ICMCTF2006 Session BP: BP Poster

Hard thin coatings are widely used to improve durability of various mechanical components. Their mechanical (adhesion to the substrates, hardness and elastic modulus) and tribological (scratch and wear resistance) properties have been evaluated in the following test procedures:

- Reciprocating wear tests for evaluation of coating friction and durability;

- Scratch-hardness tests under constant load for scratch-resistance and micro-hardness;

- Scratch-adhesion tests under increasing load for coating adhesion and toughness;

- Nano-indentation tests for coating nano-hardness and elastic modulus evaluation.

All the tests were performed on the same tester, re-configured for each test within a minute by installing corresponding replaceable modules. The Universal Nano & Micro Tester with multiple sensors (indentation and wear depth, normal and lateral forces, contact electrical resistance, acoustics, temperature) and integrated both atomic force and optical microscopes has been utilized to characterize mechanical properties of thin films, with in-situ monitoring their changes during micro and nano indentation, scratching, reciprocating, rotating and other tests.

Clear differences between ductile and brittle coatings of diamond-like carbon, tungsten carbide and titanium carbide, as well as between different deposition technologies, have been observed. For many coatings, there was an excellent correlation of their nano-hardness with wear and scratch resistance, for some coatings there was a lower degree of correlation due to either different wear mechanisms or poor adhesion. The multi-sensing technology with in-situ digital optical microscopy and periodic AFM imaging helped discover and understand the differences.

Two vacuum arc deposition techniques were compared for metal film deposition: 1) Filtered Vacuum Arc Deposition (FVAD), which applies a magnetic field to separate the plasma from macroparticles (MPs) generated in the cathode spots, and 2) Hot Refractory Anode Vacuum Arc (HRAVA) deposition, in which MPs are vaporized in the hot inter-electrode plasma. A Cu cathode and an arc current of 200A were used in both systems. The FVAD system used a 92mm diam cathode, a copper ring anode with a 122mm aperture diameter, and a 90° torus (R_maj=240mm and R_min=80mm) with an average longitudinal magnetic field 12mT. The ion current was measured by a probe biased to -40V relative to the cathode in the FVAD. In the HRAVA, the arc burned between a 30mm diam water-cooled cathode and a 32mm Mo anode separated by a 10mm gap. The substrate was placed 80mm from the electrode axis.

The FVAD film thickness was axially symmetric to within 10-20%. The focused plasma jet in the FVAD system covered a circular area, where the radius for half-thickness was ~20mm. The deposition rate was constant in time and maximal in the center of circular area (about 0.25µm/min). The mass deposition rate was about 9.5mg/min assuming bulk density.

The HRAVA deposition rate initially increased with time and saturated at a maximum of ~2.3µm/min after 1min. The plasma expanded radially and was deposited on a cylindrical area of 125mm² and height ~20mm, which was co-axial with the electrode axis. The thickness distribution was axially symmetric within 10%. The steady-state mass deposition rate was 400mg/min. Thus, the HRAVA method produces a MP-free mass throughput and cathode utilization efficiency ~40 times greater than with the FVAD system.

Industries such as the tool and forming industries are keenly interested in increasing the lifetimes of their components. This is a motivation for the choice of nitride coatings, which have been selected because of their superior mechanical properties such as high hardness as well as their excellent wear resistance. Of the various coatings, titanium nitride has become an established industrial coating that is most commonly used in the tool industry ¹. However, TiN films are oxidized easily in air at above 550@super oC, and this oxidation problem degrades their wear resistance@super 2, 3@. Therefore, nanocomposite coating materials have recently attracted increasing interest due to the unique properties, such as superhardness (H @>@ 30 GPa), combined high hardness and toughness, or hardness and low friction⁴. In this study, the quaternary TiZrAlN nanostructured thin films were synthesized by CFUBMS (Closed Field Unbalanced Magnetron Sputtering). We synthesized TiZrAlN nanostructured films with various N₂ partial pressures and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties of the TiZrAlN nanostructured films were evaluated by nano-indenter. Maximum hardness value according to the various N₂ partial pressures is obtained at 47 GPa. It is also conformed that critical value of the grain size dc needs to achieve the maximum hardness.

