It was shown experimentally that changing the indenter load P and the indentation size does not change the total deformation during indentation (εt≈const.), and that fracture does not influence the ...scale effect. For this reason the physical nature of the scale effect is revealed better by nanoindentation and under more “clean” conditions than in uniaxial deformation tests. The indentation size effect (ISE) is revealed as the change of mechanical properties determined by indentation. It was shown that reduction of the indent size leads to both increasing hardness and decreasing plasticity, determined by indentation. The phenomenological approach to the ISE (in which the power dependence of the indenter load P on the indenter displacement of h is used) made it possible to describe the dependence of nanohardness H(P) and H(h) by simple equations. Nanohardness was determined for 21 different crystals, and parameters that enabled the size dependence of H for these crystals to be calculated were determined. It is proposed to determine nanohardness at h=const. instead of P=const. and to recalculate H using our equations for fixed values of hf=1000nm for metals and hf=100nm for hard materials. The use of the developed technique makes it possible to compare results of nanohardness tests from different sources for different indenter loads.
Coatings with nanoscale architectures, such as nanocomposites or nanolaminates, offer improved mechanical properties and resistance to radiation environments due to their increased interface area per ...unit volume. Here, we present a systematic study of the evolution of structure, stress state and mechanical properties of nanoscale ZrN/SiNx multilayers with different thickness of elementary layers, grown at Ts=300°C by reactive magnetron sputter-deposition from Zr and Si3N4 targets. Both the multilayer period Λ (7–41nm range) and ZrN thickness ratio, fMe, (0.24–0.95 range) were varied. X-ray reflectivity and transmission electron microscopy revealed the presence of planar interfaces, with roughness lower than 1nm, yielding to the formation of a highly periodic layer stacking throughout the entire film thickness. X-ray diffraction (XRD) show that the presence of amorphous SiNx layer (for elementary thickness ha≥1nm) induces a change in the preferred orientation of the cubic (B1-type) ZrN layers from (111) to (002), while the ZrN layer becomes X-ray amorphous at thickness hMe lower than 2nm. Using in situ wafer curvature measurements we show that both SiNx and ZrN layers are growing under an intrinsic compressive stress state, of a constant value of −1GPa for SiNx and varying from −5.7 to −4GPa with increasing ZrN layer thickness. Nanoindentation tests revealed a gradual increase of the elastic modulus from 200 to 265GPa with fMe, while the hardness showed a maximum (H=24.1GPa) for the ZrN(8nm)/SiNx(0.4nm) multilayer, corresponding to an 3–4GPa increase compared to monolithic ZrN (21.0GPa) and Si3N4 (19.2GPa) films. We ascribe this enhancement of mechanical properties to local epitaxy and stronger bonding at (001) ZrN/SiNx interfaces when the SiNx thickness reduces down to 0.4nm, as confirmed by XRD results obtained from ZrN/SiNx superlattices grown on MgO (001) substrate.
•ZrN/SiNx nanolaminates were deposited by reactive magnetron sputtering.•Highly periodic multilayer with planar interfaces are formed.•Maximum hardness (24GPa) obtained at the thinnest SiNx layer (0.4nm)•Strengthening not related to Hall-Petch mechanism nor correlated to residual stress•Local epitaxy and stronger interfacial bonding are the main causes of hardening.
The mechanical (hardness and elastic modulus) and tribological (friction force and wear rate) properties of the Fe–Cu–Ni–Sn–VN composites produced by cold pressing and subsequent vacuum hot pressing ...at different temperatures are studied. The starting iron, copper, nickel, and tin powders have 5–50 μm particles and the vanadium nitride powder has 0.1–0.7 μm particles. When vacuum hot pressing temperature rises from 800 to 1000°C, the hardness increases from 3.75 to 5.37 GPa and the elastic modulus decreases from 176 to 125 GPa. As a result, the friction force reduces from 115 to 80 mN and the wear rate from 1.93 ∙ 10
–5
to 0.45 ∙ 10
–5
mm
3
∙ N
–1
∙ m
–1
. The factors promoting improvement of the mechanical and tribological properties of the sintered composites are discussed. In particular, the main factor improving the mechanical properties is that the grains are refined from 5–50 μm to 20–400 nm through the α → γ → α transformation when VN dissolves in α-Fe. In this case, the composite consists of a supersaturated solid solution of nitrogen and vanadium in α-iron, intermetallic Cu
9
NiSn
3
, and primary and secondary particulate vanadium nitride phases. A relationship between the structure and mechanical and tribological properties is established. The
H
/
E
and
H
3
/
E
2
parameters that describe the elastic strain resistance and plastic strain resistance correlate with the wear resistance. The sintered composites are regarded as promising materials for developing a new generation of diamond-containing composites for stone processing industry.
