Production and properties of metal-carbon composite coatings with a nanocrystalline structure

It is suggested to produce metal-carbon composite coatings by magnetron sputtering of mosaic cathodes, which are Group IV, V, and VI metals. The mosaic structure of the cathode elements are computer-optimized for each of the metals. Reflection electron diffraction studies show that the coatings have the amorphous or nanocrystalline structures, which are thermally stable. The coatings offer specific physical properties, in particular, low friction factor and high hardness.     

Sputtering pressure effects on the structural and mechanical properties of TiVCr alloy coatings

In this study, TiVCr alloy coatings were deposited on Si substrates by magnetron sputtering system at different working pressures (0.33-1 Pa). The TiVCr coatings have a composite structure with amorphous and body-centered cubic (bcc) crystal phases comprised of bundles of fine fibrous structures and V-shaped columnar structures, respectively. Compared with the amorphous zone, the crystalline zone has a denser and more compact structure. The coating microstructure became more porous as working pressure increased. Consequently, the crystal zones of the deposited coatings at 0.33 Pa obtained higher hardness (11.6 GPa) while the deposited coatings at 1 Pa achieved lower hardness (4.5 GPa).     

Microstructure and morphology of electrodeposited Ni-P alloys treated by high energy surface mechanical attrition

Fully amorphous Ni-P layer electrodeposited onto a Cu plate was subjected to severe plastic deformation using surface mechanical attrition treatment in a high energy SPEX 8000 shaker mill. Two series of experiments using different milling conditions (series I: 20 6.35-mm balls; series II: 100 1.59-mm balls) were carried out to explore the mechanism of the process and to investigate the structure of the developed coatings. The evolution of the microstructure and mechanical properties of the Ni-P layer after the deformation process was studied by x-ray diffraction, scanning electronmicroscopy and hardness measurements. We demonstrate that the different mechanical treatments controllably influence the mechanical behavior of the Ni-P metallic glass coating. When the vial of the mill is loaded with larger balls, deformation-induced Ni₃P compound particles form in the amorphous matrix resulting in a hard (HV = 17 GPa) but non-uniform coating. In the case of milling with many small balls, the increase in the surface hardness is considerably lower (7 GPa) as a consequence of reduced impact energy.     

Structure and mechanical properties of Ni-P electrodeposited coatings

The coatings with different phosphorus contents were obtained by varying the concentration of H₃PO₃ in the electroplating bath. With the increase of phosphorus content, the structure of the Ni-P electrodeposited coatings transformed from microcrystalline to a mixture of nanocrystalline and amorphous phases, then to amorphous phase. A high hardness value of 710 HV_0.1 of as-deposited Ni-P coating was obtained at 8.3 at.% phosphorus content, and high wear resistance was accordingly achieved. The refined nanocrystalline grains with average size of about 7 nm were found to be responsible for the high hardness and improved wear resistance of the as-deposited Ni-P electrodeposited coating.     

Characterization and properties Ti-Al-Si-N nanocomposite coatings prepared by middle frequency magnetron sputtering

TiN-containing amorphous Ti-Al-Si-N (nc-TiN/a-Si₃N₄ or a-AlN) nanocomposite coatings were deposited by using a modified closed field twin unbalanced magnetron sputtering system which is arc assisted and consists of two circles of targets, at a substrate temperature of 300 °C. XRD, XPS and High-resolution TEM experiments showed that the coatings contain TiN nanocrystals embedded in the amorphous Si₃N₄ or AlN matrix. The coatings exhibit good mechanical properties that are greatly influenced by the Si contents. The hardness of the Ti-Al-Si-N coatings deposited at Si targets currents of 5, 8, 10, and 12 A were 45, 47, 54 and 46 GPa, respectively. The high hardness of the deposited Ti-Al-Si-N coatings may be own to the plastic distortion and dislocation blocking by the nanocrystalline structure. On the other hand, the friction coefficient decreases monotonously with increasing Si contents. This result would be caused by tribo-chemical reactions, which often take place in many ceramics, e.g. Si₃N₄ reacts with H₂O to produce SiO₂ or Si(OH)₂ tribolay-layer.     

