https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Sun, 14 Jun 2026 10:30:48 GMT 2026-06-14T10:30:48Z http://hdl.handle.net/10985/9001 Microstructure observation and quantification of the liquid fraction of M2 steel grade in the semi-solid state, combining confocallaser scanning microscopy and X-ray microtomography GU, Guochao; PESCI, Raphaël; LANGLOIS, Laurent; BECKER, Eric; BIGOT, Regis; GUO, M.X. Microstructure is of crucial importance to the flow behavior of semi-solid slurries during the thixoforging process. Therefore, a thorough understanding of the microstructure evolution is required. In order to achieve this, high temperature confocal laser scanning microscopy (CLSM) and high energy X-ray microtomography were used to investigate the microstructure evolution of several steel grades (M2, 100Cr6 and C38LTT) during the heating process from as-received conditions to the semi-solid state. It was found that the microstructure development of M2 can be directly studied at high temperature via these two techniques. Two types of small carbides (MC and M6C) were present in the as-received state, while totally new interconnected carbides of specific size and composition were formed from liquid zones after cooling. It was also noted using CLSM that the diffusion rate of the alloying elements during the cooling of M2 was very low. This confirms that the volume fraction of the liquid phase of M2 at high temperature can be evaluated by threedimensional X-ray microtomography in situ at high temperature and on quenched specimens. Contrary to M2, the microstructure of the steel grades 100Cr6 and C38LTT in the semi-solid state can only be revealed by CLSM at high temperature. All these observations are discussed in terms of microstructural development and liquid fraction during heating. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/9001 2014-01-01T00:00:00Z GU, Guochao PESCI, Raphaël LANGLOIS, Laurent BECKER, Eric BIGOT, Regis GUO, M.X. Microstructure is of crucial importance to the flow behavior of semi-solid slurries during the thixoforging process. Therefore, a thorough understanding of the microstructure evolution is required. In order to achieve this, high temperature confocal laser scanning microscopy (CLSM) and high energy X-ray microtomography were used to investigate the microstructure evolution of several steel grades (M2, 100Cr6 and C38LTT) during the heating process from as-received conditions to the semi-solid state. It was found that the microstructure development of M2 can be directly studied at high temperature via these two techniques. Two types of small carbides (MC and M6C) were present in the as-received state, while totally new interconnected carbides of specific size and composition were formed from liquid zones after cooling. It was also noted using CLSM that the diffusion rate of the alloying elements during the cooling of M2 was very low. This confirms that the volume fraction of the liquid phase of M2 at high temperature can be evaluated by threedimensional X-ray microtomography in situ at high temperature and on quenched specimens. Contrary to M2, the microstructure of the steel grades 100Cr6 and C38LTT in the semi-solid state can only be revealed by CLSM at high temperature. All these observations are discussed in terms of microstructural development and liquid fraction during heating. http://hdl.handle.net/10985/7719 Determination of quantity and localization of liquid in the semi-solid state using both 3D X-ray microtomography and 2D techniques for steel thixoforming GU, Guochao; BECKER, Eric; PESCI, Raphaël; LANGLOIS, Laurent The distribution of liquid at the semi solid state is one of the most important parameters for steel thixoforging. It has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Both ex situ and in situ 3D X-ray microtomography characterizations have been carried out to determine the quantity and localization of liquid at high temperature of M2 steel slugs. Microtomography was first performed ex situ at room temperature on samples heated and quenched from semi-solid state. The specimens were also scanned in situ directly at high temperature. The obtained results have been compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They showed a good correlation making both approaches very efficient for the study of the liquid zones at the semi-solid state. Lien vers la version éditeur: http://www.scientific.net/SSP.192-193.191 Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/7719 2013-01-01T00:00:00Z GU, Guochao BECKER, Eric PESCI, Raphaël LANGLOIS, Laurent The distribution of liquid at the semi solid state is one of the most important parameters for steel thixoforging. It has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Both ex situ and in situ 3D X-ray microtomography characterizations have been carried out to determine the quantity and localization of liquid at high temperature of M2 steel slugs. Microtomography was first performed ex situ at room temperature on samples heated and quenched from semi-solid state. The specimens were also scanned in situ directly at high temperature. The obtained results have been compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They showed a good correlation making both approaches very efficient for the study of the liquid zones at the semi-solid state. http://hdl.handle.net/10985/9049 Microstructure investigation and flow behavior during thixoextrusion of M2 steel grade