Influence of Manganese Oxide on the Sintering Properties of Ceria-Stabilized Tetragonal Zirconia

Ceria stabilized zirconia with critical grain size is found to exhibit higher strength and higher resistance towards low temperature moisture degradation, The mechanical properties are greatly influenced by the size of the tetragonal grains. The effectiveness of doping with MnO2 (0.2 to wt %) in retarding degradation mechanical properties of ceria stabilized tetragonal zirconia (Ce-ZrO2) was evaluated by pressureless sintering within a temperature range from 1250°C-1550°C. Impact of manganese oxide to the mechanical properties and ageing resistance to the Ce-ZrO2 is truly beneficial. 0.4 wt% MnO2 at 1450°C revealed that, the tetragonal grain size was not affected by dopant level.With optimum dopant the 3 mol% ceria (3Ce-ZrO2) ceramic demonstarted the Vicker hardness of 11.8 GPa , fracture toughnessof 10.0 MPam1/2, flexural strength 920 MPa and Young modulus of 210 GPa. The 3Ce-ZrO2 doped with 0.4wt% MnO2 sintered 1450°C could be the best building block for biomedical applications.

Deformation Mechanisms of Toughening of Nanocrystalline Materials

We provide a brief review of our recent studiesconcerning the effects of various mechanisms of plasticdeformation of nanocrystalline materials on their fracturetoughness. We consider both conventional deformationmechanisms, such as lattice dislocation slip, and the deformationmechanism pronounced mostly in nanocrystalline solids, such asgrain boundary (GB) sliding and migration. We demonstrate thatwith a decrease in grain size, the effect of conventional latticedislocation slip on fracture toughness enhancement significantlydecreases. At the same time, for nanocrystalline solids withsmallest grain size fracture toughness can be increased due to GBsliding and migration. This implies that a transition from latticedislocation-mediated toughening to GB-deformation-producedtoughening can occur at a critical grain size in nanocrystallinesolids.

Molecular Dynamics as a Means to Investigate Grain Size and Strain Rate Effect on Plastic Deformation of 316 L Nanocrystalline Stainless-Steel

In the present study, molecular dynamics simulations were employed to investigate the effect of strain rate on the plastic deformation mechanism of nanocrystalline 316 L stainless-steel, wherein there was an average grain of 2.5–11.5 nm at room temperature. The results showed that the critical grain size was 7.7 nm. Below critical grain size, grain boundary activation was dominant (i.e., grain boundary sliding and grain rotation). Above critical grain size, dislocation activities were dominant. There was a slight effect that occurred during the plastic deformation mechanism transition from dislocation-based plasticity to grain boundaries, as a result of the stress rate on larger grain sizes. There was also a greater sensitive on the strain rate for smaller grain sizes than the larger grain sizes. We chose samples of 316 L nanocrystalline stainless-steel with mean grain sizes of 2.5, 4.1, and 9.9 nm. The values of strain rate sensitivity were 0.19, 0.22, and 0.14, respectively. These values indicated that small grain sizes in the plastic deformation mechanism, such as grain boundary sliding and grain boundary rotation, were sensitive to strain rates bigger than those of the larger grain sizes. We found that the stacking fault was formed by partial dislocation in all samples. These stacking faults were obstacles to partial dislocation emission in more sensitive stress rates. Additionally, the results showed that mechanical properties such as yield stress and flow stress increased by increasing the strain rate.

Atomistic Study of Deformation and Failure Behavior in Nanocrystalline Mg

ABSTRACTLarge scale molecular dynamics (MD) simulations are carried out to investigate the failure response of nanocrystalline Mg using the EAM potential under conditions of uniaxial tensile stress and uniaxial tensile strain loading. The MD simulations are carried out at a strain rate of 109s-1 for grain sizes in the range of 10 nm to 30 nm. The effect of grain size on the strength of the metal is investigated and the critical grain size for transition to inverse Hall-Petch regime is identified.