Characterisation of semi-solid material mechanical behaviour by indentation test

Bigot, Régis; Favier, Véronique; Rouff, C.

doi:10.1016/j.jmatprotec.2004.03.016

Cited by 27 publications

(19 citation statements)

References 19 publications

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“…As shown by Quaak (1996), Koke and Modigell (2003), when a semi-solid is sheared with a high enough shear rate, solid bonds between solid particles break and may release some entrapped liquid. Bigot et al (2005) showed again these properties and studied the thermal impact of the process by indentation test. The consequences of such behaviour on the flow during thixoforming in "industrial" context, is still neither completely characterized and nor fully understood, especially for high melting point alloys despite the clear interest of such a forming process.…”

Section: Introductionmentioning

confidence: 94%

Impact of experimental conditions on material response during forming of steel in semi-solid state

Becker

Favier

Bigot

et al. 2010

Journal of Materials Processing Technology

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a b s t r a c tSemi-solid forming is an effective near-net-shape forming process to produce components with complex geometry and in fewer forming steps. It benefits from the complex thixotropic behaviour of semi-solids. However, the consequences of such behaviour on the flow during thixoforming, is still neither completely characterized and nor fully understood, especially for high melting point alloys. The study described in this paper investigates thixoextrusion for C38 low carbon steel material using dies at temperatures much lower than the slug temperature. Four different process parameters were studied: the initial slug temperature, the die temperature, the ram speed and the presence of a ceramic layer at the tool/material interface. The extruded parts were found to have an exact shape and a good surface state only if the temperature was below a certain value. This critical temperature is not an intrinsic material property since its value depends on die temperature and the presence of the Ceraspray©layer. Two kinds of flow were highlighted: a homogeneous flow controlled by the behaviour of the solid skeleton characterized by a positive strain rate sensitivity, and a non homogeneous flow (macro liquid/solid phase separation) dominated by the flow of the free liquid. With decreasing ram speed, heat losses increase so that the overall consistency of the material improves, leading to apparent negative strain rate sensitivity. Finally, some ways to optimise thixoforming are proposed.

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Section: Introductionmentioning

confidence: 94%

Impact of experimental conditions on material response during forming of steel in semi-solid state

Becker

Favier

Bigot

et al. 2010

Journal of Materials Processing Technology

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“…In the case of thixoforming, mechanical loadings are about ten to twenty times lower than in hot forging [9,10]. Fig.3 shows the Von Mises equivalent stresses, calculated by the Forge2011© software, at the end of forming inside the lower part of the tool.…”

Section: Resultsmentioning

confidence: 99%

Tooling Materials and Solutions for Thixoforming of Steel

Rassili

Falzone

Lecomte-Beckers

2012

SSP

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Abstract. The aim of this work is to evaluate the thermal and mechanical loadings applied to the tools during steel thixoforming process in order to determine appropriate tool materials and solutions. This evaluation was realized thanks to experimental trials and to the finite elements simulations. The effect of these loadings on the tool's failure modes are highlighted and compared to the ones observed in classical forming processes. Beyond this, the failure modes of different tool materials and solutions are presented. The tested materials are hot-working tool steels. Other possibilities and tool coating or surface treatments are discussed as well. IntroductionDue to high slug temperature (usually higher than 1350°C), tools surfaces reach very high temperature. In hot forging, this temperature could already reach 500°C [1-3]; in thixoforging, tool temperature increase could reach 700°C and even higher. Such a temperature is higher than classical tool steels annealing temperature and could lead to a fall of the mechanical properties. In order to minimize the thermal shocks, dies are usually pre-heated from 40 to 350°C in hot forging, but this does not prevent the temperature from increasing. Thixoforging process, as hot forging is composed of three sequential steps:• Brutal contact of high temperature slug on the tool. If needed, tool closing could be done before or after this step.• Forming step during which mechanical constraints are applied to the tool.• Part ejection and tool cooling. In production, these steps are repeated in a cycle. Tool damaging could be due to different mechanisms: fatigue cracking following thermomechanical loading cycle, microstructure evolution or scaling due to hot working, geometrical modification generated by wearing or plastic deformation. These machanisms are commonly known as: (1) abrasive wearing, (2) thermal fatigue, (3) mechanical fatigue, (4) plastic deformation [4]

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“…Therefore, it is necessary to have a thorough understanding of the microstructure evolution during semi-solid processing. In partially liquid metallic alloys, the volume fraction of solid phase and its distribution (solid skeleton) are of great importance in the thixoforging process, because they crucially influence the rheological behavior [2] and therefore the flow behavior of a material during its formation [3]. Normally, the microstructure of materials in the semi-solid state is always characterized by means of quenching experiments from the partial liquid state.…”

Section: Introductionmentioning

confidence: 99%

Microstructure observation and quantification of the liquid fraction of M2 steel grade in the semi-solid state, combining confocal laser scanning microscopy and X-ray microtomography

Pesci

Langlois

et al. 2014

Acta Materialia

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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 M 6 C) 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.

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Characterisation of semi-solid material mechanical behaviour by indentation test

Cited by 27 publications

References 19 publications

Impact of experimental conditions on material response during forming of steel in semi-solid state

Impact of experimental conditions on material response during forming of steel in semi-solid state

Tooling Materials and Solutions for Thixoforming of Steel

Microstructure observation and quantification of the liquid fraction of M2 steel grade in the semi-solid state, combining confocal laser scanning microscopy and X-ray microtomography

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