scholarly journals A flow instability criterion for alloys during hot deformation

2019 ◽  
Vol 37 ◽  
pp. 319-326
Author(s):  
Peng Wang ◽  
Katharina Hogrefe ◽  
David Piot ◽  
Frank Montheillet ◽  
María Cecilia Poletti
Keyword(s):  
Hot Deformation ◽  
Flow Instability ◽  
Instability Criterion

scholarly journals The Investigation on Flow Behavior of Powder Metallurgy Ti-10V-2Fe-3Al Alloy Using the Prasad Stability Criterion

2019 ◽  
Vol 50 (11) ◽  
pp. 5314-5323 ◽  
Author(s):  
Krystian Zyguła ◽  
Marek Wojtaszek ◽  
Oleksandr Lypchanskyi ◽  
Tomasz Śleboda ◽  
Grzegorz Korpała ◽  
...  
Keyword(s):  
Powder Metallurgy ◽  
Power Dissipation ◽  
Hot Deformation ◽  
High Efficiency ◽  
Flow Instability ◽  
Flow Behavior ◽  
Material Model ◽  
Instability Criterion ◽  
Processing Maps ◽  
Compression Tests

Abstract The hot deformation behavior of Ti-10V-2Fe-3Al alloy obtained by the powder metallurgy (PM) method was investigated. Material for the research was produced by blending of elemental powders followed by uniaxial hot pressing. Thermomechanical tests of Ti-10V-2Fe-3Al compacts were carried out to determinate the stress-strain relationships at the temperature range of 800 °C to 1000 °C and strain rate between 0.01 and 10 s−1. Based on the dynamic material model (DMM) theory, processing maps at constant strain value were developed using data obtained from hot compression tests. The processing maps were elaborated for the final strain value, which was 0.9, and with flow instability criterion domains applied to it. Two critical regions associated with the flow behavior of the investigated material were revealed. Microstructural changes during hot deformation at various temperatures and strain rates were discussed. The correlation between calculated efficiency of power dissipation, flow instability criterion, and microstructure evolution was determined. The presence of defects was confirmed in regions predicted by the instability maps. The microstructure of the investigated alloy, corresponding to the high efficiency of power dissipation characterized by the occurrence of dynamic recrystallization (DRX) phenomena, was also shown. Additionally, average hardness values in relation to variable process parameters were designated. Based on the conducted studies and analysis, processing windows for Ti-10V-2Fe-3Al alloy compacts were proposed.

scholarly journals The Deformation Behavior, Microstructural Mechanism, and Process Optimization of PM/Wrought Dual Superalloys for Manufacturing the Dual-Property Turbine Disc

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1127 ◽  
Author(s):  
Baoyun Zhang ◽  
Xiaoming Liu ◽  
Hao Yang ◽  
Yongquan Ning
Keyword(s):  
Hot Deformation ◽  
Deformation Behavior ◽  
Processing Map ◽  
Flow Instability ◽  
Rapid Development ◽  
Instability Criterion ◽  
Aviation Industry ◽  
Dual Property ◽  
Turbine Disc ◽  
Microstructural Mechanism

With the rapid development of modern aviation industry, dual-property turbine disc with fine comprehensive performance plays an important role in raising the thrust-to-weight ratio of the aero-engine. For manufacturing dual-property turbine disc, the powder metallurgy superalloy (PM) with excellent creep resistance was chosen as rim material, and the wrought superalloy with fine equiaxed grains was chosen as bore material. Electron beam welding was carried out on the PM/wrought dual superalloys. Hot compression tests were conducted on the PM/Wrought dual superalloys at temperatures of 1020–1140 °C and strain rates of 0.001–1.0 s−1. Deformation behavior and microstructure evolution have been investigated to study the deformation and recrystallization mechanism during hot deformation process. The results showed that PM/Wrought dual superalloy presents the similar flow behavior to single alloys and flow stress decreases significantly with the increase of deformation temperature or the decrease of strain rate. The apparent activation energy of deformation at the strain of 0.2 was determined as being 780.07 kJ·mol−1. The constitutive equation was constructed for modeling the hot deformation of PM/Wrought dual superalloy. Meanwhile, the processing map approach was further adopted to optimize the manufacturing process for the dual-property turbine disc. Additionally, a new instability criterion was proposed: the “cliff” and “valley” in the power dissipation map are determined as sufficient conditions for flow instability. The optimum processing parameter for manufacturing the PM/Wrought dual-property turbine disc can be obtained to enhance the mechanical properties, based on the analysis of processing map technology and microstructural mechanism.

