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W M Rainforth - One of the best experts on this subject based on the ideXlab platform.
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microstructural evolution of nb v mo and v containing trip assisted steels during Thermomechanical Processing
Journal of Materials Science & Technology, 2017Co-Authors: Erfan Abbasi, W M RainforthAbstract:The microstructural evolution and precipitation behaviour of Nb–V–Mo and single V containing transformation induced plasticity assisted steels were investigated during Thermomechanical Processing. A plane strain compression testing machine was used to simulate the Thermomechanical Processing. Microstructures were characterised by optical microscopy, scanning-transmission electron microscopy and microanalysis, and X-ray diffraction analysis, and Vickers hardness was obtained from the deformed specimens. The resulting microstructure of both Nb–V–Mo and V steels at room temperature primarily consisted of an acicular/bainitic ferrite, retained austenite and martensite surrounded by allotriomorphic ferrite. The TEM analysis showed that a significant number of Nb(V,Mo)(C,N) precipitates were formed in the microstructure down to the finishing stage in Nb–V–Mo steel (i.e. 830 °C). It was also found that the V(C,N) precipitation primarily occurred in both ferrite and deformed austenite below the finishing stage. The results suggested that Nb–Mo additions considerably increased the temperature stability of microalloy precipitates and controlled the microstructural evolution of austenite. However, the microalloy precipitation did not cause a significant precipitation strengthening in both Nb–V–Mo and V steels at room temperature.
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Thermomechanical Processing route to achieve ultrafine grains in low carbon microalloyed steels
Acta Materialia, 2016Co-Authors: Peng Gong, E J Palmiere, W M RainforthAbstract:Abstract A new Thermomechanical Processing route is described for a microalloyed steel, with roughing deformation below the recrystallisation-stop temperature (T5%), followed by a rapid reheat to 1200 °C for 10s, and then finish deformation at the same temperature as the rough deformation. The new route focused on optimising the kinetics of strain-induced precipitation (SIP) and the formation of deformation-induced ferrite transformation (DITF). For comparative purposes, two experimental 0.06 wt% C steels were studied: one with 0.03 wt% Nb (Nb steel), and a second with both 0.03 wt% Nb and 0.02 wt% Ti (Nb Ti steel). Two Processing routes were studied. The first was a conventional route, which consisted of a simulated rough deformation schedule with the final roughing pass taking place at 850 °C, which produced fully unrecrystallised austenite grains during deformation with no strain-induced ferrite formation. The second, new, Thermomechanical Processing route used the same roughing step, after which the steels were reheated at 10 °C/s to a temperature of 1200 °C, isothermally held for 10s allowing for precipitate dissolution, prior to air cooling to a finishing deformation temperature of 850 °C. This route resulted in DIFT primarily on the prior-austenite grain boundaries. The precipitate solution during the reheat treatment increased the supersaturation of Nb and Ti in the austenite matrix on subsequent cooling, which therefore increased the undercooling due to the increased Ae3. The observation of nanoscale cementite in the DIFT supports the view that it formed through a massive transformation mechanism. The volume fraction of SIP after finish deformation was influenced by the supersaturation of microalloy elements in solution during heat treatment. The new process route led to a significant refinement of the final ferrite grain size.
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dissolution and precipitation behaviour in steels microalloyed with niobium during Thermomechanical Processing
Acta Materialia, 2015Co-Authors: Peng Gong, E J Palmiere, W M RainforthAbstract:Abstract The Thermomechanical Processing of high strength low allow (HSLA) steels during low-temperature roughing, followed by rapid reheating to higher temperatures was investigated to better understand the Nb dissolution kinetics in austenite, and the subsequent precipitation behaviour during the final finishing passes. For comparative purposes, two experimental 0.06 wt% C steels were studied, one containing 0.03 wt% Nb (Nb steel), and the second containing both 0.03 wt% Nb and 0.02 wt% Ti (Nb–Ti steel). Processing of these steels consisted of a simulated roughing schedule, with the final roughing pass taking place at 850 °C. The strain-induced precipitation intensity in the steels subsequently quenched where characterised using transmission electron microscopy. Following this, the steels were rapidly reheated at a rate of 10 °C/s to a temperature of 1200 °C, held at temperature for various times, and water quenched to room temperature so that both the precipitate dissolution kinetics, together with the austenite grain coarsening kinetics could be established.
Carl J. Boehlert - One of the best experts on this subject based on the ideXlab platform.
