In-situ creep law determination for modeling Spark Plasma Sintering of TiAl 48-2-2 powder

Abstract

International audienceSpark Plasma Sintering (SPS) is a process which allows powder densification, applying simultaneously a uniaxial external load and pulsed direct current of very high intensity through tools. This process is attracting significant attention, with a tremendous increase of studies in the metal powder densification field. Its growing popularity lies in the very fast heating rate and short cycle time driven by the Joule effect, which limits grain growth. However, this process implements different coupled electrical, thermal and mechanical phenomena. All this makes the process difficult to develop and to apply for routine industrial production, which has motivated the development of numerical simulation tools in order to understand and optimize the process. Up to now, very few models integrating the coupling between heat generation, electric transfer and mechanics have been proposed. In particular, a numerical predictive model for powder densification requires a good understanding of the mechanical behavior, in our case a viscoplastic compressive law (Abouaf mechanical model). In this article, we will discuss the characterization of the material during densification, focusing on the creep behaviors of dense and porous state materials used to simulate sintering in the Abouaf framework. Validations of the creep law parameters and also of the densification parameters will be presented and subsequently discussed

Spark plasma sintering of a commercial TiAl 48-2-2 powder: Densification and creep analysis

“…More characteristics of this powder are detailed elsewhere [11]. Seven different thermomechanical cycles were performed under vacuum.…”

“…After reaching maximum temperature, a dwell time of 5 min was applied [12]. For clarity, all temperatures given in the article are the set point programmed at the external surface of the mold; the protocol enabling the determination of the real sintering temperature of samples has been described elsewhere [11]. For this purpose, a specific sintering cycle was performed on a sample, with the temperature monitored by a thermocouple at the surface of the mold and a second one inserted inside the powder bed to measure the sample temperature.…”

“…In a previous study [11], creep parameters in compression were determined at 975°C according to a revised methodology initially proposed by Manière et al [20]. For all creep tests, samples were finely polished beforehand to eliminate the carbide layer, which might otherwise have altered the measurements.…”

A spark plasma sintering densification modeling approach: from polymer, metals to ceramics

“…[8]). The formulation of the regression equation using the Abouaf model is also useful because numerous experimentally determined moduli [8][9][10][26][27][28][29] ln _ e z j j…”

“…The porosity-dependent moduli are determined by hot isostatic pressing and sinter-forging tests on samples at different porosity rates [7]. A simpler approach based on die compaction and sinter-forging has been adapted to spark plasma sintering (SPS) for Ti-6Al-4V [8] and TiAl [9] and Ni [10]. These approaches facilitate the identification of all the sintering parameters, but they require extensive testing in order to reach the deconvolution of all the compulsory parameters.…”