Hot Processing Window Research Articles

Study on Hot‐Compressive Deformation Behavior and Microstructure Evolution of 12Cr10Co3MoWVNbNB Martensitic Steel

Herein, to improve the microstructure homogeneity of 12Cr10Co3MoWVNbNB steel for turbine blades after forging, the hot deformation behavior and microstructure evolution of the steel are systematically investigated using a hot‐compression experimental setup under the conditions of 950–1150 °C and strain rate of 0.001–10 s−1. A strain‐compensated constitutive equation is established based on the flow curves and the accuracy of its prediction is verified. By combining hot processing map with microstructure observation, the optimal hot processing window is determined to be 1075–1150 °C and 1–10 s−1, within which the grain size can be refined to 14.24 μm. Electron backscatter diffraction is employed to investigate the microstructural evolution and dynamic recrystallization (DRX) nucleation mechanism of the deformed samples, revealing that discontinuous DRX characterized by strain‐induced grain‐boundary migration is the dominant nucleation mechanism. Additionally, the deformation conditions significantly affect the distribution of dislocation density and local misorientation, as well as the transition from low‐angle grain boundaries to high‐angle grain boundaries, which ultimately lead to the differences in DRX fraction and microstructure.

Effect of hydrogen on hot deformation behavior and microstructure evolution of Ti65 alloy

Thermohydrogen processing (THP) is a potential method for enhancing the formability of titanium alloys. However, there has been no report on the deformation behavior and microstructure evolution of hydrogenated Ti65 alloys, which are new high-temperature titanium alloys used above 600 °C. In this study, we conducted a series of isothermal hot compression tests in the α+β and β phase field of Ti65 alloy specimens with varying hydrogen content to investigate the effect of hydrogen on high-temperature flow behavior and microstructure evolution. The results showed that after hydrogenation, the number of α phases in Ti65 alloy significantly decreased. δ hydride precipitates were observed in the specimen with 0.43 wt% hydrogen, resulting in an apparent refinement of its microstructure. Adding 0.25 wt% hydrogen reduced the deformation temperature by about 60 °C and increased deformation strain rate by nearly two orders of magnitude for Ti65 alloy. This improvement can be attributed to how hydrogen promotes dislocation movement, dynamic recrystallization (DRX), and dynamic recovery (DRV) during deformation. Similarly, as strain increases, the instability region on the hot processing map gradually decreases or even disappears due to broadening effects from added hydrogen; thus expanding its hot processing window further. This research deepens our understanding regarding deformation behavior while providing theoretical guidance for THP applications using Ti65 alloy.

Microstructure analysis, constitutive relationship, and processing map of novel pre-aged Mg-Zn-Gd-Er alloy with different deformation ranges

Abstract Pre-aged Mg-6Zn-1Gd-1Er alloy is a novel rapid aging hardening Mg alloy, and studying its hot deformation behavior has an important role in promoting the development of lightweight alloy materials. To study this, the flow stress curves of pre-aged Mg-6Zn-1Gd-1Er alloy at 180–380 °C and 10−3−10 s−1 were obtained by isothermal compression tests. The constitutive equations of the medium-high temperature deformation (MHTD) and the low-temperature deformation (LTD) were established, and their activation energies were 155.78 kJ mol−1 and 178.00 kJ mol−1, respectively. Based on the constitutive equation analysis, the glide and climb of dislocations and the cross-slip of dislocations was the deformation mechanism during MHTD and LTD, respectively. In order to determine the appropriate hot processing parameters, the hot processing map of the pre-aged Mg-6Zn-1Gd-1Er alloy under 0.2–0.8 strain was constructed based on the dynamic material model. The hot processing maps indicate that this pre-aged alloy at low temperature (180–230 °C) and high strain rates (1–10 s−1) mainly occurs flow instability, and the optimal hot processing window appears at a 330–380 °C and 10−3 to 10−2 s−1 range. Furthermore, the deformation mechanism of the stable domain with high power dissipation efficiency in the hot processing map was continuous dynamic recrystallization, discontinuous dynamic recrystallization, and particle-stimulated nucleation mechanisms.