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The Effect of Thermomechanical Processing on the Tensile, Fatigue, and Creep Behavior of Magnesium Alloy AM60
Metallurgical and Materials Transactions A, 2011Co-Authors: Zhe Chen, R. F. Decker, Jack Huang, Larry R Walker, Odis Burl Cavin, Thomas R. Watkins, S. E. Lebeau, Carl J. BoehlertAbstract:Tensile, fatigue, fracture toughness, and creep experiments were performed on a commercially available magnesium-aluminum alloy (AM60) after three Processing treatments: (1) as-THIXOMOLDED (as-molded), (2) THIXOMOLDED then Thermomechanically processed (TTMP), and (3) THIXOMOLDED then TTMP then annealed (annealed). The TTMP procedure resulted in a significantly reduced grain size and a tensile yield strength greater than twice that of the as-molded material without a debit in elongation to failure ( ε _ f ). The as-molded material exhibited the lowest strength, while the annealed material exhibited an intermediate strength but the highest ε _ f (>1 pct). The TTMP and annealed materials exhibited fracture toughness values almost twice that of the as-molded material. The as-molded material exhibited the lowest fatigue threshold values and the lowest fatigue resistance. The annealed material exhibited the greatest fatigue resistance, and this was suggested to be related to its balance of tensile strength and ductility. The fatigue lives of each material were similar at both room temperature (RT) and 423 K (150 °C). The tensile-creep behavior was evaluated for applied stresses ranging between 20 and 75 MPa and temperatures between 373 and 473 K (100 and 200 °C). During both the fatigue and creep experiments, cracking preferentially occurred at grain boundaries. Overall, the results indicate that Thermomechanical Processing of AM60 dramatically improves the tensile, fracture toughness, and fatigue behavior, making this alloy attractive for structural applications. The reduced creep resistance after Thermomechanical Processing offers an opportunity for further research and development.
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The Effect of Thermomechanical Processing on the Tensile, Fatigue, and Creep Behavior of Magnesium Alloy AM60
Metallurgical and Materials Transactions A, 2010Co-Authors: Zhe Chen, Jack Huang, Ray Decker, S. Lebeau, Larry R Walker, Odis Burl Cavin, Thomas R. Watkins, Carl J. BoehlertAbstract:Tensile, fatigue, fracture toughness, and creep experiments were performed on a commercially available magnesium-aluminum alloy (AM60) after three Processing treatments: (1) as-THIXOMOLDED (as-molded), (2) THIXOMOLDED then Thermomechanically processed (TTMP), and (3) THIXOMOLDED then TTMP then annealed (annealed). The TTMP procedure resulted in a significantly reduced grain size and a tensile yield strength greater than twice that of the as-molded material without a debit in elongation to failure (ef). The as-molded material exhibited the lowest strength, while the annealed material exhibited an intermediate strength but the highest ef (>1 pct). The TTMP and annealed materials exhibited fracture toughness values almost twice that of the as-molded material. The as-molded material exhibited the lowest fatigue threshold values and the lowest fatigue resistance. The annealed material exhibited the greatest fatigue resistance, and this was suggested to be related to its balance of tensile strength and ductility. The fatigue lives of each material were similar at both room temperature (RT) and 423 K (150 °C). The tensile-creep behavior was evaluated for applied stresses ranging between 20 and 75 MPa and temperatures between 373 and 473 K (100 and 200 °C). During both the fatigue and creep experiments, cracking preferentially occurred at grain boundaries. Overall, the results indicate that Thermomechanical Processing of AM60 dramatically improves the tensile, fracture toughness, and fatigue behavior, making this alloy attractive for structural applications. The reduced creep resistance after Thermomechanical Processing offers an opportunity for further research and development.
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effect of Thermomechanical Processing on the creep behaviour of udimet alloy 188
Philosophical Magazine, 2008Co-Authors: Carl J. Boehlert, S.c. Longanbach, T R BielerAbstract:Udimet alloy 188 was subjected to grain-boundary engineering involving Thermomechanical Processing in an attempt to improve the creep performance and determine the effects on creep deformation processes. The as-received sheet was cold-rolled to either 10, 25 or 35% reduction per pass followed by a solution treatment at 1191°C for 1 h plus air cooling. This sequence was repeated four times and the resultant microstructure and grain-boundary character distribution were described using electron backscatter diffraction. The fraction of general high-angle grain boundaries tended to increase with increased cold rolling. The 10 and 25% cold-rolled materials exhibited lower creep rates than the 35% cold-rolled material. The measured creep stress exponents and activation energies suggested that dislocation creep with lattice self-diffusion was dominant at 760°C for stresses ranging between 100 and 220 MPa. A transition in the creep exponent below the applied stresses of 100 MPa indicated that a different secondary...
