Hot Working Parameters Research Articles

Hot deformation behavior and dynamic recrystallization mechanism of GH2132 superalloy

In order to study the hot deformation and dynamic recrystallization behavior of annealed GH2132 superalloy, this paper conducted hot compression tests of GH2132 superalloy at different temperatures (950°C–1150°C) and different strain rates (0.01/s–10/s) using Thermocmaster Z thermal simulation testing machine, and made an in-depth analysis of recrystallization behavior via electron backscattered diffraction (EBSD). The results indicate that the flow stresses of GH2132 alloy first increase and then decrease at high temperature, among which the curves present a more obvious flow softening at 10/s. Continuous dynamic recrystallization (CDRX) is dominant at high temperature and low strain rate, while discontinuous dynamic recrystallization (DDRX) plays the major role at low temperature and high strain rate. The type of recrystallization has a significant impact on the formation and volume fraction of twinning. In addition, high-temperature constitutive model, hot processing map, and an unified dynamic recrystallization kinetic model of GH2132 superalloy were established. Thus, the optimal range of hot working parameters was obtained. The research results provide guidance for determining the hot working process window of GH2132 superalloy.

Hot deformation behavior and microstructural evolution of a new type of 7xxx Al alloy

Optimizing the thermal deformation parameters of Al alloys is beneficial for achieving grain refinement, avoiding microscopic defects in materials, and significantly enhancing the mechanical properties of Al alloys. In this study, the hot deformation behavior of a new type of 7xxx Al alloy was investigated through hot compression tests at strain rates of 10−3-1 s−1 and temperatures of 250–420 °C. The constitutive equation was successfully established using the hyperbolic sine form of the Arrhenius equation, accurately describing the flow stress. The hot processing map was obtained by overlaying the power dissipation map and the instability map, determining the optimal hot working parameters to be in the range of 325–373 °C, 0.45–1 s−1. In the safe region, dynamic recovery (DRV) and dynamic recrystallization (DRX) were predominant. The instability in the low-temperature region was attributed to the grain boundary pinning effect caused by grain boundary precipitation, while the instability in the high-temperature region was associated with local shear bands induced by uneven plastic strain. The hot processing map establishes a good connection with the microstructural evolution of the new type of 7xxx Al alloy under different hot deformation parameters.

Research on hot deformation behavior and microstructure evolution mechanism of GH4169 superalloy

The hot deformation behavior and microstructure evolution of GH4169 superalloy were investigated through hot compression experiments with a temperature range of 900–1100 °C and strain rates ranging from 0.01 to 5 s−1. Concurrently, the flow stress curve of the alloy was obtained and constitutive equations were established. Based on the dynamic material model, a hot working diagram was established and the hot working window was optimized. The findings demonstrate that the high-temperature softening mechanism of this alloy primarily involves dynamic recrystallization (DRX), while both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) exist. According to the hot processing map, the process parameters corresponding to the unstable areas are low temperatures and medium-high strain rates (900–985 °C, 0.15–5 s−1), and high temperatures and high strain rates (1025–1100 °C, 2.5–5 s−1). The reason is that the appearance of deformation bands and flow localization in the microstructure. The optimal hot working parameters for GH4169 are 1000 °C/0.01 s−1 and 1050–1100 °C/0.01–0.1 s−1, where the microstructure consists of uniformly distributed DRX grains. The volume fraction of DRX in GH4169 alloy rises with higher temperatures or lower strain rates. In addition, the reduction of intergranular dislocations promotes the migration of grain boundaries from low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs).

Investigation of hot deformation behavior and microstructure evolution of TC18 alloy and establishment of constitutive equation under friction-temperature correction

The effects of deformation temperature and strain rate on the microstructure evolution of TC18 alloy are studied by hot compression experiment and EBSD test, based on the double correction of friction and temperature rise in hot compression, a more accurate constitutive equation and thermal processing diagram are established. Recrystallization grain is the main microstructure of TC18 alloy during deformation from 810 °C to 930 °C. Higher deformation temperature and lower strain rate are beneficial to the occurrence of dynamic recrystallization and grain size growth. The strain rate has no significant effect on volume fraction of large and small angle boundary. After double correction of temperature rise and friction, it is found the activation energy of TC18 titanium alloy in β region and α/β region are 485.895 kJ/mol and 355.337 kJ/mol, respectively. The ideal hot working conditions of TC18 titanium alloy are 812 °C ∼ 840 °C, 0.01 s−1 ∼ 0.018 s−1 and 878 °C ∼ 915 °C, 0.178 s−1 ∼ 1.0 s−1, respectively. The unevenness of microstructure, the large size difference among grains and the large orientation difference among grains lead to the instability of hot working process. The conclusions of this paper can provide more accurate guidance for the determination of hot working parameters and the prediction of microstructure evolution during hot working of TC18 alloy.

