Part II. Oxidation of yttrium doped Cr₂AlC films in temperature range between 700 and 1200°C

Abstract

The isothermal oxidation behaviour of Cr 2 AlC films deposited with 0?1-0?3 at.%Y addition on alumina substrates was investigated at temperatures between 700 and 1200uC for hold times of 1 to 30 h. It was found that the Y atoms impede the bulk diffusion of Al and Cr atoms and, thus, the initial transformation of the disordered solid solution (Cr, Al) 2 C x to the ordered Cr 2 AlC-MAX phase. It also reduces the oxidation rate of the ordered Cr 2 AlC-MAX phase and promotes the a-Al 2 O 3 phase formation relative to the other alumina on the surface and leads to better adhesion of the layers. 0?3 at.%Y was found to promote the formation of a-Al 2 O 3 relative to the other possible phases most strongly for 700-900uC. However, 0?2 at.%Y addition was found to cause the best oxidation resistance at 1200uC. The model introduced in part I was developed further.

Magnetic model of oxidation process of Y containing Cr–Al–C films

“…The characterisation of the layer structure, surface morphology and the microstructure both after production as well as after the oxidation process was carried out by XRD, scanning electron microscopy (SEM) and transmission electron microscopy. [1][2][3] The results of magnetic measurements of Cr-Al-C thin films synthesised by HIPIMS at low deposition temperatures and bulk Cr 2 AlC samples were described in Ref. 4.…”

“…2,3 It is easiest to observe what happens after the minimum in the magnetic signal is reached by using the higher temperature of 900uC. When the minimal in the magnetic signal is reached the samples have Cr 2 AlC.…”

“…The addition of Y has an influence on the oxidation mechanism as described in previous work. 3 In summary, this amount of Y essentially slows down the diffusion process of Al, which causes an associated reduction in the growth rate of the covering oxide, and a stabilisation of the a-Al 2 O 3 on the surface of the Cr 2 AlC grain during the oxidation process. In addition, the better adhesion of the MAX phase layer to the substrate and oxide layers is achieved, where for layers without Y delamination and cracking are common problems, and with Y, they are not observed.…”

“…Several authors have published work discussing the oxidation processes of MAX phases [5][6][7] and the authors themselves have published work related to the oxidation of Cr-Al-C films. 2,3 Some theoretical and experimental studies, with regard to the magnetic properties of Cr 2 AlC, do exist but are not extensive. [8][9][10][11][12] Moreover, its magnetic structure is still not sufficiently determined.…”

“…4 This publication, along with previous work, shows that the magnetic properties of the Cr-Al-C layers are strongly dependent on the structure of the phase (Cr,Al) 2 C x solid solution or ordered Cr 2 AlC nanolaminated structure). [1][2][3] Cr-Al-C was found to have paramagnetic properties, with both a contribution from a Curie-Weiss type behavior and one contribution related to Pauli paramagnetism. The former was shown to be dominant in the as deposited films, but not in the bulk.…”