Hot Deformation Behavior during the Hot Compression of AZ31 Alloy

2010 ◽  
Vol 139-141 ◽  
pp. 545-548 ◽  
Author(s):  
Shu Li Sun ◽  
Min Gang Zhang ◽  
Wen Wu He ◽  
Jun Qi Zhou ◽  
Gang Sun
Keyword(s):  
Hot Deformation ◽  
Deformation Behavior ◽  
Flow Instability ◽  
Strain Curve ◽  
Az31 Alloy ◽  
Hot Compression ◽  
Instability Criterion ◽  
Compression Tests ◽  
Hot Deformation Behavior ◽  
Hollomon Parameter

The hot deformation behavior of as-cast AZ31 magnesium alloys have been investigated at 200~400°C and strain rates 0.001~1s-1 by means of hot compression tests on a Gleeble-1500D thermal-mechanical simulator. We have analyzed the flow stress-strain curve and presented the constitutive equation by calculating stress exponent, activation energy and Zemer-Hollomon parameter. Then, the processing map of AZ31 alloys has been developed based on the dynamic material model theories and Prasad instability criterion. The flow instability domain is observed at lower temperature and the larger power dissipation rate is emerging at 300~400°C. We have analyzed the corresponding deformation microstructures and it is characteristic of dynamic recrystallization. These results have shown that AZ31 alloy has good workability at 300~400°C and lower strain rate.

Microstructure Evolution and Processing Map of Superalloy GH720Li during Isothermal Compression

2013 ◽  
Vol 747-748 ◽  
pp. 588-593
Author(s):  
Zhao Li ◽  
Shu Hong Fu ◽  
Tao Wang ◽  
Yu Xin Zhao ◽  
Yong Zhang ◽  
...  
Keyword(s):  
Microstructure Evolution ◽  
Hot Deformation ◽  
Processing Map ◽  
Flow Instability ◽  
Plastic Instability ◽  
Instability Criterion ◽  
Compression Tests ◽  
Softening Mechanism ◽  
Deformation Parameters ◽  
Hot Processing Map

sothermal compression tests for superalloy GH720Li were conducted to investigate the effect of hot deformation parameters on microstructure evolution. The changing characteristics of flow stress during hot deformation were also studied. The flow instability area was calculated based on Prasad Plastic Instability Criterion and the hot processing map was obtained. The results showed that dynamic recrystallization was the main softening mechanism of GH720Li alloy during hot deformation. The peak and steady stress decreased significantly with an increase of test temperature and a decrease of the strain rate. Finally, three unstable areas have been found from the processing map.

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

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.

Hot Deformation Studies of a Low Carbon Steel Containing V

2013 ◽  
Vol 554-557 ◽  
pp. 1224-1231 ◽  
Author(s):  
Cecilia Poletti ◽  
Martina Dikovits ◽  
Javier Ruete
Keyword(s):  
Strain Rate ◽  
Hot Deformation ◽  
Flow Instability ◽  
True Strain ◽  
Low Carbon Steel ◽  
Dynamic Effect ◽  
Rate Sensitivity ◽  
Low Carbon ◽  
Compression Tests ◽  
Deformation Parameters

Low alloyed steels produced by continuous casting are thermomechanically treated to achieve final high mechanical properties, meaning a good combination of strength and toughness. The hot deformation mechanisms of a micro-alloyed steel containing up to 0.1wt% of V is studied by means of hot compression tests using a Gleeble®3800 device. Austenitization of samples is carried out at 1150°C during 2 minutes followed by cooling to the deformation temperature at 1Ks-1in the range of 750 – 1150°C. The studied strain rate range is from 0.01 to 80 s-1and the total true strain achieved is of 0.7. In situ water quenching is applied after the deformation to freeze the microstructure and avoid any post dynamic effect. The Ar3temperature is determined by dilatometry experiments to be 725°C for the used cooling rate. The stress values obtained from the compression tests are evaluated at different strains to determine the strain rate sensitivity and flow instability maps and thus, to predict the formability of the material in the range of studied deformation parameters. These maps are correlated to the microstructure at specific deformation parameters.

Experimental Studies of Pressure Drop and Flow Instability in Evaporative Micro-Channels

2008 ◽  
Author(s):  
Hee Joon Lee ◽  
Dongyao Liu ◽  
Shi-Chune Yao
Keyword(s):  
Pressure Drop ◽  
Flow Instability ◽  
Experimental Studies ◽  
Bond Number ◽  
Effective Length ◽  
Instability Criterion ◽  
Micro Channel ◽  
Micro Channels ◽  
Wide Range ◽  
Channel Systems

Experiments were conducted on evaporative micro-channel systems of water, containing 48 parallel channels of 353 μm hydraulic diameter. The general correlation of two-phase pressure drop for an initial design purpose of evaporative micro-channel systems reported in [1] has been validated. For the water boiling in micro-channels, flow instability was observed. The instability criterion, proposed by Kandlikar [2], is able to predict the water experimental results. However, further examination of his criterion revealed that it can not predict the results of Brutin and Tadrist’s data of n-pentane. This is because the Bond number of water is 0.01, but 0.33 for n-pentane. As a result, the growing bubble of n-pentane may not cover the whole length of the micro-channel. A general expression of the effective length of squeezed bubbles in micro-channel was established for fluids at a wide range of Bond number. Using this proposed effective length, the Brutin and Tadrist’s experimental instability data can also be predicted satisfactorily.

