Papers by Keyword: Serrated Flow

Abstract: The serrated flow phenomena in Al-Mg alloys with and without Zn were investigated after aging on several conditions, focusing on the role of precipitates. Al-6mass%Mg-0~3mass%Zn alloys were solution treated at 753~803K, quenched, and then aged at room temperature. Further artificial aging at 323~573K for 86.4ks was performed for some of them after natural aging for 2.6Ms. The serrated flow behavior was evaluated by tensile test. Microstructure was characterized by differential scanning calorimetry, transmission electron microscopy, atom probe tomography, and positron annihilation lifetime spectroscopy. The increase in the amount of Zn addition and the natural aging time lead to a delayed onset of serrated flow. The artificial aging at higher temperatures after natural aging, on the other hand, decreases the onset strain. A large number of small coherent Zn-Mg clusters are formed during natural aging in the Al-Mg-Zn alloys, which are transformed to the larger incoherent meta-stable precipitates during subsequent artificial aging. These results suggest that the mechanism of interfering with serrated flow is related to the vacancy trapping effect, which is enhanced by the coherent clusters.

Abstract: Serrated flow behavior of an 11Cr ferritic/martensitic steel was investigated through tensile tests at initial strain rates of 2×10^-510^-3 s^-1 at temperatures ranging from room temperature to 973 K. Serrated flow occurred at three temperature regions of room temperature, 573 K and 773973 K when tensile tests were conducted at a strain rate of 2×10^-4 s^-1. Serrations are also observed in the steel during tension at temperatures of 573 K and 773973 K at a strain rate of 2×10^-5 s^-1. With increasing tensile temperature, the yield stress and ultimate tensile stress of the steel were gradually decreased and quickly dropped at temperatures higher than 773 K, while the elongation of the steel was decreased to a minimum at 600 K, and then dramatically increased at temperatures higher than 600 K.

Abstract: Serrated flow behavior of the 316LN austenitic stainless steel was investigated through tensile tests at initial strain rates of 2×10^-5 to 10^-4 s^-1 at temperatures ranging from room temperature to 1048 K. Serrated flow occurred at room temperature and 6981048K at the strain rate of 2×10^-4 s^-1, as well as at temperatures of 623673 K at the strain rate of 2×10^-5 s^-1. Type A, A+B, C and E serrations appeared. The activation energy for the occurrence of serrated flow at high temperatures was about 327 kJ/mol. The dynamic strain aging caused by the interaction between substitutional solute Cr atoms and moving dislocations is considered as the mechanism of serrated flow at the temperatures higher than 973 K.

Abstract: Instable plasticity, which is normally a consequence of interactions between diffusing solute atoms and dislocations, is observed in AZ91D magnesium at room temperature. Experimental measurements of different heat treatment of AZ91D magnesium were taken to investigate different influence on PLC effect by the presence and structural state of second phase in this study. Tensile specimens were tested at room temperature at a crosshead speed of 0.6 mm/min. The results indicate that some number of large,coherent precipitates prevents serrated flow by way of trapping vacancies, but small precipitates content do not supress it.

Abstract: Flow behavior of the surface and center layers of solution-treated, peak-aged, or reversion-treated 2090 Al-Li alloy specimens has been reviewed and discussed in terms of microstructures and textures.

Abstract: Tensile specimens cut from the surface layer to the center layer of a 12.7 mm thick 2090 Al-Li alloy plate were solution treated at 550°C for 30 min and subsequently peak-aged at 190°C for 18 h. They were tensile tested along the rolling direction at 25°C at various strain rates. The solution-treated specimens gave rise to serrated flows at a strain rate of 2×10-4 s-1. On the other hand, for the peak-aged alloy, the surface-layer and subsurface-layer specimens underwent complex, serrated flows (fine and coarse types superimposed each other), whereas the center-layer and near-center-layer specimens were devoid of serrated flows. The textures of the surface-layer and subsurface-layer specimens were approximated by the {001}<110> orientation, while those of the center-layer and near-center-layer specimens were approximated by the {011}<211> orientation. The different flow behaviors were discussed based on the crystallographic textures, microstructures and the strain rates.

Abstract: A recrystallized Co-Ni-Cr-Mo based superalloy was produced by cold working of 72% and subsequent recrystallization heat treatment. Microstructural observation revealed that a full recrystallization of the cold-worked alloy occured when heat treatment was performed at and above 1273K for 1h. So that, recrystallization heat treatment was carried out in a temperature range from 1273K to 1473K for 1h~24h, by which the average grain size was controlled to 28µm～238µm. Tensile tests were carried out from room temperature (RT) to 1073K in order to understand the effect of grain size on the mechanical properties of the Co-Ni-Cr-Mo based superalloy. At RT and 943K, yield strength, tensile strength and elongation of the recrystallized alloy were improved with decreasing grain size. The alloy having a grain size less than 42µm exhibited a steady-state flow behavior in the true stress-true strain curve at 943K. However, the alloy having a grain size of 28µm showed lower yield strength than that of 42µm at 1073K. It was found that the steady state flow is closely related to the occurrence of {111}<112> deformation twinning in the Co-Ni-Cr-Mo based superalloy.