Hot Deformation Behavior of a Beta Metastable TMZF Alloy: Microstructural and Constitutive Phenomenological Analysis

A metastable beta TMZF alloy was tested by isothermal compression under different conditions of deformation temperature (923 to 1173 K), strain rate (0.172, 1.72, and 17.2 s−1), and a constant strain of 0.8. Stress–strain curves, constitutive constants calculations, and microstructural analysis were performed to understand the alloy’s hot working behavior in regards to the softening and hardening mechanisms operating during deformation. The primary softening mechanism was dynamic recovery, promoting dynamic recrystallization delay during deformation at higher temperatures and low strain rates. Mechanical twinning was an essential deformation mechanism of this alloy, being observed on a nanometric scale. Spinodal decomposition evidence was found to occur during hot deformation. Different models of phenomenological constitutive equations were tested to verify the effectiveness of flow stress prediction. The stress exponent n, derived from the strain-compensated Arrhenius-type constitutive model, presented values that point to the occurrence of internal stress at the beginning of the deformation, related to complex interactions of dislocations and dispersed phases.

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Hot working of SP-700 titanium alloy with lamellar α + β starting structure using a processing map

International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) ◽

10.1515/ijmr-2020-1110405 ◽

2020 ◽

Vol 111 (4) ◽

pp. 297-306

Author(s):

Amir Hosein Sheikhali ◽

Maryam Morakkabati

Keyword(s):

Titanium Alloy ◽

Strain Rate ◽

Hot Deformation ◽

Processing Map ◽

Microstructural Analysis ◽

Shear Bands ◽

Alpha Phase ◽

Strain Rates ◽

Compression Tests ◽

Temperature Range

Abstract In this study, hot deformation behavior of SP-700 titanium alloy was investigated by hot compression tests in the temperature range of 700-9508C and at strain rates of 0.001, 0.1, and 1 s-1. Final mechanical properties of the alloy (hot compressed at different strain rates and temperatures) were investigated using a shear punch testing method at room temperature. The flow curves of the alloy indicated that the yield point phenomenon occurs in the temperature range of 800- 9508C and strain rates of 0.1 and 1 s-1. The microstructural analysis showed that dynamic globularization of the lamellar α phase starts at 7008C and completes at 8008C. The alpha phase was completely eliminated from b matrix due to deformation- induced transformation at 8508C. The microstructure of specimens compressed at 8508C and strain rates of 0.001 and 0.1 s-1showed the serration of beta grain boundaries, whereas partial dynamic recrystallization caused a necklace structure by increasing strain rate up to 1 s-1. The specimen deformed at 7008C and strain rate of 1 s-1was located in the instability region and localized shear bands formed due to the low thermal conductivity of the alloy. The processing map of the alloy exhibited a peak efficiency domain of 54% in the temperature range of 780-8108C and strain rates of 0.001- 0.008 s-1. The hot deformation activation energy of the alloy in the α/β region (305.5 kJ mol-1) was higher than that in the single-phase β region (165.2 kJ mol-1) due to the dynamic globularization of the lamellar a phase.

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Flow Stress Prediction and Hot Deformation Mechanisms in Ti-44Al-5Nb-(Mo, V, B) Alloy

Materials ◽

10.3390/ma11102044 ◽

2018 ◽

Vol 11 (10) ◽

pp. 2044 ◽

Cited By ~ 7

Author(s):

Tianrui Li ◽

Guohuai Liu ◽

Mang Xu ◽

Bingxing Wang ◽

Tianlian Fu ◽

...

Keyword(s):

Phase Transformation ◽

Flow Stress ◽

Strain Rate ◽

Hot Deformation ◽

Microstructural Analysis ◽

Constitutive Relationship ◽

Deformation Mechanisms ◽

Compression Tests ◽

Ann Model ◽

Stress Prediction

To elucidate the hot deformation characteristics of TiAl alloys, flow stress prediction, microstructural evolution and deformation mechanisms were investigated in Ti-44Al-5Nb-1Mo-2V-0.2B alloy by isothermal compression tests. A constitutive relationship using the Arrhenius model involving strain compensation and back propagation artificial neural network (BP-ANN) model were developed. A comparison of two models suggested that the BP-ANN model had excellent capabilities and was more accurate in predicting flow stress. Based on the microstructural analysis, bending and elongation of colonies, γ and B2 grains were the main microstructural constituents at low temperature and high strain rate. Dynamic recrystallization (DRX) of γ and dynamic recovery (DRY) of β/B2 were the main deformation mechanisms. With the increase of temperature and decrease of strain rate, phase transformation played an important role. The flake-like γ precipitates in B2 grains, and a coarsening of γ lamellae via α lath dissolution during compression were observed. Additionally, the flow softening process commenced with dislocation pile-up and formation of sub-grain boundaries, followed by grain refinement, twins and nano-lamellar nucleation. Continuous DRX and phase transformation promoted the formability of Ti-44Al-5Nb-1Mo-2V-0.2B alloy.