Flow behaviors and microstructural evolutions of nickel-based ODS superalloys during hot deformation

The hot deformation behaviors of nickel-based oxide dispersion strengthened (ODS) superalloys fabricated by mechanical alloying (MA) and hot extrusion (HEX) were investigated, the hot compression tests were performed to obtain true stress-true strain curves, the influence of strain rate and temperature connected with the microstructure evolution was analyzed, and the processing map and microstructure proposed at different strain levels was used to select its hot working parameters. The results illustrated that hot working conditions, especially the temperature, strongly influenced the grain structure. Specifically, deforming under high temperatures and low strain rate conditions enhances dynamic softening via dynamic recovery (DRV), dynamic recrystallization (DRX), and grain growth to consume the stored strain energy. In addition, the size and morphology of nanoparticles are not significantly changed before and after deformation, the nanoparticles and the matrix still maintain a good interface combination, and no interfacial mismatch such as nanosvoids between the nanoparticle and matrix is detected due to their outstanding interfacial binding ability and excellent ductility of matrix.

Hot Deformation Behavior of a Hot-Isostatically Pressed Ti-6Al-4V Alloy from Recycled Powder.

In this work, a new use of mixed Ti-6Al-4V powder, consisting of the retained powder after screening for additive manufacturing and the recycled powder after multiple printing, has been exploited. The powder mixture has been hot-isostatically-pressed (HIPed) at 930 °C/120 MPa for 3 h to reach full density. The hot deformation behavior of the as-HIPed powder compacts were investigated through isothermal compression tests, kinetic analyses, and hot processing maps. Finally, the optimized hot working parameters were validated using upsetting tests. The results show that the as-HIPed Ti-6Al-4V alloy has a fine and homogeneous microstructure. The activation energies were calculated to be 359 kJ/mol in the α + β phase regime and 463 kJ/mol in the β phase regime, respectively. The optimal hot working parameters are a deformation temperature above 950 °C and strain rate higher than 0.1 s-1. The hot workability of as-HIPed powder compacts is better than the as-cast billets. The deformed microstructure can be finer than that of as-HIPed state, and the mechanical performance can be further improved by the optimal thermo-mechanical processing treatment.

Investigation of the Hot Deformation Behavior and Mechanism of a Medium-Entropy CoCr0.4NiSi0.3 Alloy

The CoCrNi-based medium-entropy alloys (MEA) have been extensively investigated due to their exceptional mechanical properties at both room and cryogenic temperatures. To investigate the hot deformation behavior and the recrystallization mechanism of the CoCr0.4NiSi0.3 medium-entropy alloy, a series of deformation tests was conducted using the MMS-100 thermal simulation tester, with deformation conditions of 0.001–1 s−1/850–1150 °C. During the hot deformation process, the flow stress initially increases up to its peak value before gradually decreasing towards a steady state level. Higher flow stress levels are observed with increasing strain rate and decreasing deformation temperature. The estimated activation energy for hot deformation of this alloy is approximately 423.6602 kJ/mol. The Arrhenius-type constitutive equation is utilized to establish a modified model while incorporating power dissipation theory and the instability criterion of a dynamic material model to construct power dissipation maps and instability maps. By superimposing these maps, hot processing maps with strains of 0.4, 0.5, and 0.7 are derived. In this investigation, it is observed that regions of instability exclusively occur when the true strain exceeds 0.4. These regions of instability on the hot processing map align well with experimental findings. The suitable range of parameters for hot-working decreases as the true strain increases. The microstructure was analyzed using electron backscatter diffraction and transmission electron microscopy (TEM) techniques. The volume fraction of dynamic recrystallization (DRX) decreases with increasing strain rate but diminishes with rising temperature. The TEM characterization elucidated the mechanism of DRX in this MEA. The presence of the long-period stacking ordered (LPSO) phase was observed in both the face-centered cubic matrix and hexagonal close-packed recrystallized grains under different deformation conditions. The LPSO phase originates from the matrix at a low strain rate, whereas it is generated during recrystallization at a high strain rate. The observed increase in flow stress of the as-cast MEA is primarily attributed to the synergistic effects arising from the interaction of the dislocation with twins and the second phase. The onset of instability is effectively suppressed within a limited range through the formation of coherent second phases such as L12, LPSO, and superlattice structures resulting from phase transitions. These second phases serve as nucleation sites for recrystallization and contribute to the strengthening of dispersion. Furthermore, their interaction with dislocations and twins significantly influences both flow stress behavior and recrystallization kinetics under hot deformation. These findings not only deepen our understanding of the underlying deformation mechanisms governing MEA but also offer valuable insights for designing CoCrNi-based alloys with improved mechanical properties at elevated temperatures.