Effect of plastic deformation on physical properties and structure of the shape memory alloy Ti<Subscript>49.5</Subscript>Ni<Subscript>50.5</Subscript>

The effect of severe plastic deformation by torsion (SPDT) in Bridgman anvils at a high pressure (6 GPa) on the physical properties and crystal structure of the shape memory alloy Ti_49.5Ni_50.5 has been studied. The behavior of the thermal expansion, electrical resistivity, absolute differential thermopower, Hall coefficient, magnetic properties, and optical characteristics of the amorphous/nanocrystalline and submicrocrystalline alloys obtained by the SPDT with subsequent heat treatment at 800 K has been discussed.     

Phase transformations and thermal stability of the structure of Ti<Subscript>3</Subscript>Al intermetallic compound at deuteration and plastic deformation

The structural transformations in Ti₃Al intermetallic compound at deuteration with concentrations x = 1.2 and 1.7, heating at 100–400°C, and shear deformation under pressure have been studied. It is established that at a given deuterium concentration deuterides with fcc and orthorhombic lattices are formed; under severe shear deformation, nanocrystalline and amorphous (or close to amorphous) deuterides arise. The reasons for the structure amorphization at deuteration and subsequent plastic deformation are discussed.     

Determination of activation energy for crystallizations in Ni–Cu–P amorphous alloys

The effect of plastic deformation on the crystallization kinetics of the ternary Ni–Cu–P amorphous alloy coatings prepared by electroless plating was investigated using differential scanning calorimetry. It was shown that the effective crystallization activation energy of the amorphous coatings is pronouncedly affected by the plastic deformation, indicating a decreasing tendency with deformation, the effective activation energy decreases from 199.02 to 163.71?kJ?mol^?1 as the plastic deformation from 0% to 40%. And, accordingly, this leads to the decrease of crystallization temperature. Analyses were presented to discuss the possible mechanism for the notable effects of plastic deformation on the crystallization kinetics of the amorphous coatings.     

Nanoindentation stress–strain curves as a method for thin-film complete mechanical characterization: application to nanometric CrN/Cr multilayer coatings

The mechanical behavior of CrN/Cr multilayer coatings deposited by rf magnetron sputtering has been investigated by nanoindentation measurements performed with indenters of different geometries. Nanoindentation stress–strain curves generated from these measurements allow us to characterize the complete mechanical behavior of these coatings in the elastic, elastoplastic, plastic and fracture deformation regimes. In particular, indentation measurements carried out with a 100-m-radius spherical indenter allowed us to study the elastic deformation regime and estimate the yield stress parameter through the initial indentation yielding point. The elastoplastic deformation regime has been studied using a 5-m-radius spherical indenter and the stationary yielding regime (fully plastic regime) has been investigated with a pyramidal indenter of Berkovich geometry. The use of a pyramidal cube-corner indenter allowed us to study coating fracture characteristics. Nanometric CrN/Cr multilayer structures as well as single CrN and Cr coatings have been characterized. The study has shown that multilayered coatings with period thicknesses less than 46 nm present values of yield stress, Youngs modulus, hardness and toughness higher than those for single-layer CrN and Cr coatings. PACS 62.20.Dc; 62.20.Qp; 68.60.Bs     

Mechanical properties of the plasma-enhanced magnetron sputtering Si-C-N coatings

The mechanical properties of plasma-enhanced magnetron sputtering Si-C-N hard coatings with various compositions are characterized. The effect of chemical composition on the microstructure and properties of coating is investigated. The results show that the microstructure and mechanical properties of Si-C-N coatings are very sensitive to chemical composition. The nanocrystalline/amorphous composite structure is beneficial to the coating's mechanical properties. It also reveals that Si-C-N coating with low Si and high C concentrations has the highest hardness (≥40 GPa) and the best wear property with dry friction coefficient about 0.2.     

