Effect of processing parameters on the microstructure and mechanical behavior of silica-calcium phosphate nanocomposite.

Silica-calcium phosphate nanocomposite (SCPC) is a bioactive ceramic characterized by superior bone regenerative capacity and resorbability when compared to traditional bioactive ceramics. The aim of the present study is to evaluate the effect of processing parameters on the microstructure and mechanical properties of SCPC. Cylinders were prepared by pressing the ceramic powder at 200, 300 or 400 MPa and sintering at 900, 1000 or 1100 degrees C for 3 h, respectively. XRD results indicate that the crystalline structure of the material is made of beta-NaCaPO(4) and alpha-cristobalite solid solutions. The increase in sintering temperature results in an increase in the grain size and the formation of a melting phase that coats the grains. TEM analyses reveal that the melting phase is amorphous and rich in silicon. The mechanical properties of SCPC cylinders are dependent on the content of the melting phase and the microstructure of the material. The ranges of compressive strength and modulus of elasticity of the SCPC are 62-204 MPa and 6-14 GPa, respectively, which are comparable to those of cortical bone. The results suggest that the interaction between crystalline and amorphous phases modulated the mechanical behavior of SCPC. It is possible to engineer the mechanical properties of SCPC by controlling the processing parameters to synthesize various fixation devices for orthopedic and cranio-maxillofacial applications.

Microstructure and Mechanical Properties of Ultrafine-Grained Copper by Accumulative Roll Bonding and Subsequent Annealing.

Recently, the accumulative roll bonding (ARB) technique has made significant progress in the production of various ultrafine-grained (UFG) metals and alloys. In this work, a UFG copper sheet was produced by ARB and subsequent annealing at 300 °C for 60 min to optimize strength and ductility. It was found that homogeneous lamellar UFG materials with a thickness of 200-300 nm were formed after six ARB passes. The microhardness and tensile strength of as-ARBed Cu increased, while the ductility and strain hardening decreased with the cumulative deformation strain. The as-ARBed specimens fractured in a macroscopically brittle and microscopically ductile way. After annealing, discontinuous recrystallization occurred in the neighboring interface with high strain energy, which was prior to that in the matrix. The recrystallization rate was enhanced by increasing the cumulative strain. UFG Cu ARBed for six passes after annealing manifested a completely recrystallized microstructure with grain sizes approximately ranging from 5 to 10 µm. Annealing treatment reduced the microhardness and tensile strength but improved the ductility and strain hardening of UFG Cu. As-annealed UFG-Cu fractured in a ductile mode with dominant dimples and shear zones. Our work advances the industrial-scale production of UFG Cu by exploring a simple and low-cost fabrication technique.