Microstructural and constitutive relationship in process modeling of hot working: The case of a 60Mg-30Pb-9.2Al-0.8B magnesium alloy

Hot compression tests in the temperature range of 493-653 K and strain rates of 0.01-10.00 s−1 were used to evaluate the hot deformation behavior of 60Mg-30Pb-9.2Al-0.8B alloy. In order to optimize the hot working parameters, the Arrhenius constitutive equation and processing map with strain compensation were established on the dynamic material model (DMM). The results show that the stress-strain curves have three different stages of rising, peaking, and steady state during the hot compression with typical characteristics of work hardening (WH), dynamic recovery (DRV), and dynamic recrystallization (DRX). In addition, the improved Arrhenius strain compensation constitutive model has a higher precision than the traditional constitutive model. By dividing the processing map into three typical regions for analysis, the maximum power efficiency is obtained at ε = 0.4. The optimum hot working parameters are temperature range of 573K∼653K, and strain rate range of 0.01 s−1∼0.1 s−1. Instability usually occurs in the region with high strain rate and low temperature, and the main form of instability is cracking.

Physical constitutive modelling of hot deformation of titanium matrix composites

Second-phase particles have complex effects on the micro- and macro-deformation behaviours of titanium matrix composites (TMCs). Therefore, it is difficult to accurately predict the microstructure evolution and flow stress during their hot working. To address this issue, this paper presents a physical unified constitutive model for TMCs. In the model, the dislocation evolution is modelled by considering the geometrically necessary dislocations introduced by the mismatches of the elastic modulus and thermal expansion coefficient between the second-phase particles and matrix material, and the dynamic recrystallization (DRX) is modelled by considering the role of second-phase particles in promoting DRX grain nucleation and inhibiting DRX grain growth. Subsequently, the constitutive equation is developed considering the contributions of thermal activation stress, hardening by dislocation multiplication, DRX softening, second-phase particles dispersion strengthening, and Hall–Petch strengthening. The developed unified constitutive model is used to quantitatively investigate the effects of second-phase particles on the flow behaviour and microstructure evolution during the hot working of the (TiC+TiB)/Ti–6Al–4V alloy. This study is of great significance for optimising the hot-working parameters of TMCs.

Achieving low activation energy and double-peak texture after hot deformation of Mg–Al–Zn–Ca–Mn–Zr alloy and enabling the strength and ductility

In this study, the hot-deformation behavior of a die-casted Mg–Al–Zn–Ca–Mn–Zr alloy was investigated in the temperature range of 548–673 K and the strain rate range of 0.0001–1 s−1. The constitutive equation and processing maps were also developed to describe the flow stress behavior. The numerical simulation result revealed an average activation energy of ∼139.4 kJ mol−1, which is lower than the previously reported AZ31 Mg alloys. Subsequently, the low activation energy imparted a high degree of dynamic recrystallization and was mainly attributed to alloying elements Ca, Mn, and Zr. For optimum hot working parameters, processing maps displayed two different domains, the temperature range of 573–673 K for a strain rate range of 0.001–0.01 s−1 with a peak efficiency of 33% and a temperature of 673 K at a high strain rate of 0.01 s−1 with a peak efficiency of 31%. The microstructure evolution confirmed the validity of parameters and revealed high dynamic recrystallization. The average grain size ∼21.1 μm, ∼15.4 μm, and ∼16.1 μm were achieved at temperatures of 573 K, 623 K, and 673 K under a strain rate of 0.001 s−1. The profuse grain refinement is attributed to the pronounced accumulation of dislocation on grain boundaries and on the eutectic phases. In addition, the morphology of the eutectic phases was broken with the increase in the strain rate and temperature. Thus, the α-Mg and eutectic phases bear the compressive stresses and promote the dynamic recrystallization activity. Last but not least, the double peak texture after hot deformation was developed, which is one of the engineers' main requirements for enhancing the Mg alloy's ductility. Based on the above discussion, the hot deformed specimens exhibited an ultimate compressive strength of ∼340 MPa and elongated to fracture >25%. Consequently, this study enables the understanding of the broad use of Mg–Zn–Al–Ca–Mn–Zr alloys for automobile applications.

