Niyazi Özdemir

Bio: Niyazi Özdemir is an academic researcher from Fırat University. The author has contributed to research in topics: Welding & Friction welding. The author has an hindex of 12, co-authored 34 publications receiving 656 citations.

Tungsten-inert gas surface alloying of a low carbon steel

Abstract: In the present study, SAE 1020 steel surface was alloyed with preplaced graphite, chromium and high-carbon-ferro-chromium powders by using a tungsten-inert gas (TIG) heat source, separately. The effects of thickness of the preplaced powder layer on the microstructure, hardness and wear resistance of the alloyed surfaces were investigated. Following the surface alloying, conventional characterization techniques, such as optical microscopy, scanning electron microscopy (SEM), energy dispersive spectrograph (EDS) and X-ray diffraction were employed for studying the microstructure of the alloyed surface. Hardness measurements were performed across the alloyed zone and wear properties of the surfaces were evaluated by a pin-on-disc abrasive wear testing method. The results indicated that different amounts of chromium, carbon and chromium with carbon could be obtained on the surface of the SAE 1020 steel, changing the thickness of the preplaced powder layer. The alloyed surfaces showed an increase in hardness and wear resistance and this was attributed to harder phases. However, the highest hardness and wear resistance surface was obtained for the high-carbon-ferro-chromium powder layer with a 2.4-mm layer. This was attributed to a higher volume friction of carbides (Cr 7 C 3 ) in the microstructure. As a result, TIG arc heat source can be used effectively for surface alloying with a preplaced powder to improve resistance of the surface of the SAE 1020 steel to wear.

Interfacial properties of diffusion bonded Ti-6Al-4V to AISI 304 stainless steel by inserting a Cu interlayer

Abstract: The joining characteristics of Ti-6Al-4V with AISI 304 stainless steel by inserting a Cu interlayer was investigated in a vacuum-free diffusion bonding process. The diffusion bonds were carried out in the temperature range of 820, 850 and 870°C for 50, 70 and 90 minutes, respectively, under 1 MPa load in argon atmosphere. The joining performances of diffusion bonded Ti-6Al-4V to AISI 304 were studied experimentally. The influence of the insert layer on the microstructure-formed interface region, bonding quality and mechanical properties have also been estimated. The microstructures formed in the diffusion region were observed and determined by scanning electron microscopy (SEM). The microhardness across and perpendicular to the interface were measured and the strength of the joints were also determined with lap-shear test.

Fatigue behaviour of AISI 304 steel to AISI 4340 steel welded by friction welding

Abstract: In the presented study, The weldability of AISI 304 austenitic stainless steel to AISI 4340 steel joined by friction welding in different rotational speeds and fatigue behaviour of friction-welded samples were investigated. Tension tests were applied to welded parts to obtain the strength of the joints. The welding zones were examined by scanning electron microscopy (SEM) and analyzed by energy dispersive spectroscopy (EDS). The Vickers microhardness distributions in welding zone were determined. Fatigue tests were performed using a rotational bending fatigue test machine and the fatigue strength has been analysed drawing S-N curves and critically observing fatigue fracture surfaces of the tested samples. The experimental results indicate that mechanical properties and microstructural features are affected significantly by rotation speed and the fatigue strength of friction-welded samples decrease due to chromium carbide precipitation in welding zone with increasing rotation speed in choosen conditions.

Linear and rotary friction welding review

Abstract: Friction welding (FW) is a high quality, nominally solid-state joining process, which produces welds of high structural integrity. Rotary friction welding (RFW) is the most commonly used form of FW, while linear friction welding (LFW) is a relatively new method being used mainly for the production of integrally bladed disc (blisk) assemblies in the aircraft engine industry. Numerous similar and dissimilar joints of structural metallic materials have been welded with RFW and LFW. In this review, the current state of understanding and development of RFW and LFW is presented. Particular emphasis is placed on the process parameters, joint microstructure, residual stresses, mechanical properties and their relationships. Finally, opportunities for further research and development of the RFW and LFW processes are identified.

Advances in friction welding process: a review

Abstract: Friction welding is now well established as one of the most economical and highly productive methods in joining similar and dissimilar metals. It is widely used in automotive and aerospace industrial applications. Friction welding is often the only viable alternative in this field to overcome the difficulties encountered in joining the materials with widely varying physical characteristics. This process employs a machine that is designed to convert mechanical energy into heat at the joint to weld using relative movement between workpieces, without the use of electrical energy or heat from other sources. This review deals with the fundamental understanding of the process. The focus is on the mechanism of friction welding, types of relative motions of the process, influence of parameters, heat generation in the process, understanding the deformation, microstructure and the properties of similar and dissimilar welded materials.