Self-Sharpening Failure Characteristic of a Si3N4 Ceramic Tool in High Speed Cutting of Inconel 718

A Si3N4 ceramic tool material with high mechanical properties was fabricated by hot-pressing sintering process. The high speed machining of Inconel 718 tests were carried out with round ceramic inserts. The failure surface and microstructure were analyzed by scanning electron microscopy (SEM) to reveal the ceramic tool failure mechanisms. The results showed that the main failure mechanisms of the Si3N4 ceramic tool were flaking, micro-chipping, abrasive wear and adhesive wear in the turning process. On the other hand, chipping, flaking and adhesive wear were the main failure reasons in the milling process. Meanwhile, some small flaking along the cutting edge and step-shaped flaking on the rake face closed to the cutting edge were found on the failure surfaces, which was a typical self-sharpening failure characteristic of the ceramic tool in the high-speed cutting process. This tool failure evolution characteristic of the ceramic tool can be attributed to its higher flexural strength and fracture toughness, which was beneficial to improve the tool life and was constrained by cutting conditions.

Experimental Study on the Effect of Water on Shear Strength Characteristic of Shale

In order to understand the shear strength characteristic of water-sensitive shale under the effect of water in the northwest of Hubei province, we carried out direct shear tests of shale in natural and water-saturated states along its bedding plane with original shale samples taken from the Guzhu expressway and analyzed the shear stress-displacement relationship under different normal stresses and explored the influence of water on shale shear deformation and strength characteristic. This study shows that the shear stress-displacement curve of shale in natural state and water-saturated state presents significant similarities and differences; compared with natural shale, water-saturated shale witnesses an obvious drop in its cohesive force, internal friction angle and residual angle of internal friction; shale in natural state presents apparent brittle failure characteristic while water-saturated shale to some extent exhibits ductile failure characteristic.