1. K. Holmbefg, A. Matthews, Coatings Tribology, Tribology Series, vol. 28, Elsevier, Amsterdam, 1994.

2. O. Knotek, M. Bohmer, T. Leyendecker, J. Vac. Sci. Technol., A 4 (1986) 2695.

3. W. D. Munz, J. Vac. Sci. Technol., A 4 (1986) 2717.

4. C. Mitterer et al. Surf. Coat. Technol. 120/121 (1999) 405-411.

The plasma chemistry and energetics of magnetron sputtered Zr and Nb in an Ar / O₂ atmosphere has been measured as a function of the O₂ partial pressure. The composition of films deposited on grounded non-intentionally heated substrates^1,2 was correlated with the dominant positive and negative ion populations in the plasma. While the oxygen deficient films were grown in the Ar⁺ dominant mode, the stoichiometric films were synthesized in the O⁺ (O^-) dominant mode. Furthermore, evidence for the presence of the high energy negative O^- ions in the Zr plasma is presented, while no high energy species could be detected in the Nb discharge. It is reasonable to assume that high energy negative O^- ions enable crystalline growth of ZrO₂ thin films, while the lack thereof may result in the formation of an amorphous structure. The here presented data are of importance for understanding the evolution of the composition and structure of thin oxide films.

¹S. Venkataraj, R. Drese, O. Kappertz, R. Jayavel, M. Wuttig. Phys. Stat. Sol. (a) 188(3) (2001) 1047-1058.

²S. Venkataraj, O. Kappertz, H. Weis, R. Drese, R. Jayavel, M. Wuttig. J. Appl. Phys. 92(7) (2002) 3599-3607.

Niobium diselenide (NbSe₂) has drawn large attention because of its wide range of interesting physical properties, such as the presence of a charge density wave transition and a superconducting transition. Similar to most of the transition metal dichalcogenides, NbSe₂ has been cited for use as an electrical conductor and as a solid lubricant at high-temperature. NbSe₂ is also a good intercalation host, and due to this sensivity to intercalated molecules, niobium diselenide films may find application as hosts for sensors materials. NbSe₂ thin films have been grown using many processes such as Van der Waals epitaxy (VDWE), pulsed laser deposition (PLD) or pulsed laser ablation, but to our knowledge a CVD route to NbSe₂ has not been reported to date.

The atmospheric pressure chemical vapour deposition (APCVD) of niobium selenide films on glass substrates was achieved by reaction of ditertiarybutylselenide with NbCl₅ at 250-600°C. X-ray diffraction showed that the NbSe₂ films were crystalline with cell constants close to those expected (a = 3.44 Å; c = 12.58 Å) - marked preferred orientation was noted at higher deposition temperature and this unexpectedly varied depending on distance from the reactor inlet. At 600°C, energy-dispersive analysis by X-rays (EDAX) showed exactly the Nb:Se ratio expected for NbSe₂. The films deposited at substrate temperatures less than 500°C were selenium rich with a niobium to selenium ratio of 1:2.5. The films produced at 600°C were dark-green powdery and poorly adhesive. Whereas the film produced below 550°C were dark-brown matt in appearance, they passed the Scotch tape test but could be scratched with a steel scalpel. SEM showed that the films were composed of hexagonal plate like crystals which become longer and thicker with increasing deposition temperature.

It has been long desired to improve the thermal stability and the oxidation resistance as well as the wear properties of thin binary ceramic films such as TiN and CrN. One of the key solutions for the problem is to add B into the films to improve the properties, constructing ternary Ti-B-N and Cr-B-N films.

In our previous work, quaternary Cr_xAl_yB_zN films were synthesized by the cathodic arc method, using Cr-Al-B alloy cathode by altering Z values from 0 to 0.10. It was found that adding B to Cr-Al-N ternary systems increases the micro-hardness while decreasing the lattice parameter of the resulting quaternary films, keeping cubic structures.

