Enhancement of mechanical and tribological properties in AISI D3 steel substrates by using a non-isostructural CrN/AlN multilayer coating

Enhancement of mechanical and tribological properties on AISI D3 steel surfaces coated with CrN/AlN multilayer systems deposited in various bilayer periods (Λ) via magnetron sputtering has been studied in this work exhaustively. The coatings were characterized in terms of structural, chemical, morphological, mechanical and tribological properties by X-ray diffraction (XRD), electron dispersive spectrograph, atomic force microscopy, scanning and transmission electron microscopy, nanoindentation, pin-on-disc and scratch tests. The failure mode mechanisms were observed via optical microscopy. Results from X-ray diffraction analysis revealed that the crystal structure of CrN/AlN multilayer coatings has a NaCl-type lattice structure and hexagonal structure (wurtzite-type) for CrN and AlN, respectively, i.e., made was non-isostructural multilayers. An enhancement of both hardness and elastic modulus up to 28 GPa and 280 GPa, respectively, was observed as the bilayer periods (Λ) in the coatings were decreased. The sample with a bilayer period (Λ) of 60 nm and bilayer number n  =  50 showed the lowest friction coefficient (∼0.18) and the highest critical load (43 N), corresponding to 2.2 and 1.6 times better than those values for the coating deposited with n = 1, respectively. The best behavior was obtained when the bilayer period (Λ) is 60 nm (n = 50), giving the highest hardness 28 GPa and elastic modulus of 280 GPa, the lowest friction coefficient (∼0.18) and the highest critical load of 43 N. These results indicate an enhancement of mechanical, tribological and adhesion properties, comparing to the CrN/AlN multilayer systems with 1 bilayer at 28%, 21%, 40%, and 30%, respectively. This enhancement in hardness and toughness for multilayer coatings could be attributed to the different mechanisms for layer formation with nanometric thickness such as the Hall–Petch effect and the number of interfaces that act as obstacles for the crack deflection and dissipation of crack energy.     

Modulation periods and ratios induced changes of microstructure and mechanical properties of AlN/ZrB2 multilayered coatings

AlN/ZrB₂ multilayered coatings were synthesized in a magnetron sputtering system. The extensive measurements were employed to investigate the influence of different nanoscale modulation periods and modulation ratios on microstructure and mechanical properties of the coatings. Analysis of X-ray diffraction, profiler and nanoindention indicated that multilayered coatings possessed much higher hardness and elastic modulus than monolithic AlN and ZrB₂ coatings. At the substrate negative bias of −80 V, maximum hardness (34.1 GPa) and elastic modulus (469.8 GPa) were obtained in the multilayer with Λ = 30 nm and t_AlN:t_ZrB2 = 1:3. This hardest multilayer showed a marked polycrystalline structure with the strong mixture of ZrB₂ (001), ZrB₂ (100), ZrB₂ (101), AlN (100) textures.     

Extraction of effective dielectric constants and the effect of process damage of low-k dielectrics for advanced interconnects

In this paper, the line-to-line parasitic capacitance of an advanced interconnects with a low-k dielectric (k < 3.0) was extracted by electrical measurement on comb-serpentine structures with various spacing. The empirical values are higher than the prediction from the filed solver, especially in the small geometries. A model was derived based on the damage of low-k dielectric during processing, which causes the increase of the dielectric constant. Then, the effective dielectric constant was evaluated by both simulation and theoretical models. The k value of damage zone was determined from blanket wafer by mercury probe after oxygen plasma treatment. Good agreement was obtained after we modified the simulation structure to include the damage zone. Especially, the concept of low-k damage due to plasma treatment was characterized for the first time. Thus, it is possible to use this model in the future study, such as the porous low-k in 65 nm or even 45 nm generations.     

