A study of the nanostructure and hardness of electron beam evaporated TiAlBN Coatings

TiAlBN coatings have been deposited by electron beam (EB) evaporation from a single TiAlBN material source onto AISI 316 stainless steel substrates at a temperature of 450 °C and substrate bias of − 100 V. The stoichiometry and nanostructure have been studied by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. The hardness and elastic modulus were determined by nanoindentation. Five coatings have been deposited, three from hot-pressed TiAlBN material and two from hot isostatically pressed (HIPped) material. The coatings deposited from the hot-pressed material exhibited a nanocomposite nc-(Ti,Al)N/a-BN/a-(Ti,Al)B₂ structure, the relative phase fraction being consistent with that predicted by the equilibrium Ti-B-N phase diagram. Nanoindentation hardness values were in the range of 22 to 32 GPa. Using the HIPped material, coating (Ti,Al)B_0.29N_0.46 was found to have a phase composition of 72-79 mol.% nc-(Ti,Al)(N,B)_1 − x+ 21-28 mol.% amorphous titanium boride and a hardness of 32 GPa. The second coating, (Ti,Al)B_0.66N_0.25, was X-ray amorphous with a nitride+boride multiphase composition and a hardness of 26 GPa. The nanostructure and structure-property relationships of all coatings are discussed in detail. Comparisons are made between the single-EB coatings deposited in this work and previously deposited twin-EB coatings. Twin-EB deposition gives rise to lower adatom mobilities, leading to (111) (Ti,Al)N preferential orientation, smaller grain sizes, less dense coatings and lower hardnesses.     

Influence of composition and processing parameters on mechanical properties and erosion response of Ni–TiB2 coatings

Abstract

Sputtered Ni–TiB₂ coatings have been shown to protect Ti–6Al–4V and Inconel 718 substrates from solid particle erosion. However, before new erosion resistant coatings can be efficiently designed, it is essential that the role of mechanical properties in determining erosion resistance be fully understood. In this investigation, nanoindentation techniques were used to quantify the effects of substrate preparation, coating composition, and sputtering process parameters on the elastic moduli and indentation hardness of thin coatings deposited on Ti–6Al–4V and Inconel 718 substrates. The influence of these parameters on coating adhesion was determined using a conventional scratch test. Elastic moduli, indentation hardnesses, and coating adhesion were correlated with erosion behaviour. The erosion resistance of the coatings that exhibited microscopic ductility is dependent on the nodule diameter and coating properties such as hardness, elastic modulus, and fracture toughness.

MST/1697     

Measurement of mechanical properties of multilayer coatings by nanoindentation

Abstract

Multilayer protective coatings of alternate aluminium and titanium diboride TiB₂ layers have been tested by nanoindentation to measure both hardness and Young's modulus values. The initial results show that the values obtained depend upon the depth of indentation. An alternative view is presented to show that by considering the percentage of each coating in contact with the indenter a single relationship between either hardness or Young's modulus and the amount of aluminium layer penetrated can be produced. This technique allows the influence of the percentage ceramic on the results obtained to be identified. Comparison of the nanoindentation results with three point bending tests show how the coating structure influences the results obtained.     

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride coatings

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride (CN_x) coatings are investigated. CN_x coatings are fabricated by a hybrid coating process with the combination of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and DC magnetron sputtering at various substrate bias voltage and target sputtering power in the order of −400 V 200 W, −400 V 100 W, −800 V 200 W, and −800 V 100 W. The deposition rate, N/C atomic ratio, and hardness of CN_x coatings as well as friction coefficient of CN_x coating sliding against AISI 52100 pin in N₂ gas stream decrease, while the residual stress of CN_x coatings increases with the increase of substrate bias voltage and the decrease of target sputtering power. The highest hardness measured under single stiffness mode of 15.0 GPa and lowest residual stress of 3.7 GPa of CN_x coatings are obtained at −400 V 200 W, whereas the lowest friction coefficient of 0.12 of CN_x coatings is achieved at −800 V 100 W. Raman and XPS analysis suggest that sp³ carbon bonding decreases and sp² carbon bonding increases with the variations in substrate bias voltage and target sputtering power. Optical images and Raman characterization of worn surfaces confirm that the friction behavior of CN_x coatings is controlled by the directly sliding between CN_x coating and steel pin. Therefore, the reduction of friction coefficient is attributed to the decrease of sp³ carbon bonding in the CN_x coating. It is concluded that substrate bias voltage and target sputtering power are effective parameters for tailoring the structural and tribological properties of CN_x coatings.     