Quaternary (Ti,Zr)1−xAlxN transition metal nitride films, with Al content x ranging from 0 to 0.37, were reactively sputter-deposited from individual metallic targets under Ar+N2 plasma discharges on ...Si substrates at Ts=270°C. The influence of Al addition on the crystal structure, phase formation, growth morphology and intrinsic stress development, electrical and mechanical properties was systematically investigated. Three distinct compositional regions were evidenced: i) for 0≤x≤0.07, films develop a columnar structure consisting of cubic TiZr(Al)N grains with (111) and (200) preferred orientation, large compressive stresses up to ~−4GPa and hardness increase from ~20 to ~24GPa, ii) for 0.09≤x≤0.16, Al incorporation favors the growth of nanocomposite films consisting of (200)-oriented cubic TiZr(Al)N nanocrystals surrounded by a highly-disordered matrix, accompanied by a decrease of compressive stress, whereas a maximum hardness H~27GPa and H/E ratio of 0.105 is reached at x~0.12 and x=0.14, respectively, and iii) x>0.16, XRD amorphous films are formed, with reduced mechanical properties. The structure–stress-properties relationship is discussed based on evolutionary growth regimes induced by incorporating a high-mobility metal in a refractory compound lattice.
► Quaternary (Ti,Zr)1−xAlxN magnetron sputtered films are studied up to x=0.37. ► Drastic change in structure is revealed depending on compositional range. ► Al addition inhibits TiZrN grain growth and favors a (200) preferred orientation. ► In situ stress measurements reveal a non-monotonous Al content dependency. ► A maximum hardness value of H=27GPa is obtained at x~0.12 (nanocomposite region).
The addition of Si into (Ti,Zr)N films is considered to be perspective for their hardness enhancement as well as improvement of oxidation and wear resistance. In the present work, the influence of ...the silicon content and deposition temperature (270 and 600°C) on the structural and mechanical properties of magnetron sputtered TiZrSiN films is investigated. The elemental composition was determined by Rutherford backscattering and wavelength dispersive X-ray spectrometry methods, the structure and phase formation were analyzed by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Depending on Si content, x, and deposition temperature, Ts, (Ti,Zr)1−xSixNy films were formed in the following states: i) single-phase, cubic (Ti,Zr)N solid solution, ii) dual-phase nanocomposite consisting of nanograins of c-(Ti,Zr)N solid solution surrounded by an amorphous SiNz phase, iii) amorphous phase. Higher deposition temperature (Ts=600°C) promotes the formation of nanocomposite structure and reduces the intrinsic compressive stress. The maximum hardness values (26–29GPa) are observed when Si content is in the range 0.07≤x≤0.15 for both deposition temperatures.
•Phase formation upon Si addition in magnetron sputtered TiZrN films is investigated.•Films evolve from cubic solid solution to nanocomposite with increase of Si content at 600°C.•Amorphous films were obtained at 270°C at higher Si content due to N-deficiency.•The maximum hardness values (26–29GPa) are observed for nanocomposite films.
A critical analysis was made of the Oliver and Pharr method for determination of the hardness and elastic moduli of materials by instrumented indentations with the continuous recording of the P–
h
...diagrams (
P
is the force acting on the indenter, h is the approach of the indenter and a sample). Mistakes and insufficient justification were revealed in the basic theoretical relations of this method. In particular, this refers to an incorrect definition of the depth of the elastic contact
h
c
, which is the base of these relalations. New refined basic relations and formulas for the determination of hardness and elastic modulus are given, in which the above defects are eliminated and which are based only on the assumption of elastic unloading of the indenter according to the classic theories of the elastic contact. In addition to the foregoing, using the data of the
P
–
h
diagram measured in the arbitrary laboratory coordinate system, an improved method of the stable determination of the contact stiffness
S
=
d
P
/dh at the
P
–h diagram position have been proposed in the commonly accepted theoretical coordinate system in which its basic classic model relations are recorded. These refinements have been derived without additional assumptions to hypotheses to the Oliver and Pharr method and additional experimental measurements.