Superior hot workability of (TiB+TiC)/Ti-6Al-4V composites fabricated by melt hydrogenation

In order to improve the poor hot workability of titanium matrix composites (TMCs), an advanced melt hydrogenation method was introduced in this study. The (TiB+TiC)/Ti-6Al-4 V composites were fabricated by melt hydrogenation which was directly melting alloys in gas mixture of H2 and Ar. Microstructure of as-cast TMCs indicated that melt hydrogenation increased the length of TiB whiskers and aggravated the clustering of reinforcements at primary β grain boundaries, which was due to the increased overheat on melt surface. Hot compression results indicated melt hydrogenation improved the hot workability of TMCs in (α + β) phase region, and the peak stress was reduced from 371 to 271 MPa at 800 °C/1 s−1 and from 119 to 60 MPa at 900 °C/0.01 s−1, respectively, which expanded the optimal hot processing window. Microstructure after hot deformation showed that the proportion of DRX grains was increased from ∼56% to ∼81%, which was mainly attributed to the accelerated migration of DRX grain boundary and the decreased density of dislocations, which was due to the dislocation consumption by DRX formation and the improved mobility of dislocations. Therefore, the improvement of hot workability resulted from the formation of more DRX grains and enhanced mobility of dislocations.

Proper (Nb,Fe) co-alloyed TiAl-based alloy with good hot deformation processing capability

In order to develop a proper (Nb,Fe) co-alloyed TiAl-based alloy with excellent hot deformation processing capability, avoiding the heavy alloying induced damage of service properties, the Ti–44Al–4Nb-0.5Fe-0.1B and Ti–44Al–2Nb–2Fe-0.1B alloys are designed and prepared. This paper mainly focuses on whether and why the hot deformation processing capability of the new alloys are improved. In view of this, thermo-compression experiments are carried out, hot deformation behavior is studied, constitutive equations are derived, hot processing maps are drawn, and hot deformation microstructure is studied. The results show that the Ti–44Al–2Nb–2Fe-0.1B alloy has lower true stress, moderate diffusion activation energy, lower stress exponent and larger hot processing window. Especially, the large hot processing window of Ti–44Al–2Nb–2Fe-0.1B alloy covers almost all the tested range of 1100 °C–1250 °C and 0.001 s−1-1.0 s−1, and meanwhile, the its power dissipation factor is higher. At lower temperatures of 1100 °C and 1150 °C, relatively more B2 phase in the Ti–44Al–2Nb–2Fe-0.1B alloy plays a good stress-strain coordination effect in the hot deformation process. At higher temperatures of 1200 °C and 1250 °C, the Ti–44Al–2Nb–2Fe-0.1B alloy is in the higher temperature phase region. Moreover, the compressed Ti–44Al–2Nb–2Fe-0.1B alloy has relatively lower dislocation density and more adequate dynamic recrystallization. In conclusion, all these results demonstrate that the Ti–44Al–2Nb–2Fe-0.1B alloy meets the design expectations, that is, this alloy with a proper (Nb,Fe) addition still has a very good hot deformation processing capability. At the same time, the Ti–44Al–2Nb–2Fe-0.1B alloy has a typical near-lamellar structure, rather than containing too much B2 phase or even containing lots of τ2 phase, so the good service properties can be expected.

Effect of Nb-V microalloying on hot deformation characteristics and microstructures of Fe-Mn-Al-C austenitic steel