Comprehensive study of hot deformation behavior and fracture mechanism of Al/Cu laminated composite

The hot deformation behavior of Al/Cu laminated composite was studied by isothermal tensile experiments in the temperature range of 200–500 °C and strain rate range of 0.001–1/s. The Arrhenius constitutive model was established to predict the flow stress by determining the constants of composites. In addition, based on the dynamic material model (DMM), the hot working map is established. The results show that the power dissipation efficiency is high under the conditions of high temperature, medium and low strain rate. When the strain is 0.25, there are few areas of stability due to the increasing frictional resistance at the interface. It is found that the dynamic recrystallization (DRX) is promoted by hot tensile and laminate structure. The softening mechanism of Al side is mainly dynamic recovery (DRV) and discontinuous dynamic recrystallization (DDRX), while that of Cu side is DRX. During the tensile process, the Al side grains always maintain stable Brass, Copper and S textures; the Cu side grains always maintain the Cube texture with stable-end orientation and when the deformation exceeds 60 %, the Goss unstable texture appears. It is conducive to dislocation movement and increases the recrystallization ratio. Then, the fracture mechanism of Al/Cu laminated composite is revealed. Due to the presence of the interface, the Cu side shows brittle fracture at room temperature. The snake-like sliding occurs on both sides of Al and Cu under hot deformation, showing ductile fracture, and the defects on Cu side are more serious than those on Al side. These results lay a foundation for optimizing the hot working parameters, improving the performance of the forming parts and clarifying the fracture damage mechanism of Al/Cu laminated composite.

Hot deformation characteristics and processing map of Ti-25Al-14Nb-2Mo-1Fe alloy under hot working process conditions

The hot working process is a proven technique to manufacture special aviation components. However, a suitable working process window for Ti-25Al-14Nb-2Mo-1Fe alloy has not been established. In this work, the hot deformation characteristics of Ti-25Al-14Nb-2Mo-1Fe alloy was systematically studied. In addition, the processing map of the alloy was established to further analyze the inherent machinability properties. Through the processing map analysis and microstructural observation, the instability and stability domains were identified. The optimum working parameters for the alloy were obtained (950–970 ℃/0.001–0.01 s−1, 1015–1100 ℃/0.001–0.01 s−1), which is conducive to optimizing the hot working parameters.

Dynamic recrystallization behavior and processing maps of 5CrNiMoV steel during hot deformation

Hot deformation tests of 5CrNiMoV steel were performed at deformation temperatures of 700 to 870 °C and strain rates of 0.001 to 0.1 s−1 using the DIL 805D thermomechanical simulator. The critical strain and volume fraction models of Dynamic Recrystallization (DRX) were constructed based on the work hardening theory. The results showed that the critical strain of DRX decreases with increasing deformation temperature and decreasing strain rate, which implies that DRX occurs easily at higher temperatures and lower strain rates. The average DRX grain size model was established to predict grain size changes during hot deformation. Based on the hot processing maps that were constructed using the Dynamic Material Model (DMM) and microstructure observation, the optimum hot working parameters for 5CrNiMoV steel are a deformation temperature of 800 °C–870 °C, a strain rate of 0.001–0.05 s−1.

