Effect of the degree of high power impulse magnetron sputtering utilisation on the structure and properties of TiN films

TiN films were deposited using high power impulse magnetron sputtering (HIPIMS) enabled four cathode industrial size coating system equipped with HIPIMS power supplies. The standard version of this system allows control over the ion bombardment during coating growth by varying the strength of the electromagnetic field of the unbalancing coils and bias voltage applied to the substrate. The coatings were produced in different coating growth conditions achieved in combined HIPIMS — direct current (dc) unbalanced magnetron sputtering (HIPIMS/UBM) processes where HIPIMS was used as an additional tool to manipulate the ionisation degree in the plasma. Four cathode combinations were explored with increasing contribution of HIPIMS namely 4UBM (pure UBM), 1HIPIMS + 3UBM, 2HIPIMS + 2UBM and 2HIPIMS (pure HIPIMS) to deposit TiN coatings. Optical emission spectroscopy (OES) measurements were carried out to examine the plasma generated by the various combinations of HIPIMS and UBM cathodes. The micro-structural study was done by scanning electron microscopy (SEM). X-ray diffraction (XRD) technique was used to calculate the residual stress and texture parameter. It has been revealed that the residual stress can be controlled in a wide range from − 0.22 GPa to − 11.67 GPa by intelligent selection of the degree of HIPIMS utilisation, strength of the electromagnetic field of the unbalancing coils and the bias voltage applied to the substrate while maintaining the stoichiometry of the coatings. The effect of the degree of HIPIMS utilisation on the microstructure, texture and residual stress is discussed. Combining HIPIMS with dc-UBM sputtering is also seen as an effective tool for improving the productivity of the deposition process

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 PVD machine (HTC-1000-4 target system). Coatings were deposited on 1 micron polished M2 High speed steel, 304 L Stainless steel and on Si (100) specimens. Prior to deposition, HIPIMS plasma sustained on a Zirconium (Zr) target was utilised 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 range of 1.84 µm, 1.96 µm and 2.13 µm at bias voltages of -95 V, -75 V and -65 volts respectively, where the difference in thickness can be attributed to the re-sputtering effect. X-ray diffraction experiments on SS specimens revealed a dominating 111 texture for all three coatings irrespective of the bias voltage. Cross-sectional transmission electron microscopy revealed extremely dense coating structures at all bias voltages, similar to the transition zone structure (Zone T) reported by Thornton. The -95 bias voltage coatings appeared extremely smooth on the top and with no dome shaped structures often associated with low ion bombardment during deposition. HIPIMS pretreatment lead to high adhesion (LC) of the coatings to the substrate. A continuous ductile perforation of the coating was observed at progressive loads greater than 65 N however no spallation of the coating was observed up to loads of 100 N. High values of hardness (40.4 GPa), Young's Modulus (424 GPa) and compressive stress (10 GPa) were recorded for coatings deposited at -95 BV. Hardness and internal stress of the coating was found increasing with more negative bias voltages. All the coatings exhibited high dry sliding wear resistance (KC) in the range of 6 x 10-15 m3N-1m-1. Cross-sectional Transmission Electron Microscopy and Atomic Force Microscopy analysis has been used to study the effect of ion bombardment obtained from HIPIMS on the structure of the coatings

Cross sectional TEM analysis of duplex HIPIMS and DC magnetron sputtered Mo and W doped carbon coatings

A FIB lift-out sample was made from a wear-resistant carbon coating deposited by high power impulse magnetron sputtering (HIPIMS) with Mo and W. TEM analysis found columnar grains extending the whole ∼1800 nm thick film. Within the grains, the carbon was found to be organised into clusters showing some onion-like structure, with amorphous material between them; energy dispersive X-ray spectroscopy (EDS) found these clusters to be Mo- and W-rich in a later, thinner sample of the same material. Electron energy-loss spectroscopy (EELS) showed no difference in C-K edge, implying the bonding type to be the same in cluster and matrix. These clusters were arranged into stripes parallel to the film plane, of spacing 7-8 nm; there was a modulation in spacing between clusters within these stripes that produced a second, coarser set of striations of spacing ∼37 nm

Defect growth in multilayer chromium nitride/niobium nitride coatings produced by combined high power impulse magnetron sputtering and unbalance magnetron sputtering technique