The flow behavior and microstructure of Fe-Mn-Al-C austenitic steel and Nb-V microalloyed Fe-Mn-Al-C austenitic steel during uniaxial hot compression deformation are systematically studied in the present paper. The flow curves of both steels are analyzed, as well as constitutive equations and processing maps are established. The results reveal that the flow softening phenomenon of Nb-V microalloyed Fe-Mn-Al-C austenitic steel is more significant at low temperatures and low strain rates. Moreover, the hot deformation activation energy of Fe-Mn-Al-C steel is marginally affected by the addition of Nb-V. The uniformly distributed nano-sized (Nb,V)C particles, which precipitate in Nb-V microalloyed Fe-Mn-Al-C steel, act as the nucleation sites for dynamic recrystallization (DRX). These particles promote the DRX and pin the grain boundaries to restrain the growth of DRX grains. Nb-V microalloying renders a positive influence on the hot deformation stability of Fe-Mn-Al-C steel and broadens the optimum hot processing window. Based on the processing map and microstructure, the optimum hot processing windows of Nb-V microalloyed Fe-Mn-Al-C steel at the strain of 0.7 are determined as 894–1025 °C/0.01–0.14 s −1 and 1050–1200 °C/0.03–0.95 s −1 . • Effect of Nb-V microalloying on hot deformation characteristics and microstructures in Fe-Mn-Al-C steel was studied. • Nb-V led to flow softening of Fe-Mn-Al-C steel at low temperatures and low strain rates. • Nb-V improved the hot deformation stability of Fe-Mn-Al-C steel. • Nb-V increased the nucleation sites for dynamic recrystallization of Fe-Mn-Al-C steel.

Fracture prediction of powder metallurgical Fe–Cu–C steel at elevated temperatures via finite element-aided hot tensile tests

Surface cracking induced by damage accumulation is a common quality problem during the hot processing of powder metallurgical (P/M) products. This study aims to clarify the damage and fracture of P/M Fe–Cu–C steel at elevated temperatures to propose its fracture criterion by combining hot tensile tests with finite element (FE) calculations. The results reveal that the FE-aided test accurately corrected the true stress and strain of the P/M steel during the Gleeble hot tensile testing. In addition, the flow behaviors and cracking tendency of the P/M steel strongly depended on the hot deformation parameters. The optimum hot processing window of P/M steel was proposed after determining the quantitative relationships between the damage and hot deformation parameters. Finally, a novel elevated temperature fracture strain model of the P/M steel was proposed based on the Zener–Hollomon parameter to construct its Cockroft and Latham fracture criterion coupling hot processing parameters. The constructed fracture criterion was further normalized and modified, and achieved an acceptable fracture predictive capability with a relative error of less than 5%, which was validated by powder forging experiments. This work provides essential information and a useful model for the fracture prediction of P/M Fe–Cu–C steel at elevated temperatures, helping to manage the surface cracking problems of P/M steel during hot processing.

Hot deformation behavior of the AA6016 matrix composite reinforced with in situ ZrB2 and Al2O3 nanoparticles

The hot deformation tests of in situ ZrB2 and Al2O3 nanoparticles reinforced AA6016 matrix composite were studied at deformation temperature of 300 °C–450 °C and strain rate of 0.001–1 s−1. In this paper, the ZrB2 and Al2O3 nanoparticles were successfully prepared by direct melt reaction method firstly. Based on experimental results, the flow stress increased rapidly with the increasing true strain and decreased with the increasing temperature. Constitutive equation of the composite can be established based on the Arrhenius constitutive model. The processing map based on dynamic material model showed two stable processable domains: Domain A(300–360 °C/0.08–0.01 s−1), which was controlled by dynamic recovery and domain B(410–430 °C/0.37–1 s−1), which was typical dynamic recrystallization structure. The microstructural changes of the samples after deformed were observed through optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). It was concluded that these two kinds of reinforced particles can greatly promote recrystallization nucleation at high temperatures. Thus, domain B is optimum hot processing window.

Hot Deformation Behavior of an Ultra-High-Strength Fe–Ni–Co-Based Maraging Steel

Hot processing behavior of an ultra-high-strength Fe–Ni–Co-based maraging steel was studied in temperature range of 900–1200 °C and strain rate range of 0.001–10 s−1. Deformation processing parameters and optimum hot working window were characterized via flow stress analysis, constitutive equation construction, hot processing map calculation and microstructure evolution, respectively. Critical strain value for dynamic recrystallization was determined through theoretical mathematical differential method: the inflection point of θ–σ and − ∂θ/∂σ − σ curves. It was found that the flow stress increased with the decrease in deformation temperature and increase in the strain rate. The power dissipation maps in the strain range of 0.1–0.6 were entirely similar with the tendency of contour lines which implied that strain had no strong effect on the dissipation maps. Nevertheless, the instability maps showed obvious strain sensitivity with increasing strain, which was ascribed to the flow localization and instability. The optimized hot processing window of the experimental steel was obtained as 1100–1200 °C/0.001–1 s−1 and 1000–1100 °C/0.001–0.1 s−1, with the efficiency range of 20–40%. Owing to high Mo content in the experimental steel, high dynamic activation energy, Q = 439.311 kJ mol−1, was achieved, indicating that dynamic recrystallization was difficult to occur in the hot deformation process, which was proved via microstructure analysis under different hot deformation conditions.

