Mechanical property and cutting performance of self-lubricating cermet tools with the addition of core-shell powders

Abstract

To study the influence of core-shell powders on the mechanical and cutting properties of self-lubricating cermet tools, two kinds of core-shell powders (h-BN@Al2O3 and c-BN@Al2O3) were prepared by the heterogeneous nucleation method, and they were used as the additive phase of (Ti,W)C cermet tools. Compared with the addition of c-BN@Al2O3, the addition of h-BN@Al2O3 produced a residual stress field around the matrix grain due to thermal mismatch, which improved the grain interface bonding strength and inhibited the crack propagation, having a better strengthening and toughening effect on (Ti,W)C cermet. The flexural strength and fracture toughness of the cermet with 5 vol% h-BN@Al2O3 were 1465 ± 30 MPa and 9.9 ± 0.3 MPa·m1/2, which were improved by 38 %/23 % and 3.6 %/4.2 % compared with that of the cermet without core-shell powders and with 5 vol% c-BN@Al2O3, respectively. The cutting performance of the cermet tool with 5 vol% h-BN@Al2O3 was also better than that of the cermet without core-shell powders and with 5 vol% c-BN@Al2O3. When machining 40Cr hardened steel, the h-BN in the core-shell particles was gradually exposed and formed a self-lubricating coating on the tool surface, which reduced the friction coefficient, cutting force, cutting temperature, surface roughness and chip deformation coefficient. Because the tool had both self-lubricating properties and excellent mechanical properties, the wear resistance was significantly improved and the tool life was extended to >8800 m. Within the effective cutting distance, the surface roughness of the workpiece was kept at 0.91–1.37 μm. The research results showed that the core-shell powders in the matrix grain can improve the mechanical properties because of the residual stress mechanism, and the cutting performance of the tools can be improved by its self-lubricating characteristics, so this self-lubricating cermet tool is an ideal dry-cutting tool.