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Darryl P Butt - One of the best experts on this subject based on the ideXlab platform.

  • Recrystallization Kinetics of 3c silicon carbide implanted with 400 kev cesium ions
    Journal of the American Ceramic Society, 2013
    Co-Authors: Daniel D Osterberg, John Youngsman, Rick Ubic, Ivar E. Reimanis, Darryl P Butt
    Abstract:

    Polycrystalline 3C silicon carbide (SiC) was implanted at room temperature with 400 keV cesium ions to a dose of 1016 ions/cm2. The samples were annealed at 600°C–1000°C for times up to 48 h to observe changes in the implantation zone crystallinity and density. The implanted regions were characterized by transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) before and after annealing. It is shown that the implantation resulted in a 217 ± 2 nm amorphous region with microstructural damage extending to ~250 nm below the surface. Recrystallization of the amorphous region was observed to begin at 725°C. Densification was determined indirectly through changes in the measured implantation zone thickness. Measurable thickness, or densification, of the implanted region was not observed until temperatures greater than ~800°C. The SiC Recrystallization began at the interface between the amorphous, damaged region, and the underlying polycrystalline material. Image analysis was used to quantify the fraction of crystalline phase as a function of time and temperature. The Recrystallization Kinetics exhibited Arrhenius dependency with an apparent activation energy of 480 kJ/mol. SIMS demonstrated that 60%–70% of the cesium was retained within the recrystallized microstructure after thermal annealing.

  • Recrystallization Kinetics of 3c silicon carbide implanted with 400 kev cesium ions
    Journal of the American Ceramic Society, 2013
    Co-Authors: Daniel D Osterberg, John Youngsman, Rick Ubic, Ivar E. Reimanis, Darryl P Butt
    Abstract:

    Polycrystalline 3C silicon carbide (SiC) was implanted at room temperature with 400 keV cesium ions to a dose of 1016 ions/cm2. The samples were annealed at 600°C–1000°C for times up to 48 h to observe changes in the implantation zone crystallinity and density. The implanted regions were characterized by transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) before and after annealing. It is shown that the implantation resulted in a 217 ± 2 nm amorphous region with microstructural damage extending to ~250 nm below the surface. Recrystallization of the amorphous region was observed to begin at 725°C. Densification was determined indirectly through changes in the measured implantation zone thickness. Measurable thickness, or densification, of the implanted region was not observed until temperatures greater than ~800°C. The SiC Recrystallization began at the interface between the amorphous, damaged region, and the underlying polycrystalline material. Image analysis was used to quantify the fraction of crystalline phase as a function of time and temperature. The Recrystallization Kinetics exhibited Arrhenius dependency with an apparent activation energy of 480 kJ/mol. SIMS demonstrated that 60%–70% of the cesium was retained within the recrystallized microstructure after thermal annealing.

L P Karjalainen - One of the best experts on this subject based on the ideXlab platform.

  • hot deformation behavior and microstructure evolution of a stabilized high cr ferritic stainless steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013
    Co-Authors: Saara Mehtonen, L P Karjalainen, David Porter
    Abstract:

    Abstract The hot deformation behavior and static microstructure evolution of a 21Cr stabilized ferritic stainless steel was studied using axisymmetric hot compression tests on a Gleeble 1500 thermomechanical simulator. The deformation was carried out at 950–1050 °C to strains of 0.2 to 0.6 using strain rates of 0.01, 0.1 and 1 s −1 . The compression was followed by a holding period of 0 to 180 s in order to study the static Recrystallization Kinetics. The electron backscatter diffraction (EBSD) technique was used in analyzing the resultant microstructures. A constitutive equation that well describes the flow stress as a function of strain, strain rate and temperature was developed. The active dynamic restoration mechanism was found to depend on the Zener–Hollomon parameter, such that continuous dynamic Recrystallization was observed under low Zener–Hollomon parameter conditions but under high Zener–Hollomon parameter microstructures were dynamically recovered, and no dynamic formation of new grains occurred. Static Recrystallization resulted in little or no grain refinement, and further, strain did not have an accelerating effect on the static Recrystallization Kinetics beyond the strain of 0.4.