Cr1−xAlxN coatings deposited by lateral rotating cathode arc for high speed machining applications

In this work, a series of Cr_1−xAl_xN (0 ≤ x ≤ 0.7) coatings were deposited on high speed steel substrates by a vacuum arc reactive deposition process from two lateral rotating elemental chromium and aluminum cathodes in a flowing pure nitrogen atmosphere. The composition, structural, mechanical, and tribological properties of the as-deposited coatings were systematically characterized by energy dispersive analysis of X-rays, X-ray diffraction, nanoindentation, and ball-on-disc tribometer experiments. All of the as-deposited CrAlN coatings exhibited a higher hardness than CrN, showing a maximum hardness of about 40 GPa (at around X = 0.63) which is twice higher than that of the CrN. The wear performance under ambient conditions of the CrAlN coatings was found much better, with both lower friction coefficient and wear rate, than TiAlN coatings deposited by the same technique. The wear rate of the CrAlN coatings against alumina counterpart was about 2-3 orders in magnitude lower than that of the TiAlN coatings. Selected CrAlN coatings with the highest hardness were also deposited on some WC-based end-mills. An evident better performance of the CrAlN-coated end-mills was observed than the TiAlN-coated ones for cutting a hardened tool steel material under high speed machining conditions.     

Effect of annealing on the composition, structure and mechanical properties of carbon nitride films deposited by middle-frequency magnetron sputtering

Carbon nitride films were deposited by middle-frequency reactive magnetron sputtering and annealed at different temperatures in nitrogen ambient. X-ray photoelectron spectroscopy, Raman scattering, transmission electron microscopy, and nano-indenter were used to characterize the as-deposited and annealed films. The analysis showed that annealing resulted in the dissociation of N and C in the films. The dissociation of C happened after 500 °C and lagged behind that of N. With the increase of annealing temperature, the disorder of sp² C decreased and the films were gradually graphitized. The microstructure changed from amorphous to fullerene-like CN_x with the annealing temperature increasing to 500 °C, and then to nitridized graphite nanocrystals at 600 °C. The graphitization resulted in a drastic decreasing of hardness and modulus of the films.     

Elektronenstrahlbehandlung von PVD‐Hartstoffschichten

Electron beam treatment of PVD – hard coatings Coatings of the type CrN_x, (Ti, Cr)N, (Ti, Al)N, Ti(C, N) and Ti(B,N) were deposited on the quenched and tempered steel C45 to investigate the effect of electron beam treatment on the structure and the properties of hard coated steels. A controlled energy input by electron beams was used to investigate the thermal behaviour of hard coatings with fixing the transformation levels by self‐quenching. Simultaneously a different case hardening of the substrate was caused providing a different effect of supporting the hard layer. There are big differences in the thermal stability of the investigated coatings. The surface hardness, adhesion and wear resistance of the composit hard coating/steel was improved in dependence on the energy input. The use of electron beam technologies enables the generation of support layers which locally increase the working behaviour of hard coated steel.     

Preparation of the hard CNx thin films using NO ambient gas by pulsed laser deposition

Pulsed laser deposition (PLD) technique has been widely used in thin film preparation because of its wonderful and excellent properties and amorphous carbon nitride (CN_x) thin films are recognized to have potential for applications like hard coating and electron field emission device. We have deposited CN_x thin films by KrF excimer laser – (λ= 248 nm) ablation of pure graphite target in pure NO gas ambient condition. In this paper, we have prepared the CN_x thin films at various ambient NO gas pressure of 1.3–26 Pa and laser fluence of 2– 5J cm^?2 on Si (100) substrate. We consider that the hardness of CN_x thin films improves due to the increase the nitrogen/carbon (N/C) ratio. The N/C ratio depended on the ambient NO gas pressure and laser fluence. We obtainedthe maximum N/C ratio of 1.0 at NO 3.3 Pa. The typical absorption of CN bonds such as sp² C–N, sp³ C–N, G band and D band were detected from the infrared absorption measurement by FTIR in the deposited CN_x thin films.     