In order to prepare for the testing, Cr_xAl_yB_zN were annealed in a vacuumed chamber at 800, 900 and 1000°C. Changes in micro-hardness and microstructure as a function of annealing temperature were studied and discussed based on X-ray diffraction method (XRD), scanning and transmission electron microscopy (SEM and TEM) and conventional micro-Vicker's hardness tests.

A reactive magnetron sputtering PVD technique was used to deposit Zr-Cu based metallic coatings onto ASP23 tool steel. A reactive gas N₂ has been used to promote the formation of a hard, nitrogen-supersaturated Zirconium (or Zirconium nitride) nanocrystalline phase in the film, surrounded by a soft and compliant amorphous, intergranular metallic phase (in this case Cu). The effect on the nanostructure of the addition of other elements such as Titanium (Ti) and Boron (B) is also evaluated.

ZrTiCu(B,N) films of approximately 2 microns thickness demonstrate a dense, amorphous morphology, as seen from SEM micrographs. No significant changes can be observed between each of the coatings; all of them presenting similar characteristics in terms of morphology, thickness and adhesion. This group of coatings shows relatively high hardness (of more than 20 GPa in many cases) with nanocrystals of ZrN as the main phase; however for coatings of higher copper content, the presence of this phase is not detected by XRD measurement; in this case only reflections of Cu were found. The coatings were also tested for wear resistance using non-perforating micro-scale abrasion and ball-on-plate reciprocating-sliding tests, with encouraging results and (at certain compositions) surprisingly low friction coefficients observed.

Wear-resistant, hard Si-C-N coatings were synthesized in a triple torch plasma reactor using a thermal plasma chemical vapor deposition process. In this reactor, three dc plasma torches are angled so that their jets converge to form a highly chemically reactive region at the substrate. Vaporized hexamethyldisilazane (HMDSN) was injected through a central injection probe, while nitrogen and/or hydrogen gases were added through the torches to the argon plasma.

Various dissociation, recombination and intermediate reactions were considered to determine what major species exist in the gas phase during the deposition of Si-C-N films. Reactant flow rates were varied to evaluate the thermodynamic equilibrium compositions across a linear temperature profile above the substrate and to identify the species that lead to the production of wear-resistant, hard Si-C-N films.

A series of experiments were conducted at low HMDSN flows (~1 sccm) and varying hydrogen and nitrogen flows. Films were characterized by micro X-ray diffraction, Fourier Transform infrared spectroscopy and scanning electron microscopy. Indentation tests were conducted on the polished film cross-sections, while wear tests were carried out on the film surfaces. At substrate temperatures below 1000°C, amorphous Si-C-N films were deposited, while higher temperatures produced crystalline composite films of α- and β-Si₃N₄ and α- and β-SiC. Films produced at low HMDSN flows display non-columnar morphology and therefore have higher wear-resistance, indicating the benefit of low reactant-to-plasma gas flow concentrations on film growth. At low HMDSN flows, increased hydrogen and decreased nitrogen flows have also shown an increase in film linear density. Only small variations in hardness and wear-resistance were observed under these conditions, indicating the importance of film morphology on mechanical performance.

In this work, CVD and PVD TiN coatings have been examined by analytical transmission and scanning electron microscopy. The aim was to describe the general microstructure of the coatings such as grain size, grain shape, twinning, dislocations, pores and epitaxy.

The PVD TiN coating exhibited a smooth surface morphology, while CVD TiN showed a more faceted surface. The PVD and CVD TiN coatings showed an inner region of small columnar grains and an outer region of large columnar grains, the aspect ratio being larger for PVD TiN. Both types of coatings were highly textured, PVD TiN along <111> and CVD TiN along <100>. Occasionally the PVD TiN grains were composed of a large number of domains, which were twin-related by a 180° rotation along <111>. The PVD and CVD TiN grains were free from W and Co. CVD TiN exhibited large amounts of these elements in the grain boundaries.

