Lingxiao Ouyang

Bio: Lingxiao Ouyang is an academic researcher from Tohoku University. The author has contributed to research in topics: Strain rate & Dynamic recrystallization. The author has an hindex of 5, co-authored 9 publications receiving 66 citations.

Hot deformation characteristics and dynamic recrystallization mechanisms of a Co–Ni-based superalloy

Abstract: The hot deformation behavior of a Co–Ni-based superalloy was systematically investigated using thermal compression tests. Stress–strain curves showed a typical dynamic softening after peak stress, especially at high temperatures and low strain rates. An Arrhenius-type constitutive equation was developed to reveal the relationship between the flow stress, strain rate, and temperature, while a processing map was constructed based on the calculations from the stress-strain curves combined with microstructural observations to determine the optimum thermal deformation conditions. The extent of recrystallization was found to increase with increasing temperature, a decreasing strain rate, or an increasing strain. A complete dynamic recrystallization (DRX) condition was reached at 1050 °C/0.01 s−1/0.7. In addition, pre-existing annealing twins were replaced by discontinuous dynamic recrystallization (DDRX) grains along the twin boundaries and the twin-DRX (TDRX) grains in the twin interior. In the case of an un-twinned matrix, a combined DDRX and continuous DRX (CDRX) process occurred at high strain rates, in contrasted with a single DDRX process taking place at low strain rates.

Hot deformation behavior and mechanism of a new metastable β titanium alloy Ti–6Cr–5Mo–5V–4Al in single phase region

Abstract: A new metastable β titanium alloy Ti–6Cr–5Mo–5V–4Al (Ti-6554) has shown good application potential in large parts. In order to study the hot deformation behavior and mechanism of the Ti-6554 alloy in the β single phase region, hot compression tests were carried out at temperatures of 800–950 °C and strain rates of 0.001–10 s−1 on the Gleeble-3500 thermal simulation machine. Strain-compensated Arrhenius constitutive model was used to predict the flow behavior of the alloy, and the correlation coefficient between the experimental and predicted values reached 0.982. Based on the hot processing map, it was found that the instability region was mainly concentrated in the high strain rate area, and the peak efficiency of power dissipation (η) region occurs in the temperature range of 913–928 °C and the strain rate of 0.001–0.0025 s-1. There was an obvious DRX phenomenon in the stability region, while the instability region was dominated by deformation band (DB) and flow localization (FL). The continuous dynamic recrystallization (CDRX) by progressive rotation of subgrains and discontinuous dynamic recrystallization (DDRX) by grain boundaries bulging could be observed. DDRX mainly occurred in high temperature and low strain rate regions, while the CDRX process occurred in the high strain rate region. As the η decreased, the deformation mechanism changed from DDRX to CDRX and further to dynamic recovery (DRV), DB, FL.

Significant improvement in yield stress of Mg-Gd-Mn alloy by forming bimodal grain structure

Abstract: Fabricating bimodal grain structure is an effective way to improve the mechanical properties of Mg alloys. In present work, the various Mn contents (0, 0.5, 1.0, 1.5 wt%) are added in Mg-1.0Gd alloy to fabricate bimodal grain structure and improve the mechanical properties. After extrusion at 300 °C, bimodal grain structure is obtained in the Mg-1.0Gd-1.0Mn and Mg-1.0Gd-1.5Mn alloys. With the increment of Mn content, the average grain sizes of dynamic recrystallization (DRX) grains are refined from 8.6 to 1.2 μm. The mechanical properties are significantly improved. The Mg-1.0Gd-1.5Mn alloy exhibits the best tensile yield stress (TYS) and ultimate tensile stress (UTS), which is 280 MPa and 293 MPa. Comparing with the Mg-1.0Gd alloy, the improvement of TYS and UTS are 165 MPa (143%) and 98 MPa (51%). The enhancement of the strength is mainly attributed to the bimodal grain structure. The formation of the bimodal grain structure and the strengthening mechanisms are also discussed.

Hot deformation characteristics and dynamic recrystallization mechanisms of a Co–Ni-based superalloy

Abstract: The hot deformation behavior of a Co–Ni-based superalloy was systematically investigated using thermal compression tests. Stress–strain curves showed a typical dynamic softening after peak stress, especially at high temperatures and low strain rates. An Arrhenius-type constitutive equation was developed to reveal the relationship between the flow stress, strain rate, and temperature, while a processing map was constructed based on the calculations from the stress-strain curves combined with microstructural observations to determine the optimum thermal deformation conditions. The extent of recrystallization was found to increase with increasing temperature, a decreasing strain rate, or an increasing strain. A complete dynamic recrystallization (DRX) condition was reached at 1050 °C/0.01 s−1/0.7. In addition, pre-existing annealing twins were replaced by discontinuous dynamic recrystallization (DDRX) grains along the twin boundaries and the twin-DRX (TDRX) grains in the twin interior. In the case of an un-twinned matrix, a combined DDRX and continuous DRX (CDRX) process occurred at high strain rates, in contrasted with a single DDRX process taking place at low strain rates.

High-temperature tensile characteristics and constitutive models of ultrahigh strength steel

Abstract: In this investigation, the isothermal tensile experiments over wide ranges of deformation parameters (strain rate and tensile temperature) are conducted for studying the high-temperature tensile behaviors of an ultrahigh strength steel. The influences of deformation parameter on high-temperature tensile behaviors, fracture characteristics and deformation mechanisms are analyzed. Moreover, Arrhenius-type phenomenological (AP) model developed by the regression method or the Nelder-Mead (NM) simplex method, and the artificial-neural-network (ANN) model developed by combining genetic algorithm (GA) and back propagation learning algorithm (BP) are proposed, respectively. The results show that the high-temperature tensile behavior of the studied steel exhibits the typical work hardening and dynamic recovery characteristics. The necking capability increases with the strain rate decreasing and tensile temperature increasing. However, the large deep dimples dramatically deteriorate the loading capability during the localized necking, leading to the poor elongation to fracture at low strain rate. Both for the modeling and verifying data, the AP model developed by the NM simplex method shows the relatively high relative coefficient (higher than 0.9963), low average absolute relative error (lower than 1.6692%) and narrow error band (controlled in ±6.8MPa), compared with the AP model developed by the regression method and the GA-BP ANN model.