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Title: Interface microstructure engineering by high power impulse magnetron sputtering for the enhancement of adhesion

Abstract

An excellent adhesion of hard coatings to steel substrates is paramount in practically all application areas. Conventional methods utilize Ar glow etching or cathodic arc discharge pretreatments that have the disadvantage of producing weak interfaces or adding droplets, respectively. One tool for interface engineering is high power impulse magnetron sputtering (HIPIMS). HIPIMS is based on conventional sputtering with extremely high peak power densities reaching 3 kW cm{sup -2} at current densities of >2 A cm{sup -2}. HIPIMS of Cr and Nb was used to prepare interfaces on 304 stainless steel and M2 high speed steel (HSS). During the pretreatment, the substrates were biased to U{sub bias}=-600 V and U{sub bias}=-1000 V in the environment of a HIPIMS of Cr and Nb plasma. The bombarding flux density reached peak values of 300 mA cm{sup -2} and consisted of highly ionized metal plasma containing a high proportion of Cr{sup 1+} and Nb{sup 1+}. Pretreatments were also carried out with Ar glow discharge and filtered cathodic arc as comparison. The adhesion was evaluated for coatings consisting of a 0.3 {mu}m thick CrN base layer and a 4 {mu}m thick nanolayer stack of CrN/NbN with a period of 3.4 nm, hardness of HK{sub 0.025}=3100,more » and residual stress of -1.8 GPa. For HIPIMS of Cr pretreatment, the adhesion values on M2 HSS reached scratch test critical load values of L{sub C}=70 N, thus comparing well to L{sub C}=51 N for interfaces pretreated by arc discharge plasmas and to L{sub C}=25 N for Ar etching. Cross sectional transmission electron microscopy studies revealed a clean interface and large areas of epitaxial growth in the case of HIPIMS pretreatment. The HIPIMS pretreatment promoted strong registry between the orientation of the coating and polycrystalline substrate grains due to the incorporation of metal ions and the preservation of crystallinity of the substrate. Evidence and conditions for the formation of cube-on-cube epitaxy and axiotaxy on steel and {gamma}-TiAl substrates are presented.« less

Authors:
; ;  [1];  [2]
  1. Materials and Engineering Research Institute, Sheffield Hallam University, Howard Street, Sheffield S1 1WB (United Kingdom)
  2. (United States)
Publication Date:
OSTI Identifier:
20982731
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 5; Other Information: DOI: 10.1063/1.2697052; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ADHESION; CHROMIUM NITRIDES; COATINGS; CURRENT DENSITY; DEPOSITION; DROPLETS; EPITAXY; ETCHING; FLUX DENSITY; GLOW DISCHARGES; HARDNESS; MICROSTRUCTURE; NIOBIUM NITRIDES; PLASMA; POLYCRYSTALS; PRESSURE RANGE GIGA PA; RESIDUAL STRESSES; SPUTTERING; STAINLESS STEEL-304; TRANSMISSION ELECTRON MICROSCOPY