Structural and mechanical properties of titanium and titanium diboride monolayers and Ti/TiB2 multilayers

Nano-multilayers represent a new class of engineering materials that are made up of alternating nanometer scale layers of two different components. In the present work a titanium (Ti) monolayer was combined with titanium diboride (TiB₂) to form a Ti/TiB₂ nano-multilayer. Designed experimental parameters enabled an evaluation of the effects of direct current bias voltage (U_b) and bilayer thickness (Λ) during multilayer deposition on the mechanical properties of reactively sputtered Ti/TiB₂ multilayer films. Their nanostructures and mechanical properties were characterized and analyzed using X-ray photoelectron spectroscopy (XPS), low-angle and high-angle X-ray diffraction (XRD), plan-view and cross-sectional high-resolution transmission electron microscopy (HRTEM), and microindentation measurements. Under the optimal bias voltage of U_b = − 60 V, it was found that Λ (varied from 1.1 to 9.8 nm) was the most important factor which dominated the nanostructure and hardness. The hardness values obtained varied from 12 GPa for Ti and 15 GPa for TiB₂ monolayers, up to 33 GPa for the hardest Ti/TiB₂ multilayer at Λ = 1.9 nm. The observed hardness enhancement correlated to the layer thickness, followed a relation similar to the Hall-Petch strengthening dependence, with a generalized power of ∼ 0.6. In addition, the structural barriers between two materials (hcp Ti/amorphous TiB₂) and stress relaxation at interfaces within multilayer films resulted in a reduction of crack propagation and high-hardness.     

Microstructure and mechanical properties of TiAlN/SiO2 nanomultilayers synthesized by reactive magnetron sputtering

TiAlN/SiO₂ nanomultilayers with different SiO₂ layer thickness were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nano-indentation. The results indicated that, under the template effect of B1-NaCl structural TiAlN layers, amorphous SiO₂ was forced to crystallize and grew epitaxially with TiAlN layers when SiO₂ layer thickness was below 0.6 nm, resulting in the enhancement of hardness and elastic modulus. The maximum hardness and elastic modulus could respectively reach 37 GPa and 393 GPa when SiO₂ layer thickness was 0.6 nm. As SiO₂ layer thickness further increased, SiO₂ transformed back into amorphous state and broken the coherent growth of nanomultilayers, leading to the decrease of hardness and elastic modulus.     

Increasing mechanical strength of mesoporous silica thin films by addition of tetrapropylammonium hydroxide and refluxing processes

The incorporation of mesopores into silica films is an effective way to reduce the dielectric constant. However, the pores reduce the film mechanical strength. This study investigates two steps for preparing coating solution. One was the reflux of the silica colloid at 70 °C. The other was the addition of TPAOH (tetrapropylammonium hydroxide) into the colloid. The reflux step can increase the mechanical strength, reduce the flat band voltage and reduce the leakage current of the films. Nevertheless, the low-k value (k represents dielectric constant) increases as the porosity of the film falls. Adding a slight amount of TPAOH before the reflux process can recover both the porosity and the low k value, while maintaining the high mechanical strength and the low flat band voltage. Results of this study demonstrate that two more steps (the addition of TPAOH and the reflux) in the preparation of the coating solution can increase the film hardness and elastic modulus from 0.8 to 1.4 GPa and from 5.8 to 9.9 GPa respectively, while maintaining the low-k value close to 2.05.     

Ultra low-dielectric-constant methylated mesoporous silica films with high hydrophobicity and stability

Vapor phase treatment with tetraethyl orthosilicate (TEOS) is used to improve the performance of methylated mesoporous silica films spin-coated on silicon wafers. Subsequent calcination leads to formation of ultra low dielectric-constant (k) films with high hydrophobicity and structural stability. The k value of the films is about 1.75, and remains as low as 1.82 in an 80%-relative-humidity environment over seven days. Mechanical strength (elastic modulus and hardness) is high enough to withstand the stresses that occur during the chemical mechanical polishing and wire bonding process (E = 10.9 GPa). Effects of the methyl group and TEOS vapor treatment on the structural stability and hydrophobicity are systematically studied.     

