Yejun Zhu

Comparative investigation on wear behavior and self-sharpening phenomenon of polycrystalline cubic boron nitride and monocrystalline cubic boron nitride grains in high-speed grinding

High-speed grinding experiments were conducted on a nickel-based superalloy Inconel718 with the monolayer brazed wheel containing monocrystalline cubic boron nitride grains and polycrystalline cubic boron nitride grains. Comparative investigation on the wear behavior and self-sharpening phenomenon of polycrystalline cubic boron nitride and monocrystalline cubic boron nitride grains was carried out based on the fractal analysis. The results obtained indicate that the wear process of the monocrystalline cubic boron nitride grain cutting edges is, in order, attritious wear → large fracture → micro fracture → large fracture → attritious wear, while that of the polycrystalline cubic boron nitride grain cutting edges is micro fracture → attritious wear → micro fracture. Micro fracture of polycrystalline cubic boron nitride grain occurs easily in the particular zone where large impact load is formed due to the first contact between the grain cutting edges and the workpiece material. The fractal dimension of monocrystalline cubic boron nitride wheel is 2.040–2.047, while that of the polycrystalline cubic boron nitride wheel is 2.049–2.054, which indicates that the polycrystalline cubic boron nitride grain cutting edges are finer than that of the monocrystalline cubic boron nitride counterparts. Compared to monocrystalline cubic boron nitride grains, better performance, that is, smaller radial wheel wear, lower grinding force and forces ratio, is obtained for polycrystalline cubic boron nitride grains due to micro fracture behavior and self-sharpening phenomenon in high-speed grinding.

Comparative Investigation on Brazing Behavior, Compressive Strength, and Wear Properties of Multicrystalline CBN Abrasive Grains

In order to fabricate the abrasive wheels with good grain self-sharpening capacity, two types of multicrystalline CBN grains, that is, polycrystalline CBN (PCBN) and binderless CBN (BCBN), were brazed using Cu-Sn-Ti alloy, respectively. Comparative investigation on the brazing interface, compressive strength, and wear properties of the different grains was carried out. Results obtained show that the PCBN grains have more intricate reaction, more complicated resultants, and thicker reaction layer than the BCBN counterparts under the identical brazing conditions. Though the average compressive strength of the PCBN grains is similar to that of BCBN ones, stronger self-sharpening action by virtue of the microfracture behavior takes place with BCBN grains during grinding. As a consequence, compared to the brazed PCBN wheels and the conventional monocrystalline CBN (MCBN) ones, longer service life is obtained for the brazed BCBN wheels.