Demystifying the role of sintering additives with “complexion”

Microstructure and mechanical properties of WC–40vol%Al2O3 composites hot pressed with MgO and CeO2 additives

“…Harmar [26] has well explained the interfacial kinetic engineering and the Dillon-Harmer [27] complexion types I-VI. A clean boundary was classed as complexion II; one with sub-monolayer dopant absorption but low mobility as I; and classes III-VI related to boundaries with increasing thickness, segregation and mobility.…”

Wetting of grain boundaries in Al by the solid Al3Mg2 phase

“…Thin films of interfacial phases were observed in GBs in metals (works of Luo and coworkers [16,36,37]), in oxides ( [17], see also concept of complexions by Harmer et al [18][19][20][21][22]), in interphase boundaries (Kaplan and coworkers [23][24][25]). According to those developments the GB wetting tie-lines continue as prewetting (or GB solidus or solvus) lines in the one-phase (Al) area.…”

Segregation of anion (Cl−) impurities at transparent polycrystalline α-alumina interfaces

“…Therefore, the characteristic concentration corresponds to the first order GB complexion transition of the interface from complexion I (single layer adsorption) to complexion III (bilayer adsorption) as described in Ref. 21 Fig . 6 shows the evolution of the atomistic structure of a (11.1) GB with increasing dopant concentration.…”

“…As the concentration increases further, multilayers and an intergranular film of anion impurity atoms are formed at the GB. According to the theory of complexion proposed by Harmer and coworkers, 21 Higher order complexions increase the GB mobility and mass transport. 21 Possibly anion impurities can cause the higher order complexions at lower concentrations than cation dopants due to their larger size.…”

“…According to the theory of complexion proposed by Harmer and coworkers, 21 Higher order complexions increase the GB mobility and mass transport. 21 Possibly anion impurities can cause the higher order complexions at lower concentrations than cation dopants due to their larger size. Combining this factor with the earlier discussed significantly higher segregation energies for anion segregation than cation dopants, may lead to the inference that anion segregation can increase the GB mobility and transport and hence, cause the enhanced grain growth at high temperatures nullifying the effect of cation dopants, as was observed by Dittmann et al 13 during the sintering of Cl containing TiO 2 nano powders.…”