Improving strength and toughness of vitrified bond by adding nano-rare earth oxides

To improve the strength and toughness of vitrified bond in CBN grinding wheel, composite bonds are prepared by adding different fractions of nano-sized CeO₂, Sm₂O₃, Y₂O₃, La₂O₃ or Er₂O₃ as additives. X-ray diffractor (XRD) and scanning electron microscope (SEM) are used to analyze their phases and micro structures, and three-point bending test and single-edge notched beam test to indicate their mechanical properties. Results show that the flexural strengths of samples with 2vol% Ce₂O or Er₂O₃ are 187 MPa and 194 MPa, respectively, which are 13.3% and 17.6% higher than 165 MPa of basic bond, while the other oxides could not improve the strength. On the other hand, all the five oxides could improve the fracture toughness and Er₂O₃ does the best by 2.7 MPa·m^1/2 at 2.5vol%, i.e. 108.2% higher than 1.3 MPa·m^1/2 of the basic bond. The composite bond with 2vol% nano-Er₂O₃ and CBN grains (concentration 200%) are used to prepare test samples, which possess good bonding between bond and grain and flexural strength of 102 MPa.