Investigating the wear characteristics of engineered surfaces: low-temperature plasma nitriding and TiN + MoS x hard-solid lubricant coating

Significant progress has been made in the past decade in plasma nitriding with a majority of the research work focusing on improving hardness and wear resistance of the nitrided surface through the reduction of nitriding temperature, pressure or time. Hard-solid lubricating coatings have also been extensively studied for lowering the wear rate and coefficient of friction of traditional hard coatings such as TiN by the combined effect of hardness and solid lubrication. In this study, the wear characteristics of low-temperature plasma-nitrided steel substrate performed using a Saddle-field fast atom beam source and TiN + MoS _x hard-solid lubricant coating deposited by a closed-field magnetron-sputtering technique have been investigated. The thin hard layer in plasma-nitrided substrates exhibited much higher hardness and lower wear compared to the untreated substrate in pin-on-disc wear testing. In addition, the study of the wear track morphology of the nitrided samples evidenced significant reduction of deeper ploughing and plastic deformation due to higher hardness and load supporting of the nitrided layer. On the other hand, due to the incorporation of MoS₂ in TiN coating, the wear resistance and coefficient of friction were greatly improved in TiN + MoS _x coating compared to pure TiN coating. In contrast to TiN coating, a relatively smoother wear track with less abrasive wear also supported the beneficial effects of adding MoS₂ in TiN coating.     

Structure and mechanical properties of low temperature magnetron sputtered nanocrystalline (nc-)Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings

This paper reports on the structure and mechanical properties of ~ 2 μm thick nanocomposite (nc-) Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings deposited on 100Cr6 steel substrates, using low temperature (~ 200 °C) DC reactive magnetron sputtering. The carbon content was varied with acetylene partial pressure in order to obtain single layer coatings with different a-C:H carbon phase fractions. The nanocrystalline Ti(N,C) phase is approximately stoichiometric for all coatings and the a-C:H phase fraction increases from 31 to 47 at.% as the coatings stoichiometry changed from TiC_1.34 N_0.51 to TiC_2.48 N_0.48, respectively. TiC_1.34 N_0.51 coatings showed the highest nanoindentation hardness (H) of ~ 14 GPa and a modulus (E_r) of ~ 144 GPa; H reduced to < 6 GPa and E_r to < 70 GPa for TiC_2.48 N_0.48 coatings. nc-Ti(N,C)/a-C:H coatings are promising candidates for applications where better matching of the modulus between a relatively low modulus substrate, hard loading support layer and low modulus-high H/E ratio top layer is required.     

Nanocomposite Hard Coatings: Deposition Issues and Validation of their Mechanical Properties

The limitations of conventional coatings due to inferior hardness or poor oxidation stability can be overcome by nanocomposite hard coatings such as nc‐TiN/a‐SiN_x, which consists of nanocrystalline TiN and a non‐crystalline tissue phase of SiN_x which are mutually immiscible. The properties of nanocomposite coatings, especially their increased hardness, can be explained by their nanostructure, which leads to a maximum hardness at typically 80 atomic percent of the crystalline phase. We show that enhanced hardness can only be attained when the silicon nitride phase is sufficiently nitrided. The accurate and reliable measurement of the hardness and elastic modulus requires the use of appropriate nanoindentation equipment and a careful tip correction with periodical validation. It is shown that for a correct hardness determination of a few microns thick nanocomposite coatings, an indentation depth of 100 nm is sufficient. The maximum hardness of our nc‐TiN/a‐SiN_x coatings deposited by a hybrid UBM/arc‐PVD process is about 40 GPa. This value represents a global hardness value, due to the nanocomposite structure there may be a local hardness variation of about ±10 %.     

Mechanical properties of in situ Al2O3 formed Al–Si composite coating via atmospheric plasma spraying

In this study, mechanically alloyed Al–12Si/SiO₂ composite powder was deposited onto an aluminum substrate by atmospheric plasma spraying. The composite coating consisting of in situ formed Al₂O₃ reinforced hypereutectic Al–18Si matrix alloy was achieved. The produced coatings were extensively analyzed with respect to X-ray diffraction (XRD). The XRD patterns of the coatings include Al, Si and Al₂O₃ phase formation. Mechanical properties of layers were examined by Dynamic Ultra-micro hardness test machine for estimating Young’s modulus due to load–unload sensing analysis. The hardness and Young’s modulus of the composite coatings sprayed at different plasma current and the distance were measured under 200, 400, 600, 800 and 1000 mN of applied peak loads by indentation technique. The effects of spray distance and arc current on the hardness and Young’s modulus have been investigated. Additionally, it was observed that the arc current and spray distance strongly influence the mechanical properties of the coatings.     