GU, Guochao; PESCI, Raphaël; LANGLOIS, Laurent; BECKER, Eric; BIGOT, Regis The microstructure investigation and flow behavior during thixoforging of M2 steel parts were investigated. Partial remelting was performed at processing temperatures ranging from 1290 ◦C to 1340 ◦C corresponding to a liquid fraction range between 10% and 30% (according to differential scanning calorimetry measurements and quantitative image analyses). A conventional microstructure for thixoforming process was obtained: spherical solid grains surrounded by liquid phase. The microstructure across the heated billets was relatively homogeneous with bigger grain size near the surface. Successful thixoextrusion for producing parts was finally achieved at processing temperatures. By investigating the microstructure and load-displacement curves, different mechanisms in various forming stages were proposed. Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/9049 2015-01-01T00:00:00Z GU, Guochao PESCI, Raphaël LANGLOIS, Laurent BECKER, Eric BIGOT, Regis The microstructure investigation and flow behavior during thixoforging of M2 steel parts were investigated. Partial remelting was performed at processing temperatures ranging from 1290 ◦C to 1340 ◦C corresponding to a liquid fraction range between 10% and 30% (according to differential scanning calorimetry measurements and quantitative image analyses). A conventional microstructure for thixoforming process was obtained: spherical solid grains surrounded by liquid phase. The microstructure across the heated billets was relatively homogeneous with bigger grain size near the surface. Successful thixoextrusion for producing parts was finally achieved at processing temperatures. By investigating the microstructure and load-displacement curves, different mechanisms in various forming stages were proposed. http://hdl.handle.net/10985/22901 Effects of Process Parameters on Microstructure and Mechanical Properties of Semi-Solid Al-7Si-0.5Mg Aluminum Alloy by Gas Induced Semi-Solid Process GUOCHAO, GU; LIXIN, Xiang; RUIFEN, Li; WENHUA, Xu; YUPENG, Lu; PESCI, Raphaël Al-7Si-0.5Mg aluminum alloy semi-solid slurry with good spherical grains was prepared by gas induced semi-solid process (GISS) and the effects of both holding time and medium alloy addition on the microstructure of the semi-solid slurry were investigated. These two parameters have a great influence on the solid fraction, the size and the sphericity of the grains. With holding time increased from 85 s to 270 s, the solid phase fraction of the semi-solid slurry decreased from ~0.77 to ~0.67, the average grain size increased from ~95 μm to ~225 μm and the average shape factor decreased from ~0.80 to ~0.33. When medium alloy addition varied in the range of 0.5–2.0 wt%, a better slurry microstructure was obtained at about 1.5 wt%. Compared with the conventional liquid die-casting, the semi-solid die-casting improved the mechanical properties of tensile bars; yield strength, tensile strength and elongation of tensile bars reached ~240 MPa, ~307 MPa and ~8.8% after heat treatment, respectively. In conclusion, GISS process can prepare the semi-solid slurry with uniform and round microstructure, and the semi-solid die-casting can improve mechanical proper ties of Al-7Si-0.5Mg aluminum alloy. Thu, 01 Sep 2022 00:00:00 GMT http://hdl.handle.net/10985/22901 2022-09-01T00:00:00Z GUOCHAO, GU LIXIN, Xiang RUIFEN, Li WENHUA, Xu YUPENG, Lu PESCI, Raphaël Al-7Si-0.5Mg aluminum alloy semi-solid slurry with good spherical grains was prepared by gas induced semi-solid process (GISS) and the effects of both holding time and medium alloy addition on the microstructure of the semi-solid slurry were investigated. These two parameters have a great influence on the solid fraction, the size and the sphericity of the grains. With holding time increased from 85 s to 270 s, the solid phase fraction of the semi-solid slurry decreased from ~0.77 to ~0.67, the average grain size increased from ~95 μm to ~225 μm and the average shape factor decreased from ~0.80 to ~0.33. When medium alloy addition varied in the range of 0.5–2.0 wt%, a better slurry microstructure was obtained at about 1.5 wt%. Compared with the conventional liquid die-casting, the semi-solid die-casting improved the mechanical properties of tensile bars; yield strength, tensile strength and elongation of tensile bars reached ~240 MPa, ~307 MPa and ~8.8% after heat treatment, respectively. In conclusion, GISS process can prepare the semi-solid slurry with uniform and round microstructure, and the semi-solid die-casting can improve mechanical proper ties of Al-7Si-0.5Mg aluminum alloy. http://hdl.handle.net/10985/8954 Microstructure Evolution and Material Flow of Steel in Semi-solid Forming Process GU, Guochao; BECKER, Eric; PESCI, Raphaël; LANGLOIS, Laurent The present study aims to identify and characterize the development of microstructure and deformation characteristics of steel grades in semi-solid state which is affected by the change in morphologies of microstructure at high temperature. Thixoextrusion tests with different combinations of forming temperature and forming speed were performed. It was identified that several process parameters, such as initial billet and die temperatures or forming speed, affect thermal exchanges thereby influencing the microstructure evolution and material flow. Furthermore, 2D and 3D microstructure characterization was performed on the same sample which was partial remelted and quenched. Reconstructed 3D images were compared with the ones obtained with a Scanning Electron Microscope and an Energy Dispersive Spectrometry system. The good agreement between 2D SEM observations and 3D X-ray microtomography results makes these two techniques efficient to characterize steels in the semi-solid state. Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/10985/8954 2011-01-01T00:00:00Z GU, Guochao BECKER, Eric PESCI, Raphaël LANGLOIS, Laurent The present study aims to identify and characterize the development of microstructure and deformation characteristics of steel grades in semi-solid state which is affected by the change in morphologies of microstructure at high temperature. Thixoextrusion tests with different combinations of forming temperature and forming speed were performed. It was identified that several process parameters, such as initial billet and die temperatures or forming speed, affect thermal exchanges thereby influencing the microstructure evolution and material flow. Furthermore, 2D and 3D microstructure characterization was performed on the same sample which was partial remelted and quenched. Reconstructed 3D images were compared with the ones obtained with a Scanning Electron Microscope and an Energy Dispersive Spectrometry system. The good agreement between 2D SEM observations and 3D X-ray microtomography results makes these two techniques efficient to characterize steels in the semi-solid state. http://hdl.handle.net/10985/11021 Deformation behavior and microstructure evolution of steel during the entire thixoforging process for improving the process controlling GU, Guochao; PESCI, Raphaël; BECKER, Eric; LANGLOIS, Laurent; BIGOT, Regis After analazing,the microstructure of the thixoforged parts, some mechanisms of material flow are proposed. Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/11021 2015-01-01T00:00:00Z GU, Guochao PESCI, Raphaël BECKER, Eric LANGLOIS, Laurent BIGOT, Regis After analazing,the microstructure of the thixoforged parts, some mechanisms of material flow are proposed. http://hdl.handle.net/10985/9128 In Situ Microstructure Observation Of Steel Grades In The Semi-Solid State For Thixoforging Process By Using Confoncal Laser Scanning Microscopy GU, Guochao; PESCI, Raphaël; BECKER, Eric; LANGLOIS, Laurent; BIGOT, Regis The microstructure plays a crucial role for steel semi-solid forming process, and particularly for the steel thixoforging process, since it determines the thixotropic flow behavior of materials in the semi-solid state. Therefore, it is necessary to well understand the microstructure evolution during high speed heating and forming. Classically, it is investigated on a solid material quenched from semi-solid state by 2D characterization techniques. However, the semi-solid microstructure could probably not be preserved in the solid state by quenching due to complicated phase transformations or high diffusion rate of alloying elements during cooling, especially at low liquid fractions. In order to avoid this, a new in situ technique - high temperature Confocal Laser Scanning Microscopy (CLSM) - was developed and used for studying the microstructure evolution directly at high temperature. The present study aims at providing an experimental investigation of the microstructure evolution on several steel grades (M2, 100Cr6 and C38LTT) during heating from the as-received state to the semi-solid state (heating rate: ~200°C/min) and finally cooled to the solid state (cooling rate: ~200°C/min). It has been found that the temperature sensitivity of liquid fraction (ΔT/ Δfl) of these grades is much different. In addition, during cooling, there is a significant difference in diffusion rate of alloying elements between these grades. In M2, thanks to the high content of alloying elements and their low diffusion rate, the semi-solid temperature range is greater and its microstructure in the semi-solid state could be preserved by quenching process or even at a low cooling rate. On the contrary, the microstructure of other steel grades 100Cr6 and C38LTT in semi-solid state can only be revealed by CLSM at high temperature, because of the lower volume fraction of alloying elements and their high diffusion rate. It is very interesting to use high temperature CLSM to in situ investigate the microstructure evolution in the semi-solid state, especially at low liquid fraction. Since the microstructure of M2 in the semi-solid state can be reserved after cooling, it is possible to identify liquid area by the post-mortem examination. Therefore, the material flow behavior of thixoforged parts could be investigated. Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/9128 2015-01-01T00:00:00Z GU, Guochao PESCI, Raphaël BECKER, Eric LANGLOIS, Laurent BIGOT, Regis The microstructure plays a crucial role for steel semi-solid forming process, and particularly for the steel thixoforging process, since it determines the thixotropic flow behavior of materials in the semi-solid state. Therefore, it is necessary to well understand the microstructure evolution during high speed heating and forming. Classically, it is investigated on a solid material quenched from semi-solid state by 2D characterization techniques. However, the semi-solid microstructure could probably not be preserved in the solid state by quenching due to complicated phase transformations or high diffusion rate of alloying elements during cooling, especially at low liquid fractions. In