Study On SiC Whiskers And Nanoparticles Synergistically Toughening Al₂O₃-bascd Ceramic Cutting Tool And Its Cutting Performance

Alumina is usually used as the matrix of ceramic cutting tools because of its unique properties such as good wear resistance, high melting point, great corrosive resistance and low cost. Many efforts have been made to improve its strength and toughness in order to overcome its brittleness and broaden its application. In the present work, one-dimensional material SiC whiskers and zero-dimensional material SiC nano particles were added into Al2O3 matrix and Al2O3-SiCw-SiCnp advanced ceramic cutting tools with good mechanical properties at room temperature were fabricated. The high temperature mechanical properties of AW20P5 and the evaluation mechanisms were investigated. The cutting performance of AW20P5 when, turning austic stainless steel 1Cr18Ni9Ti was studied.The effect of the p-SiC whiskers ((β-SiCw) and β-SiC nano particles (β-SiCnp) with different properties on the mechanical properties of the ceramic cutting tools was studied. The results showed that the β-SiCw-Ⅱ and β-SiCnp-Ⅱ with fine microstructure had the optimum toughening and strengthening effect. A process for the dispersion of the whiskers and nano particles was proposed. The whiskers and nano particles were distributed in the matrix uniformly without agglomeration.The effect of the contents of whiskers and nano particles as well as the sintering parameters on the mechanical properties of the Al2O3-SiCw-SiCnp ceramic cutting tools was studied. The toughening and strengthening mechanisms of the whiskers and nano particles as well as their synergistic effects were investigated. The results showed that the composite with 20vo1% SiCw+5vol% SiCnp sintered at 1700℃ for 30min had the optimum comprehensive mechanical properties with flexural strength of 730 MPa, fracture toughness of 5.6 MPa-m1/2 and Vicker’s hardness of 18.0 GPa. The toughening and strengthening mechanisms of the SiC whiskers were whisker bridging, whisker pullout and crack deflection. The toughening and strengthening mechanisms of the SiC nano particles were fine grain size, mixed fracture mode, crack deflection and microcracks. The synergistic toughening and strengthening effects between SiC whiskers and SiC nano particles improved the mechanical properties of the cutting tools.The high temperature mechanical properties of the advanced AW20P5 ceramic cutting tools were studied. The results showed that the flexural strength increased and subsequently decreased with the increasing of the testing temperature. The maximum flexural strength was 673 MPa at the testing temperature of 850℃. With the increasing of the testing temperature, the fracture toughness of the ceramic cutting tools decreased and subsequently increased at 1200℃ and obvious plasticity was observed. The degradation of the mechanical properties at elevated temperatures was ascribed to the oxidation of SiC and the decrease of the modulus. The improvement of the mechanical properties at elevated temperatures was ascribed to the healing of the microcracks and defects as well as the decrease of the interfacial stresngth.The cutting performance of the advanced AW20P5 ceramic cutting tools when continuously wet-turning ausentic stainless steel 1Cr18Ni9Ti was studied. A comparation on the cutting performance between AW20P5 and commercial SG4 was conducted. The optimum cutting parameters with cutting speed of 140 m/min, depth of 0.3 mm and feed of 0.2 mm/r were obtained using the orthogonal experiment method. The cutting performance and wear mechanisms of AW20P5, AW5P20 and SG4 when continuously wet-turning ausentic stainless steel 1Crl8Ni9Ti were investigated. The results showed that AW20P5 had good cutting performance and the wear mechanisms were abrasive wear and adhesive wear. The cutting performance of AW5P20 was better than that of SG4. The wear mechanisms of AW5P20 were abrasive wear and adhesive wear while the wear mechanism of SG4 was adhesive wear.