Study On Fabrication And Cutting Performance Of Nano-Scale Zirconia Toughening Alumina Matrix Ceramic Tool Materials

Transformation toughening mechanism of zirconia and nano-scale grain toughening mechanisms were used to improve the fracture toughness of alumina matrix ceramic tool materials by adding nano-scale zirconia into micron-scale alumina matrix .Two kinds of nano-scale zirconia toughening alumina matrix ceramic tool materials were fabricated successfully. The relationship among the hot pressing technology, mechanical properties and microstructure, factors affectinig the stability of tetragonal zirconia and the cutting performance were deeply investigated .Nano-scale zirconia toughening alumina matrix ceramic tool materials A15Zc and A20Z(c+m) were fabricated successfully. The optimum fabrication technology is a fabrication temperature of 1550℃, a duration time of 30min and a fabrication pressure of 30 MPa. And their flexural strength, fracture toughness and Vickers hardness are 812.83MPa, 5.5MPam^1/2, 16.68GPa and 869.48MPa, 5.85MPam^1/2, 16.09GPa respectively. The main toughening mechanisms are transformation toughening , crack deflection, crack bend and grain bridging.The effect of nano-scale TiC, micron-scale TiC and micron-scale TiN on microstructure and mechanical properties of nano-scale zirconia toughening alumina matrix ceramic tool materials were investigated systematically. Ceramic tool materials A5Tn20Z (Al₂O₃-3Y-ZrO₂-TiCn) fabricated by adding nano-scale TiC into Al₂O₃-3Y-ZrO₂ composite materials have optimal mechanical properties when its fabrication technology is a fabrication temperature of 1650℃, a duration time of 30min and a fabrication pressure of 30MPa, and its flexural strength, fracture toughness and Vickers hardness are 904.7MPa, 4.16MPa·m^1/2, 17.43GPa respectively. The fracture toughness of A5T_m20Z (Al₂O₃-3Y-ZrO₂-TiCm) fabricated by adding micron-scale TiC into Al₂O₃-3Y-ZrO₂ composite materials decreased. Ceramic tool material A5N_p20Z (Al₂O₃-3Y-ZrO₂-TiNm) fabricated by adding micron-scale TiN into Al₂O₃-3Y-ZrO₂ composite materials have optimal mechanical properties when its fabrication technology is a fabrication temperature of 1600℃, a duration time of 30min and a fabrication pressure of 30MPa, and its flexural strength, fracture toughness and Vickers hardness are 845.14MPa, 4.87MPa-m^1/2 and 16.40GPa respectively.Compared to the commercial ceramic tool SG4, the cutting performance of nano-scale ZrO₂ toughening Al₂O₃ matrix ceramics tool materials, such as A15Zc and A20Z(c+m), in machining the hardened 40Cr alloy steel, the hardened 45 # steel, the hardened T10A steel and cast iron HT200 were researched respectively .When the hardened 40Cr alloy steel was machined, the tool flank wear width of A15Zc and A20Z(c+m) was increased with an increase in the depth of cut and the effect of cutting speed on cutting performance was small. A15Zc and A20Z(c+m) have stronger wear resistance than SG4 at the smaller depth of cut. The main wear patterns were tool wear on the rake face and flank, and the main wear mechanisms were bonding wear on tool rake face and abrasive wear on tool flank. When the hardened 45 # steel was manchined at the low speed of 99.5m/min, the wear resistance of A15Zc and A20Z(c+m) is the same as that of SG4, while the wear resistance of A15Zc and A20Z(c+m) is better than that of SG4 at the high speed of 268.5m/min. The main wear patterns were tool wear on rake face and flank, and the main wear mechanisms were bonding wear on tool rake face and abrasive wear on tool flank. When the hardened T10A steel was machined, SG4 can not machine normally, the wear resistance of A15Zc is better than that of A20Z(c+m) at the low speed of 93.4m/min. And the main wear patterns were tool wear on tool rake face and flank, and the main wear mechanisms were bonding and abrasive wear. However, the wear resistance of A15Zc at the high cutting speed of 262.8m/min is poorer than that at the low cutting speed of 93.4m/min. And A20Z(c+m) can not continue machining at the high cutting speed of 262.8m/min after the cutting distance of 1200m. And the main wear patterns of A15Zc ceramic tool are tool wear on rake face and flank wear as well as slight notch wear, and the main wear mechanisms are bonding and abrasive wear on tool rake face, and abrasive wear on tool flank. When machining cast iron HT200, the wear resistance of A15Zc is better than that of A20Z(c+m), and tool flank wear width of A15Zc and A20Z(c+m) at the low speed of 115m/min is bigger than that at the high cutting speed of 320m/min. The wear patterns at the low cutting speed are tool wear on rake face and flank as well as notch wear, and the wear mechanisms arre bonding and abrasive wear. The wear patterns at the high cutting speed are tool wear on flank and notch wear, and the wear mechanisms are fatigue and abrasive wear.