P.Eh. Hovsepian

Recent progress in large scale manufacturing of multilayer/superlattice hard coatings

Since the early fundamental research on superlattice structured hard coatings in the late 1980s, rapid progress has been achieved to produce nanoscale compositionally modulated multilayer structures. It has been shown that the periodicity of the multilayers is strongly controlled by the substrate rotation and the actual deposition rate. Appropriate multi-target geometry and controlled target poisoning by optimised pumping conditions lead to deposition conditions similar in their economy to the deposition of typical monolithically grown binary hard coatings. The combined steered cathodic are/unbalanced magnetron technology guaranties sufficient adhesion (L-C > 50 N) of the usually highly stressed coatings as well as smooth surfaces due to UBM deposition (R-a m). This paper has described the properties of coatings dedicated to high temperature performance: TiAlN/CrN (period 3.03 nm), to tribological applications: TiAlYN/VN (period 3.62 nm) and combined wear and corrosion resistance CrN/NbN (period 3.2 nm). All the coatings investigated were found to crystallise into B1 NaCl f.c.c. structures, and exhibited {110} and {111} or {100} preferred orientations for TiAl/CrN, TiAlYN/VN and CrN/NbN superlattice coatings, respectively. The residual stress was found to be compressive in the range of -4.0 to -8.5 GPa for TiAlYN/VN and between -1.8 and -7.5 GPa for CrN/NbN, depending on the stoichiometry and the bias voltage during coating deposition. Corresponding to the high stress values, the plastic hardness of the coatings was measured to be 55-60 GPa for TiAlN/CrN, 42-78 GPa for the TiAlYN/VN system and between 42 and 56 GPa for CrN/NbN, depending on the bias voltage. Oxidation resistance at temperatures exceeding 900 degreesC was typical for TiAlN/CrN. The TiAlYN/VN coating showed superior tribological properties with a coefficient of friction mu = 0.4 and low sliding wear of 1.26 X 10(-17) m(2) N-1 after 1.1 million cycles against an Al2O3 ball in a pin-on-disc test. CrN/NbN exhibited two orders of magnitude lower passive current densities than electroplated hard Cr and a pitting potential of 450 mV during polarisation in acetate buffer solution. When Nb+ ion etching was used, the CrN/NbN superlattice coating deposited on 304L, stainless steel showed high pitting potentials in the range of 750-1000 mV in the same corrosive medium

Deposition of nanoscale multilayer CrN/NbN physical vapor deposition coatings by high power impulse magnetron sputtering

Nanoscale multilayer CrN/NbN physical vapor deposition (PVD) coatings are gaining reputation for their high corrosion and wear resistance. However, the CrN/NbN films deposited by ABS™ (arc bond sputtering) technology have some limitations such as macrodroplets, porosity, and less dense structures. The novel HIPIMS (high power impulse magnetron sputtering) technique produces macroparticle-free, highly ionized metal plasma, which brings advantages in both surface pretreatment and coating deposition stages of the PVD process. In this study, nanoscale multilayer CrN/NbN PVD coatings were pretreated and deposited with HIPIMS technology and compared with those deposited by HIPIMS-UBM (unbalanced magnetron) and by the ABS™ technique. In all cases Cr+ etching was utilized to enhance adhesion by low energy ion implantation. The coatings were deposited at 400 °C with substrate biased (Ub) at −75 V. During coating deposition, HIPIMS produced significantly high activation of nitrogen compared to the UBM as observed w...

Combined steered cathodic arc/unbalanced magnetron grown C/Cr nanoscale multilayer coatings for tribological applications

Abstract C/Cr nano-scale multilayer coatings have been produced by the combined steered cathodic arc/unbalanced magnetron sputtering technique. The coating was deposited by non-reactive unbalanced magnetron sputtering from three graphite targets and one chromium target at deposition temperatures of 250, 350 and 450 °C. In scratch adhesion tests C/Cr coatings deposited on M2 HSS showed values exceeding critical load of 70 N. The XRD and TEM analysis revealed the amorphous nature of the coatings. Higher deposition temperatures led to an increase in crystallinity. Raman spectroscopy also showed that the amount of the carbon disorder depends on the deposition temperature, increasing from 68 to 86% for deposition temperatures of 250 and 450 °C, respectively. In pin-on-disc tests, C/Cr coatings exhibit a low coefficient of friction of between 0.1 and 0.2, when sliding against 100Cr6 steel ball. These low values were retained for tests in air, de-ionised water and engine oil. Remarkably low sliding wear coefficients of 2×10 −17 m 3 /Nm for the coating and 1×10 −19 m 3 /Nm for the counterpart were measured after 22.6 km sliding distance. However, the increased crystallinity of the coatings produced at higher deposition temperature leads to an increase in the friction coefficient. The C/Cr coatings, used as an overcoat on TiAlCrYN coated cemented carbide end mills, led to reduction of the rake and the flank wear rates by factor of 7 when machining extremely abrasive Ni based alloys.

