Crystallography of magnetron sputtered TiN coatings on steel substrates

Structure formation processes in TiN coatings deposited by reactive CFUBMS on steel substrates have been investigated by X-ray diffraction experiments in symmetric Bragg-Brentano (B-B) and grazing incidence asymmetric Bragg diffraction (GIABD) modes and by SEM. The results show that the deposits with thicknesses of 500 and 4000 nm are built-up of polycrystalline stoichiometric TiN, in addition to which, some negligible amount of Ti-O and Ti-N-O phases have also been observed predominantly at their surfaces. In the thinner 500 nm films only columnar crystallites with {1 1 1}, {2 0 0} and {2 2 0} crystallographic planes parallel to the surface were formed. The share of the micro-volumes belonging to the 〈1 1 1〉 out-of-plane texture component varied between 70% and 80% depending on the target current (I_d) used (4 or 8 A in the present experiments). During the more advanced stages of growth the 〈1 1 1〉 texture weakens and new texture components appear; the process being more pronounced when the application has been performed at higher I_d values. The obtained crystallographic texture results for the thinner films and their changes during the more advanced stages of the coatings formation are discussed with particular consideration of the crystallography of the TiN lattice and the anisotropy of its elastic parameters. Based on a precise estimation of the interplanar distances, d_{〈u v w〉}, corresponding to the main texture components of the investigated films in the direction along the surface macro-normal, it has been revealed that the elastic strain, ε_{〈u v w〉}, caused by the compressive residual macro-stresses acting parallel to the film surfaces and the corresponding elastic stored energy, U_{〈u v w〉}, values obey the following relationships: ε_{〈1 1 1〉}>ε_{〈2 2 0〉}> ε_{〈2 0 0〉} and U_{〈1 1 1〉}>U_{〈2 2 0〉}>U_{〈2 0 0〉}, respectively. The observed ε_{〈u v w〉} and U_{〈u v w〉} anisotropy is found to be more pronounced in the thinner coatings and is such that, at more advanced stages of growth, it would be expected to favour the transition from 〈1 1 1〉 to 〈2 0 0〉 out-of-plane preferred orientation. However, the experimental results do not confirm this expectation, which points out that the texture-formation at these stages is not governed solely by the minimization of the stored elastic energy, but is a rather complicated process depending on a larger number of factors, some of which are discussed in the paper.     

Wear resistance of TiN coatings implanted with Al and N ions

Titanium nitride (TiN) coatings were prepared on HS 6-5-2 high-speed steel cutting inserts and next implanted either with Al ions (fluence 2×10¹⁷ ions/cm²) or with Al and N ions (fluence (1+1)×10¹⁷ ions/cm²) on the rake face. Microhardness and friction coefficient of the implanted surfaces were examined. A noticeable increase of microhardness in Al implanted inserts has been observed.The elemental composition and structural properties of the surface layer were examined by glow discharge optical emission spectroscopy (GDOES) and gliding angle X-ray diffraction (XRD).The tests of turning of 40 H constructional steel with the cutting inserts have shown an improvement in the implanted inserts, especially marked in those implanted with Al+N.     

Characterization of deep level defects in Si irradiated with MeV Ar+ ions using constant capacitance time analyzed transient spectroscopy

An isothermal spectroscopic technique called time analyzed transient spectroscopy (TATS) in the constant capacitance (CC) mode has been used to characterize electrically active defects in the MeV Ar⁺ implanted silicon. The problems associated with high defect density and the presence of damaged region in the as-implanted material are overcome by CC-TATS method. The CC-TATS spectra of the as-implanted sample shows two positive peaks and an attendant negative peak. Two distinct traps have also been identified using thermally stimulated capacitance method modified to operate in constant capacitance mode. Variable pulse width measurements using CC-TATS show exponential capture kinetics in contrast to extremely slow capture observed in conventional deep level transient spectroscopy (DLTS) experiment. The results indicate that trapping behaviour is due to point-like defects associated with extended defects such as dislocation and stacking fault.     

