Effectiveness Of Boron Nitride Coating In Boron Composites PDF Download

"In recent years, the superabrasive cubic boron nitride (cBN) grinding wheels have been widely used in the automotive and aerospace industries. Many studies have been performed to increase the efficiency of the grinding tools. These studies include investigating the bonding force between the cBN grits and the bond coat. Although the cBN grits have an outstanding performance in the grinding applications, their performance inside different bond coats may vary. Therefore, in this thesis, the Ni-based cBN composite coatings, including NiP-cBN, NiP/Ni10wt%W-cBN and NiP/Ni20wt%W-cBN were studied. The grit adhesion study on NiP-cBN, NiP/Ni10wt%W-cBN and NiP/Ni20wt%W-cBN coatings has been conducted. A new testing technique has been proposed by scratching the single grit embedded inside coating away using a flat-bottom stylus. Different grit behaviors were observed. The grits were either dislodged, partially dislodged, fractured or fully bonded inside the bond coat. Grits that were completely dislodged were used for the adhesion study. The tangential force and energy for all the dislodged grits were reported. It was found out that the bond force between the grit and the bond coat is majorly influenced by the bond depth of the grit. Although there was no significant difference in the tangential force and energy among different types of coatings, evidence of plastic deformation was observed on the NiP/Ni20wt%W coatings. Mechanical properties, including hardness, reduced modulus and the time-dependent strain rate sensitivity (SRS) on NiP, Ni10wt%W and Ni20wt%W coatings were studied. The grain sizes of all the coating were also reported. The hardness and reduced modulus of Ni-W coatings were higher than those of the Ni-P coating. Between the two Ni-W coatings, sample with higher W content has higher hardness and lower reduced modulus values. Two different nanoindentation techniques, constant load (CL) method and constant strain rate (CSR) method, were performed to evaluate the strain rate sensitivity of the coatings. The CSR SRS results on all the coatings were higher than the CL SRS results. The Ni-P coating has a higher SRS value compared with the Ni-W coating. The two Ni-W coatings with different W contents have similar SRS results. Tungsten segregation near the grain boundaries is assumed to lead to the lower SRS value. The small grain size of the Ni-P sample is the major reason for its high SRS value"--