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Hot Deformation Behavior and Softening Mechanism of As-Cast S32750 Super Duplex Stainless Steel at Low and High Strain Rates

Journal of Materials Engineering and Performance ◽

10.1007/s11665-020-04571-w ◽

2020 ◽

Vol 29 (2) ◽

pp. 727-738

Author(s):

Wu Min ◽

Liu Baosheng ◽

Zhang Shoulu ◽

Li Guoping ◽

Wang Lixin ◽

...

Keyword(s):

Stainless Steel ◽

Duplex Stainless Steel ◽

Hot Deformation ◽

Deformation Behavior ◽

High Strain ◽

Strain Rates ◽

Super Duplex Stainless Steel ◽

Hot Deformation Behavior ◽

High Strain Rates ◽

Softening Mechanism

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The Effect of α-Al(MnCr)Si Dispersoids on Activation Energy and Workability of Al-Mg-Si-Cu Alloys during Hot Deformation

Advances in Materials Science and Engineering ◽

10.1155/2020/3471410 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Xiaoguo Wang ◽

Jian Qin ◽

Hiromi Nagaumi ◽

Ruirui Wu ◽

Qiushu Li

Keyword(s):

Activation Energy ◽

Aluminum Alloys ◽

Constitutive Equation ◽

Hot Deformation ◽

Flow Instability ◽

Void Formation ◽

Activation Energies ◽

Compression Tests ◽

Softening Mechanism ◽

Dynamic Softening

The hot deformation behaviors of homogenized direct-chill (DC) casting 6061 aluminum alloys and Mn/Cr-containing aluminum alloys denoted as WQ1 were studied systematically by uniaxial compression tests at various deformation temperatures and strain rates. Hot deformation behavior of WQ1 alloy was remarkably changed compared to that of 6061 alloy with the presence of α-Al(MnCr)Si dispersoids. The hyperbolic-sine constitutive equation was employed to determine the materials constants and activation energies of both studied alloys. The evolution of the activation energies of two alloys was investigated on a revised Sellars’ constitutive equation. The processing maps and activation energy maps of both alloys were also constructed to reveal deformation stable domains and optimize deformation parameters, respectively. Under the influence of α dispersoids, WQ1 alloy presented a higher activation energy, around 40 kJ/mol greater than 6061 alloy’s at the same deformation conditions. Dynamic recrystallization (DRX) is main dynamic softening mechanism in safe processing domain of 6061 alloy, while dynamic recovery (DRV) was main dynamic softening mechanism in WQ1 alloy due to pinning effect of α-Al(MnCr)Si dispersoids. α dispersoids can not only resist DRX but also increase power required for deformation of WQ1 alloy. The microstructure analysis revealed that the flow instability was attributed to the void formation and intermetallic cracking during hot deformation of both alloys.

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Constitutive Equation for 3104 Alloy at High Temperatures in Consideration of Strain

High Temperature Materials and Processes ◽

10.1515/htmp-2014-0238 ◽

2016 ◽

Vol 35 (6) ◽

pp. 599-605 ◽

Cited By ~ 1

Author(s):

Fuqiang Zhen ◽

Jianlin Sun ◽

Jian Li

Keyword(s):

Hot Deformation ◽

Flow Behavior ◽

Temperature Correction ◽

Strain Rates ◽

Compression Tests ◽

Hot Deformation Behavior ◽

Element Analysis ◽

Hollomon Parameter ◽

The Finite Element Analysis ◽

Effects Of Temperature

AbstractThe flow behavior of 3104 aluminum alloy was investigated at temperatures ranging from 250°C to 500°C, and strain rates from 0.01 to 10 s−1 by isothermal compression tests. The true stress–strain curves were obtained from the measured load–stroke data and then modified by friction and temperature correction. The effects of temperature and strain rate on hot deformation behavior were represented by Zener–Hollomon parameter including Arrhenius term. Additionally, the influence of strain was incorporated considering the effect of strain on material constants. The derived constitution equation was applied to the finite element analysis of hot compression. The results show that the simulated force is consistent with the measured one. Consequently, the developed constitution equation is valid and feasible for numerical simulation in hot deformation process of 3104 alloy.

