Hüseyin Uzun

Microstructure, hardness and electrical properties of silver-based refractory contact materials

Abstract The electrical conductivity, hardness and microstructure of Ag–W and Ag–WC refractory contact materials have been investigated. Ag–W composites containing 30, 35, 45 and 85 wt.% of silver and Ag-40 wt.% WC composite produced by powder metallurgy were used for this investigation. The effect of graphite addition on hardness and electrical conductivity of Ag–WC composite was also evaluated. The present results show that the electrical conductivity of Ag–W composite increased with increasing Ag content, but decreased its hardness. The addition of WC to Ag increased its hardness, but decreased its electrical conductivity as compared with the addition of W to Ag. The addition of 3 wt.% C to Ag-37 wt.% WC composite decreased both its hardness and electrical conductivity.

Ballistic impact performance of composite structures

One of the materials commonly used in the aerospace and automotive industries is polymer-based composites. It also has potential for even greater usage. In this paper the ballistic impact performance of some polymer-based composites is experimentally considered. This entailed the manufacture of a number of thermosetting resin composite specimens using the hand lay-up process. Thereafter ballistic testing was carried out using a variety of commonly available firearms with the resulting properties experimentally obtained using mechanical and ultrasonic methods. The results were compared relatively with previous studies. Finally the potential benefits for using such materials on an armoured saloon car is highlighted.

Microstructure and mechanical properties of friction stir welded particulate reinforced AA2124/SiC/25p–T4 composite

The purpose of the study is to present the feasibility of the joining of similar AA2124/SiC/25p–T4 composite plates by friction stir welding (FSW). Microstructure properties, microhardness, and tensile tests have been performed to evaluate the weld zone characteristics and the performance of AA2124/SiC/25p–T4 composite joints. The phase structure of a similar AA2124/SiC/25p–T4 composite weld was determined from X-ray diffraction (XRD). The temperature in the weld zone have been evaluated using thermocouples in order to demonstrate the FSWed joint of the AA2124/SiC/25p–T4 composite without melting. The obtained results revealed that FSW can be used in the joining of similar AA2124/SiC/25p–T4 composite plates. XRD measurements show that SiO2 phase was detected in the weld zones. It was determined that the peak temperatures achieved at 15 mm away from the weld center varied between 201°C and 270°C. In addition, the tensile strength of AA2124/SiC/25p–T4 butt joints was found to be approximately 20% lower than that of the base composite. The originality of this study is one of the preliminary studies on the detailed examination of the microstructural and mechanical properties of the AA2124/SiC/25p–T4 composite joint by FSW.

Effect of Heat Treatment on Microstructure, Mechanical Properties and Fracture Behaviour of Ship and Dual Phase Steels

Grade A (GA) and high strength steel DH36 ship steels possessing different chemical compositions were used, and strength properties of GA steel and DH36 steel were compared. Additionally, 4 types of dual phase (DP) steels with different martensite volume fractions (MVFs) were produced from GA steel by means of heat treatment and they were compared with other steels through conducting microstructure, microhardness, tensile and impact tests. The fracture surfaces of specimens (DH36, GA and DP steels) exposed to tensile and Charpy impact tests were investigated by scanning electron microscope. Furthermore, it was found that the specimens quenched from 800 and 900 °C had better strength than DH36 steel. The tensile test results indicated that the tensile strength of DP steel water quenched from 900 °C was 3 times that of GA steel and twice that of DH36 steel.

Microstructural and mechanical properties of dual-phase steels welded using GMAW with solid and flux-cored welding wires

Abstract The aim of this study is to demonstrate the transformation of grade-A steel into dual-phase steel by heat treatment, and the joint performance of dual-phase steels welded by means of the gas metal arc welding process using both solid and flux-cored welding wires. Dual-phase steels with different contents of martensite were obtained by intercritical annealing in different temperature ranges of a grade-A shipbuilding steel, followed by water quenching. The experimental results revealed that the tensile strength of the dual-phase steels joined by solid wire is higher than that of the flux-cored wire joints. The microstructure of grade-A steel consists of ferrite and pearlite, while the dual-phase steels consist of ferrite and martensite. On the other hand, while the martensitic phase is especially encountered in the weld metal of the dual-phase steels joined with the solid wire, the ferrite phase is more common in the weld metal of the flux-cored wire joints.