Connecting Creep Constitutive Parameters to Microstructural Deformation in Sn

Hot Deformation Behavior of AA3102 Aluminum Alloy: Constitutive Modeling, Microstructural Evolution and Numerical Simulation

This study systematically investigates the hot deformation behavior and microstructural evolution of AA3102 aluminum alloy through isothermal uniaxial compression tests conducted at 400–550 °C and strain rates of 0.01–10 s−1. Previous studies on 3xxx-series Al–Mn alloys have mainly considered temperature and strain-rate effects while neglecting strain-dependent material parameter variations, limiting prediction accuracy under large deformation and obscuring dynamic softening mechanisms. Here, the experimental flow stress data were corrected for interfacial friction and adiabatic temperature rise. A sixth-order strain-compensated Arrhenius constitutive model was then developed to describe the coupled effects of temperature, strain rate, and strain. Full-strain-range power dissipation and flow instability maps were constructed using the dynamic material model, while optical microscopy and DEFORM-3D simulations were employed to clarify microstructural evolution and deformation inhomogeneity. The model achieved a correlation coefficient of 0.9841 and an average absolute relative error of 3.67%, demonstrating high predictive accuracy. No flow instability was detected within the investigated range, indicating excellent hot formability. The favorable compression-processing window was identified as 500–550 °C and 0.1–1 s−1, while the peak power-dissipation efficiency increased from 30.55% at ε = 0.2 to 32.90% at ε = 0.8. Optical-microstructural observations suggest that increasing temperature and decreasing strain rate are associated with an increasing contribution of dynamic recrystallization relative to dynamic recovery. Finite-element results further reveal pronounced spatial variations in strain, temperature, strain rate, and stress during compression. These findings provide baseline constitutive and thermomechanical information for subsequent AA3102 hot-extrusion optimization.

High-temperature compression testing and microstructural characterization of near-α titanium alloy TC30 for flow-forming applications

1340 Effect of deformation temperatures on microstructure and mechanical properties in an Al containing low Si TRIP steel

An Al containing low Si TRIP steel was subjected to different deformation temperatures in austenite non-recrystallization region during thermo-mechanical processes. The microstructural characteristics were analyzed by means of optical microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron back scattered diffraction (EBSD), and its effects on mechanical properties were investigated. The results show that lower deformation temperature strongly promotes the proeutectoid ferrite formation at the expense of bainite, which causes an increase in the amount of retained austenite (RA). Compared with the case of higher deformation temperature in austenite non-recrystallization region, the steel processed by lower deformation temperature exhibits higher elongation and excellent combination of strength and ductility because of higher fractions of polygonal ferrite and RA particles with different size that provide sustained transformation induced plasticity (TRIP) effect over a significantly wide strain range. The un-transformed RA in fractured tensile specimen has much smaller grain size and higher carbon content in comparison to the case before fracture.

Modified constitutive approach to flow stress, activation energy evolution, and processing map in a low-carbon bainitic steel

In this study, the hot deformation behavior of a low-carbon bainitic steel is systematically examined within a temperature range of 1073–1373 K (800–1100 °C) and for strain rates from 0.01 to 10  s − 1 using isothermal uniaxial compression testing. Commonly-used constitutive models typically assume constant material parameters during deformation; however, material constants can vary during deformation. To address this, a modified hyperbolic sine constitutive model is implemented to more accurately predict flow stress behavior under varying thermo-mechanical conditions. The modified model exhibited strong predictive capability with experimental data, achieving a low average absolute relative error of approximately 5% and a correlation coefficient of 0.98. Activation energy analysis revealed a clear temperature dependence, with activation energy decreasing at higher temperatures due to enhanced dislocation mobility. The activation energy was also shown to progressively decrease with increasing strain, due to dynamic recrystallization mechanisms. Processing maps were developed for different strain levels based on the dynamic materials model, revealing the effect of strain on instability zones. The optimal hot deformation conditions were identified to be in the range of 1250–1350 K (977–1077 °C) at 0.02 to 0.12  s − 1 , to facilitate dynamic recrystallization, leading to formation of a uniformly refined prior austenite grain microstructure.

Deformation of Quenched and Tempered Low-Carbon Steel: Part I—Quasi-Static Behavior

Aging-Induced Microstructural Evolution and Fracture Mechanisms of 35Cr45NiNb Alloy Under High-Temperature Tensile Deformation

Centrifugally cast 35Cr45NiNb alloy has been widely employed in ethylene-cracking furnace tubes owing to its excellent carburization and creep resistance. However, the influence of microstructural degradation and temperature on its high-temperature tensile behavior remains poorly investigated. In this study, an accelerated aging method at 1200 °C for 230 h (A1) and 430 h (A2) was employed to simulate approximately 4 and 8 years of service at 1050 °C, based on the Larson-Miller parameter. The equivalence was validated by the nearly identical precipitate area fractions of the A1 specimen (16.6%) and an ex-service specimen (14.8%). Combined with SEM and EBSD characterization, tensile tests at 950, 1000, and 1050 °C were conducted to elucidate the relationship between microstructure and high-temperature tensile properties. During aging, the skeletal interdendritic M7C3 carbides transformed into blocky M23C6, NbC evolved into the brittle G-phase (Ni16Nb6Si7), fine secondary M23C6 precipitates formed, and the initially continuous primary-carbide network progressively coarsened. Yield and ultimate tensile strengths decreased monotonically with increasing temperature, whereas aging produced pronounced hardening at the expense of ductility, as secondary-carbide precipitation strengthening outweighed the weakening of the primary carbide network. The fracture mode transitioned from mixed quasi-cleavage fracture at 950 °C, initiated by stress concentration at coarse phase interfaces, to ductile rupture at 1000 and 1050 °C. GND analysis further revealed an aging-dependent transition in the dominant deformation mechanism, from dislocation pile-up at the carbide network, to recrystallization after prolonged aging.