Influence of Cutting Surface Condition and Composition on High-Temperature Oxidation Behavior of Ti2 Al C MAX Phase Ceramics
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2024-11-22 |
| Journal | ECS Meeting Abstracts |
| Authors | Naoya Yamaguchi, Manabu OKADA, Yen-Ling Kuo, Makoto Nanko |
Abstract
Section titled āAbstractāTi 2 AlC, one of the MAX phase ceramics, has metal-like properties (electrical conductivity, high fracture toughness and good machinability) and ceramic-like properties (low density, high-temperature oxidation resistance and high bending strength). Ti 2 AlC ceramics can be cut with cemented carbide tools and the mechanical strength does not decrease significantly after cutting. Ti 2 AlC ceramics have potential as high-strength machinable ceramics for use in high temperature components. However, the oxidation resistance of Ti 2 AlC ceramics decreases after cutting because the cutting damages inhibit the formation of protective Al 2 O 3 scale. There are few discussions on the effect of cutting surface conditions on oxidation resistance of Ti 2 AlC ceramics. The continued growth of the protective Al 2 O 3 scale requires a sufficient Al supply during high-temperature oxidation. The oxidation resistance of Ti 2 AlC ceramics is reduced when a non-protective TiO 2 scale forms on the surface. As one of the common methods to prevent the growth of the TiO 2 scale is Nb addition in Ti-based alloys and compounds. The oxidation resistance of as-machined Ti 2 AlC ceramics may be improved by increasing the amount of Al and Nb additions. This study reports the influences of cutting surface conditions and composition on oxidation behavior of Ti 2 AlC ceramics. Commercial Ti, Al, C and Nb powders were mixed in Ti:Al:C:Nb molar ratios of 2:1.2:0.9:0 and 1.9:1.2:0.9:0.1 with the corresponding samples receiving the designations Al1 and Al1.2Nb. The powder mixture was annealed for 12 h in a vacuum at 1300Ā°C. The synthesized powder was consolidated over 15 min using a pulsed electric current sintering technique at 1300Ā°C, in a vacuum, and under a uniaxial pressure of 30 MPa. The phases present in the sintered samples were also identified by XRD. Milling tests were performed on a 4 x 4 mm sample surface using a 2 mm diameter end-mill mounted on a plane milling machine. Dry cutting was performed with a spindle speed, feed rate, and cut depth of 4000 rpm, 46 mm/min, and 100 Ī¼m. Threading tests were cut into an JIS-M6 bolt shape with a thickness of 3 mm with a lathe and diamond saw. The surface roughness of each sample was measured using a surface texture measuring instrument. The samples were heated in an electric furnace at 1200Ā°C for 4 h in laboratory air. The surface and cross-sections of the oxidized samples were observed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The main peaks of all sintered samples in these XRD patterns were identified as originating from Ti 2 AlC and minor peaks originating from TiAl 3 (Al-rich phase). The average arithmetic mean roughness ( R a ) values of the end-milled and threaded surfaces were 0.8 and 4.5 Ī¼m. The SEM and EDX results show that a continuous Al 2 O 3 scale formed on the end-milled surface of Al1.2 and Al1.2Nb after the oxidation test. The results of SEM and EDX investigations indicate that a non-protective TiO 2 scale had formed on the threaded surface of Al1 and a continuous Al 2 O 3 scale with a thickness of less than 4 Ī¼m was formed on the threaded surface of Al1.2Nb after the oxidation test. The Al-rich phase provided the Al necessary for the formation of a continuous Al 2 O 3 scale on the end-milled surface. The oxidation resistance of Ti 2 AlC ceramics was greatly reduced in the case of screw-like shapes with high R a values and many corners on the cutting surface. The addition of Nb improves the oxidation resistance of Ti 2 AlC ceramics under such cutting surface conditions. The cause of non-protective oxidation was the destruction of the Al 2 O 3 scale because of the growth of TiO 2 scale. The TiO 2 scale tends to form at corners where continuous Al 2 O 3 scale formation is difficult. One of the factors that improves the oxidation resistance of Ti 2 AlC ceramics with screw shapes is the suppression of TiO 2 growth by Nb addition. The higher Al concentration and the addition of Nb remarkably increase the oxidation resistance of the Ti 2 AlC ceramics after cutting.