Epitaxy was frequently found for both PVD and CVD TiN deposited on WC grains. The orientation relationships on the basal planes of WC are the same for CVD TiN, PVD TiN and CVD TiC, with growth of close-packed planes on close-packed planes with close-packed directions being parallel. The orientation relationship on the prism planes of WC is the same for CVD TiN and CVD TiC, while it is different for PVD TiN.

Ceramic materials have excellent hot hardness and good chemical and thermal stability making surface properties ideal for engineering products. Zirconium Nitride(ZrN) & Titanium Nitride(TiN)coatings produced by Physical Vapor deposition(PVD),are used for their excellent mechanical and tribological applications in various industrial sector. These coatings are particularly attractive for their excellent corrosion resistance which further enhances their lifetime and service quality.

In present investigation corrosion resistance of TiN & ZrN thin film of varying thickness(1.5 µm and 2.0 µm) in environments having different pH(3.5%NaCL,11pH Na₂SO₄ and 0.1NHCl) were studied. D.C polarization and A.C impudence spectroscopy studies had also been carried out. SEM studies before and after corrosion resistance was done. In case of 3.5%NaCl, large difference in corrosion was observed for both the types of films(1.5 µm TiN 42.61mpy and 2.0 µm TiN 25.34 mpy,1.5 µm ZrN 22.7 mpy & 2.0 µm ZrN 2.861mpy). Similar behaviour of TiN &ZrN thin films was observed for 0.1NHCl. The difference is less in case of 11pH Na₂SO₄ (1.5 µm TiN 15.79 mpy and 2.0 µm TiN 18.54 mpy,1.5 µm ZrN 6.710 mpy & 2.0 µm ZrN3.579 mpy) indicating formation of stable film in alkaline environment.

Aluminizing onto the surface of iron-based alloys originates an iron-aluminide intermetallic diffusion coating is an effective method for improvement of oxidation and corrosion resistance at high temperature.

The aluminium deposition on ferritic steel as HCM12 A (P-122) by chemical vapour deposition in fluidized bed reactor (CVD-FBR) has been studied. A thermodynamic study of partial pressures of the gaseous species present in the system during the CVD process was previously studied using Thermo Calc software. On having studied the influence of the HCl input ratio in the H₂+HCl reactive gaseous mixture (it is obtained by SEM, EDX and XRD) that the increase of the HCl input ratio a few thicker Al-coatings and formed by Fe-Al intermetallic phases were obtained. On having increased the deposition time, it increases also the Al-layer thickness and it is formed by Fe₂Al₅ and FeAl₃ intermetallic phases.

Polyurethanes (PUs) are used in many industrial and biomedical applications because they show wide mechanical and chemical properties. In the present study, the surface chemical-physics properties of PUs membranes are modified by low-temperature RF-plasma treatment. Then these treated membranes are used for the separation of an azeotropic methyl t-butyl ether/methanol mixture by membrane-based pervaporation (PV) technique¹.

PUs membranes were prepared from a 15 percent solution of PU in tetra hydro furane. The solution was cast on a clean glass plate to produce approx. 50 µm films and finally the films were dried in nitrogen atmosphere at 60°C to evaporate the solvent. The plasma treatments were performed by using RF low-pressure glow discharges at 13.56 MHz in different atmospheres. Oxygen, nitrogen, SF₆ gases and acrylic acid vapour (AAc) were used in the plasmas. Contact angle measurement, AFM and XPS techniques were used for surface characterization of the membranes. PV tests were also carried out before and after plasma treatment.

The obtained results show that plasma modification occurs in a mechanism particular for each gas studied. XPS data indicate the presence of surface species that are not found in the untreated PUs membranes. For example, with oxygen plasma treatment there is a conversion of single C-O bonds into C=O functionalities. With nitrogen plasma, an increase in the double and triple bonds involving N atoms is observed. Finally with AAc, the incorporation of more electronegative groups like COO was found at the surface. The polar character of the treated membranes for oxygen, nitrogen and Acac gases increased, as displayed by an increase in the wettability. A higher selectivity in the PV process was observed for the plasma treated membranes using AAc.

