Residual Stresses in Soft Magnetic FeTiB and FeZrN Films Obtained by Magnetron Deposition

Abstract

The coercive field of soft magnetic ferromagnets is a structure-sensitive property and, in particular, is substantially affected by residual stresses. In the present study, the phase and structural states and residual stresses of the FeTiB and FeZrN films of various compositions, which were prepared by magnetron deposition on glass substrates and subsequent 1-h annealing at temperatures of 200–600 °C, were investigated by X-ray diffraction. The formation of a nanocrystalline structure is observed. It comprises different phases having different lattice parameters and unit-cell volumes and is characterized by high level of microstrains of grains as well; the microstrains predetermine the formation of high compressive stresses in the deposited films. As the annealing temperature increases, the compressive stresses decrease and, at certain temperatures, gradually transform into thermal tensile stresses, which are induced by the difference in the thermal expansion coefficients of the film and substrate. Thus, the heat treatment is the efficient way to improve the soft magnetic properties of the studied class of film materials produced by magnetron deposition.

FeZrN Films: Magnetic and Mechanical Properties Relative to the Phase-Structural State

“…The high hardness of the as-deposited films is also determined by the high microstrain in the grains ( Table 1 ) and high compressive stresses formed in the films during magnetron deposition, as was shown earlier in our work [ 31 ]. According to [ 46 ], the values of hardness and compressive stresses formed in the films are related by the dependence H ~−3 σ .…”

“…In a similar sequence of the films I → II → IV → V → III, the grain size of the bcc phase decreases (Figure 6), which also makes the contribution to the observed increase in the hardness of these films (Figure 7), according to the Hall-Petch law H~D −1/2 [44,45]. The high hardness of the as-deposited films is also determined by the high microstrain in the grains (Table 1) and high compressive stresses formed in the films during magnetron deposition, as was shown earlier in our work [31]. According to [46], the values of hardness and compressive stresses formed in the films are related by the dependence H ~−3σ.…”

“…Thus, the hardness of the films II and V annealed at 600 °C decreases by 18% and 23%, respectively ( Figure 7 ). This is explained by (1) the change of compressive stresses to tensile stresses of lower values [ 31 ], (2) a decrease in the effect of solid solution hardening due to the depletion of the αFe-based solid solution of zirconium and nitrogen ( Figure 6 ), (3) as well as the formation of the columnar structure ( Figure 5 e,f) [ 47 , 48 , 49 ]. The annealing of the amorphous film VI at 500 °C leads to the increase in the hardness by ~26% ( Figure 7 , Table 2 ) due to the formation of a nanocrystalline structure in the films [ 46 ] and, in this regard, the actions of other, in comparison with the amorphous structure, strengthening mechanisms [ 50 ].…”

“…This can be caused by the columnar agglomeration of grains (the films II and IV) or by compressive residual stresses (the films I, II, and V) combined with positive magnetostriction of the ferromagnetic phase [ 56 ]. The magnetoelastic anisotropy field 3 λ s σ / M s ( M s = 1.3 T, λ s = 10 −5 is the saturation magnetostriction, and σ = 10 9 Pa is the residual stresses [ 31 ]) does not exceed 24 kA/m for the films, and the anisotropy field in all films, except for films I and VI, fits into this range. After annealing, for all films, except for films III and IV, the coercive field decreases and the anisotropy field weakens.…”

“…Since the early 2000s, the authors of the presented work have been carried out studies of the Fe-Me IVa -X system soft-magnetic films (Fe-Zr-C, Fe-Zr-N and Fe-Ti-B) [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ], wherein the large amount of systematic and comprehensive experimental data on Fe-Zr-N films were obtained [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. The studied film compositions were chosen using the physical-chemical approach to the alloy design in order to ensure the formation of a two-phase structure (αFe-based phase + MeX) under appropriate preparation conditions of the film [ 32 ].…”