Transmission electron microscopy and x-ray diffraction investigation of the microstructure of nanoscale multilayer TiAlN/VN grown by unbalanced magnetron deposition

Cubic NaCl-B1 structured multilayer TiAlN/VN with a bi-layer thickness of approximately 3 nm and atomic ratios of (Ti+Al)/V = 0.98 to 1.15 and Ti/V = 0.55 to 0.61 were deposited by unbalanced magnetron sputtering at substrate bias voltages between -75 and -150 V. In this paper, detailed transmission electron microscopy and x-ray diffraction revealed pronounced microstructure changes depending on the bias. At the bias -75 V, TiAlN/VN followed a layer growth model led by a strong (110) texture to form a T-type structure in the Thornton structure model of thin films, which resulted in a rough growth front, dense columnar structure with inter-column voids, and low compressive stress of -3.8 GPa. At higher biases, the coatings showed a typical Type-II structure following the strain energy growth model, characterized by the columnar structure, void-free column boundaries, smooth surface, a predominant (111) texture, and high residual stresses between -8 and -11.5 GPa.

Structure and properties of ZrN coatings deposited by high power impulse magnetron sputtering technology

Monolayer ZrN coatings were deposited exclusively by the novel high power impulse magnetron sputtering (HIPIMS) technology in an industrial scale physical vapour deposition (PVD) machine (HTC-1000-4 target system). Coatings were deposited on 1 μm polished M2 high speed steel, on 304L stainless steel (SS), and on Si (100) specimens. Prior to deposition, HIPIMS plasma sustained on a zirconium (Zr) target was utilized to pretreat the specimens. Coatings were deposited at 400 °C in a mixed N2 and Ar atmosphere using 2 magnetrons in HIPIMS mode and at three different substrate bias voltages (Ubias) keeping all other process parameters constant. The thicknesses of the coatings measured by the ball cratering technique were in the ranges of 1.84, 1.96, and 2.13 μm at bias voltages of −95, −75, and −65 V, respectively, where the difference in thickness can be attributed to the resputtering effect. X-ray diffraction experiments on SS specimens revealed a dominating 111 texture for all three coatings irrespective of...

Combined cathodic arc/unbalanced magnetron grown CrN/NbN superlattice coatings for applications in the cutlery industry

Abstract Hard CrN/NbN superlattice coatings Δ=2.7 nm, were grown at low temperatures (250°C) by combined cathodic arc/unbalanced magnetron technique to coat knife blades produced from 1% carbon steel in an industrially sized four-target PVD coater. The deposition process combines the advantages of metal ion etching by Cr + ions generated by steered arc discharge to guarantee high adhesion and unbalanced magnetron sputtering to deposit smooth CrN/NbN superlattice coatings The coatings’ structure, residual stress, the phase and the chemical composition have been investigated by XRD, SEM, X-TEM and SNMS techniques. The XRD measurements and hardness measurements revealed that the temperature treatment during the deposition process did not deteriorate the initial properties of the blade material. It was found that both the initial cutting power and the wear performance of the blades depend on the coating thickness and coating stoichiometry. CrN/NbN coatings with stoichiometric composition and thickness in the range of 3 μm showed the best compromise between initial sharpness and edge retention according to ISO cutting standards. Low-temperature CrN/NbN superlattice coated craft and textile blades showed an increase in lifetime by a factor of 10 when compared with uncoated ones and currently used Cr 2 O 3 coated textile blades. The CrN/NbN proved to be superior to commercially available CrN and various carbon-based PVD coatings tested under the same conditions.

Influence of the bias voltage on the structure and mechanical performance of nanoscale multilayer CrAlYN∕CrN physical vapor deposition coatings

The effects of bias voltage on the microstructure and the related tribological properties of CrAlYN∕CrN nanoscale multilayer superlattice coatings were investigated. The coatings were deposited at 450°C substrate temperature by combined high power impulse magnetron sputtering (HIPIMS) and unbalanced magnetron sputtering techniques. The substrates were 304 stainless steel, M2 high speed steel for structural analysis and mechanical testing, as well as cemented carbide substrates end mills for dry high speed milling applications. Substrates were pretreated by HIPIMS etching. The bias voltage Ub was varied between −75 and −150V. The chemical composition was determined by neutral mass spectroscopy. The microstructure was characterized by x-ray diffraction and cross sectional transmission electron microscopy. All coatings had a single phase B1 fcc structure. The chemical composition was not affected by the bias voltage. Local epitaxial or axiotaxial growth attributed to the HIPIMS etching pretreatment was obser...

