steel, superalloy and Ti alloys machining other type of cuttting tools are used. One of the reason for not preferring silicon nitride based materials is the reactions between the cutting tool and the machined part. Therefore, the purpose of the study was to investigate the possible reactions between ceramic cutting tools and the machined parts and then heat treating the joined parts at the temperatures of around 1000°C that is thought to be occuring during the machining operation. The principle of the joining techniqueis simple: a metallic foil is sandwiched between two ceramic pieces with the foil in contact with two copper electrodes capable of carrying the discharge from a capacitor. The capacitor is then discharged while simultaneously applying pressure to the joint. The resulting high energy pulse vaporizes the interlayer which then bonds to the ceramics on either side of the foil. Some of the mechanical test results are given below and detailed information about this technique can be found S. Turan et al. J. Am. Ceram Soc., 82, 1242, 1999. EXPERIMENTAL STUDIES Different types of SiAlON and Si3N4 ceramics are joined successfully using 10 mm thick stainless steel or Inconel foils as an interlayers. After joining, in order to find the effect of heat treatment on the interfacial structure, some of the samples were heat treated (HT) 1000° C in air. Specimens for scanning electron microscope (SEM) investigations was prepared by cutting slices perpendicular to the width of the joint. After polishing, SEM samples wereexamined in a ZEISS Supra 50 VP FEG SEM attached with an energy dispersive X-ray spectrometer (EDX-OXFORD Instruments), wavelength dispersive X-ray spectrometer (WDX-OXFORD Instruments) and a electron bacscatter diffractometer,(EBSD-OXFORD Instruments). EXPERIMENTAL RESULTS ANDDISCUSSION Reactions between Ti and TixCyNz coated Si3N4 Examples of interfacial structures in back-scattered SEM images and line scan WDX analysis of the as-received and heat treated Ti and TixCyNz coated Si3N4 specimens are given below.Foils and reaction layers (RL) especially after HT can be clearly distinguished due to sufficient atomic number contrast. In as-joined specimen only small amount of Si diffuses into the Ti interlayer as the diffusion of Si in Ti lower activation energy than O2 and N2. TiCN C C N N Ti Ti Si Si CONCLUSIONS Oxide ceramics have higher shear strengths than both carbide and nitride ceramics when joined using AlxNiyYz foil. When AlxNiyYz foil was used better joints were obtained. Nitride ceramics have similar shear strengths to carbide ceramics. . Line scan WDX analysis showed that in all systems, Si from the ceramic side diffuses into TiCN coating as the diffusion of Si in both foils has much lower activation energy than N, Al and O. After heat teatment it was observed that Si diffusion was increased from ceramic side to foil. But in TixCyNz coated Si3N4 system, Si diffussion was almost blocked by means of this coating. In this study, extended reactions were observed at various silicon nitride based materials and determined that Si3N4 coated TixCyNz cutting tool is an alternative way to machining Ti alloys. As a future work heat treatment should be carried out at lower temperatures and more detailed TEM studies should be employed to observe much thinner reaction layer. We are sorry not to present detailed EFTEM results due to the delayed installation of our JEOL 2100 F attached with GIF Tridiem, STEM, EDX and HAADF. For furher information please contact Servet Turan, Orkun Tunckan and Hilmi Yurdakul (sturan@anadolu.edu.tr, otunckan@anadolu.edu.tr, hyurdakul@anadolu.edu.tr)