Role of grain constraint on the martensitic transformation in ceria‐doped zirconia

Abstract

Zirconia polycrystals have historically suffered from catastrophic cracking during the tetragonal-monoclinic martensitic transformation. Recently, transformation-induced cracking has been avoided by doping to achieve crystallographic compatibility between the transforming phases. However, these materials showed depressed transformation temperatures and incomplete transformation, the causes for which are yet unknown. In this work, we probe these phenomena by performing a comparative study of sintered pellets and powders. We characterize the thermally induced transformation in a series of ZrO 2-CeO 2 compositions by in situ diffraction and calorimetry and develop a thermodynamic model of the system. In compositions exhibiting reduced cracking, we find that transformation temperatures are depressed in pellets but not in powders. Correspondingly, we measure significant compressive strains in pellets consistent with thermodynamically expected transformation temperature depression, demonstrating the influence of grain constraint and the resultant pressure build-up. However, we find that both pellets and powders exhibit incomplete transformation. In pellets, this is attributed to early exhaustion of autocatalysis caused by grain constraint, whereas in powders, this is attributed to insufficient driving force for distributed heterogeneous nucleation.

Delving into the Discrepancy of Phase Developments between Powder and Shaped Pellets of BaCO3

“…The main aim of this work was to analyze this peculiar phase development pattern of BaCO 3 in connection to the same being given a shape (via compaction and heat-treatment) or kept free as loose powders. A similar difference on other materials has been recently investigated by our group , and others. , Prof. Schuh’s group conducted research on different ZrO 2 –CeO 2 systems in the form of pellet and oligocrystalline powders. The findings indicated that the sintered zirconia ceramic had a strongly suppressed phase transformation temperature.…”

Limits of critical grain size for the tetragonal phase stabilization in CaO‐doped ZrO2 ceramic and associated benefits

“…This suggests that the shaped ceramic experienced a hindrance during sintering that eventually restricted the growth of grains. In our first report, we tried explaining this using a factor, labeled “consolidation factor.” Few months later, Prof. Schuh's research group at MIT, USA 10 observed similar effect (consolidation factor) for binary ZrO 2 –CeO 2 systems. The authors observed that the phase transformation temperature was strongly suppressed in sintered zirconia ceramics.…”

Phase transformation and incompatibility at grain boundaries in zirconia-based shape memory ceramics: a micromechanics-based simulation study

“…In the case of SMAs, previous work has investigated the tendency of Cu-based SMAs to fracture along grain boundaries due to strain incompatibilities there [16][17][18]. In SMCs, grain boundary strain incompatibility is less studied, although recent work has provided significant insights [9,[19][20][21]. Pang et al [19] investigated the two-dimensional compatibility of the martensiteaustenite interface via the application of the cofactor conditions as a possible factor controlling the cracking of bulk polycrystalline zirconia-based SMCs.…”

“…Their results suggested that samples with excellent interface compatibility could avoid cracking during thermal cycles and bulk compatibility is not necessarily the dominant cause of transformation-induced fracture. The same authors [20] analyzed the differences in thermally-induced transformation behaviors between ZrO 2 -CeO 2 oligocrystalline powders and sintered pellets. The role of grain boundaries in the damage evolution of yttria-doped zirconia subject to thermal cyclic loading was also discussed in [9,21].…”