In recent years, high power impulse magnetron sputtering (HIPIMS) has caught the attention of users due to its ability to produce dense coatings. However, microscopic studies have shown that HIPIMS deposited coatings can suffer from some surface imperfections even though the overall number of defects can be significantly lower compared to, for example, arc deposited coatings of similar thicknesses. Defects can degrade the coating performance thus any kind of defect is undesirable. To better understand the nature of these imperfections and the science of their formation, a series of Chromium Nitride/Niobium Nitride (CrN/NbN) coatings were deposited using HIPIMS technique combined with unbalanced magnetron sputtering (UBM) by varying deposition times (t = 15 to 120 minutes). All other deposition parameters were kept constant in order to deposit these coatings with a consistent deposition rate and stoichiometry. In addition, coatings were deposited using pure UBM technique to compare the defects generated by these two different physical vapour deposition approaches. High-resolution scanning electron microscopy images revealed that HIPIMS/UBM and pure UBM CrN/NbN coatings have similar types of defects which could be categorised as: nodular, open void, cone-like and pinhole. Interestingly, there was no evidence of droplet formation in HIPIMS/UBM deposited coatings. The defect density calculation indicated that the defect density of HIPIMS/UBM coatings increased (from 0.48 to 3.18%) with the coating thickness. A coating produced in a relatively clean chamber had a lower defect density. Potentiodynamic polarisation experiments showed that the fluctuation in corrosion currents in HIPIMS/UBM coatings reduced with the coating thickness. This indicated that though visible on the surface, most of these defects did not penetrate thorough the whole thickness of the coating

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(TM) (are 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 ABSTM technique. In all cases Cr+ etching was utilized to enhance adhesion by low energy ion implantation. The coatings were deposited at 400 degrees C with substrate biased (Ub) at -75 V. During coating deposition, HIPIMS produced significantly high activation of nitrogen compared to the UBM as observed with mass spectroscopy. HIPIMS-deposited coatings revealed a bilayer period of 4.1 nm (total thickness: 2.9 mu m) and hardness of 3025 HK0.025. TEM results revealed droplet free, denser microstructure with (200) preferred orientation for the HIPIMS coating owing to the increased ionization as compared to the more porous structure with random orientation observed in UBM coating. The dry sliding wear coefficient (K-c) of the coating was 1.8 X 10(-15) m(3) N-1 m(-1), whereas the steady state coefficient of friction was 0.32. Potentiodynamic polarization tests revealed higher E-corr values, higher pitting resistance (around potentials +400 to +600 mV), and lower. corrosion current densities for HIPIMS deposited coatings as compared to the coatings deposited by ABS or HIPIMS-UBM. The corrosion behavior of the coatings qualitatively improved with the progressive use of HIPIMS from pretreatment stage to the coating deposition step. (C) 2008 American Vacuum Society

A novel sputtering technique: Inductively Coupled Impulse Sputtering (ICIS)

Sputtering magnetic materials with magnetron based systems has the disadvantage of field quenching and variation of alloy composition with target erosion. The advantage of eliminating magnetic fields in the chamber is that this enables sputtered particles to move along the electric field more uniformly. Inductively coupled impulse sputtering (ICIS) is a form of high power impulse magnetron sputtering (HIPIMS) without a magnetic field where a high density plasma is produced by a high power radio frequency (RF) coil in order to sputter the target and ionise the metal vapour. In this emerging technology, the effects of power and pressure on the ionisation and deposition process are not known. The setup comprises of a 13.56 MHz pulsed RF coil pulsed with a duty cycle of 25 %. A pulsed DC voltage of 1900 V was applied to the cathode to attract Argon ions and initiate sputtering. Optical emission spectra (OES) for Cu and Ti neutrals and ions at constant pressure show a linear intensity increase for peak RF powers of 500 W – 3400 W and a steep drop of intensity for a power of 4500 W. Argon neutrals show a linear increase for powers of 500 W – 2300 W and a saturation of intensity between 2300 W – 4500 W. The influence of pressure on the process was studied at a constant peak RF power of 2300 W. With increasing pressure the ionisation degree increased. The microstructure of the coatings shows globular growth at 2.95×10−2 mbar and large-grain columnar growth at 1.2×10−1 mbar. Bottom coverage of unbiased vias with a width of 0.360 μm and aspect ratio of 2.5:1 increased from 15 % to 20 % for this pressure range. The current work has shown that the concept of combining a RF powered coil with a magnet-free high voltage pulsed DC powered cathode is feasible and produces very stable plasma. The experiments have shown a significant influence of power and pressure on the plasma and coating microstructure