Properties of TiAlCN/VCN Nanoscale Multilayer Coatings Deposited by Mixed High-Power Impulse Magnetron Sputtering (HiPIMS) and Unbalanced Magnetron Sputtering Processes—Impact of HiPIMS During Coating

Nanoscale multilayer TiAlCN/VCN coating has been deposited by pure unbalanced magnetron sputtering (UBM) and high-power impulse magnetron sputtering (HiPIMS)-UBM techniques. The V+ HiPIMS etching used in both processes has shown excellent adhesion (Lc > 50) of the coating to the substrate. The plasma compositional analysis of V+ HiPIMS etching has shown high metal-to-gas ion ratio with ionization states of V up to 5+. Moreover, during the coating of TiAlCN/VCN, the plasma analysis has confirmed the higher production rate of metal ions in the case of HiPIMS-UBM in contrast to pure UBM. This has resulted to a denser closed columnar microstructure of the coating during the HiPIMS-UBM technique than UBM. A thermogravimetric analysis has shown increased oxidation-resistance temperature for coatings deposited by HiPIMS-UBM (w780°C) with significantly lower mass gain. The scanning electron microscope and X-ray diffraction studies of the oxidized surface of the coating have revealed the formation of lubricant Magneli phase oxides of V2O5 and TiO2 at elevated temperature. The wear coefficient of the coating deposited by HiPIMS-UBM has shown two orders of magnitude lower value than that for the UBM-deposited coatings, which represents significant advantage for coatings deposited by UBM. This enhanced performance in oxidation-resistance dry sliding wear conditions can be attributed to the extremely dense structure of the HiPIMS coatings, which could be promising in elevated temperature applications.

Influence of ion bombardment on structure and tribological performance of nanoscale multilayer C/Cr PVD coatings

Abstract Low friction C/Cr coatings have been successfully deposited by the combined steered cathodic arc/unbalanced magnetron sputtering technique. The present paper focuses on the properties, tribological performance and microstructure evolution of C/Cr coatings as a function of the bias voltage Ub ranging from −65 to −350 V. As the bias voltage increases from −65 to −95 V, the structure changes from columnar to dense structure which comprises of randomly distributed onionlike carbon clusters. Further increase in the bias voltage to −350 V led to segregation and self-organisation of the carbon atoms induced by the high energy ion bombardment and finally to the formation of a new type self-organised multilayer structure. On the other hand, the phase composition transforms from graphitic (sp2 C–C bonded) to Me carbon (Cr–C bonded), where the content of the carbide phase increases with increasing the bias voltage. The C/Cr coatings showed an excellent adhesion (Lc>70 N), with hardness ranging from 8·23 to 25 GPa depending on the bias voltage. Pin on disc tests showed that the friction coefficient was reduced from 0·22 to 0·16 when the Ub was increased from −65 to −95 V. A strong correlation was found between the microstructure, the residual stress, the sp2/sp3 content and the coating friction behaviour. Dry high speed milling trials on automotive aluminium alloy (Al–Si8Cu3Fe) showed that C/Cr coated cemented carbide end mills enhance the tool performance and the tool life compared with the uncoated tools by a factor of 2, suggesting the potential for dry high speed machining of ‘sticky’ alloys.

Tracing C changes in a C/CrC PVD coating using Raman spectroscopy and EELS

A C/CrC coating was deposited by unbalanced magnetron sputtering of graphite and Cr metal targets in argon atmosphere for low friction tribological applications. The coating possessed a nanocomposite structure with amorphous carbon embedded in a metastable fcc CrC matrix. The nanocomposite structure was annealed at 750°C in Ar+5%H2 atmosphere for 30 minutes to evaluate its thermal stability. Microstructures of the as-deposited and annealed coating were characterised using Raman spectroscopy and cross sectional transmission electron microscopy coupled with electron energy loss spectroscopy (TEM/EELS). Raman spectroscopy suggested the presence of graphitic carbon in the coating after annealing. EELS (ELNES of C K) combined with HRTEM investigation of the cross sections revealed graphitic C at the very top (~200nm) of the coating and amorphous C at the remaining part of the coating after annealing at 750°C. The advantages and limitations of Raman spectroscopy and TEM techniques in studying C/CrC coating are also discussed.