Yashodhan Purandare

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...

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...

ZrN coatings deposited by high power impulse magnetron sputtering and cathodic arc techniques

Zirconium nitride (ZrN) coatings were deposited on 1 μm finish high speed steel and 316L stainless steel test coupons. Cathodic Arc (CA) and High Power Impulse Magnetron Sputtering (HIPIMS) + Unbalanced Magnetron Sputtering (UBM) techniques were utilized to deposit coatings. CA plasmas are known to be rich in metal and gas ions of the depositing species as well as macroparticles (droplets) emitted from the arc sports. Combining HIPIMS technique with UBM in the same deposition process facilitated increased ion bombardment on the depositing species during coating growth maintaining high deposition rate. Prior to coating deposition, substrates were pretreated with Zr+ rich plasma, for both arc deposited and HIPIMS deposited coatings, which led to a very high scratch adhesion value (LC2) of 100 N. Characterization results revealed the overall thickness of the coatings in the range of 2.5 μm with hardness in the range of 30–40 GPa depending on the deposition technique. Cross-sectional transmission electron mic...

Target poisoning during CrN deposition by mixed high power impulse magnetron sputtering and unbalanced magnetron sputtering technique

Target poisoning phenomenon in reactive sputtering is well-known and has been studied in depth over the years. There is a clear agreement that this effect has a strong link on the quality, composition, properties, and pronouncedly on the deposition rate of physical vapor deposition coatings. With the introduction of ionized physical vapor deposition techniques such as the relatively novel high power impulse magnetron sputtering (HIPIMS), which have highly ionized plasmas of the depositing species (metal and gas ions), target poisoning phenomenon is highly contested and thus has been left wide open for discussion. Particularly, there have been contradicting reports on the presence of prominent hysteresis curves for reactive sputtering by HIPIMS. More work is needed to understand it, which in turn will enable reader to simplify the coating deposition utilizing HIPIMS. This work focuses on the study of chromium (Cr) targets when operated reactively in argon + nitrogen atmosphere and in different ionizing con...

Development of ZnTe layers using an electrochemical technique for applications in thin-film solar cells

Zinc telluride layers were grown by an electrochemical technique using acidic and aqueous solutions containing ZnCl2 and TeO2. The layers were deposited on glass/fluorine-doped tin oxide substrates using a two-electrode system. The deposited ZnTe layers were characterized using x-ray diffraction, x-ray fluorescence, Raman spectroscopy, optical absorption, photoelectrochemical cell measurements, scanning electron microscopy and 3D-atomic force microscopy (3D-AFM) for the structural, optical, electrical and morphological properties. The electrodeposited ZnTe layers grow as columns, and have cubic crystal structure, the band gap in the range of (2.00–2.20) eV and p-type electrical conductivity. Surface morphology studies using SEM indicate the presence of two types of material clusters varying in size up to ~125 nm. 3D-AFM studies with higher magnification show that the material tends to grow as columns with different sizes leaving gaps in between in some areas.

Development of superlattice CrN/NbN coatings for joint replacements deposited by high power impulse magnetron sputtering

The demand for reliable coating on medical implants is ever growing. In this research, enhanced performance of medical implants was achieved by a CrN/NbN coating, utilising nanoscale multilayer/superlattice structure. The advantages of the novel high power impulse magnetron sputtering technology, namely, its unique highly ionised plasma, were exploited to deposit dense and strongly adherent coatings on CoCr implants. Transmission electron microscopy analysis revealed coating superlattice structure with bi-layer thickness of 3.5 nm. CrN/NbN deposited on CoCr samples showed exceptionally high adhesion, critical load values of LC2 = 50 N in scratch adhesion tests. Nanoindentation tests showed high hardness of 34 GPa and Young’s modulus of 447 GPa. Low coefficient of friction (μ) 0.49 and coating wear coefficient (KC) = 4.94 × 10−16 m3 N−1 m−1 were recorded in dry sliding tests. Metal ion release studies showed a reduction in Co, Cr and Mo release at physiological and elevated temperatures (70 °C) to almost undetectable levels (<1 ppb). Rotating beam fatigue testing showed a significant increase in fatigue strength from 349 ± 59 MPa (uncoated) to 539 ± 59 MPa (coated). In vitro biological testing has been performed in order to assess the safety of the coating in biological environment; cytotoxicity, genotoxicity and sensitisation testing have been performed, all showing no adverse effects.