Deformation and Fracture Characterization of an Mg-Sn-Ca Alloy Using 3D Processing Maps

The deformation and fracture characterization of an Mg−2Sn−1Ca alloy were studied through uniaxial isothermal compression tests. The flow stress curves, the efficiency of power dissipation, the instability parameter and the fracture behavior of an Mg−2Sn−1Ca alloy under the condition of various hot working parameters were investigated according to the experimental data. Processing maps were established by superimposing the instability map over the power dissipation map. It was found that flow stress reduces with increases in the deformation temperature and decreases in the strain rate. The processing of Mg−2Sn−1Ca alloys should avoid the instability region in which the conditions are high strain under high temperature and low strain under low temperature. At 473 K or a high strain rate, unidirectional cracks and fish scale cracks can be produced, and cracks can be avoided under the optimum processing area of 623–723 K/0.001–0.1 s−1.

Hot deformation and dynamic recrystallization behavior of a Cu-9Ni-6Sn-0.04Cr alloy

Hot deformation behavior of Cu-9Ni-6Sn-0.04Cr alloy has been investigated by isothermal compression tests in the temperature range of 750 ∼ 900 ℃ and the strain rate range of 0.01 ∼ 10 s−1. By using Arrhenius equation, the activation energy Q of Cu-9Ni-6Sn-0.04Cr alloy is 218 kJ/mol. The predicted flow stresses obtained from the established constitutive equation are consistent with the experimental results for the alloy. The results indicate that proposed constitutive equation offers a high precision for predicting the hot deformation behavior of the Cu-9Ni-6Sn-0.04Cr alloy. In addition, according to the evolution of microstructures, dynamic recrystallization process is the main softening mechanism during hot deformation in Cu-9Ni-6Sn-0.04Cr alloy. Combining the characteristics of dynamic recrystallization process with Zener–Hollomon parameter value, it is shown that continuous dynamic recrystallization is the main dynamic recrystallization mechanism in the high Z value condition. Moreover, and continuous dynamic recrystallization and discontinuous dynamic recrystallization are the main dynamic recrystallization mechanisms in the middle and low Z value condition, the discontinuous dynamic recrystallization is dominated by bulging and nucleation. This study can provide reliable hot working parameters for Cu-Ni-Sn alloy fabrication.

An investigation on the hot workability and microstructural evolution of a novel dual-phase Mg–Li alloy by using 3D processing maps

Hot compression tests of a novel dual-phase Mg–Li alloy were performed in temperature range of 200–400 °C and strain rate range of 0.01–10s−1. 2D and 3D processing maps were established using Prasad's and Murty's instability criteria (methods) based on the dynamic materials model. It was found that one instability region obtained based on Prasad's instability criterion exist in the domain of power dissipation efficiency at a strain of 0.7. Prasad's and Murty's instability criteria are difficult to accurately characterize the instability characteristics of the alloy. The accuracy processing map rectified was obtained by means of Murty's and Prasad's instability criteria and microstructural analysis. On the basis of the processing map rectified, the optimum hot working parameters were obtained to be the temperature range of 320–400 °C and strain rate range of 0.01–0.4s−1 with the peak power dissipation efficiency. In this domain, the α phase undergone dynamic recrystallization (DRX) and dynamic recovery (DRV). The β-phase occurred DRX during the hot deformation. The instability regions lie in the temperature range of 200–250 °C with strain rate range of 0.01–1s−1 and the temperature range of 200–312 °C with strain rate range of 1–10s−1. Microstructural observations indicate that characteristics of the flow instabilities were flow localization, deformation twinning, the adiabatic shear bands and macro/micro cracking. The rectified processing map was successfully verified by the hot rolling test. The rectified processing map could accurately characterize workability characteristics of a novel dual-phase Mg–Li alloy and could be used for the optimization of hot working process parameters.

Hot compressive deformation and microstructural evolution of 60NiTi alloy

Hot deformation behavior and microstructure of 60NiTi alloy during hot compressive deformation were investigated using Gleeble−3500 thermal simulation test machine in the temperature range of 500−650 °C and strain rate range of 0.001−1 s−1. The constitutive equation of hot compression was constructed and the hot processing maps were plotted. When the compression temperature rose or the strain rate declined, the peak stress reduced. The hot deformation activation energy was calculated as 327.89 kJ/mol, and the proper hot working parameters of compression temperature of 600−650 °C and strain rate of 0.005−0.05 s−1 were obtained. The recrystallization degree increased with increasing compression temperature. When the strain rate increased, both dislocation density and number of twins were improved, and the Ni3Ti phase tended to aggregate. Ni3Ti precipitation phase was beneficial to inducing dynamic recrystallization of the 60NiTi alloy. The dynamic recovery, dynamic recrystallization and twinning took place during hot compressive deformation of the 60NiTi alloy.