order to avoid this, a new in situ technique - high temperature Confocal Laser Scanning Microscopy (CLSM) - was developed and used for studying the microstructure evolution directly at high temperature. The present study aims at providing an experimental investigation of the microstructure evolution on several steel grades (M2, 100Cr6 and C38LTT) during heating from the as-received state to the semi-solid state (heating rate: ~200°C/min) and finally cooled to the solid state (cooling rate: ~200°C/min). It has been found that the temperature sensitivity of liquid fraction (ΔT/ Δfl) of these grades is much different. In addition, during cooling, there is a significant difference in diffusion rate of alloying elements between these grades. In M2, thanks to the high content of alloying elements and their low diffusion rate, the semi-solid temperature range is greater and its microstructure in the semi-solid state could be preserved by quenching process or even at a low cooling rate. On the contrary, the microstructure of other steel grades 100Cr6 and C38LTT in semi-solid state can only be revealed by CLSM at high temperature, because of the lower volume fraction of alloying elements and their high diffusion rate. It is very interesting to use high temperature CLSM to in situ investigate the microstructure evolution in the semi-solid state, especially at low liquid fraction. Since the microstructure of M2 in the semi-solid state can be reserved after cooling, it is possible to identify liquid area by the post-mortem examination. Therefore, the material flow behavior of thixoforged parts could be investigated. http://hdl.handle.net/10985/9057 Application of X-ray Microtomography to Quantify the Liquid Fraction of M2 Steel for Semi-solid Forming process GU, Guochao; BECKER, Eric; PESCI, Raphaël; LANGLOIS, Laurent Thixoforging, one variant of semi-solid metal processing in which the metallic alloys are processed at low liquid fraction (0.1< Fl < 0.3), is used to produce complex parts with high mechanical properties. Steel thixoforging faces more challenges as compared to that of low melting point materials due to high processing temperature and lack of understanding of the thermomechanical behavior of materials in the given conditions. It is crucial to study the microstructure in the semi-solid state to improve the understanding of the thixoforging process since the material behavior strongly depends on main parameters: the liquid fraction, its distribution as well as the coherence of the solid skeleton. The microstructure has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Here, the characterization of the volume fraction and distribution of liquid in the semi-solid state with high energy 3D X-ray microtomography is investigated on M2 steel grade as a ‘model’ alloy. The obtained results are compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They show a good correlation making both approaches very efficient for the study of the liquid zones in the semi-solid state. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/9057 2013-01-01T00:00:00Z GU, Guochao BECKER, Eric PESCI, Raphaël LANGLOIS, Laurent Thixoforging, one variant of semi-solid metal processing in which the metallic alloys are processed at low liquid fraction (0.1< Fl < 0.3), is used to produce complex parts with high mechanical properties. Steel thixoforging faces more challenges as compared to that of low melting point materials due to high processing temperature and lack of understanding of the thermomechanical behavior of materials in the given conditions. It is crucial to study the microstructure in the semi-solid state to improve the understanding of the thixoforging process since the material behavior strongly depends on main parameters: the liquid fraction, its distribution as well as the coherence of the solid skeleton. The microstructure has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Here, the characterization of the volume fraction and distribution of liquid in the semi-solid state with high energy 3D X-ray microtomography is investigated on M2 steel grade as a ‘model’ alloy. The obtained results are compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They show a good correlation making both approaches very efficient for the study of the liquid zones in the semi-solid state. http://hdl.handle.net/10985/8947 Effects Of Thermal Exchange On Material Flow During Steel Thixoextrusion Process BECKER, Eric; GU, Guochao; PESCI, Raphaël; LANGLOIS, Laurent Semi-solid processing is an innovative technology for near net-shape production of components, where the metallic alloys are processed in the semi-solid state. Taking advantage of the thixotropic behavior of alloys in the semi-solid state, significant progress has been made in semi-solid processing. However, the consequences of such behavior on the flow during thixoforming are still not completely understood. To explore and better understand the influence of the different parameters on material flow during thixoextrusion process, thixoextrusion experiments were performed using the low carbon steel C38. The billet was partially melted at high solid fraction. Effects of various process parameters including the initial billet temperature, the temperature of die, the punch speed during process and the presence of a Ceraspray layer at the interface of tool and billet were investigated through experiments and simulation. After analyzing the results thus obtained, it was identified that the aforementioned parameters mainly affect thermal exchanges between die and part. The Ceraspray layer not only plays a lubricant role, but also acts as a thermal barrier at the interface of tool and billet. Furthermore, the thermal effects can affect the material flow which is composed of various distinct zones. