Guolong Zhao

Microstructure and Mechanical Properties of Al2O3-TaCw Ceramic Cutting Tool Materials

Three kinds of in-situ growth TaC whiskers toughening Al2O3 matrix ceramic cutting tool materials were prepared by two steps, which were in-situ synthesis of TaC whiskers in Al2O3 matrix powder by carbothermal reduction process and hot pressing of the composites respectively. The preparation process, microstructure, mechanical properties and toughening mechanisms of the composites were investigated. The in-situ synthesized TaC whiskers had a diameter of 0.1-0.5μm and an aspect ratio of 10-30. The composite containing 20vol.% TaC had the optimal comprehensive mechanical properties with flexural strength of 638MPa, fracture toughness of 6.5MPa·m1/2 and hardness of 17.4GPa. The improvement of the mechanical properties was attributed to the TaC particles and whiskers which induced the toughening and strengthening effects such as crack deflection, crack branching, grain and whisker fracture, interface debonding and whisker pullout. The fracture mode of the composites was the combination of intergranular and transgranular fracture which also improved the mechanical properties of the composites.

Synthesis of Al2O3 Ceramics Matrix Composites by Thermal Explosion under Pressure and Hot Pressing

Three kinds of Al2O3 ceramics matrix composites, such as Al2O3-TiB2, Al2O3-SiC and Al2O3-TiC, were prepared by two steps, which were synthesis of the composites by thermal explosion under a pressure of 20MPa and hot pressing of the composites at 1700°C under a pressure of 32MPa respectively. The preparation process, the composition and the microstructure of the composites were investigated in detail. The Gibbs free energy and the adiabatic temperature (Tad) of three exothermic synthesis reactions were calculated. Disc-shaped and elongated TiB2 grains were synthesized in the Al2O3-TiB2 composite. Some whiskers and platelet grains were synthesized in the Al2O3-SiC composite. Nano-particles were synthesized in the Al2O3-TiC composite and distributed both within the Al2O3 matrix grains and along the grain boundaries.

Study on Fracture Performance of In Situ Growth Whisker Toughened Composite Ceramic Tool

Three kinds of whisker toughened composite ceramic tools were prepared by carbothermal reduction process and their fracture performance was investigated in cutting the quenched 45 steel. The results suggest that the ratio of C to N has an effect on the fracture resistance of ceramic tool, and the whisker in tool material can inhibit the crack propagation and desquamation of grains. At the low cutting speed, the main fracture mode was conchoidal desquamation on the tool rake face and severe oxidation wear and some diffusion wear happened. At the medium cutting speed or high cutting speed, a combination of mechanical load and thermal load applied on the tool and adhesion was caused between workpiece material and tool material, and so the fracture mode was break-off of the cutting edge.

Study on Wear Performance of Whisker-Toughening Ceramic Cutting Tools Synthesized by the Carbothermal Reduction Process

The cutting performance and wear mechanisms of whisker-toughening ceramic cutting tools synthesized by carbothermal reduction process have been studied when cutting the hardened alloy steel 40Cr. It is indicated that the wear resistance of ceramic tools is affected by the molar ratio of C and N in tool materials. At low cutting speed, the main tool wear mechanisms are abrasive wear and oxidation wear. At middle and high cutting speed, the tool wear mechanisms are controlled by abrasive wear, adhesive wear, diffusion wear and oxidation wear simultaneously. Adding whiskers to the matrix material is one of the effective means to improve the wear resistance of ceramic cutting tools.