Structure and mechanical properties of Ti-Al-Si-N protective coatings deposited from separated plasma of a vacuum arc

Protective coatings of the Ti-Al-Si-N system have been deposited from vacuum arc by sputtering a cathode of composition 78Ti-16Al-6Si in nitrogen. The coatings of the Ti-Al-Si-N system have been studied using X-ray diffraction analysis to examine phase compositions and substructure, atomic force microscopy to analyze the topography, X-ray fluorescence to define the chemical composition, and nanoindentation to measure hardness and elastic modulus. It has been found that as the nitrogen pressure in the deposition chamber increases, in the Ti-Al-Si-N system the transition from nanocrystalline (to 0.04 Pa) to nanocomposite (0.04–0.66 Pa) and X-ray amorphous (0.66–1.1 Pa) coatings takes place, and at a pressure of 2.7 Pa, the amount of the crystalline phase abruptly increases again. The highest mechanical characteristics and thermal stability have been shown by a coating having the nanocrystalline structure and nanocomposite coatings with a low content of amorphous phase, whose hardness attains 47 GPa.     

Nb–Al–N thin films: Structural transition from nanocrystalline solid solution nc-(Nb,Al)N into nanocomposite nc-(Nb,Al)N/a–AlN

Structures and mechanical properties of thin films of the Nb–Al–N system produced by magnetron sputtering of targets from niobium and aluminum in the Ar–N₂ atmosphere have been studied. It has been shown that as the aluminum concentration increases, the structure of a thin film transforms from the nanocrystalline into the nanocomposite one, which consists of nanocrystallites of solid solutions in a matrix of amorphous aluminum nitride. Hardness, elastic modulus, and yield strength of Nb–Al–N thin films have been studied by nanoindentation in the mode of continuous control of the contact stiffness. It has been found that the transition of the structures of Nb–Al–N thin films from the nanocrystalline to the nanocomposite structures results in an increase of hardness and decrease of elastic modulus due to the formation of a thin amorphous interlayer between grains of nanocrystallites. A high hardness to elastic modulus ratio of Nb–Al–N nanocomposite thin films indicates that the films are a promising material for wear-resistant coatings.     

Microstructural size effects on the hardness of nanocrystalline TiN/amorphous-SiNx coatings prepared by magnetron sputtering

It has been postulated that equiaxed nanocrystalline (<10 nm) TiN grains embedded in a thin amorphous silicon nitride (a-SiN_x) phase are a prerequisite to obtain ultrahard TiN/a-SiN_x coatings. The present study correlates hardness and microstructure of TiN/a-SiN_x coatings with Si contents between 0 and 17 at.%. The coatings have been deposited by magnetron sputtering in industrial-scale physical vapour deposition systems. Transmission electron microscopy studies revealed that increasing the silicon content causes the TiN grain size to decrease. This is accompanied by a change in grain morphology: At Si contents lower than 1 at.% TiN grains become columnar, while at Si contents higher than 6 at.% equiaxed grains with diameters of 6 nm form. For silicon contents between 1 and 6 at.%, a transition region with nanocrystalline columnar grains exists. This nanocrystalline columnar microstructure causes maximum hardness values of more than 45 GPa for TiN/a-SiN_x coatings as determined by nanoindentation. The elongated and equiaxed nanocrystalline TiN grains exhibit almost theoretical strength as dislocation-based deformation mechanisms are constrained.     

高速电弧喷涂FeAlNbB非晶纳米晶涂层的组织与性能

为了提高钢铁材料的耐磨性和硬度,利用高速电弧喷涂技术在45钢基体上制备了FeAlNbB非晶纳米晶涂层.采用扫描电镜(SEM)、能谱分析仪(EDAX),透射电镜(TEM)和X射线衍射仪等设备对涂层的组织结构和相组成进行了分析,研究了非晶纳米晶的形成机制.实验结果表明:FeAlNbB非晶纳米晶涂层是非晶相、α-Fe、FeAl纳米晶和Fe3Al微晶共存的多相组织,涂层中非晶相含量约36.2%,纳米晶尺寸约14.1 nm;涂层组织均匀,结构致密,平均孔隙率约2.3%;非晶纳米晶涂层具有较高的硬度,其耐磨性是相同实验条件下制备的3Cr13涂层的2.2倍.     