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10985/8947 2010-01-01T00:00:00Z BECKER, Eric GU, Guochao PESCI, Raphaël LANGLOIS, Laurent Semi-solid processing is an innovative technology for near net-shape production of components, where the metallic alloys are processed in the semi-solid state. Taking advantage of the thixotropic behavior of alloys in the semi-solid state, significant progress has been made in semi-solid processing. However, the consequences of such behavior on the flow during thixoforming are still not completely understood. To explore and better understand the influence of the different parameters on material flow during thixoextrusion process, thixoextrusion experiments were performed using the low carbon steel C38. The billet was partially melted at high solid fraction. Effects of various process parameters including the initial billet temperature, the temperature of die, the punch speed during process and the presence of a Ceraspray layer at the interface of tool and billet were investigated through experiments and simulation. After analyzing the results thus obtained, it was identified that the aforementioned parameters mainly affect thermal exchanges between die and part. The Ceraspray layer not only plays a lubricant role, but also acts as a thermal barrier at the interface of tool and billet. Furthermore, the thermal effects can affect the material flow which is composed of various distinct zones. http://hdl.handle.net/10985/8948 Effets des échanges thermiques sur l'écoulement de l'alliage semi-solide mis en forme par thixoextrusion BECKER, Eric; GU, Guochao; PESCI, Raphaël; LANGLOIS, Laurent Le comportement d’un alliage mis en forme à l’état semi-solide n’est toujours pas bien compris. Afin d’établir l'influence de différents paramètres sur l'écoulement de la matière, un processus de thixoextrusion expérimental a été réalisé sur un acier. Les effets de la température initiale du lopin et de l’outillage, de la vitesse de mise en forme et de la présence d'une couche de Ceraspray® à l'interface de l'outil et du lopin ont été étudiés par des expériences et confrontés à la simulation.; Semi-solid processing is an innovative technology for near net-shape production of components, where the metallic alloys are processed in the semi-solid state. Taking advantage of the thixotropic behavior of alloys in the semi-solid state, significant progress has been made in semi-solid processing. However, the consequences of such behavior on the flow during thixoforming are still not completely understood. To explore and better understand the influence of the different parameters on material flow during thixoextrusion process, thixoextrusion experiments were performed using the low carbon steel C38. The billet was partially melted at high solid fraction. Effects of various process parameters including the initial billet temperature, the temperature of die, the punch speed during process and the presence of a Ceraspray layer at the interface of tool and billet were investigated through experiments and simulation. After analyzing the results thus obtained, it was identified that the aforementioned parameters mainly affect thermal exchanges between die and part. Furthermore, the thermal effects can affect the material flow which is composed of various distinct zones. Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/10985/8948 2011-01-01T00:00:00Z BECKER, Eric GU, Guochao PESCI, Raphaël LANGLOIS, Laurent Le comportement d’un alliage mis en forme à l’état semi-solide n’est toujours pas bien compris. Afin d’établir l'influence de différents paramètres sur l'écoulement de la matière, un processus de thixoextrusion expérimental a été réalisé sur un acier. Les effets de la température initiale du lopin et de l’outillage, de la vitesse de mise en forme et de la présence d'une couche de Ceraspray® à l'interface de l'outil et du lopin ont été étudiés par des expériences et confrontés à la simulation. Semi-solid processing is an innovative technology for near net-shape production of components, where the metallic alloys are processed in the semi-solid state. Taking advantage of the thixotropic behavior of alloys in the semi-solid state, significant progress has been made in semi-solid processing. However, the consequences of such behavior on the flow during thixoforming are still not completely understood. To explore and better understand the influence of the different parameters on material flow during thixoextrusion process, thixoextrusion experiments were performed using the low carbon steel C38. The billet was partially melted at high solid fraction. Effects of various process parameters including the initial billet temperature, the temperature of die, the punch speed during process and the presence of a Ceraspray layer at the interface of tool and billet were investigated through experiments and simulation. After analyzing the results thus obtained, it was identified that the aforementioned parameters mainly affect thermal exchanges between die and part. Furthermore, the thermal effects can affect the material flow which is composed of various distinct zones.