  • effect of silicon and aluminium on austenite static Recrystallization Kinetics in high strength trip aided steels
    Isij International, 2012
    Co-Authors: Pasi Suikkanen, M C Somani, David Porter, Visa Tatu Emil Lang, L P Karjalainen
    Abstract:

    High-strength transformation-induced-plasticity steels contain high concentrations of silicon or aluminium or a combination of the two. The effects of up to 1.5 wt.% Si and up to 1.9 wt.% Al on the static Recrystallization Kinetics of austenite in 0.2C–2.0Mn–0.6Cr steel have been investigated and the activation energies of deformation (Qdef) and static Recrystallization (Qsrx) have been determined. Addition of aluminium increases Qdef and Qsrx more strongly than addition of silicon. Aluminium alloying also retards static Recrystallization more strongly than silicon alloying. In both cases, the effects of silicon and aluminium are non-linear saturating towards the highest concentrations studied.

  • the influence of aluminum on hot deformation behavior and tensile properties of high mn twip steels
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
    Co-Authors: A S Hamada, L P Karjalainen, M C Somani
    Abstract:

    Abstract The influence of aluminum (0–3 wt.%) on the high-temperature flow stress and Recrystallization Kinetics of two austenitic 25 wt.% Mn-bearing TWIP steels were investigated and compared with the behavior of a low-carbon steel. In addition, tensile properties were determined over the temperature range from −80 to 200 °C. It was observed that the hot deformation resistance is slightly higher for the 25Mn3Al than for the 25Mn steel, but in both steels significantly higher than for the low-carbon steel. The static Recrystallization Kinetics is significantly retarded in both steels compared to the rate in the low-carbon steel. The activation energies of hot deformation and static Recrystallization are higher than those for the low-carbon steel. In contrast to the high temperature behavior, below RT, the 25Mn steel possessed a higher tensile strength and a higher work hardening rate than the 25Mn3Al steel due to strain-induced martensite formation. With increasing temperature up to 200 °C, the deformation mode changed gradually to mechanical twinning. In the 25Mn3Al steel, the elongation increased with decreasing temperature as a result of enhanced mechanical twinning.

  • high temperature flow stress and Recrystallization behavior of high mn twip steels
    Isij International, 2007
    Co-Authors: A S Hamada, M C Somani, L P Karjalainen
    Abstract:

    The flow stress behavior and Recrystallization Kinetics in the hot rolling temperature range have been investigated in five Fe‐Mn‐Al (Mn: 25 wt%, Al: 0‐8 wt%) TWIP steels by compression testing on a Gleeble simulator. Results were compared with corresponding properties of carbon and austenitic stainless steels. Microstructures were examined by electron microscopy. The results show that the flow stress level of the TWIP steels is considerably higher than that of low-carbon steels and depended on the Al concentration close to 6 wt%, while the structure is austenitic at hot rolling temperatures. At higher Al contents, the flow stress level becomes significantly lowered due to the presence of ferrite. The static Recrystallization Kinetics is slower compared to that of carbon steels, but it is faster than typical of Nb-microalloyed or austenitic stainless steels. High Mn content is a reason for the high flow stress as well as for slow softening. Al has a minor role only, but in the case of austenitic‐ferritic structure, softening of the ferrite phase occurs very rapidly that also contributes to overall faster softening. The grain size is effectively refined by the dynamic and static Recrystallization processes.

M C Somani - One of the best experts on this subject based on the ideXlab platform.

  • effect of silicon and aluminium on austenite static Recrystallization Kinetics in high strength trip aided steels
    Isij International, 2012
    Co-Authors: Pasi Suikkanen, M C Somani, David Porter, Visa Tatu Emil Lang, L P Karjalainen
    Abstract:

    High-strength transformation-induced-plasticity steels contain high concentrations of silicon or aluminium or a combination of the two. The effects of up to 1.5 wt.% Si and up to 1.9 wt.% Al on the static Recrystallization Kinetics of austenite in 0.2C–2.0Mn–0.6Cr steel have been investigated and the activation energies of deformation (Qdef) and static Recrystallization (Qsrx) have been determined. Addition of aluminium increases Qdef and Qsrx more strongly than addition of silicon. Aluminium alloying also retards static Recrystallization more strongly than silicon alloying. In both cases, the effects of silicon and aluminium are non-linear saturating towards the highest concentrations studied.