Large area Ba1 − xSrxTiO3 thin films for microwave applications deposited by pulsed laser ablation

Large area Ba_1 − xSr_xTiO₃ (BST) thin films with x = 0.4 or x = 0.5 were deposited on 75 mm diameter Si wafers in a pulsed laser deposition (PLD) chamber enabling full-wafer device fabrication using standard lithography. The deposition conditions were re-optimized for large PLD chambers to obtain uniform film thickness, grain size, crystal structure, orientation, and dielectric properties of BST films. X-ray diffraction and microstructural analyses on the BST films grown on Pt/Au/Ti electrodes deposited on SiO₂/Si wafers revealed films with (110) preferred orientation with a grain size < 100 nm. An area map of the thickness and crystal orientation of a BST film deposited on SiO₂/Si wafer also showed (110) preferred orientation with a film thickness variation < 6%. Large area BST films were found to have a high dielectric tunability of 76% at an electric field of 400 kV/cm and dielectric loss tangent below 0.03 at microwave frequencies up to 20 GHz and a commutation quality factor of ~ 4200.     

Band alignment of Cd(1 − x)ZnxS produced by spray pyrolysis method

Cd_(1 − x)Zn_xS thin films have been grown on glass substrates by the spray pyrolysis method using CdCl₂ (0.05 M), ZnCl₂ (0.05 M) and H₂NCSNH₂ (0.05 M) solutions and a substrate temperature of 260 °C. The energy band gap, which depends on the mole fraction × in the spray solution used for preparing the Cd_(1 − x)Zn_xS thin films, was determined. The energy band gaps of CdS and ZnS were determined from absorbance measurements in the visible range as 2.445 eV and 3.75 eV, respectively, using Tauc theory. On the other hand, the values calculated using Elliott-Toyozawa theory were 2.486 eV and 3.87 eV, respectively. The exciton binding energies of Cd_0.8Zn_0.2S and ZnS determined using Elliott-Toyozawa theory were 38 meV and 40 meV, respectively. X-ray diffraction results showed that the Cd_(1 − x)Zn_xS thin films formed were polycrystalline with hexagonal grain structure. Atomic force microscopy studies showed that the surface roughness of the Cd_(1 − x)Zn_xS thin films was about 50 nm. Grain sizes of the Cd_(1 − x)Zn_xS thin films varied between 100 and 760 nm.     

Effect of grain size on mechanical properties in CrAlN/SiNx multilayer coatings

Both CrAlN and SiN_x coatings were deposited sequentially by RF magnetron sputtering. During sputtering, thickness of SiN_x layer was set to be 1 nm, while that of CrAlN layer was controlled to be 4, 20, 40, 100, and 200 nm. According to XRD results, it was revealed that grain size of the CrAlN coatings increased from 3.6 nm to 24.2 nm with the increasing thickness. From HRTEM images, the variation on grain size was attributed to the amorphous SiN_x layer, which significantly retarded the continuous growth of CrAlN layer. Hardness of the CrAlN/SiN_x coatings with various bilayer thicknesses was measured by nanoindentation. The relationship between grain size and hardness could be interpreted by the Hall-Petch equation, and an improved hardness around 32 GPa was achieved.     

Microstructure and mechanical properties of CrAlN/SiNx nanostructure multilayered coatings

Multilayered CrAlN and SiN_x films were deposited periodically by radio frequency reactive magnetron sputtering. In the CrAlN/SiN_x multilayered coatings, the thickness of CrAlN layer was fixed at 4 nm, while that of SiN_x layer was adjusted from 4 nm to 0.3 nm. The dependence of the SiN_x layer thickness on the preferred orientation, crystalline behavior and mechanical properties of multilayered coatings were discussed with the aid of XRD patterns and HRTEM. It was demonstrated that amorphous SiN_x layer transformed to a crystallized one when the thickness decreased from 4 nm to 0.3 nm. The crystalline SiN_x layer grew epitaxially, formed the coherent interface with the CrAlN layer, and the columnar structure was exhibited. The critical layer thickness for the transition from amorphous SiN_x to a crystallized one was found to be around 0.4 nm, and maximum hardness of 33 GPa was revealed.     

