This paper describes a study of explosively welded titanium-carbon steel S355J2+N plates. Following the welding, plates underwent heat treatment at temperature of 600°C for 90 min with cooling in furnace to 300°C and in air to room temperature. The structure of the bonding was examined by using light, scanning electron (SEM) and transmission electron microscopy. The mechanical properties before and after heat treatment were examined applying three-point bending tests with cyclic loads and hardness measurements. Fracture surfaces were investigated using computer tomography and SEM. It has been found that the bonding areas are characterized by a specific chemical composition, microstructure and microhardness. Between the steel and the Ti cladding, a strongly defected transition zone was formed and melted areas with altered chemical composition were observed. It was also demonstrated that the heat treatment commonly applied to welded steel-Ti plates had a significant and negative impact on the microstructure and mechanical properties of the welded plates due to formation of brittle intermetallic phases.
Abstract. In the study, there were investigated the effects of friction stir processing (FSP) which was applied in order to improve the surfaces of notched specimens made of S235JR and S355J2 carbon steels, on their fatigue crack growth rates in the air. There were presented the results of comparative fatigue tests conducted at asymmetric tension (R= -0.2) for these steels treated by means of FSP and for the ones in the delivery state. The method of successive etched material layers used revealed the presence of internal tensile stresses in the surface layers of treated specimens. Crack growth rates were described on the basis of non-linear fracture mechanics, taking the effects of internal stresses into account.
The aim of this research was to examine the mechanical and fatigue properties of friction stir welded Sc-modified 5 mm thick AA2519-T62 extrusion. The joint was obtained using the following parameters: 800 rpm tool rotation speed, 100 mm/min tool traverse speed, 17 kN axial, and MX Triflute as a tool. The investigation has involved microstructure observations, microhardness distribution analysis, tensile test with digital image correlation technique, observations of the fracture surface, measurements of residual stresses, low cycle fatigue testing, and fractography. It was stated that the obtained weld is defect-free and has joint efficiency of 83%. The failure in the tensile test occurred at the boundary of the thermo-mechanically affected zone and stir zone on the advancing side of the weld. The residual stress measurements have revealed that the highest values of longitudinal stress are localized at the distance of 10 mm from the joint line with their values of 124 MPa (the retreating side) and 159 MPa (the advancing side). The results of low cycle fatigue testing have allowed establishing of the values of the cyclic strength coefficient (k′ = 504.37 MPa) and cyclic strain hardening exponent (n′ = 0.0068) as well as the factors of the Manson–Coffin–Basquin equation: the fatigue strength coefficient σ′f = 462.4 MPa, the fatigue strength exponent b = −0.066, the fatigue ductility coefficient ε′f = 0.4212, and the fatigue ductility exponent c = −0.911.
In this research the three different FSW joints of Titanium Grade 1 have been performed by using tool made of W25Re alloy with different welding velocity values. In order to investigate the influence of FSW process on microstructure of joined material the light microscope observations have been performed on the etched samples. It has been reported that significant grain refinement occurs in the stir zone in all analyzed samples. On the other hand, occurrence of weld defects, such as tunneling defect and kissing bond has been noticed. The microhardness analysis of the cross-section of the obtained joints indicates on microhardness increasing in the stir zone by 40-60 HV0,1 compared to the base material. Peak hardness of stir zone in the researched samples has tendency to decrease along with increasing of welding velocity. The strength of obtained joints was designated in the uniaxial tensile tests and confronted with strength of base material. Despite the occurrence of weld defects the established joints efficiency contains in range 92-94%. It has been stated that Young’s modulus of Titanium Grade 1 FSW joints is 15-19% lower in comparison to the base material. At the same time, no significant influence of FSW on the ductility of material were observed.
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