Grain Growth Behavior of Al₂O₃ Nanomaterials: A Review

Abstract

Emergence of engineering nanomaterials to render exceptional properties require understanding the thermodynamics and kinetics of grain growth and eliciting role of grain boundary mobility therein. Grain boundary mobility in alumina (Al2O3) has shown several repercussions on the evolution of microstructure to render drastic differences in the mechanical- (hardness, yield strength), optical- (transmittance), electrical- (conductivity), magnetic- (susceptibility), and electrochemical- (corrosion) properties. Consequently, the role of surface energy and the effect of temperature in equilibrating the grain shape and size are presented herewith. Several statistical or deterministic computational modeling have been attempted by researchers to elicit the dominating grain growth mechanisms. But, the limitations extend from the memory of computer and number of atoms in a simulation, or feeding the boundary conditions without incorporation of the initial microstructure to arrive at the dominating growth mechanism parameters. Contrastingly, the role of dopants in Al2O3 to either enhance or impede the grain growth is presented via various complexions responsible for transitions at the grain boundary interface. Six complexions resulting various grain boundary interface, strongly affect the grain boundary mobility, and sideline the dopant contributions in deciding the overall grain boundary mobility. It has also been presented that grain growth exponent increases with decreasing grain size, and additionally, secondary reinforcement of carbon nanotube (CNT) in Al2O3 impedes the grain mobility by as much as four times. The effect of temperature is found to be more pronounced, and has shown to enhance the grain boundary mobility by as much as six orders of magnitude.

Superhydrophobic Surfaces

“…This angle is subtended with no curvature on the surface, that is, with straight edges joining as a hexagon [19,20]. This is similar to the grain growth phenomena in which flat-faced, six-sided grains subtend internal angles of 120 ∘ [21]. Thus, for hydrophobic surfaces, an increased surface roughness can further enhance the CA.…”

Grain Boundary Complexions and Phase Transformations in Al- and Cu-Based Alloys

“…The presence of GBFs (or more general-GB complexions) strongly influences the grain growth as well as GB character distribution in oxides and metallic alloys [54,[56][57][58][59]63,75,76,79,80,83,106,[123][124][125][126][127][128][129][130][151][152][153][154][155][156][157][158][159][160]. It has been known for a long time that impurities can shift the borders between GBs with special and general structure and properties [142,143,220,221].…”

“…In any case, the mechanical properties of the GB phase strongly influence the overall strength of a material [76,[120][121][122]. Since GB layers influence the mobility of individual GBs, they also change the migrational ability of the GB ensemble in a polycrystal and, thus, the grain growth [54,[56][57][58][59]63,75,76,79,80,83,106,[123][124][125][126][127][128][129][130]. Most pronounced here is the transition from normal to abnormal grain growth (i.e., from single modal to the bi-or multimodal distribution of grain size).…”

“…DSC also permits to observe the indications of GB phase transformations in nanocrystalline ceramics [151][152][153][154][155][156][157][158][159][160]. The GB phase transformations can also lead to abnormal grain growth and radical changes in the GB character distribution [54,[56][57][58][59]63,75,76,79,80,83,106,[123][124][125][126][127][128][129][130]151,[154][155][156][157][158][159].…”

Thermal stability of consolidated metallic nanomaterials

“…More examples of observations of nanograin growth in nanostructured oxides of aluminium, zirconium, titanium, tin and other metals can be found in earlier reviews. 51,52 The role of triple junctions in inhibition of grain growth in Y 2 O 3 was analyzed in detail by Chokshi. 53 …”