Structural and noise characterization of VO2 films on SiO2/Si substrates

Multi-technique structural and electrophysical investigations of VO₂ films on SiO₂/Si substrates are carried out to study the microscopic nature of fluctuator defects — sources of lowfrequency flicker noise. It is established that the noise intensity is determined by the magnitude of the microstress fluctuations 〈ε 〉={〈(δc/c)²〉}, where c is the lattice parameter along the c-axis parallel to [011] direction in the blocks of which the film is formed. The dimensions of the blocks were determined in the direction of the c-axis (t _c∼1000 Å). The suggestion is put forward that the samples contain two types of fluctuator defects: 1) V atoms jumping between the two nearest interstitial sites and 2) V atoms jumping between these interstitial sites near lattice defects. Pis’ma Zh. Tekh. Fiz. 23, 58–65 (July 12, 1997)     

X射线测量高速钢上不同厚度氮化钛涂层残余应力

采用多弧离子镀在AISIM2高速钢(HSS)上沉积了TiN硬涂层,试样中基体厚度为1mm,涂层厚度分别为3.0、5.0、7.0、9.0和11.0μm.应用X射线衍射(XRD)分析了TiN涂层中残余应力,测量了TiN(220)衍射晶面在五种不同倾斜角(Ψ=0°,20.7°,30°,37.8°和45°)下的X射线衍射峰.结果表明:在3～11μm涂层厚度范围内,TiN涂层中均表现出残余压应力且残余压应力值较大.TiN涂层中残余应力大致分布在-3.22～-2.04GPa之间,本征应力分布在-1.32～-0.14GPa,热应力约为-1.86～-1.75GPa.TiN涂层中残余应力值随涂层厚度变化是非线性增加的,随厚度增加表现出先增大后减小的变化趋势,多项式拟合后发现约在8.5μm厚时残余应力达到最大值.     

The effects of pre-implantation of steel substrates on the structural properties of TiN coatings

We have studied the effects of nitrogen pre-implantation of AISI C1045 steel substrates on the microstructure and microhardness of deposited TiN coatings. The substrates were implanted at 40 keV, to the fluences from 5 × 10¹⁶ to 5 × 10¹⁷ ions/cm², which was followed by deposition of 1.3-μm thick TiN coatings by reactive sputtering. Structural characterization of the samples was performed by standard and grazing incidence X-ray diffraction analysis, Rutherford backscattering spectroscopy and transmission electron microscopy. Microhardness was measured by the Vicker’s method. Nitrogen implantation up to 2 × 10¹⁷ ions/cm² induces the formation of Fe₂N phase in the near surface region of the substrates, which becomes more pronounced for higher fluences. Microstructure of the deposited TiN coatings shows a strong dependence on ion beam pre-treatment of the substrates. The layers grown on non-implanted substrates have a (200) TiN preferential orientation, and those grown on implanted substrates have (111) TiN preferential orientation. The change in preferred orientation of the layers is assigned to a developed surface topography of the substrates induced by ion implantation, and possible effects of distorted and altered crystalline structure at the surface. Ion implantation and deposition of TiN coatings induce an increase of microhardness of this low performance steel for more than eight times.     

Structural characterization of plasma-sprayed hydroxylapatite coatings

Plasma-sprayed hydroxylapatite coatings, widely used on metallic surgical implants to improve their adhesion to bone, are formed by rapid quenching of molten, or partly molten, particles which impact the substrate at high velocity. the performance of these coatings in the body depends upon their structure, which is not well understood. Coatings prepared under a range of spraying conditions have been studied by X-ray diffraction (XRD). differential thermal analysis (DTA), thermogravimetric analysis (TGA) and solid-state nuclear magnetic resonance spectroscopy (NMR). The results suggest that particles partly melt and lose combined water at lower plasma torch input powers forming a glass, by quenching of the liquid phase, and an OH-depleted hydroxylapatite residual crystalline phase. At higher power inputs an increasing amount of P₂O₅ is also lost and the coatings contain CaO and Ca₄P₂O₉. Heat treatment of coatings in air at 600°C results in crystallization of the glass phase and reaction with water vapour to form hydroxylapatite. The results show that XRD is relatively insensitive to some of the structural details of hydroxylapatite coatings which may be significant to their performance. NMR provides more structural information and is a significant tool for coating characterization.Sadly Professor McPherson died after completing this paper. He made a distinctive contribution to the fields of ceramics and thermal spraying and will be missed by the international community.     

Si(100)衬底上激光分子束外延制备高质量TiN薄膜

采用激光分子束外延(LMBE)技术在Si(100)上制备了高质量的TiN薄膜.对N2分压和激光脉冲能量对TiN薄膜晶体结构、生长模式和表面形貌影响的研究表明,TiN单晶薄膜呈(200)择优取向,在N2分压为10-1 Pa时,薄膜的结晶度高且表面平整致密.随着N2分压的增加,TiN(200)衍射峰向低角度移动.激光脉冲能...     