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Characteristics of Dynamic Recrystallization during Hot Deformation for High Nitrogen Stainless Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.715-716.115 ◽

2012 ◽

Vol 715-716 ◽

pp. 115-121

Author(s):

Hai Wen Luo ◽

Xu Dong Fang ◽

Rui Zhen Wang ◽

Zhan Yin Diao

Keyword(s):

Dynamic Recrystallization ◽

Stainless Steels ◽

Hot Deformation ◽

Strain Rates ◽

Peak Strain ◽

High Nitrogen ◽

Flow Curves ◽

Grain Sizes ◽

Nitrogen Contents ◽

High Nitrogen Stainless Steel

Dynamic recrystallization was studied for the stainless steels with nitrogen contents of 0.56% to 1.08% during hot deformation at temperatures of 900~1200 with strain rates ranging from 0.003 to 42 s-1. It was found that flow stress could increase remarkably with increasing nitrogen content. Flow curves during the deformation by 0.1~42/s at temperatures of 900~1200°C show a single peak, indicating the occurrence of dynamic recrystallization during deformation. The peak strain seems to decrease with increasing N content, suggesting that higher content of N facilitates dynamic recrystallization. The quenched microstructures were analyzed by optical microscopy, EBSD and TEM. The recrystallized grain sizes on the quenched specimens were measured and its dependence on temperature and strain rate was analyzed. At high temperature, continuously dynamically recrystallized microstructures were observed; whilst at low temperature, necklace-like partially recrystallized microstructures were found. Key words: High nitrogen stainless steel; dynamic recrystallization; stress-strain curves

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Hot Deformation Behavior of a Ni-Based Superalloy with Suppressed Precipitation

Metals ◽

10.3390/met11040605 ◽

2021 ◽

Vol 11 (4) ◽

pp. 605

Author(s):

Franco Lizzi ◽

Kashyap Pradeep ◽

Aleksandar Stanojevic ◽

Silvana Sommadossi ◽

Maria Cecilia Poletti

Keyword(s):

Dynamic Recrystallization ◽

Strain Rate ◽

Hot Deformation ◽

Strain Rates ◽

Compression Tests ◽

Deformation Bands ◽

Stress Softening ◽

Relative Stress ◽

The Matrix ◽

Thermomechanical Processes

Inconel®718 is a well-known nickel-based super-alloy used for high-temperature applications after thermomechanical processes followed by heat treatments. This work describes the evolution of the microstructure and the stresses during hot deformation of a prototype alloy named IN718WP produced by powder metallurgy with similar chemical composition to the matrix of Inconel®718. Compression tests were performed by the thermomechanical simulator Gleeble®3800 in a temperature range from 900 to 1025 °C, and strain rates scaled from 0.001 to 10 s−1. Flow curves of IN718WP showed similar features to those of Inconel®718. The relative stress softening of the IN718WP was comparable to standard alloy Inconel®718 for the highest strain rates. Large stress softening at low strain rates may be related to two phenomena: the fast recrystallization rate, and the coarsening of micropores driven by diffusion. Dynamic recrystallization grade and grain size were quantified using metallography. The recrystallization grade increased as the strain rate decreased, although showed less dependency on the temperature. Dynamic recrystallization occurred after the formation of deformation bands at strain rates above 0.1 s−1 and after the formation of subgrains when deforming at low strain rates. Recrystallized grains had a large number of sigma 3 boundaries, and their percentage increased with strain rate and temperature. The calculated apparent activation energy and strain rate exponent value were similar to those found for Inconel®718 when deforming above the solvus temperature.

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Study on the Hot Deformation Characterization of Borated Stainless Steel by Hot Isostatic Pressing

Materials ◽

10.3390/ma14237110 ◽

2021 ◽

Vol 14 (23) ◽

pp. 7110

Author(s):

Yanbin Pei ◽

Xuanhui Qu ◽

Qilu Ge ◽

Tiejun Wang

Keyword(s):

Stainless Steel ◽

Hot Deformation ◽

True Strain ◽

Hot Isostatic Pressing ◽

Microstructural Analysis ◽

Critical Conditions ◽

True Strain Rate ◽

Isostatic Pressing ◽

Different Temperatures ◽

Borated Stainless Steel

Borated stainless steel (BSS) specimens have a boron content of 1.86 wt%, and are prepared by hot isostatic pressing (HIP) conducted at different temperatures, ranging from 1000 to 1100 °C and a constant true strain rate (0.01, 0.1, 1 and 10 s−1). These tests, with observations and microstructural analysis, have achieved the hot deformation characteristics and mechanisms of BSS. In this research, the activation energy (Q) and Zener–Hollomon parameter (Z) were contrasted against the flow curves: Q = 442.35 kJ/mol. The critical conditions associated with the initiation of dynamic recrystallization (DRX) for BSS were precisely calculated based on the function between the strain hardening rate with the flow stress: at different temperatures from 1000 to 1100 °C: the critical stresses were 146.69–254.77 MPa and the critical strains were 0.022–0.044. The facts show that the boron-containing phase of BSS prevented the onset of DRX, despite the saturated boron in the austenite initiated DRX. The microstructural analysis showed that hot deformation promoted the generation of borides, which differed from the initial microstructure of HIP. The inhomogeneous distribution of elements in the boron-containing phase was caused by hot compression.

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