Thermal stability of CrN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanometric coatings deposited on stainless steel

Thin CrN _x coatings are often used as protective coatings for steel. In these applications, coated parts might be subjected to high temperatures that can alter the coatings structural and mechanical properties. In this work, the properties of nanometric CrN _x coatings deposited by reactive magnetron sputtering on AISI 304L stainless steel were studied by transmission electron microscopy, glazing incident X-ray diffraction, Atomic Force Microscopy, and nanoindentation. The effect of annealing, both in air and vacuum, on the coating crystal structure, surface morphology and hardness were also investigated. It was found that annealing in vacuum-induced phase transformation from CrN to Cr₂N, while after annealing in air only Cr₂O₃ phase was present. Surface roughness did not increase for annealing in vacuum. CrN _x coatings with higher Cr₂N phase content showed lower roughness increase for annealing in air. Measured hardness was >10 GPa for as-deposited CrN _x samples. An increase in hardness up to >20 GPa was found for vacuum-annealed samples.     

Effect of bias voltage on microstructure and mechanical properties of arc evaporated (Ti, Al)N hard coatings

In the present study, authors report on the effect that substrate bias voltage has on the microstructure and mechanical properties of (Ti, Al)N hard coatings deposited with cathodic arc evaporation (CAE) technique. The coatings were deposited from a Ti _{0· 5}Al _{0· 5} powder metallurgical target in a reactive nitrogen atmosphere at three different bias voltages: U _B ?=??? 25, ?50 and ?100 V. The coatings were characterized in terms of compositional, microstructural and mechanical properties. Microstructure of the coatings was investigated with the aid of X-ray diffraction in glancing angle mode, which revealed information on phase composition, crystallite size, stress-free lattice parameter and residual stress. Mechanical properties were deduced from nano-indentation measurements. The residual stress in all the coatings was compressive and increased with increasing bias voltage in a manner similar to that reported in literature for Ti–Al–N coatings deposited with CAE. The bias voltage was also found to significantly influence the phase composition and crystallite size. At ?25 V bias voltage the coating was found in single phase fcc-(Ti, Al)N and with relatively large crystallites of ~ 9 nm. At higher bias voltages (?50 and ?100 V), the coatings were found in dual phase fcc-(Ti, Al)N and fcc-AlN and the size of crystallites reduced to approximately 5 nm. The reduction of crystallite size and the increase of compressive residual stress with increasing bias voltage both contributed to an increase in hardness of the coatings.     

Influence of boron doping on mechanical and tribological properties in multilayer CVD-diamond coating systems

Titanium alloy (Ti6Al4V) substrates were deposited with smooth multilayer coatings, by hot filament chemical vapour deposition technique. The effect of boron doping on lattice parameter, residual stresses, hardness and coefficient of friction in multilayer-diamond coating system was studied. The frictional behaviour of the coatings was studied using a ball-on-disc micro-tribometer by sliding the coated samples of titanium alloy (Ti6Al4V) substrates against alumina (Al₂O₃) balls, and increasing normal load from 1 to 10 N. The average friction coefficient decreased from 0.36 to 0.29 for undoped multilayer-diamond coating system and from 0.33 to 0.18 for boron- doped (BD) multilayer-diamond coating system. The average indentation depths for undoped and BD multilayer- diamond coating systems were found to be equal to ～>58 and ～65 nm, respectively, and their hardness values were 60 and 55 GPa, respectively.     

Structure of CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.5) deposited by arc sputtering of graphite

The structure of a-C and CN _x coatings 1–3 μ thick deposited on metal substrates by arc-pulse sputtering of graphite target in nitrogen background at P = (10^?2 ?5) Pa was studied by transmission electron microscopy and scanning electron microscopy. Concentration and depth distribution of nitrogen in CN _x depend on progressive saturation of graphite target. Nitrogen-free coatings (x = 0) consist of amorphous matrix with multiwalled nanotubes. Structure of carbon nitride coatings depends on nitrogen concentration. Over the range of C_N/C_C < 0.15 and C_N/C_C > 0.4 CN _x coatings are amorphous. The structure of CN_0.15<x<0.4 is a mixture of two types of amorphous domains, one of which is decorated by microcrystalline inclusions. The same structured inclusions were found on graphite target modified by electric arc. The obtained results allow understanding the dependence of the CN_0≤x≤0.5 coatings properties on nitrogen concentration.     

