Evolution of residual compressive stress regions in Co-diffused Bi-2212 engineering ceramics with annealing temperature

The role of diffusion annealing temperatures intervals 600–850 °C on durable tetragonal phase, surface morphology, and main mechanical performance parameters of Co surface-layered Bi 2.1 Sr 2.0 Ca 1.1 Cu 2.0 O y (Bi-2212) samples has extensively been examined by scanning electron microscopy (SEM), Electron Dispersive X-ray (EDX) technique and microindentation Vickers hardness ( H v ) tests. The experimental findings have shown that every material prepared has presented different composition distributions on the specimen surface as a consequence of the successful production of materials. Besides, the mechanical characteristics and durable tetragonal phase have been noted to enhance significantly with the enhancement of annealing temperature up to 650 °C due to the formation of new slip systems, surface residual compressive stress regions, connections between grains, and chemical bonding between the foreign and host atoms. Further, the optimum temperature has led to the reduction in stored internal strain energy and degree of granularity in the Co-diffused Bi-2212 crystal system. In this respect, the sample with the least sensitive to the external forces has exhibited the highest elastic modulus of 0.5445 GPa, shear modulus of 17.8515 GPa, yield strength of 181.5 MPa, and resilience of 369.1 MPa under 0.295 N. Accordingly, the cracks and dislocations have preferred to propagate throughout the transcrystalline regions, and crack growth size was easily controlled. Similarly, the saturation limit region has begun at relatively higher applied test load magnitudes. Conversely, the excess annealing temperature has caused the increase in the agglomeration of cobalt ions throughout the intergranular regions. Correspondingly, the activation of stress-induced phase transformation has been triggered seriously. Bi-2212 ceramic compound exposed to the optimum diffusion annealing temperature exhibits the most uniform surface view and crystalline quality with the densest surface morphology and the largest particle distributions and orientations. Moreover, every material studied has perfectly presented the characteristic indentation size effect behavior. The examination of granularity degree depending on elasticity moduli has verified all the H v test results and discussions. All in all, this study guides the use of engineering ceramics in more application areas due to the increase in their service life.