  • the influence of aluminum on hot deformation behavior and tensile properties of high mn twip steels
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
    Co-Authors: A S Hamada, L P Karjalainen, M C Somani
    Abstract:

    Abstract The influence of aluminum (0–3 wt.%) on the high-temperature flow stress and Recrystallization Kinetics of two austenitic 25 wt.% Mn-bearing TWIP steels were investigated and compared with the behavior of a low-carbon steel. In addition, tensile properties were determined over the temperature range from −80 to 200 °C. It was observed that the hot deformation resistance is slightly higher for the 25Mn3Al than for the 25Mn steel, but in both steels significantly higher than for the low-carbon steel. The static Recrystallization Kinetics is significantly retarded in both steels compared to the rate in the low-carbon steel. The activation energies of hot deformation and static Recrystallization are higher than those for the low-carbon steel. In contrast to the high temperature behavior, below RT, the 25Mn steel possessed a higher tensile strength and a higher work hardening rate than the 25Mn3Al steel due to strain-induced martensite formation. With increasing temperature up to 200 °C, the deformation mode changed gradually to mechanical twinning. In the 25Mn3Al steel, the elongation increased with decreasing temperature as a result of enhanced mechanical twinning.

  • high temperature flow stress and Recrystallization behavior of high mn twip steels
    Isij International, 2007
    Co-Authors: A S Hamada, M C Somani, L P Karjalainen
    Abstract:

    The flow stress behavior and Recrystallization Kinetics in the hot rolling temperature range have been investigated in five Fe‐Mn‐Al (Mn: 25 wt%, Al: 0‐8 wt%) TWIP steels by compression testing on a Gleeble simulator. Results were compared with corresponding properties of carbon and austenitic stainless steels. Microstructures were examined by electron microscopy. The results show that the flow stress level of the TWIP steels is considerably higher than that of low-carbon steels and depended on the Al concentration close to 6 wt%, while the structure is austenitic at hot rolling temperatures. At higher Al contents, the flow stress level becomes significantly lowered due to the presence of ferrite. The static Recrystallization Kinetics is slower compared to that of carbon steels, but it is faster than typical of Nb-microalloyed or austenitic stainless steels. High Mn content is a reason for the high flow stress as well as for slow softening. Al has a minor role only, but in the case of austenitic‐ferritic structure, softening of the ferrite phase occurs very rapidly that also contributes to overall faster softening. The grain size is effectively refined by the dynamic and static Recrystallization processes.

Roland E Loge - One of the best experts on this subject based on the ideXlab platform.

Nathalie Bozzolo - One of the best experts on this subject based on the ideXlab platform.

  • influence of strain rate on subsolvus dynamic and post dynamic Recrystallization Kinetics of inconel 718
    Acta Materialia, 2019
    Co-Authors: A Nicolay, G Fiorucci, Jeanmichel Franchet, Jonathan Cormier, Nathalie Bozzolo
    Abstract:

    Abstract Influence of strain rate on dynamic and post-dynamic Recrystallization Kinetics of Inconel 718 is investigated by performing hot compression tests at constant strain rate in the range [ 0.001 ; 1 ] s − 1 in the δ -subsolvus domain, with or without post-deformation holding at the deformation temperature. Dynamically and post-dynamically recrystallized grains are distinguished based on their internal misorientations, using EBSD data with enhanced angular resolution. For the applied deformation conditions ( T = 980 ° C and e = 0.7 ), dynamic Recrystallization is inhibited at e ˙ > 0.1 s − 1 . On the other hand, very fast post-dynamic Recrystallization is promoted by high strain rates, with characteristic times which can be as short as few seconds to achieve full Recrystallization. Most of previous works on the effect of strain rate on dynamic Recrystallization Kinetics were done by quenching samples right after deformation, without discriminating dynamically and post-dynamically recrystallized grains. Those works led to the conclusion that increasing strain rate beyond a critical value leads to an increase in dynamic Recrystallization Kinetics. Experimental quenching delays cannot be shorter that few seconds, which is shown here to be sufficient to get a significant increase in recrystallized fraction by post-dynamic mechanisms. Based on the present work, post-dynamic evolutions are actually very likely to be responsible for the apparent increase in dynamic Recrystallization Kinetics at high strain rates which has often been reported previously.

  • mean field modelling of dynamic and post dynamic Recrystallization during hot deformation of inconel 718 in the absence of δ phase particles
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Meriem Zouari, Nathalie Bozzolo, Roland E Loge
    Abstract:

    Dynamic and post-dynamic Recrystallization Kinetics were investigated during hot-working of Inconel 718 as a function of temperature, strain and strain rate in the single phase domain. The post-dynamic evolution was found to be extremely fast and impacting significantly the grain size. A two-site mean field model including both dynamic and post-dynamic evolution was used to predict the recrystallized fraction, the average grain size and the stress–strain curves in different thermomechanical conditions.