Aerospace industry has to continuously improve the manufacturing technology and reduce parts costs while challenged by the increasing use of new and tough materials and coatings. Therefore the development of special tools for the machining of these alloys is a key factor to achieve longer tool life, better finishing quality of the part or process speed up.

Special versions of PLATIT LARC^® Cr_1-xAl_xN/SiN_y and Ti_1-xAl_xN/SiN_y nanocomposite coatings were developed for critical cutting operations such as rough and finish milling of the Ni-based alloys Inconel 718 and IN 100, used in turbine components. Further tests were carried out in austenitic A286 ferrous superalloy material. Optimum tools and cutting edge designs have to be engineered in every cases.

The coating was tuned in terms of hardness, friction properties, wear resistance and adhesion to bring the best performance according to the application demands. A strong emphasis will be on the high-temperature stability of Cr and Ti-based nanocomposite coatings and about results of annealing experiments. The influence of the Si content on the film properties will be then discussed.

Plasma enhanced chemical vapor deposition (PECVD) processes open up wide parameter spaces (most notably lower substrate temperatures) than CVD techniques. This is because the plasma electrons can directly impart energy into the gas species on the order of 1 eV (> 10,000 K) instead of relying on strictly thermal surface processes. Modulated plasmas in turn can provide even greater control over the deposition conditions by tailoring a gas phase/surface phase synergy to achieve optimum growth conditions for the desired films. Electron beam-generated plasmas have demonstrated intriguing results in etching and surface nitriding applications^* due to their low electron temperatures, high densities and scalability. This work will discuss recent progress on PECVD of SiO_x films using pulsed electron beam generated plasmas with organic precursors such as TEOS and HMDSO. In these systems, long pulse length (~ 1 millisecond) plasmas showed no dependence on plasma duty factor. Shorter pulse lengths, comparable to gas and surface phase reaction times were expected to have a significant effect on the process deposition rate and the final film quality. These film characteristics will be discussed and compared with complementary time-resolved ion flux measurements (in situ mass spectrometry) and global plasma parameters (from electrostatic probes). These processes have been tailored for display applications on flexible substrates (low temperature, low damage) and with analogous SiN_x processes.

^*Work supported by the Office of Naval Research¹D. Leonhardt, S.G. Walton, C. Muratore, and R.A. Meger, Surf. Coat. Technol. 188-189, 299-306 (2004).

The decrease of iron alloys density constitutes a major challenge of iron manufacturers, especially for automotive applications. Amongst the different solutions involved to reach this goal, Fe-Mg alloys are expected to improve the mechanical properties-to-density ratio due to the extremely low density of Mg. However, due to the coast of synthesis of bulk Fe-Mg alloys, coatings deposited by PVD processes constitute a cheap method to investigate their potential interest and to characterise their mechanical properties as a function of their Mg content.

In this paper, we investigate the structural and mechanical properties of as-deposited Fe-Mg coatings obtained by co-sputtering in pure argon of Fe and Mg targets on glass and steel substrates. In a first part, we describe the reactor, consisting in two targets parallel to the rotating substrate-holder allowing the deposition of homogeneous coatings on large-area substrates, and the original target configuration developed at the laboratory to sputter magnetic targets such as iron. Then, we present the structural evolution of as-deposited Fe-Mg coatings as a function of their Mg content. Their hardness, determined by NHT, as well as their brittleness, measured by means of scratch testing under progressive load, is also presented. Hence, the structural evolution of the coatings is investigated as a function of the annealing temperature and is related to the evolution of their hardness. Finally, some corrosion resistance tests are performed from open-circuit measurements on as-deposited and annealed coatings deposited on glass slides. Finally, we discuss the potential interests of such coatings, as well as protective coatings of construction steels, as for synthesis of bulk alloys.