Studies of the Oxidation Stability, Mechanical Characteristics of Materials Based on MAX Phases of the Ti-AL-(C, N) Systems, and of the Possibility of Their Use as Tool Bonds and Materials for Polishing

摘要

Thermogravimetry and differential thermal analysis have been used to study the resistance to the air oxidation of high-density samples of Ti_3AlC_2, Ti_2AlC and Ti_2Al(C_(1-x)N_x) solid solutions. It has been shown that the Ti_3AlC_2 samples are more stable than Ti_2AlC and Ti_2Al(C_(1-x)N_x) solid solutions and as the nitrogen content of the solid solution increases to x = 0.75, the oxidation resistance decreases. The following characteristics have been exhibited by the material containing 89 wt % Ti_3AlC_2 (the rest being Al_2O_3 and TiC) having density 99% of theoretical: bending strength R_(bm) = 500 MPa, compressive strength R_(cm) = 700 MPa, fracture toughness K_(Ic) = 10.2 MPa·m~(0.5), hardness HRA = 70 GPa, H_V= 4.6 GPa, Young modulus = 149.4 ± 28.7 GPa. After sintering with diamonds or cBN (50wt %) at 5.5-7.7 GPa and 1350-1960℃ for 0.07-1.0 h the Ti_3AlC_2 MAX phase decomposes to form TiC and TiAl or TiB_2 and a thin layer of Al_4C_3 forms at the interface with diamond. The Al_4C_3 decomposition in a composite material due to the interaction with the air moisture results in the crack initiation along the diamond perimeter, which brings about the material fracture in 1-2 weeks. It has been found that the Ti_3AlC_2 powder is efficient for polishing natural and synthetic jewelry crystals and competitive in polishing efficiency and quality with ACM 2/1 grade diamond.