Face-centered cubic (Al1 − xCrx)2O3

We report the discovery of a face-centered cubic (Al_1−xCr_x)₂O₃ solid solution [0.60 < x < 0.70] in films grown onto Si substrates using reactive radio frequency magnetron sputtering from Al and Cr targets at 400 °C. The proposed structure is NaCl-like with 33% vacancies on the metal sites. The unit cell parameter is 4.04 Å as determined by X-ray diffraction. The films have a <100> preferred crystallographic orientation and exhibit hardness values up to 26 GPa and an elastic modulus of 220-235 GPa.     

Synthesis of nanocrystalline xCuFe2O4-(1 − x)BiFeO3 magnetoelectric composite by chemical method

xCuFe₂O₄-(1 − x)BiFeO₃ spinel-perovskite nanocomposites with x = 0.1, 0.2, 0.3 and 0.4 were prepared using citrate precursor method. X-ray diffraction (XRD) analysis showed phase formation of xCuFe₂O₄-(1 − x)BiFeO₃ calcined at 500 °C. Transmission electron microscopy (TEM) shows formation of nanocrystallites of xCuFe₂O₄-(1 − x)BiFeO₃ with an average particle size of 40 nm. Variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Coercivity, saturation magnetization and squareness have been found to vary with concentration of ferrite phase and annealing temperature due to the increase in crystallite size. Squareness and coercivity increased with an increase in annealing temperature up to 500 °C and then decreased with a further increase in temperature to 600 °C. Magnetoelectric effect of the nanocomposites was found to be strongly depending on the magnetic bias and magnetic field frequency.     

Nanoindentation study of single-crystal NaTh2(PO4)3

The single crystals of sodium dithorium orthophosphate NaTh₂(PO₄)₃ (NThP) were studied by means of micro/nanoindentation. The NThP hardness was found to be Н_N = 8.76 ± 0.18 GPa and the elastic modulus Е_N = 144 ± 1 GPa. Microhardness anisotropy of the NThP crystal unequal faces is insignificant. The non-uniformity of plastic strain observed for the NThP is caused by fracture initiation and growth in the imprint. The average fracture toughness index (K_Ic) for the NThP is estimated to be equal to 0.56 MPa m^0.5.     

Annealing effects on microstructure and mechanical properties of sputtered multilayer Cr(1 − x)AlxN films

Multilayer Cr_(1 − x)Al_xN films with a total thickness of 2 μm were deposited on high-speed steel by medium frequency magnetron sputtering from Cr and Al-Cr (70 at.% Al) targets. The samples were annealed in air at 400 °C, 600 °C, 800 °C and 1000 °C for 1 hour. Films were characterized by cross-sectional scanning electron microscopy and X-ray diffraction analysis. The grain size of the as-deposited multilayer films is about 10 nm, increasing with the annealing temperature up to 100 nm. Interfacial reactions have clearly changed at elevated annealing temperatures. As-deposited films' hardness measured by nanoindentation is 22.6 GPa, which increases to 26.7 GPa when the annealing temperature goes up to 400 and 600 °C, but hardness decreases to 21.2 GPa with further annealing temperature increase from 600 to 1000 °C. The multilayer film adhesion was measured by means of the scratch test combined with acoustic emission for detecting the fracture load. The critical normal load decreased from 49.7 N for the as-deposited films to 21.2 N for the films annealed at 1000 °C.     

Nanoindentation study of magnetron-sputtered CrN and CrSiN coatings

CrN and CrSiN coatings were deposited on stainless steel substrate by reactive magnetron sputtering. The coatings were characterized for phases, chemical composition, microstructure, and mechanical properties by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM)/energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), and nanoindentation technique, respectively. The cubic phase was the only phase observed in both the coatings as observed in XRD results. A dense morphology was observed in these coatings deposited with high nitrogen and Si contents, 50:50 and 18.65 at.%, respectively. Nanoindentation measurement of CrN coatings, with Ar + N₂ proportions of 60:40, showed maximum hardness (H) and modulus (E) of 21 ± 0.85 GPa and 276 ± 13 GPa, respectively. The CrN coatings deposited in pure N₂ atmosphere showed H and E values of 27 ± 1.62 and 241 ± 10 GPa, respectively. The measured H and E values of CrSiN coatings were found to be 28 ± 1.40 GPa and 246 ± 10 GPa, respectively. The improved hardness in both the coatings was attributed mainly to a reduction in crystallite size, decrease in surface roughness, and dense morphology. The incorporation of Si into the CrN coatings has improved both hardness and Young’s modulus.     

