Papers by Keyword: Hot Deformation

Abstract: This study investigates the deformation behaviour of the CM247LC superalloy through a combination of physical experimentation and computational analysis. High temperature deformation was conducted at 600°C, 800°C, and 1000°C with a strain rate of 0.001 s⁻¹ and 50% of deformation. This research integrates microstructural analysis and mathematical equations to enhance understanding of the alloy's response under varying conditions. The findings reveal that at 600°C, the superalloy exhibits high flow stress and significant ultimate strength due to limited dynamic recovery (DRV) and restricted dynamic recrystallization (DRX). The increase in yield strength from 708 MPa at 600°C to 814 MPa at 800°C is attributed to effective precipitation strengthening from the γ' phases, corroborated by FEM simulations that show higher average yield strength values ranging from 875 MPa to 900 MPa at 800°C. Microstructural analysis indicates the role of finely dispersed carbides at lower temperatures and their coarsening at higher temperatures, which affects the material's strain-hardening behaviour and softening mechanisms. While physical simulations provide empirical data on mechanical properties and microstructural changes, FEM simulations predict stress-strain distributions and identify potential instability regions.

Abstract: The laser powder bed fusion (L-PBF) technique was utilized to manufacture a hybrid M789-N709 alloy by depositing M789 steel on wrought N709 steel. The tensile strength of the M789-N709 interface generated during the process has been established to be higher than that of the base materials. In the previous work of the current authors, extensive characterization of the M789-N709 interface (before and after heat treatment) was performed by means of electron backscatter diffraction, electron probe microanalysis, transmission electron microscopy with energy dispersive spectroscopy, and atom probe tomography analyses, to understand the mechanisms associated with its superior strength. In the present work, since the application of the hybrid alloy is targeted towards an elevated temperature environment, the individual high-temperature mechanical properties of M789 and N709 steels were acquired at various temperatures and strain rates using a Gleeble 563 thermomechanical system. Then, based on the flow curves, phenomenological-, and physical-based constitutive material models were established. These constitutive models can be utilized to accurately assess the high-temperature response of the hybrid alloy system using finite element analysis programs. This work demonstrates the application of thermomechanical processing and constitutive modeling in the field of metal additive manufacturing.

Abstract: Today environmental aspects are of great importance in the sustainability of the planet, in this aspect anti-corrosive treatments facilitate the durability of metal structures. Among the most widely used anticorrosive metals is Zinc and its alloys. In the deep galvanizing process of large steel structures, tanks containing Zinc in a molten state at a temperature of 460 °C are necessary. Then, to protect elements that are too large or that need to be treated "in situ", metallization is used, which consists of projecting molten zinc wire on the metal surface that has previously been subjected to a process sandblasting (mechanical abrasion). The two main methods of metalizing are electric arc and flame. In the present work an industrial wiredrawing draft has been studied, determining the drawing force and the power required in each stage. For this purpose, linear strain hardening model vs non-linear strain hardening model that takes strain rate hardening into account has been proposed for its implementation in the analytical model of the process and finite element model (FEM) has been developed too. The use of Hall Petch equation has been allowed to get a prediction of the evolution of the grain size during the wiredrawing sequence.

Abstract: A novel type of titanium alloy was investigated in this article. The microstructure and mechanical properties of Ti-3573 and Ti-3873 titanium alloys were observed and measured after 20% hot deformation, respectively. The results shown that both titanium alloys occurred dynamic recrystallization (DR) during hot deformation. The tensile strength of Ti-3873 titanium alloy was better than that of Ti-3573 titanium alloy. Both titanium alloys have fine secondary α-phase which appeared granular or acicular near the β-grain boundaries or within the β-grain after hot deformation. Better tensile strength (847 MPa) of Ti-3873 titanium alloy is contributed to the higher content of β-phase stable element (Mo). The improvement plasticity (12 %) of Ti-3573 titanium alloy is due to the occurrence of dynamic recrystallization during hot deformation.