Citation Formats

Ehiasarian, A. P., Wen, J. G., Petrov, I., and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 and Materials Science Department, University of Illinois, Urbana, Illinois 61801. Interface microstructure engineering by high power impulse magnetron sputtering for the enhancement of adhesion. United States: N. p., 2007. Web. doi:10.1063/1.2697052.
Ehiasarian, A. P., Wen, J. G., Petrov, I., & Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 and Materials Science Department, University of Illinois, Urbana, Illinois 61801. Interface microstructure engineering by high power impulse magnetron sputtering for the enhancement of adhesion. United States. doi:10.1063/1.2697052.
Ehiasarian, A. P., Wen, J. G., Petrov, I., and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 and Materials Science Department, University of Illinois, Urbana, Illinois 61801. Thu . "Interface microstructure engineering by high power impulse magnetron sputtering for the enhancement of adhesion". United States. doi:10.1063/1.2697052.
@article{osti_20982731,
title = {Interface microstructure engineering by high power impulse magnetron sputtering for the enhancement of adhesion},
author = {Ehiasarian, A. P. and Wen, J. G. and Petrov, I. and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 and Materials Science Department, University of Illinois, Urbana, Illinois 61801},
abstractNote = {An excellent adhesion of hard coatings to steel substrates is paramount in practically all application areas. Conventional methods utilize Ar glow etching or cathodic arc discharge pretreatments that have the disadvantage of producing weak interfaces or adding droplets, respectively. One tool for interface engineering is high power impulse magnetron sputtering (HIPIMS). HIPIMS is based on conventional sputtering with extremely high peak power densities reaching 3 kW cm{sup -2} at current densities of >2 A cm{sup -2}. HIPIMS of Cr and Nb was used to prepare interfaces on 304 stainless steel and M2 high speed steel (HSS). During the pretreatment, the substrates were biased to U{sub bias}=-600 V and U{sub bias}=-1000 V in the environment of a HIPIMS of Cr and Nb plasma. The bombarding flux density reached peak values of 300 mA cm{sup -2} and consisted of highly ionized metal plasma containing a high proportion of Cr{sup 1+} and Nb{sup 1+}. Pretreatments were also carried out with Ar glow discharge and filtered cathodic arc as comparison. The adhesion was evaluated for coatings consisting of a 0.3 {mu}m thick CrN base layer and a 4 {mu}m thick nanolayer stack of CrN/NbN with a period of 3.4 nm, hardness of HK{sub 0.025}=3100, and residual stress of -1.8 GPa. For HIPIMS of Cr pretreatment, the adhesion values on M2 HSS reached scratch test critical load values of L{sub C}=70 N, thus comparing well to L{sub C}=51 N for interfaces pretreated by arc discharge plasmas and to L{sub C}=25 N for Ar etching. Cross sectional transmission electron microscopy studies revealed a clean interface and large areas of epitaxial growth in the case of HIPIMS pretreatment. The HIPIMS pretreatment promoted strong registry between the orientation of the coating and polycrystalline substrate grains due to the incorporation of metal ions and the preservation of crystallinity of the substrate. Evidence and conditions for the formation of cube-on-cube epitaxy and axiotaxy on steel and {gamma}-TiAl substrates are presented.},
doi = {10.1063/1.2697052},
journal = {Journal of Applied Physics},
number = 5,
volume = 101,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}
  • HIPIMS (High Power Impulse Magnetron Sputtering) discharge is a new PVD technology for the deposition of high-quality thin films. The deposition flux contains a high degree of metal ionization and nitrogen dissociation. The microstructure of HIPIMS-deposited nitride films is denser compared to conventional sputter technologies. However, the mechanisms acting on the microstructure, texture and properties have not been discussed in detail so far. In this study, the growth of TiN by HIPIMS of Ti in mixed Ar and N{sub 2} atmosphere has been investigated. Varying degrees of metal ionization and nitrogen dissociation were produced by increasing the peak discharge currentmore » (I{sub d}) from 5 to 30 A. The average power was maintained constant by adjusting the frequency. Mass spectrometry measurements of the deposition flux revealed a high content of ionized film-forming species, such as Ti{sup 1+}, Ti{sup 2+} and atomic nitrogen N{sup 1+}. Ti{sup 1+} ions with energies up to 50 eV were detected during the pulse with reducing energy in the pulse-off times. Langmuir probe measurements showed that the peak plasma density during the