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The effect of Thermomechanical Processing on the microstructure and creep behavior of Udimet alloy 188
Superalloys 2008 (Eleventh International Symposium), 2008Co-Authors: S.c. Longanbach, Carl J. BoehlertAbstract:Udimet 188 alloy was subjected to Thermomechanical Processing in attempt to understand the effects of cold-rolling deformation on the microstructure and tensile-creep behavior. Commercially available sheet was cold rolled to varying amounts of deformation (between 5%-35% reduction in sheet thickness) followed by a solution treatment at 1191oC for one hour followed by air cooling. This sequence was repeated four times to induce a favorable grain boundary character distribution containing a high volume fraction of low-energy grain boundaries. The resultant microstructure was characterized using electron backscattered diffraction. The effect of the Thermomechanical Processing treatment on the hightemperature (760-815oC) creep behavior was evaluated. Conventional lever-arm creep experiments were performed in an open air environment. The measured creep stress exponents (5.76.4) suggested that dislocation creep was dominant at 760oC for stresses ranging between 100-220MPa. The material exhibited a significant extent of grain boundary cracking. The Thermomechanical Processing treatments which resulted in the greatest fractions (~0.8) of special grain boundaries (low-angle boundaries + coincident site lattice boundaries) also exhibited the lowest creep rates. Thus a correlation was exhibited between the grain boundary character distribution and the minimum creep rates. Creep rupture experiments were performed at T=815oC and σ=165MPa and the Thermomechanical Processing treatment which resulted in the greatest special boundary fraction also resulted in the greatest average time-to-rupture.
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The effect of Thermomechanical Processing on the creep behavior of Alloy 690
Materials Science and Engineering: A, 2008Co-Authors: Carl J. BoehlertAbstract:Abstract The effect of Thermomechanical Processing on the microstructure and elevated-temperature creep behavior of Alloy 690 was investigated. Commercially available sheet was subjected to four cycles of cold rolling to 25% deformation followed by annealing at 1000 °C for 1 h. Both the resultant microstructure and the original microstructure were characterized using electron backscattered diffraction. The Thermomechanically processed microstructure exhibited a slightly lower fraction of twins and a smaller average grain size than the original microstructure. Tensile–creep experiments were performed in an open-air environment at temperatures between 650 and 690 °C and stresses between 75 and 172 MPa. The measured creep stress exponents (4–5) activation energies (320–368 kJ/mol) suggested that dislocation creep with lattice self-diffusion was dominant. The Thermomechanically processed microstructure exhibited significantly worse creep resistance than the original as-processed microstructure. Thus, cyclic strain and annealing Processing, which has been shown to improve the ductility-dip cracking susceptibility of Alloy 690, is not recommended for enhancing the creep resistance.
Sebastián F. Medina - One of the best experts on this subject based on the ideXlab platform.
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Evolution of Microstructure and Precipitation State During Thermomechanical Processing of a Low Carbon Microalloyed Steel
Microscopy and Microanalysis, 2012Co-Authors: P. Valles, Manuel Gómez, Sebastián F. Medina, Ángeles Pérez Pastor, O. VilanovaAbstract:The increasing demand of sources of energy such as oil and natural gas induces at the steel industry a development on low carbon microalloyed steels for pipeline applications in order to achieve excellent mechanical properties of strength and toughness at a reduced cost. To obtain an adequate fine-grained final structure, the strict control of Thermomechanical Processing and accelerated cooling is crucial. Depending on the Thermomechanical Processing conditions and chemical composition, pipeline steels can present different microstructures. Several authors have found that the microstructure of acicular ferrite usually provides an optimum combination of mechanical properties. Higher levels of austenite strengthening before cooling promote a refinement of final microstructure but can also restrict the fraction of low temperature transformation products such as acicular ferrite.
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evolution of microstructure and precipitation state during Thermomechanical Processing of a x80 microalloyed steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Manuel Gómez, P. Valles, Sebastián F. MedinaAbstract:Abstract A series of anisothermal hot torsion tests were carried out to simulate hot rolling on a high-strength low-carbon CMnNbMoTi microalloyed steel corresponding to an industrial X80 grade for pipeline construction. Mean Flow Stress was graphically represented against the inverse of temperature to characterize the evolution of austenite microstructure during rolling, which was also studied by optical microscopy and SEM on samples quenched from several temperatures. On the other hand, particles precipitated at different temperatures during rolling were analyzed by means of TEM using the carbon extraction replica technique and their size distribution and mean size were determined, as well as their morphology, nature and chemical composition. The effect of rolling temperature and austenite strengthening obtained at the end of Thermomechanical Processing on final microstructure and precipitation state was studied. Austenite strengthening was characterized by means of the parameter known as accumulated stress (Δ σ ). It was found that ferrite grains are finer and more equiaxed when the austenite is more severely deformed during finishing (higher values of Δ σ ) but lower values of Δ σ generate a higher density of acicular structures after cooling, which should improve the balance of mechanical properties. The increase in strength associated to acicular ferrite compared to polygonal ferrite is revealed by the higher values of Vickers microhardness measured on samples corresponding to low Δ σ . On the other hand, (Ti, Nb)-rich carbonitrides can be found from reheating and their size keeps a constant value near 20–30 nm during Thermomechanical Processing. A second population of much finer (Nb, Mo)-rich carbonitrides whose size is close to 5 nm forms from lower temperatures, near 1000 °C. The accomplishment of two different levels of Δ σ at the end of hot rolling schedule does not seem to introduce major differences in precipitation state before final cooling.