Abstract: Dislocations play a critical role in metal forming processes, and accurate values of dislocation density are important in modelling these processes. However, direct determination of the dislocation density is challenging. In this study, electron backscatter diffraction is used to estimate the evolution of geometrically necessary dislocation density as a function of plastic strain, strain rate and temperature in hot compression of AA7050 alloy. The geometrically necessary dislocation density was found to increase at a higher strain rate and lower temperature; the higher dislocation density in these samples promoted continuous dynamic recrystallisation leading to grain refinement. At lower strain rates and higher temperatures, the dislocation densities were lower and dislocations formed into walls, channels and cells. These observations agree with accepted theories of dislocation evolution and demonstrate the capability of electron backscatter diffraction to provide representative dislocation density values as well as comprehensive information linking plastic flow with microstructural evolution.Keywords: electron backscatter diffraction (EBSD), geometrically necessary dislocations (GNDs), hot deformation, AA7050

Abstract: The development and introduction of new nickel-based heat-resistant alloys with a special combination of an increased complex of physicomechanical properties is a priority task for modern materials science.

Abstract: The hot deformation behavior of Ti-Al-Nb-Zr-Mo-Cr titanium alloy has been investigated using a Gleeble-1500D thermal simulation test machine in the temperature range of 855°C~1015°C,at constant strain rate from 0.01 s^-1 to 10s^-1 and with height reduction of 45%. The flow curves characteristic under different deformation parameters show significant difference. According to the stress-strain curves of the alloy and its stress characteristics, the Arrhenius constitutive equation was obtained. The average activation energy is about 541 kJ/mol in the α+β field, and about 243 kJ/mol in the β field, respectively. Based on the dynamic materials model, the processing map is generated, which shows that the peak efficiency domain appears at the temperature of 874°C~900°C and the strain rate of 0.001 s^-1~0.06s^-1 with a peak efficiency of 0.58 at about 887°C/0.001s^-1.

Abstract: The hot deformation behavior of spray-formed AlSn20Cu alloy during hot compression deformation was studied, and the constitutive equation of AlSn20Cu alloy was established. The samples of spray-formed AlSn20Cu alloy were compressed on Gleeble-3500 thermal simulation test machine. The error of the true stress caused by adiabatic heating effect in the experiment was corrected. The constitutive equation of spray-formed AlSn20Cu alloy could be represented by Zener-Hollomon parameter in a hyperbolic sine function. The results showed that the deformation temperatures and strain rates had a notable effect on the true stress of the alloy. At the identical deformation temperature, the true stress increased with the increase of strain rate. When the strain rate was constant, the stress decreased with the increase of deformation temperature. After hot compression deformation, the tin phase was elongated along the direction perpendicular to the compression axis with short strips and blocks. With the increase of deformation temperature and the decrease of strain rate, Sn phase distribution became more homogeneous.

Abstract: The δ-TRIP steel has attracted wide attention from researchers and industry, as it possesses the mechanical properties of the third-generation advanced automotive steels, and the lower density achieved by the addition of light element aluminum. However, there have been few studies on the hot deformation behavior of δ-TRIP steel at high temperature, which is critical for the design of the hot rolling process. In the present study, hot compression tests were carried out on a 980 MPa δ-TRIP steel to achieve a better understanding of the deformation behavior at high temperatures from 800°C to 1150°C. Combined with the electron backscatter diffraction (EBSD) analysis, the results showed that δ-TRIP steel was a positive strain-rate sensitive material, and its soften was contributed by dynamic re-crystallization of ferrite and austenite during deformation at high temperature. The hot deformation activation energy (Q = 327.485 kJ/mol) of the experimental steel was calculated, and the strain index was 5.65. Besides, the related constitutive equation and the flow stress equation were also established.

Abstract: The effect of processing parameters on meta-dynamic recrystallization (MDRX) and the microstructural characteristics evolution of TiAl alloy with high Nb containing during annealing period were studied through double-pass hot compression tests. The results indicated that the occurrence of MDRX had a strengthening effect to flow behavior of the present alloy, resulting in grain equalization. And the high temperature and large strain were beneficial for the occurrence of MDRX, resulting in the increase of recrystallization grains. For the present alloy, MDRX rate is low, hence, enough annealing time is needed for MDRX during inter-pass annealing. Besides, dislocation density is consumed with the occurrence of MDRX.