pulse was 3 x 10{sup 16} m{sup -3}. Plasma density, and ion flux ratios of N{sup 1+}: N{sub 2}{sup 1+} and Ti{sup 1+}: Ti{sup 0} increased linearly with peak current. The ratios exceeded 1 at 30 A. TiN films deposited by HIPIMS were analyzed by X-ray diffraction, and transmission electron microscopy. At high I{sub d}, N{sup 1+}: N{sub 2}{sup 1+} > 1 and Ti{sup 1+}: Ti{sup 0} > 1 were produced; a strong 002 texture was present and column boundaries in the films were atomically tight. As I{sub d} reduced and N{sup 1+}: N{sub 2}{sup 1+} and Ti{sup 1+}: Ti{sup 0} dropped below 1, the film texture switched to strong 111 with a dense structure. At very low I{sub d}, porosity between columns developed. The effects of the significant activation of the deposition flux observed in the HIPIMS discharge on the film texture, microstructure, morphology and properties are discussed.« less
  • Reactive sputtering by high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) of a Zr target in Ar/H{sub 2} plasmas was employed to deposit Zr-H films on Si(100) substrates, and with H content up to 61 at. % and O contents typically below 0.2 at. % as determined by elastic recoil detection analysis. X-ray photoelectron spectroscopy reveals a chemical shift of ∼0.7 eV to higher binding energies for the Zr-H films compared to pure Zr films, consistent with a charge transfer from Zr to H in a zirconium hydride. X-ray diffraction shows that the films are single-phase δ-ZrH{sub 2} (CaF{submore » 2} type structure) at H content >∼55 at. % and pole figure measurements give a 111 preferred orientation for these films. Scanning electron microscopy cross-section images show a glasslike microstructure for the HiPIMS films, while the DCMS films are columnar. Nanoindentation yield hardness values of 5.5–7 GPa for the δ-ZrH{sub 2} films that is slightly harder than the ∼5 GPa determined for Zr films and with coefficients of friction in the range of 0.12–0.18 to compare with the range of 0.4–0.6 obtained for Zr films. Wear resistance testing show that phase-pure δ-ZrH{sub 2} films deposited by HiPIMS exhibit up to 50 times lower wear rate compared to those containing a secondary Zr phase. Four-point probe measurements give resistivity values in the range of ∼100–120 μΩ cm for the δ-ZrH{sub 2} films, which is slightly higher compared to Zr films with values in the range 70–80 μΩ cm.« less
  • Both the industrially favorable deposition technique, high power impulse magnetron sputtering (HIPIMS), and the industrially popular rotating cylindrical magnetron have been successfully combined. A stable operation without arcing, leaks, or other complications for the rotatable magnetron was attained, with current densities around 11 A cm{sup -2}. For Ti and Al, a much higher degree in ionization in the plasma region was observed for the HIPIMS mode compared to the direct current mode.
  • The commonly used current-voltage characteristics are foundinadequate for describing the pulsed nature of the high power impulsemagnetron sputtering (HIPIMS) discharge, rather, the description needs tobe expanded to current-voltage-time characteristics for each initial gaspressure. Using different target materials (Cu, Ti, Nb, C, W, Al, Cr) anda pulsed constant-voltage supply it is shown that the HIPIMS dischargestypically exhibit an initial pressure dependent current peak followed bya second phase that is power and material dependent. This suggests thatthe initial phase of a HIPIMS discharge pulse is dominated by gas ionswhereas the later phase has a strong contribution from self-sputtering.For some materials the dischargemore » switches into a mode of sustainedself-sputtering. The very large differences between materials cannot beascribed to the different sputter yields but they indicate thatgeneration and trapping ofsecondary electrons plays a major role forcurrent-voltage-time characteristics. In particular, it is argued thatthe sustained self-sputtering phase is associated with thegeneration ofmultiply charged ions because only they can cause potential emission ofsecondary electrons whereas the yield caused by singly charged metal ionsis negligibly small.« less
  • Self-sputtering runaway in high power impulse magnetron sputtering is closely related to the appearance of multiply charged ions. This conclusion is based on the properties of potential emission of secondary electrons and energy balance considerations. The effect is especially strong for materials whose sputtering yield is marginally greater than unity. The absolute deposition rate increases {approx}Q{sup 1/2}, whereas the rate normalized to the average power decreases {approx}Q{sup -1/2}, with Q being the mean ion charge state number.