Features of the Initial Stage of the Formation of Ti-Zr-Ni Quasicrystalline Thin Films

Abstract

Using the methods of X-ray diffraction, transmission and scanning microscopy, the features of the initial stage of the formation of the quasicrystalline phase in thin films of Ti-Zr-Ni are studied. The films were obtained by magnetron sputtering of a target of the composition Ti41Zr38.3Ni20.7 (at. %) with deposition on substrates at T  300 K and further vacuum annealing. It was established that immediately after deposition, the films are X-ray amorphous, nanostructured. An analysis of the radial distribution functions shows that immediately after deposition, the structural state of a disordered cluster, which is topologically close to icosahedral, prevails in the near atomic medium. It is concluded that the atoms are not arranged randomly, but form a "transitional" structure with an imperfect order like three shells of the Bergman cluster stacking using icosahedrons and dodecahedrons. Such a structure is a "prepared" nucleus for the further formation of the icosahedral phase upon heating. An analysis of the annealing results suggests that the qualitative nature of the transition from the pseudo-amorphous to the quasicrystalline phase and the scale of the transformations are determined by the annealing time and temperature, as well as by the film thickness. The smaller the thickness, the more the annealing processes are inhibited. It was shown that by annealing the films of a thickness of 6 μm or more at 500 C for more than 28 h, single-phase quasicrystalline coatings with a quasicrystallinity parameter aq of about 0.5245 nm can be obtained.

STRUCTURAL-PHASE TRANSFORMATIONS IN MAGNETRON DEPOSITED FILMS OF Ti-Zr-Ni SYSTEMS DURING ANNEALING IN VACUUM

“…It was found that the temperature range of coexistence of these phases with an annealing duration of 1 h extends to 700 C. for an hour at temperatures of 400 (1); 450 (2); 500 (3); 550 (4), and 600 C (5) Using long-term annealing, we found that annealing for 28 h at 470 C leads to the formation of a singlephase quasicrystalline state. An increase in the annealing time to 50 h promotes the appearance of reflection (653) from the approximant phase.…”

“…As shown in [5,6], in the initial state, immediately after deposition, the films are X-ray amorphous, with a disordered state that is topologically close to icosahedral in the nearest atomic environment. The system of diffraction maxima is formed when the annealing temperature reaches 400 C (Fig.…”

“…Since this is unacceptable for the same phase, this fact means that there is not a QC phase, but a new phase that has not been detected previously [10][11][12]. We identified this phase as a crystal approximant 2/1 [5]. Initially, such a phase with the structure type was observed in the Zn-Mg-Al system [13].…”

“…It is of interest to study the features of the formation of the AP phases, "relatives" of QCs, and the subsequent study of their properties. Earlier [5], we first noted the existence of the 2/1AP phase in the Ti-Zr-Ni system.…”

STABILITY OF THIN QUASI-CRYSTALLINE Ti-Zr-Ni FILMS AND RELATED CRYSTALLINE PHASES UNDER LOW-ENERGY TRANSIENT PLASMA IRRADIATION

“…Previously, we worked out a laboratory technique for the formation of coatings with an icosahedral quasicrystalline phase with a fairly perfect structure. The features of the formation of thin-film coatings with quasicrystalline and crystalline phases of the Ti-Zr-Ni system are described in detail in [9,10]. According to the first experiments on the modification of crystalline Ti-Zr-Ni phases, the formation of the quasicrystalline and crystal-approximant phases occurs as a result of high-speed quenching under pulsed action with a heat load of 0.6 MJ/m 2 .…”