Promoting microstructural homogeneity during flash sintering of ceramics through thermal management

Flash sintering (FS) is a novel field-assisted sintering technology, where the ceramic is heated internally by the Joule effect. While FS promises a tremendous reduction of ceramic firing time and furnace temperature, it has been applied only at the laboratory scale to date. The key limitation of scaling up the technique to the industrial manufacturing level is the intrinsic difficulty managing the heat generation and obtaining homogenous microstructures in components of industrial interest. Heterogeneous regions primarily originate from the different types of thermal gradients that develop during FS; therefore, the management of heat generation is crucial to achieve uniformity. In this article, we discuss the advantages of controlling the microstructural homogeneity of ceramics during FS, and the technical routes to achieve this. The origin and formation mechanisms of thermal gradients upon flash sintering are outlined. Possible approaches to reduce thermal and microstructural gradients are identified. The opportunities and challenges in scale-up of FS are discussed from both industrial and scientific perspectives.

Powder Metallurgy Manufacturing of Iron Aluminides with Different Aluminium Contents and Magnesium Addition by Reactive Hot Pressing

In this work, iron aluminide materials, which are promising candidates for high temperature applications, are manufactured through reactive hot pressing of elemental powder mixes, facilitating a straightforward preparation of well-densified materials with a high degree of microstructural homogeneity. The impact of varying Al additions on reaction behavior, microstructural and compositional features of the resulting materials is evaluated. Furthermore, the effect of adding 1 wt. % Mg on reactivity and phase formation is illustrated. The results show that reactive hot pressing of elemental powders in the Fe-Al and Fe-Al-Mg systems at 1000 °C results in residual porosities well below 5 %. Magnesium addition significantly increased reactivity between constituents, leading to slightly improved densification without exhibiting potentially detrimental segregation phenomena. The processing approach presented in this work leads to material characteristics which are promising in the context of developing materials with favorable mechanical and tribological performance at elevated temperatures.