Hetero-epitaxy and structure characterization of Si films on 6H-SiC substrates

In order to realize the non-ultraviolet application of SiC optoelectronic devices, Si/6H-SiC heterojunctions were prepared by the low-pressure chemical vapour deposition at 850 °C. The X-ray diffraction (XRD) and the selected area electron diffraction (SAED) results indicate that Si thin films have a monocrystalline structure and were grown along the (111) crystal plane. The rationality of the (111) growth plane was also analyzed by the theoretical calculation. High-density structural defects such as stacking faults and twins were observed on Si films by the high-resolution transmission electron microscopy. This phenomenon was also validated by the SAED patterns of defect-rich regions on Si films.     

Structural characterization of thin amorphous Si films

We present a study of structural changes occurring in thin amorphous silicon (a-Si). The a-Si films were deposited on single-crystalline Si substrates held at room temperature or 200 °C by magnetron sputtering of a Si target in pure Ar atmosphere, and therefore the films were hydrogen-free. All samples were annealed in vacuum and subsequently studied by EPR and GISAXS. A strong decrease in the dangling bonds content at lower annealing temperatures, and then an increase of it at around 550 °C, suggested significant structural changes. In parallel the samples were studied by GISAXS which confirmed changes at the nanometric scale attributed to voids in the material. A nice correlation of the results of the two techniques shows advantages of this approach in the analysis of structural changes in a-Si material.     

Contact damage in TiN coatings on steel

Damage mechanisms beneath Vickers indentations are examined on 5 μm TiN film deposited on stainless steel substrate as a function of load. Prominent mode of cracking includes surface edge cracks and subsurface inclined cracks. No interfacial delaminations were noted at the TiN/steel interface. The tangential traction, radial stress and shear stress distribution around an axisymmetric indentation field are used to assess the driving force for crack propagation.     

Irradiation effects in MgF2 coatings on Si and GaAs substrates

Heavy-particle irradiation effects have been investigated as a potential method for inducing ion-beam mixing and thereby improving the adhesion between a thin-film MgF₂ anti-reflection coating and substrates with optical or electro-optical applications. The nature of the ion-beam-induced alterations of MgF₂ films deposited on Si or GaAs substrates and subsequently irradiated with 210 keV Xe⁺ ions was studied using Rutherford backscattering and scanning electron microscopy. The results are compared with those obtained in previous studies of MgF₂ films deposited on LiF substrates.     

Structural and textural characterization of LiFePO4 thin films prepared by pulsed laser deposition on Si substrates

LiFePO₄ thin films were grown on silicon (100) substrates by pulsed laser deposition using Traditional Geometry (TG) and Off-Axis Geometry (OAG) deposition chambers. We examined and compared the structure and composition of the so formed thin films. The nails observed on the OAG-film present an amorphous “body” and a crystallized “head”. The Fe/P ratio determined using energy dispersive spectrometry combined with high angle annular dark field images reveals a metallic iron heart surrounded by LiFePO₄ shell. On the other hand, the protuberances on TG-film are pure iron. The focused ion beam prepared cross-section of the film suggests the presence of iron particles and iron dendritic like filaments inside the LiFePO₄ layer.     

Improvement of microstructural and mechanical properties of plasma sprayed Mo coatings deposited on Al-Si substrates by pre-mixing of Mo with TiN powder

The present work embodies development of a new class of mechanically improved Mo-TiN coating material using plasma spray technique. The coatings are developed on Al-Si alloy at different torch input power levels ranging from 15 kW to 30 kW. Pre-mixing of TiN with molybdenum enhances adhesion strength and hardness of the coatings. Maximum adhesion strength of 22 MPa (±0.75) and hardness of 748 HV (±30) are found for the coating when molybdenum is pre-mixed with 10% TiN. FESEM micrographs of the as-sprayed coatings showed formation of plate-like structures of splats which indicates TiN sites as reinforcement in Mo matrix. X-ray diffraction study reveals the formation of both MoO2 and TiN as minor phases in the coating microstructure. The significant enhancement of mechanical properties like adhesion strength and hardness is attributed towards the presence of these phases.     

The erosion behaviour of TiN coatings on steels

The erosion behaviour of physical vapour-deposited titanium nitride has been studied using both blunt particle and angular particle erodent streams. The mechanisms of erosive loss have been identified and related to the microstructure and internal stress state of the coatings. High levels of internally stored energy (which scales with coating thickness and internal stress) induce spalling in erosion testing using blunt erodents. Consequently, it is found that thick coatings are more resistant to angular particle erosion whilst thin coatings have longer lifetimes when exposed to blunt erodents. Scratch adhesion testing has been performed on all erosion specimens and attempts made to correlate the critical load for coating failure, with the failure mechanisms observed in erosive wear. Whilst no correlation can be found between erosion resistance and critical load, good correlations between the failure mechanisms found in erosion and scratch testing can be made.     