Hot Deformation Behavior and Microstructure Evolution of a TiBw/Near α-Ti Composite with Fine Matrix Microstructure

The hot deformation behavior and microstructure evolution of a 7.5 vol% TiBw/near α-Ti composite with fine matrix microstructure were investigated under the deformation conditions in a temperature range of 800–950 °C and strain rate range of 0.001–1 s−1 using plane strain compression tests. The flow stress curves show different characteristics according to the various deformation conditions. At a higher strain rate (1 s−1), the flow stress of the composite continuously increases until a peak value is reached. The activation energy is 410.40 kJ/mol, much lower than the activation energy of as-sintered or as-forged composites. The decreased activation energy is ascribed to the breaking of the TiBw reinforcement during the multi-directional forging and the resultant fine matrix microstructure. Refined reinforcement and refined matrix microstructure significantly improve the hot deformation ability of the composite. The deformation conditions determine the morphology and fraction of α and β phases. At 800–900 °C and 0.01 s−1 the matrix α grains are much refined due to the continuous dynamic recrystallization (CDRX). The processing map is constructed based on the hot deformation behavior and microstructure evolution. The optimal hot processing window is determined to be 800–950 °C/0.001–0.01 s−1, which lead to CDRX of primary α grains or dynamic recovery (DRV) and dynamic recrystallization (DRX) of β phase.

Compressive response and microstructural evolution of bimodal sized particulates reinforced (TiB+La2O3)/Ti composites

The hot deformation behavior and microstructural evolution of bimodal sized particulates reinforced (TiB+La2O3)/Ti composites are investigated in the temperature range of 850–1100 °C and strain rate range of 0.001–1 s−1 using isothermal compression tests. The constitutive equations in different phase regions are established in terms of the flow stress data, and the apparent activation energies are calculated to be 753 kJ/mol in α+β phase region and 185 kJ/mol in β phase region, which are much higher than those of matrix alloy due to the incorporation of bimodal sized reinforcements. The optimal hot processing window for (TiB+La2O3)/Ti composites is determined at 900–950 °C/0.01–0.1 s−1, which is associated with the continuous dynamic recrystallization (CDRX) of primary α grains and dynamic globularization of lamellar α. The necklace recrystallization of β grains and dynamic recovery (DRV) of lamellar α are observed in β phase region, and the instability mechanisms include inhomogeneous deformation and breaking or debonding of TiB whiskers. Additionally, TEM observations are used to study the effects of reinforcements on microstructural evolution. The results indicate that both micro-sized TiB and submicro-sized La2O3 can impede dislocation movement and TiB can facilitate the dynamic recrystallization (DRX) of α phase and grain refinement.

High temperature deformation behavior and processing map of hot isostatically pressed Ti-47. 5Al-2Cr-2Nb-0. 2W-0. 2B alloy using gas atomization powders

The hot compressive deformation behavior of hot isostatically pressed Ti-47. 5Al-2Cr-2Nb-0. 2W-0. 2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323−1473 K and strain rate range of 0.001−0.5 s−1 . The calculated activation energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6 kJ/mol based on the constitutive relationship models developed with the Arrhenius-type constitutive model respectively considering the strain rate and deformation temperature. The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution. Meanwhile, the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions. Finally, the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353−1453 K and the low strain rate of 0.001−0.1 s−1 was obtained.