SiO2层晶化对TiN/SiO2纳米多层膜结构和性能的影响

采用多靶磁控溅射法制备了一系列具有不同SiO2调制层厚的TiN/SiO2纳米多层膜.利用X射线衍射、X射线能量色散谱、扫描电子显微镜、高分辨电子显微镜和微力学探针表征和研究了多层膜的生长结构和力学性能.结果表明,具有适当厚度(0.45～0.9 nm)的SiO2调制层,在溅射条件下通常为非晶态,在TiN层的模板作用下晶化并与TiN层共格外延生长,形成具有强烈(111)织构的超晶格柱状晶多层膜;与此相应,纳米多层膜产生了硬度和弹性模量异常增高的超硬效应(最高硬度达45 GPa).随着SiO2层厚度的继续增加,SiO2层转变为非晶态,阻断了多层膜的共格外延生长,使纳米多层膜形成非晶SiO2层和纳米晶TiN层的多层结构,多层膜的硬度和弹性模量逐渐下降.     

Lamp processing- and heat treatment-induced structural transformations of an amorphous Al<Subscript>85</Subscript>Ni<Subscript>10</Subscript>La<Subscript>5</Subscript> alloy: Hardness and local plasticity

We have studied the structural transformations and deformation behavior of an amorphous Al₈₅Ni₁₀La₅ alloy during nanoindentation and uniaxial tension tests and assessed the influence of crystalline phases resulting from lamp processing and heat treatment. Our results confirm the high effectiveness of lamp processing: at identical phase compositions, the lamp processing time is shorter by more than two orders of magnitude. The microplasticity of the amorphous alloy has been shown to manifest itself in both nanoindentation and uniaxial tension tests. The high proportion of local plasticity in the work of indentation has been accounted for in terms of possible intercluster sliding. The observed lamp processing- and heat treatmentinduced changes in the hardness of the alloy reflect changes in its phase composition and the percentages of the amorphous and crystalline phases, which does not rule out a cluster mechanism of local deformation or its deceleration by nanocrystalline phases in the amorphous–nanocrystalline structure.     

Influence of multi-interfacial structure on mechanical and tribological properties of TiSiN/Ag multilayer coatings

The TiSiN/Ag multilayer coatings with bilayer periods of ~50, 65, 80, 115, 150, and 410 nm have been deposited on Ti6Al4 V alloy by arc ion plating. In order to improve the adhesion of the TiSiN/Ag multilayer coatings, TiN buffer layer was first deposited on titanium alloy. The multi-interfacial TiSiN/Ag layers possess alternating TiSiN and Ag layers. The TiSiN layers display a typical nanocrystalline/amorphous microstructure, with nanocrystalline TiN and amorphous Si₃N₄. TiN nanocrystallites embed in amorphous Si₃N₄ matrix exhibiting a fine-grained crystalline structure. The Ag layers exhibit ductile nanocrystalline metallic silver. The coatings appear to be a strong TiN (200)-preferred orientation for fiber texture growth. Moreover, the grain size of TiN decreases with the decrease of the bilayer periods. Evidence concluded from transmission electron microscopy revealed that multi-interfacial structures effectively limit continuous growth of single (200)-preferred orientation coarse columnar TiN crystals. The hardness of the coatings increases with the decreasing bilayer periods. Multi-interface can act as a lubricant, effectively hinder the cracks propagation and prevent aggressive seawater from permeating to substrate through the micro-pores to some extent, reducing the friction coefficient and wear rates. It was found that the TiSiN/Ag multilayer coating with a bilayer period of 50 nm shows an excellent wear resistance due to the fine grain size, high hardness, and silver-lubricated transfer films formed during wear tests.     