Study of coatings based on titanium oxides and oxynitrides using a set of methods

A set of methods has been applied to study the properties of titanium oxide and oxynitride coatings on steel. It is established that the coatings consist of two phases with a nanocrystalline and an amorphous structure with a high proportion (～50 %) of grain boundaries; anatase is the dominant crystalline phase. The obtained results can be applied in the development of coatings for stents as well as for manufacturing hydrogen accumulators.     

Synthesis of composite calcium-phosphate coatings via pulsed photon processing

The phase composition and mechanical properties of coatings generated on a Ti surface via the ion sputtering of a hydroxyapatite (HA) target and a compound (hydroxyapatite and Ti) target with subsequent pulsed photon processing (PPP) with incoherent xenon lamp radiation are investigated. It is found for the first time that pulsed photon processing accelerates the crystallization of amorphous films of Ca–P–O–H and Ca–P–O–H–Ti compositions, during which tricalcium phosphate Ca₃(PO₄)₂, titanium oxide TiO₂ (rutile, anatas), and perovskite CaTiO₃ are formed, depending on the radiation dose and the ratio between Ti and Ca phases (Ti/Ca) with hydroxyapatite structure. It is found that pulsed photon processing of initial amorphous coatings greatly increases their hardness (up to 10.9 GPa) and adhesion (up to 29.0 MPa).     

Correlation between bioactivity and structural properties of titanium dioxide coatings grown by atomic layer deposition

TiO₂ coatings were grown on Ti and Si by Atomic Layer Deposition (ALD) from titanium ethoxide and water at 300 °C in a wide range of the reaction cycles number N = 100-2000. TiO₂ coatings were found to be amorphous at low value of N < 300 while the coatings grown at N ≥ 300 revealed anatase polycrystalline structure. The TiO₂ coatings bioactivity was evaluated by hydroxyapatite forming ability by the technique of soaking in Simulated Body Fluid (SBF). Correlation between bioactivity and structural properties of TiO₂ was determined. X-ray diffraction and scanning electron microscopy with electron probe microanalysis showed that amorphous TiO₂ coating did not induce the hydroxyapatite growth whereas anatase resulted in the hydroxyapatite forming on the samples surfaces which confirmed TiO₂ anatase bioactivity.     

Adhesive strength, superhardness, and the phase and elemental compositions of nanostructured coatings based on Ti-Hf-Si-N

New superhard coatings based on Ti-Hf-Si-N with good physical and mechanical properties have been fabricated. A comparative analysis of the physical, mechanical, and tribomechanical characteristics of the coatings has been performed. The values of hardness, modulus of elasticity, elastic recovery, adhesive strength, friction coefficient, and wear rate of the coatings have been determined and calculated. The specific features of deformation and fracture of the coatings deposited on a steel substrate during the adhesion tests have been described. It has been shown that the parameters measured during scratching make it possible to distinguish the threshold values of the critical load, which lead to different (cohesive and adhesive) types of failure of the coatings during tribological tests. The stoichiometry for different series of samples with Ti-Hf-Si-N coatings has been determined using Rutherford backscattering, secondary ion mass spectrometry, and energy dispersive microanalysis.     

Influence of the defect and structural state of FCC and BCC metals on the intensity of mechanodynamic penetration of helium atoms

The specific features of the mechanodynamic penetration of helium under plastic deformation into fcc (Cu) and bcc (Fe, Nb) metals with different initial defect structures (single-crystal, nanocrystalline, and porous samples) are investigated. The intensity of mechanodynamic penetration into these metals is shown to depend on the type of bonding (metallic or covalent), which determines the degree of localization of the plastic flow of these metals, as well as on the type of defect structure and on the character of plastic flow (dislocation deformation, twinning, grain-boundary sliding). Curves of helium extraction from samples at different strains are obtained. It is found that the helium release exhibits a wide variety of peaks depending on the degree and character of plastic deformation of the metals under investigation. This suggests that the metals contain different types of helium traps, which determine the content of helium and the specific features of its release in the temperature range studied.     

