Crack healing in Y-doped Cr₂AlC-MAX phase coatings

Abstract

Self-healing materials facilitate a design concept which includes damage management, where damage that is inflicted during operation can be healed autonomously. It has been shown that the M n+1 AX n phases Ti 3 AlC 2 , Ti 2 AlC and Cr 2 AlC exhibit such behaviour. Cracks are filled and hence healed by oxidation products of the M and A elements in the MAX phase at the high operating temperatures in which they are used. After crack healing the fracture strength is recovered to the level of the virgin material. In this work, the Cr 2 AlC-MAX phase was shown to exhibit excellent self-healing properties. Cracks of maximum widths of approximately 500 nm and 4 μm could be healed after a 3-5 h anneal at 900 and 1200°C, respectively. In this system, the addition of Y on the rate of oxidation and on the self-healing behaviour was investigated.

From structural ceramics to 2D materials with multi-applications: A review on the development from MAX phases to MXenes

“…Berger and Boucher [103] reported that the addition of yttrium (Y) is one of the ways to promote the growth of Al 2 O 3 in Cr 2 AlC. Y-containing Cr 2 AlC coating exhibits an excellent self-healing ability to repair microcracks of 43 μm in length and 200 nm in width at 900 for ℃ 1 h in air [103]. To further improve the healing efficiency of MAX phases, controlling the crack-filling phases with chemical stability and mechanical match to the MAX phases and promoting growth of such filling phases is necessary to consider.…”

“…Therefore, promotion of the rapid growth of Al 2 O 3 should be considered in the crack healing of MAX materials. Berger and Boucher [103] reported that the addition of yttrium (Y) is one of the ways to promote the growth of Al 2 O 3 in Cr 2 AlC. Y-containing Cr 2 AlC coating exhibits an excellent self-healing ability to repair microcracks of 43 μm in length and 200 nm in width at 900 for ℃ 1 h in air [103].…”

“…The distinct crack healing ability [80,81,83,85,87,89,98,100,103] and other attractive high temperature properties including high strength [47,48], nonsusceptibility to thermal shock [88,90,91], good oxidation resistance [48,62,105], and good ablation resistance [95], make the MAX phases the materials of choice for applications in combustion gas turbines, heat elements, and liners for industrial furnaces, nozzles, hypersonic vehicles, refractories, and coatings. In addition, MAX particles are also good healing agents in ceramic and metal matrix composites to repair damages.…”

Sputtering and Characterization of MAX‐Phase Forming Cr–Al–C and Ti–Al–C Coatings and Their Application on γ‐Based Titanium Aluminides

“…The crack in the MAX-phase coatings fills with oxide of predominantly alumina to form a covering protection layer on the crack flanks. [13] The successful synthesis of these thin films by the utilization of several coating techniques, e.g., magnetron sputtering or plasma spraying and the application as protective layers for metallic high temperature alloys has been published in numerous previous work. [8,[14][15][16][17] The alumina forming MAX-phases are in particularly promising as protective coatings for γ-TiAl-based titanium aluminide alloys.…”

Mechanical characterisation of the protective Al2O3 scale in Cr2AlC MAX phases

“…Cr 2 AlC presents a density of 5.23 g/cm 3 , high Young's modulus (288 GPa), intermediate fracture toughness (5.2 MPa √ m), good flexural (354 MPa) and compression strengths (1160 MPa) [3,4,12]. Furthermore, bulk Cr 2 AlC materials are good electrical and thermal conductors, show excellent oxidation resistance at high temperature in air and exhibit self-healing mechanisms at high temperature [13][14][15]. However, their high-temperature mechanical properties are largely unknown, and the mechanism responsible for the oxidation resistance is not fully understood.…”