Effect of the high doze of N<Superscript>+</Superscript>(10<Superscript>18</Superscript> cm<Superscript>–2</Superscript>) ions implantation into the (TiHfZrVNbTa)N nanostructured coating on its microstructure,elemental and phase compositions,and physico-mechanical properties

Structure and properties of (TiHfZrVNbTa)N nanostructured multicomponent coatings implanted with a very high (10¹⁸ cm^–2) dose of N⁺ions have been studied. As a result of the implantation a multilayer structure has been formed in the surface layer of the coating. The structure is composed of amorphous, nanocrystalline (disperse) and nanostructured (with the initial sizes) nanolayers. In the depth of the coating two phases (with the fcc and hcp structures) having a small volume content are formed. The nitrogen concentration near the surface attains 90 at % and then decreases with the depth. In the initial state after the deposition the coating nanohardness values are from 27 to 34 GPa depending on the conditions of the deposition. As a result of the implantation the hardness is decreased approximately by the depth of the projective ions range, i.e., to 12 GPa and then increases with the depth to 23 GPa. The investigations were conducted using the Rutherford backscattering, scanning electron microscopy with the microanalysis, high resolution electron microscopy (with local microanalysis), X-ray diffraction, nanoindentation, and wear tests.     

Study of (Zr,Ti)CN, (Zr,Hf)CN and (Zr,Nb)CN films prepared by reactive magnetron sputtering

(Zr,Ti)CN, (Zr,Hf)CN and (Zr,Nb)CN coatings, in which Ti, Hf and Nb were added to ZrCN base compound, have been prepared by reactive magnetron sputtering. The coatings, with two different non-metal/metal ratios, were comparatively investigated in terms of elemental and phase composition, texture, surface morphology, hardness and friction performance. It has been shown that the films exhibit nanocomposite structures, consisting of a mixture of crystalline metal carbonitride and amorphous carbon. As compared with ternary ZrCN coatings, the quaternary coatings were found to exhibit superior mechanical and friction characteristics. In general, the films with higher non-metal content revealed finer morphologies, higher hardness and lower friction coefficient. Depending on the coating type and non-metal/metal ratio, the hardness values ranged from about 21 to 29 GPa, being higher than those of ZrCN reference films. The coefficients of friction varied from 0.2 to 0.5, the lowest values being obtained for the coatings with the highest non-metal content.     

射频反应溅射(Al,Ti)N涂层的微结构与力学性能

采用Al-Ti镶嵌复合靶在不同氮分压下制备了一系列(Al,Ti)N涂层,并采用EDS,AFM,XRD,TEM和微力学探针表征了涂层的沉积速率、化学成分、微结构和力学性能,研究了氮分压对涂层的影响.结果表明,氮分压对(Al,Ti)N涂层影响显著:合适的氮分压可以得到化学计量比的(Al,Ti)N涂层,涂层为单相组织,并呈现(111)择优取向,最高硬度和弹性模量分别达到36.9GPa和476GPa.过低的氮分压不但会造成涂层贫氮,而且涂层中的Al含量偏低,硬度不高.氮分压过高,由于存在"靶中毒"现象,尽管涂层的成分无明显变化,但会大大降低其沉积速率,并使涂层形成纳米晶或非晶态结构,涂层的硬度也较低.     

Nanoindentation studies on amorphous, nanoquasicrystalline and nanocrystalline Zr8oPt2o and Zr75Pd25 alloys

Nanoindentation studies on rapidly solidified Zr80Pt20 and Zr75Pd25 binary alloys with nanocrystalline, nanoquasicrystalline, and amorphous microstructures are reported. The results indicate that the hardness and elastic modulus are the highest for a mixture of amorphous and nanoquasicrystalline state among the various microstructures studied. Nanoquasicrystalline phase has high hardness and elastic modulus in comparison to amorphous and nanocrystalline phases. The hardness to modulus ratio is close to 0.1 in both the alloys, irrespective of the phase/phase mixture studied indicating that the bonding in these alloys is of covalent nature. In Zr80Pt20, all the phases/phase mixtures have higher hardness and modulus in comparison to similar microstructures in Zr75Pd25 due to higher bond energies caused by more negative heat of mixing in the former case.     