Mostafa Alizadeh - One of the best experts on this subject based on the ideXlab platform.
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Modification of microstructure and mechanical properties of Al–Zn–Mg/3 wt.% Al2O3 composite through semi-solid Thermomechanical Processing using variable loads
International Journal of Materials Research, 2017Co-Authors: Mohsen Hajizamani, Mostafa AlizadehAbstract:Abstract The microstructure and mechanical properties of Al–Zn–Mg/3 wt.% Al2O3 composite were modified through a Thermomechanical Processing technique. The powders were cold pressed and solid state sintered for 90 min under argon atmosphere. Thermomechanical Processing was then applied to the solid state sintered samples, which consisted of cold pressing followed by partial remelting for 30 min under argon atmosphere. Four different loads in the Thermomechanical Processing were used to investigate the effects of compressive loads on the microstructures and the mechanical properties. The results revealed modifications in the microstructure of the Thermomechanically processed samples with the optimum combination of properties in the sample modified by applying the load of 250 MPa. Increasing the Thermomechanical Processing load decreased the amounts of porosity by about 7 %, decreased the average grain size to about 4 μm, enhanced the compressive yield strength to about 295 MPa, and increased the microhardn...
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modification of microstructure and mechanical properties of al zn mg 3 wt al2o3 composite through semi solid Thermomechanical Processing using variable loads
International Journal of Materials Research, 2017Co-Authors: Mohsen Hajizamani, Mostafa AlizadehAbstract:Abstract The microstructure and mechanical properties of Al–Zn–Mg/3 wt.% Al2O3 composite were modified through a Thermomechanical Processing technique. The powders were cold pressed and solid state sintered for 90 min under argon atmosphere. Thermomechanical Processing was then applied to the solid state sintered samples, which consisted of cold pressing followed by partial remelting for 30 min under argon atmosphere. Four different loads in the Thermomechanical Processing were used to investigate the effects of compressive loads on the microstructures and the mechanical properties. The results revealed modifications in the microstructure of the Thermomechanically processed samples with the optimum combination of properties in the sample modified by applying the load of 250 MPa. Increasing the Thermomechanical Processing load decreased the amounts of porosity by about 7 %, decreased the average grain size to about 4 μm, enhanced the compressive yield strength to about 295 MPa, and increased the microhardn...
M. Filonov - One of the best experts on this subject based on the ideXlab platform.
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Structure and Properties of Ti-19.7Nb-5.8Ta Shape Memory Alloy Subjected to Thermomechanical Processing Including Aging
Journal of Materials Engineering and Performance, 2013Co-Authors: S. Dubinskiy, Vladimir Brailovski, S. Prokoshkin, V. Pushin, K. Inaekyan, V. Sheremetyev, M. Petrzhik, M. FilonovAbstract:In this work, the ternary Ti-19.7Nb-5.8Ta (at.%) alloy for biomedical applications was studied. The ingot was manufactured by vacuum arc melting with a consumable electrode and then subjected to hot forging. Specimens were cut from the ingot and processed by cold rolling with e = 0.37 of logarithmic thickness reduction and post-deformation annealing (PDA) between 400 and 750 °C (1 h). Selected samples were subjected to aging at 300 °C (10 min to 3 h). The influence of the Thermomechanical Processing on the alloy’s structure, phase composition, and mechanical and functional properties was studied. It was shown that Thermomechanical Processing leads to the formation of a nanosubgrained structure (polygonized with subgrains below 100 nm) in the 500-600 °C PDA range, which transforms to a recrystallized structure of β-phase when PDA temperature increases. Simultaneously, the phase composition and the β → α″ transformation kinetics vary. It was found that after conventional cold rolling and PDA, Ti-Nb-Ta alloy manifests superelastic and shape memory behaviors. During aging at 300 °C (1 h), an important quantity of randomly scattered equiaxed ω-precipitates forms, which results in improved superelastic cyclic properties. On the other hand, aging at 300 °C (3 h) changes the ω-precipitates’ particle morphology from equiaxed to elongated and leads to their coarsening, which negatively affects the superelastic and shape memory functional properties of Ti-Nb-Ta alloy.