Multilayer coatings with layer thicknesses in the nanometer range have been shown to exhibit original mechanical properties: these include pronounced softening of some elastic moduli, large increase ...in yield strength and hardening effect. Such original properties are related to the high interface density and reduced grain sizes associated with these systems. In the first part of this article, the elastic and plastic properties of metal/metal, metal/nitride and nitride/nitride nanoscale multilayers are briefly outlined. The origin of large compressive stress commonly observed in PVD films grown with energetic particles is then presented and illustrations given for the case of epitaxial multilayers for which different stress sources exist. The second part focuses on recent experimental results obtained for three multilayered systems, Mo/Ni, TiN/Cu and ZrN/W, corresponding to different crystal structure and lattice mismatch combinations. Two issues will be addressed: the interdependence between interfacial mixing and elastic softening in Mo/Ni superlattices and the mechanical behaviour of TiN/Cu and ZrN/W multilayers combining ‘hard’ and ‘soft’ materials. These multilayers were grown epitaxially on either MgO (001) or Al
2O
3(112¯0) substrates by a dual ion beam sputtering technique. Low-angle and high-angle X-ray diffraction experiments as well as Transmission Electron Microscopy observations were used to characterize the microstructure and crystalline orientation, structure of interfaces and type of growth defects. Elastic properties were studied by Brillouin light scattering and hardness values determined from nanoindentation tests. For selected samples, a combined FIB-TEM technique was implemented to image the deformed nanolaminates beneath the indentor.
The Al―Mg―B films were deposited on silicon substrates by direct current magnetron sputtering from the AlMgB14 target at low discharge power and at substrate temperature ranging from 100 to 500°C. ...The deposited films have been annealed at 1000°C in vacuum, and characterized by X-ray diffraction, atomic force microscopy, Fourier transform infra-red spectroscopy, nano- and micro-indentation, and scratch testing. The films exhibit lower hardness than the bulk AlMgB14 material, which is due to their amorphous structure in which the strong intra-icosahedron B―B bonds are almost lacking and the weaker B―O bonds are predominant. After the annealing, a reduction of a number of B―O bonds and a formation of crystallites in the films lead to an increase in the nanohardness and elastic modulus. The as-deposited films exhibit a low coefficient of friction of 0.08–0.12. First-principles studies show that the icosahedra in amorphous AlMgB14-based materials are not fully developed, which is the reason of their lower mechanical performance.
•Al―Mg―B films were deposited at different substrate temperatures.•The as-deposited films were amorphous, whereas the annealed ones were nanostructured.•Mechanical properties were analyzed as functions of substrate and annealing temperatures.•Ab-initio MD simulations of AlMgB14-based materials were carried out.•Both experimental and theoretical investigations enabled one to explain film properties.
Al-Mg-B and Al-Mg-B-C films were deposited by DC magnetron sputtering from the AlMgB14 and B4C targets on silicon substrates at different discharge power densities at both the targets. The deposited ...films were characterized by atomic force microscopy, X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nanoindentation, scratch and pin-on-disk testing. All the deposited films were found to be X-ray amorphous. The film roughness, nanohardness and elastic modulus increase with the discharge power densities at both targets. An introduction of carbon is accompanied by the formation of the strong C-B4 units that strengthen Al-Mg-B-C films. The films exhibit a coefficient of friction in the range of 0.09–0.20. First-principles calculations show that the amorphous AlMgB14-based materials consist of the fragments of boron icosahedra, for which reason they possess the hardness that is lower than the hardness of the crystalline counterparts. Based on experimental and theoretical results, it is assumed that the observed strength enhancement can be assigned to an improvement of the B-B icosahedron-like network and film densification.
•Al-Mg-B-C films are prepared by magnetron sputtering AlMgB14 and B4C targets•An effect of discharge power on film properties is studied•Film roughness, nanohardness and elastic modulus increase with discharge power•First-principles calculations are performed to interpret film properties•The plausible mechanism of strength enhancement is suggested.
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