Hard plasmachemical a-SiCN coatings

The amorphous SiCN coatings have been plasmachemically (PECVD) deposited onto silicon substrates using the heksamethyldisylazan as the basic precursor. The effect of the deposition temperature on the structure, chemical composition, and mechanical properties of the coatings has been studied. It has been found that at temperatures below 400°C the deposition of hydrogenated amorphous SiCN (a-SiCN:H) coatings, whose hardness does not exceed 23 GPa, takes place. At the further increase of the temperature the distribution of the Si–C, Si–N, and C–N strong bonds in coatings does not practically change, while the number of C–H, Si–H and N–H weak hydrogen bonds decreases. As a result of such a redistribution of chemical bonds, at the temperature 600–700°C a-SiCN coatings are deposited with hardness up to 32 GPa. The annealing in vacuum at 1200°C is shown not to noticeably affect the structure, hardness, and elastic modulus of a-SiCN coatings.     

Investigation of Galvanic Chromous Structures

X-ray methods have been used to study the structure of galvanic chromous coatings, which were deposited by chrome acid electrolytes with different additions. The possibility of producing crystalline and amorphous chromous deposits has been established using x-rays. The influence of thermo-processing on the structure and some mechanical characteristics of coatings were investigated. It was shown that during the process of heating, the hardness of crystalline deposits reduced dramatically at about 400^°C. At the same time it was observed that the hardness of amorphous deposits increased significantly.     

Fabrication of nano-structured HA/CNT coatings on Ti6Al4V by electrophoretic deposition for biomedical applications

In order to improve the bone bioactivity and osteointegration of metallic implants, hydroxyapatite (HA) is often coated on their surface so that a real bond with the surrounding bone tissue can be formed. In the present study, cathodic electrophoretic deposition (EPD) has been attempted for depositing nanostructured HA coatings on titanium alloy Ti6Al4V followed by sintering at 800 degrees C. Nano-sized HA powder was used in the EPD process to produce dense coatings. Moreover, multiwalled carbon nanotubes (CNTs) were also used to reinforce the HA coating for enhancing its mechanical strength. The surface morphology, compositions and microstructure of the monolithic coating of HA and nanocomposite coatings of HA with different CNT contents (4 to 25%) on Ti6Al4V were investigated by scanning-electron microscopy, energy-dispersive X-ray spectroscopy and Xray diffractometry, respectively. Electrochemical corrosion behavior of the various coatings in Hanks' solution at 37 degrees C was investigated by means of open-circuit potential measurement and cyclic potentiodynamic polarization tests. Surface hardness, adhesion strength and bone bioactivity of the coatings were also studied. The HA and HA/CNT coatings had a thickness of about 10 microm, with corrosion resistance higher than that of the substrate and adhesion strength higher than that of plasma sprayed HA coating. The properties of the composite coatings were optimized by varying the CNT contents. The enhanced properties could be attributed to the use of nano-sized HA particles and CNTs. Compared with the monolithic HA coating, the CNT-reinforced HA coating markedly increased the coating hardness without deteriorating the corrosion resistance or adhesion strength.     

Solid nanocrystalline fullerite-containing carbon coatings

Solid carbon coatings with a high content of nanocrystalline fullerite have been obtained using unbalanced magnetron sputtering of graphite under conditions of pulsed high-voltage ion bombardment of the film growing on a substrate. It is established that samples possessing the maximum hardness (18.8 GPa) are characterized by maximum values of the volume fraction of fullerite in the coating (50%), coherent scattering domain size (53 nm), degree of preferred grain orientation (85%), relative deformation of the lattice (1.02%), and internal compressive stresses (2.91 GPa). The observed behavior is consistent with the mechanism of strengthening that accounts for the phenomenon of superhardness in nanocrystalline and nanocomposite materials. This assumption is confirmed by the results of investigation of the morphology of growing coatings.     

等离子熔覆铁基非晶纳米晶复合涂层及其性能

利用等离子熔覆技术在A3钢表面制备了一层与基体呈冶金结合的、性能良好的非晶纳米晶复合涂层.涂层有非晶相和纳米相组成,根据衍射峰的半高宽,计算出铁基涂层中平均晶粒尺寸为22～24nm.对涂层进行XRD、SEM、EDS、TEM和DSC分析,并利用显微硬度计和电化学工作站研究涂层的硬度和耐蚀性能,研究表明所制备的铁基涂层具有良好的性能.     