Structural properties of swift heavy ion beam irradiated Fe/Si bilayers

The Fe/Si multilayers were prepared by electron beam evaporation in a cryo-pumped vacuum deposition system. Ag⁺ and Au⁺ ions of 100 MeV at two different fluencies such as 1 × 10¹² ions/cm² and 1 × 10¹³ ions/cm² at a pressure of 10^− 7 torr were used to irradiate the Fe/Si samples. The irradiated samples were analyzed by High-Resolution XRD and it reveals that the irradiated films are having polycrystalline nature and it confirms the formation of the β-FeSi₂. The structural parameters such as crystallite size (D), strain (ε) and dislocation density (δ) have been evaluated from the XRD spectrum. The role of the substrates and the influence of swift heavy ions on the formation of β-FeSi₂ have been discussed in this paper.     

Structural characterization of basalt-based glass–ceramic coatings

There are a lot of technologically interesting characteristics of glass–ceramics, which are hard, wear resistant, oxidation and corrosion resistant ceramic materials. In the present study, the production of the basalt-based glass–ceramic coating by atmospheric plasma spray technique and their structural characterization were reported. Basalt-based glass coating was performed on AISI 1040 steel substrate which was pre-coated with Ni–5 wt% Al by using plasma spray gun. Basalt coatings of the glass form were crystallized at 800, 900 and 1000 °C for 1–4 h in orders to transform to the glass–ceramic structure. The presence of augite [(CaFeMg)SiO₃], diopside [Ca(Mg_0.15Fe_0.85)(SiO₃)₂] and aluminian diopside [Ca(Mg,Al)(Si,Al)₂O₆] crystalline phases formed in the basalt-based glass–ceramic coating layer was detected by X-ray diffraction analysis. Optical microscopy with micrometer was used for metallographic examinations. Differential scanning calorimeter was used for determining the crystallization temperature of glass form basalt-based coatings. Microhardness measurements were carried out on the basalt-based glass–ceramic coating layer with Vickers indenter. The hardness of coating layers is changing between 1009 and 1295 HV_0.05 depending on crystallization temperature and process times. It was found that, the higher the crystallization temperature, the more the crystalline phases were resulted. In addition, the lower the crystallization temperature and the longer the treatment time, the harder the coating layer became.     

Intrinsic toughness of interfaces between SiC coatings and substrates of Si or C fibre

The critical energy release rate for separation of SiC coatings from single crystal Si substrates or surfaces of carbon fibres, along their well-defined interfaces can be determined quite accurately from analysis of the spontaneous delamination of coatings under bi-axial stress, when such coatings exceed a critical thickness. Direct evaluations have been made of the specific work of delamination along the interface for SiC coatings from single crystal Si substrates, for both the case of coatings under bi-axial compression, as well as under bi-axial tension. The critical energy release rate for coatings in tension was 5.1 J m², and that for coatings under compression was 5.9 J m². The higher value of the latter is attributed to relative slippage between coating and substrate before lift-off of the former. Corresponding determination of the critical energy release rate for delamination of SiC coatings under bi-axial tension from surfaces of anisotropic Pitch-55 carbon fibres gave an answer of 5.5 J m². These values compare very well with expectations from surface energies of strong solids.     

Characterization of tribo-layers on self-lubricating plasma-assisted chemical-vapor-deposited TiN coatings

Recently, several new solid lubricants and modern lubrication concepts have been developed to achieve lower friction and wear and thus longer lifetime in severe tribological applications. The aim of this study is to characterize tribo-layers formed during ball-on-disc testing on low-friction, Cl-containing TiN coatings deposited by plasma assisted chemical vapor deposition and to clarify their formation mechanism. Characterization of the transfer layers was done by optical microscopy, optical profilometry, Raman spectroscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. Differential scanning calorimetry was used to provide information on the chlorine-influenced chemical reactions of the coatings in ambient air. Iron oxide layers of a thickness in the nm-range have been found on low-chlorine containing TiN coatings (<3 at.% Cl) showing friction coefficients of approximately 0.8, whereas on TiN coatings with higher chlorine contents (>3 at.% Cl) rutile layers were preferably formed, resulting in friction coefficients below 0.2. This self-lubrication mechanism can be explained by the in-situ formation of easy-shearable titanium oxides in the contact zone in the presence of humidity and oxygen.