Interfacial fracture for TiN/SiNx nano-multilayer coatings on Si(1 1 1) characterized by nanoindentation experiments

Fracture behavior for TiN/SiN_x nano-multilayer coatings on Si(1 1 1) substrates, deposited using magnetron sputtering Ti and Si, is characterized by nanoindentation experiments, and the morphologies of the indentations are revealed by scanning electron microscopy, along with in situ atomic force microscopy (AFM) in nanoindentation experiments. During nanoindentation experiments, under the condition that the displacement limit mode is used and a strain rate is kept at 0.05/s, an interfacial (between the coating and substrate) fracture is observed as the maximum indenter displacement into the coating reaches 2500 nm, and the corresponding unloading segment in the load–displacement curve shows an obvious discontinuity. This discontinuity is attributed to the rebound of the detached film during unloading. The interfacial fracture toughness for TiN/SiN_x nano-multilayer coating on Si(1 1 1), which is strongly dependent on the preferred orientation for the TiN layer as well as the interfaces between TiN and SiN_x layer in the multilayer stack, is calculated.     

Nanoindentation-induced deformation behaviour of diamond-like carbon coatings on silicon substrates

The deformation behaviour of diamond-like carbon (DLC) coatings on silicon substrates induced by indentation has been investigated. DLC coatings, deposited by a plasma-assisted chemical vapour deposition technique, were subjected to nanoindentation over a range of maximum loads from 100 mN to 300 mN. The resulting load-displacement plots displayed pop-ins for maximum loads of 200 mN and above, with no distinct pop-out for any of the loads studied. Compressive deformation of the coating, up to a strain of ∼ 9%, was observed. The coating-substrate composite was devoid of cracks at lower loads, but at the maximum load of 300 mN, ring cracks in the coating and a median crack in the substrate were observed. Furthermore, cracking, {111} slip and localized phase transformations were observed in the silicon substrate. The onset of these structural changes was correlated to the mechanical behaviour during indentation.     

Corrosion properties of titanium based hard coatings on steel

Titanium nitride TiN, titanium boronitride Ti(B,N) and titanium carbonitride Ti(C,N) coatings were deposited by PA-CVD on tempering and stainless steel substrates. The deposition process can be supervised by OES. The coatings were characterized XRD, SEM and WDS as well as hardness, adhesion and friction tests. Electrochemical impedance measurements and cyclic voltammetry in praxis relevant media were carried out. Mechanical and corrosion properties of the coatings can be controlled by the PA-CVD process parameters. The incorporation of chlorine in the coating can be varied by the process parameters with TiCl₄ or completely avoided using metallo-organic precursors. No influence of the chlorine content on the corrosion behavior was observed. Even coatings with extremely high chlorine content still exhibit an excellent corrosion resistance. Thus, the microstructure of the coating is the key to the corrosion properties of hard coatings on steel. A new micro electrochemical scanning droplet technique with a lateral resolution of 150 μm allows the investigation of TiN-coated substrates of complex geometry. The PA-CVD technique permits the deposition of dense and pinhole free coatings. On structures with simulated aspect ratios less than 3, a dense protective coating is proved. However, if the formation of micro pores is not suppressed by the optimal choice of deposition parameters, low-alloyed steel substrates corrode through pores, causing a detachment of the coating. On layers deposited on stainless steel, no sign of substrate corrosion could be detected. A model for the corrosion mechanism is given in Fig. 17.     

High-throughput characterization of mechanical properties of Ti-Ni-Cu shape memory thin films at elevated temperature

Hardness and Young's moduli values for Ti_xNi_90−xCu₁₀ (37 at.% < x < 67 at.%) thin films from a continuous composition spread type materials library, annealed at 500 °C for 1 h, were determined at room temperature (martensitic state) and 80 °C (austenitic state) using high-throughput nanoindentation experiments. These values are found to increase as the compositions deviate from Ti contents close to 50 at.%. The increases in hardness is correlated to the presence of Ti-rich and (Ni,Cu)-rich precipitates resulting in precipitate hardening and grain size refinement (Hall-Petch effect). The increase of the Young's moduli is rationalized by considering the significantly higher Young's moduli of the different precipitate phases and applying the rule of mixtures. The contributions of the precipitate phases and the matrix to the combined Young's modulus were estimated by evaluating the load-displacement curves in detail. The obtained results are in good agreement with the Young's moduli determined from thin film curvature measurements [R. Zarnetta et al., Smart Mater. Struct. 19 (2010) 65032]. Thus, the experimental restrictions for nanoindentation experiments at elevated temperatures are concluded to not adversely affect the validity of the results.