Dielectric properties of Ba(Ti1 − xZrx)O3 solid solutions

This paper reports the structural and dielectric properties of Ba(Ti_1 − xZr_x)O₃ (x = 0-0.3) ceramics. Single-phase solid solutions of the samples were determined by X-ray diffraction. Microscopic observation by scanning electron microscope revealed dense, single-phase microstructure with large grains (20-60 μm). The evolution of dielectric behavior from a sharp ferroelectric peak (for x ≤ 0.08) to a round dielectric peak (for 0.15 ≤ x ≤ 0.25) with pinched phase transitions and successively to a ferroelectric relaxor (for x = 0.3) was observed with increasing Zr concentration. Compared with pure BaTiO₃, broaden dielectric peaks with high dielectric constant of 25,000-40,000 and reasonably low loss (tanδ: 0.01-0.06) in the Ba(Ti_1 − xZr_x)O₃ ceramics have been observed, indicating great application potential as a dielectric material.     

First-principles calculations of structural, electronic, and elastic properties of MgZrSi2O7

For the first time, the recently synthesized pyrochlore MgZrSi₂O₇ [J. Xu et al., Mater. Chem. Phys. 128 (2011) 410] has been analyzed using the first principles calculations. The electronic and elastic properties were predicted; in particular, the band gap is indirect and has the value of 6.75 eV. The bulk modulus equals to 186.51 ± 1.95 GPa. Anisotropy of elastic properties was analyzed by comparing the upper and lower estimates of the shear moduli. In addition, directional dependence of the Young's modulus was calculated and visualized; its value varies in the range from 249.7 GPa (along the a, b, c crystallographic axes) to 136.84 GPa (along the bisector direction in any of the ab, bc, ac planes).     

Elastic modulus and hardness of CaTiO3, CaCu3Ti4O12 and CaTiO3/CaCu3Ti4O12 mixture

Three ceramic systems, CaTiO₃ (CTO), CaCu₃Ti₄O₁₂ (CCTO) and intermediate nonstoichiometric CaTiO₃/CaCu₃Ti₄O₁₂ mixtures (CTO.CCTO), were investigated and characterized. The ceramics were sintered at 1100 °C for 180 min. The surface morphology and structures were investigated by XRD and SEM. Elastic modulus and hardness of the surfaces were studied by instrumented indentation. It was observed that CCTO presented the higher mechanical properties (E = 256 GPa, hardness = 10.6 GPa), while CTO/CCTO mixture showed intermediate properties between CTO and CCTO.     

Investigation of the tribological behavior and its relationship to the microstructure and mechanical properties of a-SiC:H films elaborated by low frequency plasma assisted chemical vapor deposition

Amorphous hydrogenated silicon carbide (a-SiC:H) coatings are promising candidates for tribological applications in the mechanical and aeronautical industries. Alternately high values of hardness H (15 < H < 32 GPa) and elastic modulus E contribute to their good wear resistance as well as to a low friction coefficient. The latter has been found to vary in the range 0.1 < μ < 0.65, depending upon the microstructure of the layers. The roughness of the films determined by atomic force microscopy is in all cases low (Ra ~ 5 nm). Comparisons between the tests carried out in air and those performed under vacuum conditions point to a substantial role of the adhesive part of the friction coefficient in vacuum. They also highlight the role played by the transfer layer between the film and the pin in producing a low friction coefficient for several coatings. This transfer layer consists chiefly of silicon and oxygen (O/Si ~ 2), whilst low quantities of carbon are also present.