Papers by Keyword: Aging Behaviour

Abstract: Mg-5Y-3Nd-Zr-xGd (x=0 and 4 wt.%) alloys were prepared by metal mould casting, and aging behavior, mechanical properties and fracture morphology were investigated. The result shows that after T6 treatment, the massive eutectic phase in as-cast alloys dissolved and finer Mg5RE phase precipitated dispersively in the matrix, and mechanical properties were improved simultaneously. Mg-5Y-3Nd-4Gd-Zr alloy exhibits good age hardening behavior and the peak hardness is about 20% higher than the Gd-free alloy. Gd addition can significantly improve mechanical properties of the alloy especially at the elevated temperature. The ultimate tensile strength and yield strength of Mg-5Y-3Nd-4Gd-Zr alloy at 250°C, with the value of 276 and 168 MPa, respectively, are over 20% higher than those of the Gd-free alloy. It is mainly attributed to the increase and homogeneous distribution of the fine heat-resistant Mg5RE precipitate in the matrix.

Abstract: The characterization of the aging behavior of raw natural rubber (NR) coagulated by microorganisms (NR-m) was performed on a rubber processing analyzer (RPA) by tests of frequency sweep, strain sweep and stress relaxation, respectively. With the prolongation of the aging time, the storage modulus (G'), storage torque (S'), complex viscosity (η^*) and stress relaxation time of raw NR-m decreased while the damping factor (tanδ) were increased. As the oscillation frequency was increasing, the G' rose gradually but the tanδ decreased. The η^* diminished over the whole range of frequency shear rate (γ_ƒ) values. Its change remained all almost the same at low strain shear rate (γ_s) but began to decrease sharply when the rate reached a higher value. The S' soared up in the region of less than 10°, but began to slow down after that point.

Abstract: This paper attempts to reveal the aging behaviors of natural rubber (NR) used in isolation bearings. Using various degradation factors like thermal oxidation, ultraviolet, ozone, low temperature ozone, salt water and acid rain, a series of environmental accelerated aging tests were conducted to investigate the aging characteristics. From the test results, it was clarified that the thermal oxidation is the dominant degradation factor, which hardens the rubbers and results in a significant drop of performance. This study is fundamental to predicting the lifecycle of NR isolation bearings.

Abstract: The microstructure and property of T91/10CrMo910 dissimilar steel welded joints after one and two years service have been studied by OM, TEM, EDS and Vickers hardness test in this paper. The results showed that after one year service the microhardness of T91/10CrMo910 dissimilar steel welded joints increased clearly and after two years service chromium element diffused or transferred from the welding line or T91 matrix to 10CrMo910 matrix. Coarse lath martensite was the characteristic of the microstructure of T91/10CrMo910 dissimilar steel welded joints, and the martensite laths became fragment after one and two years service. More carbide particles had been observed after one year service than that after two year service, which had a good agreement with the results of the micro-Vickers hardness test.

Abstract: In this study, a room temperature aging behavior of Ba(Ti0.99Fe0.01)O3 was investigated. It was found that the dielectric constant decreased with time and ferroelectric P-E hysteresis loops became constricted loops after aging. Moreover, the room temperature aging behavior under various stresses was also observed. It was found that the relative changes of dielectric constant with time of Ba(Ti0.99Fe0.01)O3 ceramics under stress were lower than those under the stress-free condition. For P-E hysteresis loop measurement, it can be observed that P-E hysteresis loop of Ba(Ti0.99Fe0.01)O3 ceramics became constricted loops and remanant polarizations (Pr), saturated polarizations (Ps) were decreased after aging under all stress levels. These results suggested that the applied stress may partly clamp the domain wall motion, and altered the aging behavior of the ceramics.