The effect of (Ti + Al): V ratio on the structure and oxidation behaviour of TiAlN/VN nano-scale multilayer coatings

Nano-scaled multilayered TiAlN/VN coatings have been grown on stainless steel and M2 high speed steel substrates at U-B = - 85 V in an industrial, four target, Hauzer HTC 1000 coater using combined cathodic steered arc etching/unbalanced magnetron sputtering. X-ray diffraction (XRD) has been used to investigate the effects of process parameters (Target Power) on texture evolution (using texture parameter T*), development of residual stress (sin(2) psi method) and nano-scale multilayer period. The composition of the coating was determined using energy dispersive X-ray analysis. The thermal behaviour of the coatings in air was studied using thermo-gravimetric analysis, XRD and scanning electron microscopy. The bi-layer period varied between 2.8 and 3.1 nm and in all cases a {1 1 0} texture developed with a maximum value T* = 4.9. The residual stress varied between -5.2 and -7.4 GPa. The onset of rapid oxidation occurred between 628 and 645 degreesC depending on the (Ti+Al):V ratio. After oxidation in air at 550 degreesC AlVO4, TiO2 and V2O5 Phases were identified by XRD with the AlVO4, TiO2 being the major phases. The formation of AlVO4 appears to disrupt the formation of Al2O3 which imparts oxidation resistance to TiAlN based coatings. Increasing the temperature to 600 and 640 degreesC led to a dramatic increase in the formation of V2O5 which was highly oriented (0 0 1) with a plate-like morphology. At 640 degreesC there was no evidence of the coating on XRD. Increasing the temperature to 670 degreesC led to further formation of AlVO4 and a dramatic reduction in V2O5. (C) 2003 Elsevier B.V. All rights reserved

Long-term behaviour of Nb and Cr nitrides nanostructured coatings under steam at 650°C. Mechanistic considerations.

There is an increasing demand for steam power plants to operate in super-critical conditions i.e. temperatures in excess of 600°C. Under these conditions creep resistant ferritic steels oxidize and therefore require coatings in order to last. Physical vapor deposition and especially High Power Impulse Magnetron Sputtering deposited CrN/NbN nano-scale multilayer coatings with a 2.45 Cr/Nb ratio showed excellent performance when exposed to 650 °C in pure steam environment up to 2,000 h. However the role of Nb in offering protection is unclear. In order to study the long term behaviour of this type of coatings as well as to determine the influence of Nb on their oxidation resistance, a CrN/NbN coating with a 1.16 Cr/Nb ratio was studied for 12,650 h. The coating is hard, well adhered and resistant to environmental corrosion, which are properties required in particular for coatings to be applied on turbine blades. The coating also protects P92 from steam oxidation at 650º C, however coating growth defects influence significantly the oxidation resistance. The long-time exposure allowed to study the protection/ degradation mechanisms provided by this type of ceramic coatings. It was found that oxide nodules grow due to the presence of coating defect originated from substrate defects. Moreover, the higher Nb CrN/NbN coating slowly oxidizes, consuming the coating to a large extent after 12,650 h. As a result, protective oxides containing Cr and Nb are developed, remaining well attached to the substrate for at least the test duration, and preventing further substrate oxidation by steam. Interestingly, thin voids present in the as deposited coating self-heal by forming Cr rich oxides, which block steam to reach the substrate

Plasma analysis of Inductively Coupled Impulse Sputtering of Cu, Ti and Ni

Inductively coupled impulse sputtering (ICIS) is a new development in the field of highly ionised pulsed PVD processes. For ICIS the plasma is generated by an internal inductive coil, replacing the need for a magnetron. To understand the plasma properties, measurements of the current and voltage waveforms at the cathode were conducted. The IEDFs were measured by energy resolved MS and plasma chemistry was analysed by OES and then compared to a model. The target was operated in pulsed DC mode and the coil was energised by pulsed RF power, with a duty cycle of 7.5 %. At a constant pressure (14 Pa) the set peak RF power was varied from 1000-4000 W. The DC voltage to the target was kept constant at 1900 V. OES measurements have shown a monotonic increase in intensity with increasing power. Excitation and ionisation processes were single step for ICIS of Ti and Ni and multi-step for Cu. The latter exhibited an unexpectedly steep rise in ionisation efficiency with power. The IEDFs measured by MS show the material- and time- dependant plasma potential in the range of 10-30 eV, ideal for increased surface mobility without inducing lattice defects. A lower intensity peak, of high energetic ions, is visible at 170 eV during the pulse