“…From this observation, it can be concluded from the onset strain of fragmentation that the fracture strength of a β-Ta layer is lower than a α-Ta layer with an equivalent film thickness. This observation is in accordance with findings in literature [22]. The reason behind this phenomenon is the difference in the respective crystallographic unit cells of α-and β-Ta; α-Ta, which is present in the ductile bcc unit cell deforms plastically prior to crack formation, while the tetragonal β-Ta is brittle and has therefore only a limited capacity for plastic deformation.…”
“…From this observation, it can be concluded from the onset strain of fragmentation that the fracture strength of a β-Ta layer is lower than a α-Ta layer with an equivalent film thickness. This observation is in accordance with findings in literature [22]. The reason behind this phenomenon is the difference in the respective crystallographic unit cells of α-and β-Ta; α-Ta, which is present in the ductile bcc unit cell deforms plastically prior to crack formation, while the tetragonal β-Ta is brittle and has therefore only a limited capacity for plastic deformation.…”
“…Kapton® material is known to deform plastically from 4–5% of macoscopic strain. Actually, the plastic deformation of the substrate should be localized between the film fragments induced by cracks 34 that may enhance the buckling phenomenon. Figure 1 AFM images highlighting the multi-cracking and subsequent buckling of a CoFeB 20 nm-film obtained at different strain states.…”
Section: Resultsmentioning
confidence: 99%
“…7 of ref. 34 for Ta- α films for which the stresses are in situ measured by x-ray diffraction. We believe that this difference between σ xx and σ yy is sufficiently important for reminiscence in the residual state after discharge.…”
This article presents a study whose purpose is to elucidate the damage effects in thin films on their magnetic response. Co40Fe40B20 and Ni80Fe20 films of different nanometric thicknesses were stretched by more than 10% and in situ probed by atomic force microscopy measurements to determine their irreversible mechanical behavior (multi-cracking, buckling). Once these phenomena have been well identified, magnetic behavior of these stretched systems has been studied by ferromagnetic resonance to measure resulting magnetic anisotropy and damping evolutions. All of these experimental studies show that the magnetic properties are mainly affected by the stresses generated during the damage but not by the local discontinuities induced by the numerous cracks and buckles. This is in particular confirmed by the almost zero sensitivity to the damage of the magnetic properties of Ni80Fe20 alloy which is known for its vanishing magnetostriction.
“…Additionally, the most intense reflection, (002), shows significantly higher intensity than that of the corresponding standard powder diffraction pattern that indicates that the coating grows predominantly with a (002) orientation. The presence of the (002) texture is frequently observed on β-Ta coatings prepared by the other sputter deposition techniques [21,22]. The average grain size of the coating was estimated to be ~18 nm by applying the Scherrer formula for peak broadening of the low angle (002) reflection, after the correction of instrumental line broadening [23].…”
Section: In Vitro Bioactivity Evaluationmentioning
confidence: 99%
“…As is well known, the grain size dependence of hardness for polycrystalline metals can be described by the classical Hall-Petch relationship. The hardness value changes from 15 GPa for the β-Ta film with a grain size of 32.3 nm [25] to [16][17][18][19][20][21][22][23] GPa for the β-Ta films with grain sizes in range of 5−15 nm [26]. According to the Archard's theory [27], the wear resistance is proportional to the hardness of Figure 4a shows the representative load-displacement (P-h) curves of the β-Ta coating and uncoated Ti-6Al-4V measured using a nanoindentation tester equipped with a Berkovich indentor under a maximum load of 20 mN.…”
Section: Crystalline Structure and Microstructure Of Ta Coatingmentioning
A β-Ta nanocrystalline coating was engineered onto a Ti-6Al-4V substrate using a double cathode glow discharge technique to improve the corrosion resistance and bioactivity of this biomedical alloy. The new coating has a thickness of~40 µm and exhibits a compact and homogeneous structure composed of equiaxed β-Ta grains with an average grain size of~22 nm, which is well adhered on the substrate. Nanoindentation and scratch tests indicated that the β-Ta coating exhibited high hardness combined with good resistance to contact damage. The electrochemical behavior of the new coating was systematically investigated in Hank's physiological solution at 37 • C. The results showed that the β-Ta coating exhibited a superior corrosion resistance as compared to uncoated Ti-6Al-4V and commercially pure tantalum, which was attributed to a stable passive film formed on the β-Ta coating. The in vitro bioactivity was studied by evaluating the apatite-forming capability of the coating after seven days of immersion in Hank's physiological solution. The β-Ta coating showed a higher apatite-forming ability than both uncoated Ti-6Al-4V and commercially pure Ta, suggesting that the β-Ta coating has the potential to enhance functionality and increase longevity of orthopaedic implants.
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