Hot deformation behavior and microstructure evolution of flaky Ti3AlC2 particles reinforced pure Al composite

Optimizing the hot working parameters of metal matrix composites is beneficial for improving the microstructure of the matrix and the distribution of the reinforcements and eliminating materials defects. In this work, the hot deformation behaviors of the 20 vol% flaky Ti3AlC2 particles reinforced pure Al composite at strain rates of 10−3–1 s−1 and temperatures of 350–500 °C were investigated by hot compression tests. Friction correction equations were used to correct the flow stress data. The constitutive equations and processing maps were successfully established. The flow stresses of the Ti3AlC2/Al composite were precisely described through the hyperbolic sine constitutive equation. The true stress exponent was calculated to be 8, similar to the creep process with invariant microstructure. The particle rotation caused by the deformation of the Al matrix led to the alignment of the Ti3AlC2 flakes. The optimum hot working parameters of the composite are in the range of 410–500 °C, 0.18–1 s−1 based on the processing maps. Dynamic recrystallization (DRX) had a higher proportion in the optimum safe region. The high temperature-low strain rate unstable region was associated with superplastic. The instability in the low temperature-low strain rate region stemmed from the interface microcracks generated by the rotation of Ti3AlC2 flakes. The processing map theory can be well correlated with the microstructure evolution of the composite under different deformation parameters.

Understanding processing map and microstructural evolution of powder metallurgy Ti-6Al-4V within a wide range of deformation temperatures

The hot deformation behavior and microstructural evolution of powder metallurgy (PM) Ti-6Al-4V are investigated using the Arrhenius constitutive model, hot processing map, microstructure observation, and hot deformation mechanism analysis. The optimal processing parameters obtained from the hot processing map are 1323–1423 K at 0.1–1 s−1, and 1423–1523 K at 1–10 s−1. Hot deformation in β region is attractive for PM Ti-6Al-4V. The dominant hot deformation mechanism of PM Ti-6Al-4V is dynamic recrystallization (DRX) in the (α + β) and β regions. Continuous dynamic recrystallization (CDRX) is the dominant mechanism in the (α + β) region. The combination of CDRX and discontinuous dynamic recrystallization (DDRX) is the preferred mechanism in the β region. The power-dissipation efficiency is affected by DRX, which consumes dislocations and refines the microstructure. Specific hot working parameters for thermomechanical processing (TMP) of PM Ti-6Al-4V are identified.

Deformation behavior and phase transformation of a dual-phase Mg−8.9Li−2.7Al-0.85Si alloy under compression test at elevated temperatures

The hot deformation behaviors of a dual-phase Mg− 8.9Li− 2.7Al-0.85Si alloy were investigated via hot compression tests conducted at temperatures ranging from 423 K to 573 K and strain rates varying from 0.001 s−1 to 1 s−1. Processing maps were established based on dynamic material modeling (DMM) at true strains of 0.4 and 0.6. The optimized parameters for hot working are 523–573 K with strain rates of 0.001–0.05 s−1 at a strain of 0.6. The flow instability domains are primarily distributed in the superposition area with low temperatures and high strain rates. While the Mg− 8.9Li− 2.7Al-0.85Si alloy deformed at 423 K with a strain rate of 1 s−1, considerable deformation twinning formed in the α-Mg phases, and the β-Li phases were severely deformed and broken. The proportion of dynamic recrystallization in the β-Li phases was markedly higher than that in the α-Mg phases. When the temperature increased to 573 K at a lower strain rate, the coordination deformation ability between the α-Mg and β-Li phases was improved by more active slip systems, but the proportion of dynamic recrystallization was relatively low at a strain rate of 0.01 s−1. The secondary α-Mg precipitated in the β-Li grain boundary when the alloy deformed at 573 K and a strain rate of 0.001 s−1, which is described as deformation-induced phase transformation. The α-Mg phases with micron scales and massive α/β interfaces can hinder dislocation movement, leading to grain refinement and strength enhancement.