(Ti,Al,Si,C)N nanocomposite coatings synthesized by plasma-enhanced magnetron sputtering

Materials’ surface service property could be enhanced by transition metal nitride hard coatings due to their high hardness, wear and high temperature oxidation resistance, but the higher friction coefficient (0.4-0.9) of which aroused terrible abrasion. In this work, quinternary (Ti,Al,Si,C)N hard coating 3-4 μm was synthesized at 300 °C using plasma enhanced magnetron sputtering system. It was found that the coating's columnar crystals structure was restrained obviously with the increase of C content and a non-columnar crystals growth mode was indicated at the C content of 33.5 at.%. Both the XRD and TEM showed that the (Ti,Al,Si,C)N hard coatings had unique nanocomposite structures composed of nanocrystalline and amorphous nc-(Ti,Al)(C,N)/nc-AlN/a-Si₃N₄/a-Si/a-C. However, the coatings were still super hard with the highest hardness of 41 GPa in spite of the carbon incorporation. That a-C could facilitate the graphitization process during the friction process which could improve the coating's tribological performance. Therefore, that nanocomposite (Ti,Al,Si,C)N coatings with higher hardness (>36 GPa) and a lower friction coefficient (<0.2) could be synthesized and enhance the tribological performance and surface properties profoundly.     

Effect of interface structure on deformation behavior of crystalline Cu/amorphous CuZr sandwich structures

The effect of interface types (namely, sharp interface and graded interface) and its thickness on the deformation behavior of crystalline/amorphous/crystalline sandwich structures (CACSSs) under tensile loading are studied using molecular dynamics simulation. Compared with the CACSSs with sharp interface, the CACSSs with gradient interface consistently exhibit good plasticity when the interface thickness is larger than 6 nm, due to the coupling effects among crystalline layer, amorphous layer and crystalline–amorphous interface. With the increase of interface thickness, the plastic deformation mechanism of CACSSs with gradient interface changes from the local plastic deformation in amorphous layer to the homogeneous plastic deformation.     

晶界对纳米多晶铝中冲击波阵面结构影响的分子动力学研究

用分子动力学方法研究了纳米多晶铝在冲击加载下的冲击波阵面结构及塑性变形机理.模拟研究结果表明:在弹性先驱波之后,是晶界间滑移和变形主导了前期的塑性变形机理;然后是不全位错在界面上成核和向晶粒内传播,然后在晶粒内形成堆垛层错、孪晶和全位错的过程主导了后期的塑性变形机理.冲击波阵面扫过之后留下的结构特征是堆垛层错和孪晶留在晶粒内,大部分全位错则湮灭于对面晶界.这个由两阶段塑性变形过程导致的时序性塑性波阵面结构是过去未见报道过的. 关键词： 晶界 塑性变形 冲击波阵面 分子动力学     

Self-blocking of shear bands and the delocalization of plastic flows in amorphous alloys upon megaplastic deformation

Features of the formation of shear bands and nanocrystalline phases upon the megaplastic deformation of amorphous alloys based on iron, nickel, and titanium at room temperature in a Bridgman chamber are analyzed via transmission electron microscopy. It is shown that the transition from strongly localized to quasi-homogeneous plastic deformation occurs at a definite stage of the inhomogeneous plastic flow. Mechanisms based on the self-blocking of propagating shear bands by particles of the nanocrystalline phase that emerge due to a dissipative increase in the temperature along the front of shear bands are proposed for the delocalization of plastic flow.     

Influence of deformation on the structural transformation of the Pd<Subscript>40</Subscript>Ni<Subscript>40</Subscript>P<Subscript>20</Subscript> amorphous phase

The influence of plastic deformation on the structure of the Pd₄₀Ni₄₀P₂₀ amorphous alloy has been investigated using X-ray diffraction and measurements of the velocity of sound. It has been revealed that the rolling of the sample leads to a change in the structure of the amorphous phase (distortion of the first coordination sphere) and that the structural transformations are more pronounced in the near-surface region of the sample. The rolling also results in a decrease in the transverse velocity of sound. The observed effects decrease with time. It has been demonstrated that the revealed effects are associated with the inelastic deformation of the amorphous alloy.