Thermal, structural and in vitro dissolution of antimicrobial copper-doped and slow resorbable iron-doped phosphate glasses

This paper focuses on investigating and comparing the effects of CuO and Fe2O3 addition on the bioactive response of glass having composition [xCuO or Fe2O3 + (100 - x) (0.2CaO + 0.2SrO + 0.1Na(2)O + 0.5P(2)O(5))] (in mol%), where x is ranging from 0 up to 5. The addition of CuO was found to increase the hot processing window and the dissolution rate leading to a fast surface layer precipitation. Using IR and Raman spectroscopies, we related this change in the bioactive response of this glass to the progressive depolymerization of the glass network induced by the addition of CuO. On the other hand, the addition of Fe2O3 was found to reduce the hot processing window and the dissolution rate as no depolymerization of the network occurs due to the formation of P-O-Fe bonds at the expense of P-O-P bonds. All the glasses were found to dissolve congruently and in a controlled manner. Finally, the antimicrobial properties of the copper-doped glasses were examined and compared to bioactive glasses which are known to exhibit good antimicrobial properties. The CuO addition leads to higher antimicrobial properties than the commercial bioactive glass S53P4 and total bacterial elimination could be obtained.

Hot deformation characteristics of AZ80 magnesium alloy: Work hardening effect and processing parameter sensitivities

Isothermal compression experiment of AZ80 magnesium alloy was conducted by Gleeble thermo-mechanical simulator in order to quantitatively investigate the work hardening (WH), strain rate sensitivity (SRS) and temperature sensitivity (TS) during hot processing of magnesium alloys. The WH, SRS and TS were described by Zener-Hollomon parameter (Z) coupling of deformation parameters. The relationships between WH rate and true strain as well as true stress were derived from Kocks-Mecking dislocation model and validated by our measurement data. The slope defined through the linear relationship of WH rate and true stress was only related to the annihilation coefficient Ω. Obvious WH behavior could be exhibited at a higher Z condition. Furthermore, we have identified the correlation between the microstructural evolution including β-Mg17Al12 precipitation and the SRS and TS variations. Intensive dynamic recrystallization and homogeneous distribution of β-Mg17Al12 precipitates resulted in greater SRS coefficient at higher temperature. The deformation heat effect and β-Mg17Al12 precipitate content can be regarded as the major factors determining the TS behavior. At low Z condition, the SRS becomes stronger, in contrast to the variation of TS. The optimum hot processing window was validated based on the established SRS and TS values distribution maps for AZ80 magnesium alloy.

Flow behavior and processing maps of Ti-44.5Al-3.8Nb-1.0Mo-0.3Si-0.1B alloy

The flow behavior of Ti-44.5Al-3.8Nb-1.0Mo-0.3Si-0.1B alloy was investigated by means of uniaxial hot compression tests performed with a Gleeble 3500 simulator within a temperature range of 1100–1250 °C and a strain rate region of 0.01–1 sˆ(−1) up to a true deformation of 0.7. The results show that the flow stress increases with increasing strain rate and decreasing temperature. The flow stress curves were composed of three stages: work hardening, softening and steady. Processing maps were developed on the basis of the dynamic materials model. The microstructure of specimens deformed at different conditions was analyzed and connected with the processing map. The predominant flow stability region and instability region mechanism of this alloy were validated by microstructure observation. Based on the constructed processing maps and microstructure analysis, the optimal hot processing window of this alloy corresponds to the temperature range of 1200–1250 °C and strain rate range of 0.01–0.5 sˆ(−1). The excellent deformability of this alloy is ascribed to soft β phase and hard α2/γ lamellar colonies decomposition at elevated temperature.

Deformation behavior and microstructural evolution of hydrogenated Ti44Al6Nb alloy during thermo-compression at 1373–1523 K

The effect of hydrogen on the hot deformation behaviors of Ti44Al6Nb alloy is investigated at temperature range from 1373K to 1523K and the strain rate range from 0.001s−1 to 1s−1 on Gleeble-1500D thermo-simulation machine. Experimental results show that the peak stress shows a decreasing trend with increasing hydrogen content, which indicates that hydrogen promotes a solid solution softening effect additional to that produced by dynamic recrystallization (DRX) and hydrogen-induced dislocation movement, the fraction of DRX increases with the increase of hydrogen content, while the fraction of LABs and the dislocation density decrease with the increase of hydrogen content. Similarly, the deformation activation energy of hydrogenated titanium aluminides is calculated to be 382.9kJ/mol compared with that of 485.7kJ/mol for unhydrogenated alloy indicating that hydrogen promotes the onset of DRX. The hot processing window is constructed based on the dynamic material model (DMM), which is broadened by hydrogen suggesting that hydrogen contributes to the hot workability of high Nb contained titanium aluminides.