Stability Analysis and Network Design of Evaporative Micro-Channels

2008 ◽  
Author(s):  
Hee Joon Lee ◽  
Shi-Chune Yao
Keyword(s):  
Flow Instability ◽  
Narrow Channel ◽  
Bond Number ◽  
Instability Criterion ◽  
Micro Channel ◽  
Network Systems ◽  
Channel Network ◽  
Micro Channels ◽  
Channel Expansion ◽  
Expanding Channel

During the operation of evaporative micro-channels, flow instability could be encountered. This phenomenon usually occurs when the Bond number of the fluid in the micro-channels is less than unity, so that a growing bubble is severely squeezed in the narrow channel and expands towards both upstream and downstream simultaneously. To reduce the flow instability, installation of an inlet orifice at the upstream, or making the micro-channel expanding at the downstream are found to be effective. An instability model for micro-channels was established, which takes into account the effects of both the inlet orifice and the channel expansion. Experiments of evaporating water micro system of 48 parallel micro-channels with 353 μm hydraulic diameter were conducted. The instability criterion of evaporative micro-channels with the effects of inlet orifice and expanding channel area are validated. Furthermore, to assist the general design of complex micro-channel network systems, a computational scheme is developed.

Flow Instability in the Orthogonal Machining of CP Titanium

1997 ◽  
Vol 119 (3) ◽  
pp. 307-313 ◽  
Author(s):  
J. Sheikh-Ahmad ◽  
J. A. Bailey
Keyword(s):  
Shear Strain ◽  
Formation Process ◽  
Chip Formation ◽  
Flow Instability ◽  
Pure Titanium ◽  
Plastic Instability ◽  
Shear Localization ◽  
Instability Criterion ◽  
Commercially Pure Titanium ◽  
Orthogonal Machining

An experimental and analytical investigation of flow instability and shear localization in the orthogonal machining of grade 2 commercially pure titanium was made. A criterion for thermo-plastic instability was developed from torsion test results and applied to the analysis of the chip formation process. It was shown that flow instability followed by flow localization occurs when machining titanium at all cutting speeds and that a transition in the chip type from uniform to segmented does not occur. Orthogonal machining experiments were conducted in the speed range from 8.75 × 10−5 to 3.20 m/s for various depths of cut and the shear strain in the chip was calculated. It was shown that shear localization occurred in the chip formation process when the uniform shear strain involved in producing a chip segment reached a critical value and that this critical shear strain correlates fairly well with the instability shear strain predicted by the thermo-plastic instability criterion.

High Temperature Deformation Behaviour and Processing Maps of AZ81 Magnesium Alloy

2011 ◽  
Vol 686 ◽  
pp. 168-175 ◽  
Author(s):  
Hui Min Liao ◽  
Ming Zeng ◽  
Si Yuan Long ◽  
Han Xue Cao
Keyword(s):  
High Temperature ◽  
Flow Stress ◽  
Magnesium Alloy ◽  
Strain Rate ◽  
Hot Deformation ◽  
Flow Instability ◽  
Temperature Deformation ◽  
Stable Phase ◽  
Processing Temperature ◽  
Processing Maps

The hot compression deformation behavior of AZ81 magnesium alloy was studied with Gleeble-1500 thermal simulation machine at the strain rate of 0.003 ~ 3.0s-1 and temperature of 340 ~ 430 °C. The results show that, the flow stress decreases when the deformation temperature increases and strain rate decreases; the peak stress increases with decrease of the temperature and the increase of the strain rate; the critical strain that comes into stable phase increases obviously. It is that the high temperature flow stress model of AZ81 magnesium alloy is constructed by introduceing Zener-Hollomon parameters, its average deformation activation energy is 169.48 kJ / mol. Processing maps of AZ81 magnesium alloy is also calculated and analyzed by the dynamic model of the material. Useing hot deformation processing maps, the flow instability zone is determined and the best process parameters access to the test parameters during hot deformation are as follow: thermal processing temperature range of 380 °C ~ 420 °C, strain rate range of 0.01 ~ 0.03 S-1.

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