Microcrystallization Effects Induced by Laser Annealing in Cr-Al-C Ion-Beam-Sputtered Films

Abstract

The microcrystallization effects induced by the real-time laser annealing in Cr-Al-C ion-sputtered films with an off-stoichiometric composition are studied. The laser annealing has been performed during Raman experiments with tunable laser power densities. Morphostructural changes induced during laser annealing were investigated by scanning electron microscopy. It has been proven that real-time laser annealing in the high-laser-power-density mode promotes quite clearly the formation of nanograins through surface microcrystallization. Detailed Raman analysis allowed for the observation of the optical modes that unequivocally identifies the low-symmetry 211 MAX phase in both low- and high-power-density modes. Such findings confirming the microcrystallization as well as the stabilization of the grain boundaries by carbon nanoclustering are confirmed by X-ray diffraction results, where the single-phase hexagonal 211 was unequivocally proven to form in the high-laser-power-density mode. The microcrystallization via laser annealing was also found to be beneficial for the elastic behavior, as the hardness values between 16 and 26 GPa were found after laser annealing, accompanied by a significantly high Young's bulk modulus. Such large values, larger than those in bulk compounds, are explicable by the nanometric grain sizes accompanied by the increase of the grain boundary regions.

Keywords: laser annealing; microcrystallization; structural phase transformation; ternary compounds; thin films.

Figure 1

Schematics of the ion-assisted deposition process. Top-mounted ion source sputters the target while laterally mounted assisting ion source furnishes additional energy that help atoms to better bond on the substrate.

Figure 2

Area of the surface of Cr₅₆Al₂₁C₂₃ as-deposited thin film. Rastering effects due to the assisting ion source are revealed by SEM images.

Figure 3

Area of the surface of Cr₅₆Al₂₁C₂₃ after laser annealing in HLPD regime. Occurrence of small crystallites is observed. Approximate position of the laser spot is shown.

Figure 4

Raman spectra of the sample 1 recorded in three different laser-annealing regimes: LLPD at 2.5 mW/cm², LLPD at 4 mW/cm², and HLPD at 6 mW/cm².

Figure 5

XRD patterns of the films as-deposited (bottom) and films annealed at 700 °C (top).

Figure 6

Load-displacement curves recorded for laser-annealed LLPD samples at 4 mWcm² as well as for the sample laser annealed in the HLPD mode at 6 mW/cm².