Hot Deformation Behavior and Processing Map of Ti-6Al-3Nb-2Zr-1Mo Titanium Alloy

Abstract The isothermal compression tests were performed over the ranges of temperatures 820∼1060 °C and strain rates 0.001∼1 s −1 on a Gleeble-3800 simulator. The constitutive equation of Ti-6Al-3Nb-2Zr-1Mo alloy has been established to describe the changing rule of flow stress with the strain rate and deformation temperature. The apparent activation energies have been calculated to be 764.71 kJ/mol in the dual phase region and 126.94 kJ/mol in the single phase region. The processing maps have been constructed based on the dynamic material model (DMM) and the Prasad's instability criterion at strains of 0.4 and 0.7. The maps exhibit a stable domain in the temperature range of 840∼1060 °C and strain rate range of 0.001∼0.1 s −1 with two peaks in power dissipation of 51%, occurring at 940 °C/0.001 s −1 and 880 °C/1 s −1 , respectively. The high efficiency values of power dissipation indicate dynamic recrystallization (DRX)/globalization in these fields. Based on the constructed processing maps, the optimal hot processing window of this alloy corresponds to the temperature range of 840∼1060 °C and the low strain rate range of 0.001∼0.1 s −1 . The microstructures of the specimens deformed at different conditions were analyzed and connected with the processing map. It is found that in processing of the alloy at 820 °C and a higher strain rate (≥1 s −1 ) an instability deformation will take place easily.

Characterization of hot processing parameters of powder metallurgy TiAl-based alloy based on the activation energy map and processing map

Abstract The hot deformation behavior of powder metallurgy Ti–47Al–2Nb–2Cr alloy was studied by using the activation energy map and processing map in this work. The isothermal compression tests were performed over a range of temperatures 950–1200 °C and strain rates 0.001–0.1 s − 1 on a Gleeble-1500D hot working simulator. The hot working flow behavior and softening of flow stress were discussed. The variation of calculated Q value with hot processing parameters has been presented, it was found that the Q value increases with increasing temperature and strain rate on the whole. Based on the constructed processing maps, the optimal hot processing window of this alloy corresponds to the temperature range of 1025–1075 °C and the low strain rate of 0.001–0.004 s − 1 , with a peak efficiency of 55% at 1050 °C/0.001 s − 1 . Meanwhile, the instability maps were developed with the help of the comparison between Murty and Prasad instability criteria. The instability domain that should be kept away is located at high strain and strain rate higher than 0.01 s − 1 for the whole deformation temperature. Both of the optimal process conditions and the predominant flow instability mechanism of PM TiAl-based alloy were validated by microstructure observation involving DRX refined microstructure and cracking, respectively.

Hot deformation behavior of in situ nano ZrB2 reinforced 2024Al matrix composite

Abstract The hot deformation behavior of in situ 5 wt.% nano ZrB 2 /2024Al composite was studied at deformation temperatures of 350–450 °C and strain rates of 0.001–10 s −1 . The results show that the flow stress depends strongly on the deformation temperature and strain rate, and especially exhibits a strain hardening at high temperature and high strain rate, related to the introduction of nanoparticles (ZrB 2 : 15–40 nm). The kinetic equation was constituted and indicates that the key deformation mechanism is dynamic recrystallization (DRX), which is in accordance with the deformed microstructures. The processing maps (PMs) exhibit two deterministic domains of domain 1 (380–410 °C/0.018–0.032 s −1 ) and domain 2 (440–460 °C/0.075–0.56 s −1 ), where domain 2 has the higher power dissipation efficiency, higher strain rate, meaning more safety and higher efficiency for the hot processing. At the same time, the deformed specimen exhibits equiaxed and fine grains in domain 2, i.e., a typical DRX structure, thus is suggested as the optimum hot processing window for this nanocomposite.