Ph.D. Tezi Görüntüleme | |||||||||||||||||||||
|
|
||||||||||||||||||||
| Summary: In order to make comparison, two different size of particles, ranged in 90-53µm (group B) and 49-16,5µm (group K) were used. For each group of composites, containing 3%, 4%, 6%, and 7% of B_4C particles in volume, were manucfactured by using vortex method and permanent mold casting techniques. Tensile, hardness and three body abrasive wear test were conducted for composites at room temperature. The microstructure, fracture surface and wear surface of the specimens were characterized using scanning electron microscopy. Particle recovery rate was deacresed and the porosity content was increased with the increasing particle ratios. Dispersion of the larger size particles was more uniform while finer particles showed particle-particle and particle-porosity clustering which was increased with increasing particle ratio. SEM, energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) studies showed that no interfacial reaction product was formed due to low casting temperature and the short time period that liquid alloy and B4C are interacted.When the particle volume fraction was increased, the macro hardness of both groups of composites was increased. But this increase was significant for finer particles. The yield, the tensile strength and the elongations of the composites were decreased while the Young modulus increased with increasing particle volume fraction. The lack of formation of ductile dimples, as the dominant fracture mode, is essentially attributed to the presence of discontinuous B4Cp reinforcement that avoids the plastic flow in the composite matrix. The fracture surface of composites containing smaller size of B_4C particles exhibits interfacial decohesion at the clustered regions due to intense local stress concentration at these large deffects. On the other hand, the fracture mode of composites, containing larger particles, includes ductile failure of the matrix and local brittle fracture of B_4C particles.The results of three body abrasive wear tests show that increasing volume fraction and particle size gave lower volume loss and specific wear rates. Keywords: Metal matrix composites, Boron carbide, Particle-reinforced composites,Vortex method, Abrasive wear
| |||||||||||||||||||||