Plasticity and fracture of sapphire at room temperature: Load-controlled microcompression of four different orientations

Size and plasticity effects in zirconia micropillars compression

“…Once plasticity was activated, the size effect was similar to BCC metals for MgO soft slip systems, while hard slip systems showed a behavior rather similar to GaAs [25] and Si micropillars [26]. Deformation by dislocation glide during micropillar compression could also be activated at room temperature in high strength ceramic monocrystals like sapphire [27], silicon carbide [28] and silicon nitride [29]. With respect to zirconia, Lai and co-workers [30] have recently shown that single-crystal or oligocrystalline micropillars of zirconia highly doped with Ce and Y can display shape memory and superelastic effects in association with phase transformation under compression, while the presence of other plastic phenomena has not been discussed.…”

“…The activation of dislocation movement at room temperature does not normally occur in bulk ceramic specimens without confinement. This is no longer valid at the small scale, where, for example, monocrystals of alumina, chromia, silicon carbide and silicon nitride [27][28][29]48] have been deformed plastically under compression by slip. The participation of dislocation glide is likely to happen here since the stress level reached without fracture is comparable to that in confined deformation by grinding, where dislocation activity is dominant [49].…”

Sample size induced brittle-to-ductile transition of single-crystal aluminum nitride

“…Fig. 8a shows the comparison of the maximum plastic strain and ultimate strength of AlN with other highstrength single crystals and amorphous alloys tested by micro-compression with pillar diameters ranging from $500 nm to 5 lm [22,25,[27][28][29][40][41][42][43][44]. The general trend from these data, regardless of deformation mechanisms, is that the higher strength of materials typically accompany with lower plasticity.…”

“…However, for strong and relatively brittle ceramics, the size dependence of their strength and ductility has not been well explored [4,[22][23][24]. Recently, the size induced plasticity has been observed in covalent and ionic crystals, such as sapphire [25], GaAs [26], SiC [27] and MgO [28], during room-temperature microcompression. These studies indicate that decreasing sample sizes to the order of micrometer scale can suppress cracking and leads to the change in the deformation behavior from brittle to ductile [29,30].…”

Micropillar compression inside zirconia degraded layer

“…In effect, a ductile behavior could be observed by reducing the sample size below some critical value that lies roughly between tens and hundreds of nanometers. Several materials conventionally known as "brittle" have shown plasticity features at the small scale: Si [16], GaAs [17], MgO [18] Al 2 O 3 [19] and SiC [20]. At the same time, superelastic and shape-memory effects were recently observed by Lai et al [21] during compression of tetragonal zirconia micropillars highly doped with Y and Ce.…”