DEVELOPMENT OF NEW TOOL MATERIALS OF FRICTION STIR WELDING OF STEELS

Abstract

In order to enhance the performance of friction stir welding (FSW) tool materials for welding of hard alloys such as steel, development of new tool materials is necessary. The purpose of the present work is to prepare new tool materials of titanium carbo-nitride TiCN based cermet with 20wt% and 25wt% nickel (Ni) metallic binder by powder metallurgy manufacturing processes namely pressure-less sintering (PLS) and spark plasma sintering (SPS), and estimate the potential of the sintered cermets in frictions stir welding conditions of ductile alloys as aluminum alloys and hard alloys as steel. TiCN-20wt% Ni cermets were prepared by pressure less sintering under uniaxial pressure of 150 and 200 MPa at 1550 °C sintering temperature. While, TiCN-25wt% Ni cermets were prepared by spark plasma sintering under 50 MPa at 1250 and 1350 °C sintering temperatures. The microstructure and compound phases of the cermet samples were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Mechanical properties such as hardness and fracture toughness of prepared samples has been measured. The performance of the cermet samples as FSW tool (pin) was studied during welding of (5052 & 6061) Al alloys and mild steel. Density more than 95%, hardness and fracture toughness up to 9.17 GPa & 11.5 MPa.m0.5 have been achieved with cermet sample prepared using pressure less method. Cermet samples of TiCN + Ni composition have poor compaction during sintering using spark plasma. Cermet samples that prepared by pressure less sintering shows better resistance than spark plasma sintering samples against the heavy loading during friction stir welding.