Fabrication and evaluation of SixNy coatings for total joint replacements

Wear particles from the bearing surfaces of joint implants are one of the main limiting factors for total implant longevity. Si(3)N(4) is a potential wear resistant alternative for total joint replacements. In this study, Si(x)N(y)-coatings were deposited on cobalt chromium-discs and Si-wafers by a physical vapour deposition process. The tribological properties, as well as surface appearance, chemical composition, phase composition, structure and hardness of these coatings were analysed. The coatings were found to be amorphous or nanocrystalline, with a hardness and coefficient of friction against Si(3)N(4) similar to that found for bulk Si(3)N(4). The low wear rate of the coatings indicates that they have a potential as bearing surfaces of joint replacements. The adhesion to the substrates remains to be improved.     

Mikrostruktur und Eigenschaften lichtbogengespritzter Schichten auf Eisenbasis

Microstructure and properties of Fe‐based wire arc sprayed coatings Innovative iron based feedstocks for wire arc spraying are a promising alternative for conventional carbide reinforced feedstocks for wear applications. Recently the main area of research is focused on improving the properties of deposited functional coatings by varying the wire composition. The influence on the crystalline structure and the dimension of the hard phases in the resulting microstructure is of particular interest in this context. The objective of the investigation is to produce coatings with an amorphous phase, submicron and nanocrystalline structure. The forming of the amorphous phase is influenced by high cooling rates of the molten and partly molten particles impinging on the substrate. Thus, the achieved coatings are characterized by high hardness as well as high corrosion and wear resistance. The present paper introduces iron based coatings produced by wire arc spraying. Due to the application of cored wires with a modified alloy composition the forming of an amorphous phase as well as a submicron‐ and nanocrystalline structure is promoted. The filling of the cored wires are based on FeB with a eutectic composition and is varied by adding Cr₃C₂, FeSi, FeCrC and AlMg. The adding of further elements like Cr, C, Si, Al and Mg should improve the forming of the amorphous phase. The deposited coatings are analyzed regarding to the resulting coating properties and phase composition in connection with the composition of the cored wires. XRD‐analysis’ proved that the Fe‐based coatings contain an amorphous phase.     

Nanostructure transition in Cr-C-N coatings deposited by pulsed closed field unbalanced magnetron sputtering

Cr-C-N coatings with different compositions, i.e. (C + N)/Cr atomic ratios (x) of 0.81-2.77, were deposited using pulsed closed field unbalanced magnetron sputtering by varying the chromium and graphite target powers, the pulse configuration and the ratio of the nitrogen flow rate to the total gas flow rate. Three kinds of nanostructures were identified in the Cr-C-N coatings dependent on the x values: a nano-columnar structure of hexagonal closed-packed (hcp) Cr₂(C,N) and face-centered cubic (fcc) Cr(C,N) at x = 0.81 and 1.03 respectively, a nanocomposite structure consisting of nanocrystalline Cr(C,N) embedded in an amorphous C(N) matrix at x = 1.26 and 1.78, and a Cr-containing amorphous C(N) structure at x = 2.77. A maximum hardness of 31.0 GPa and a high H/E ratio of 1.0 have been achieved in the nc-Cr(C,N)/a-C(N) nanocomposite structure at x = 1.26, whereas the coating with a Cr-containing amorphous C(N) structure had a minimum hardness of 10.9 GPa and a low H/E ratio of 0.08 at x = 2.77. The incorporation of carbon into the Cr-N coatings led to a phase transition from hcp-Cr₂(C,N) to fcc-Cr(C,N) by the dissolution into the nanocrystallites, and promoted the amorphization of Cr-C-N coatings with the precipitation of amorphous C(N). It was found that a high x value over 1.0 in the Cr-C-N coatings is the composition threshold to the nanostructure transition.     

Structure,composition, and mechanical properties of thin films of transition metals diborides

The effect of the deposition conditions on the structure, composition, and mechanical properties of thin films of diborides of transition metals that have been produced by high frequency magnetron sputtering. It has been shown that depending on the applied bias voltage and substrate temperature coatings of various structures are formed: from amorphous-like to nanocrystalline. Under the optimal energy conditions (bias voltage 50 V and substrate temperature 500°C) superstoichiometric thin films of transition metals diborides of grain sizes 20–30 nm, hardness 44 GPa, and anomalously high recovering of the imprint depth have been produced.