Papers

ICMCTF2002 Session B3-1: Structure and Properties of Hard Coatings

Tuesday, April 23, 2002 8:30 AM in Room Golden West

Tuesday Morning

Start	Invited?	Item
8:30 AM		B3-1-1 Effects of Low-energy Ion Irradiation During Nucleation and the Early Stages of Film Growth D. Adamovic, E.P. Münger, V. Chirita, L. Hultman (Linköping University, Sweden); J.E. Greene (Frederick Seitz Materials Research Laboratory, University of Illinois) Low-energy (<50 eV)ion-surface interactions play a crucial role during nucleation and the early stages of film growth. We use embedded-atom method molecular dynamics simulations to monitor the atomistic kinetics characterizing the bombardment of two-dimensional (2D) compact Pt nanoclusters on Pt(111) at 1000K. Incident atoms (Pt, Ar, Xe) with energies between 5 and 50 eV at several incidence angles are followed in separate simulations of ~ 20 ps each. The study concentrates on clusters with between 3 and 37 atoms and of various shapes. Our simulations reveal three major classes of events. They are cluster preservation, i.e. no change in shape or position, cluster reconfiguration, involving edge-diffusion and/or concerted dimer/trimer gliding and cluster disruption (rim atom scattering and/or total disintegration). Two of the most commonly observed events are the formation of three-dimensional (3D) clusters and the hopping and/or push out/exchange mechanism with rim atoms. Other typical processes observed are permanent or temporary dislodgement of cluster atoms onto the surface as well as the creation of surface vacancies. Our results suggest that cluster preservation and reconfiguration events primarily occur at incident energies below 30 eV, while cluster disruption prevails at higher energies. The effects on adatoms and cluster migration rates as well as the intra- and interlayer mass transport processes induced by low-energy bombardment are detailed. The role of energy and momentum transfer in driving these processes is also discussed. The results provide detailed insights regarding the effects of low-energy ion irradiation on microstructure and surface morphological evolution during nucleation and growth of films deposited by sputtering and ion-assisted techniques.
9:10 AM		B3-1-3 The Effect of the Substrate on the Annealing Behaviour of W-Si-N Sputtered Films C. Louro, A. Cavaleiro (University of Coimbra, Portugal) W-based sputtered films display a wide spectrum of properties, which make them useful in a variety of different fields, including diffusion barriers, particularly when presenting amorphous structure, and tribological applications associating high hardness and thermal/chemical stability. Research studies performed on the effect of annealing temperature on the properties of these films showed that improvements on their mechanical properties can be obtained. In this paper attention is focused on the comparison of hardness values obtained in previous research works and on W-Si-N films, before and after annealing in Ar/H₂ atmosphere up to 1000°C. Moreover, the effect of the substrate (different thermal expansion coefficients in the range 5-18x10^-6 K^-1) used for the films deposition on the hardness, Young's modulus and cohesion/adhesion of the films was also studied. . The films were deposited from a W target incrusted with 16 round (diameter = 12mm) pieces with partial pressure ratios P_N2/P_Ar in the range [0-1], that leads to atomic ratios Si/W in the range [0.25-0.8] and at.%N in the range [0-50%]. The hardness of the as-deposited film reaches in some cases 30GPa. After annealing at 1000°C an increase of the hardness was observed (up to 44GPa). Depending on the substrate used in the deposition, changes in mechanical properties of the films were detected. Most of the films are amorphous after deposition and undergo structural transformations after thermal annealing.
9:30 AM		B3-1-4 Growth and Properties of Metastable δ-TaN_X Layers C.-S. Shin, Y.-W. Kim, N. Hellgren, D. Gall, J.E. Greene, I. Petrov (Frederick Seitz Materials Research Laboratory, University of Illinois) TaN_x is presently used in a variety of hard coating, wear-resistant, and diffusion barrier applications. However, the Ta-N system is inherently complex with more than 11 reported equilibrium and metastable phases and there has been little systematic study of the synthesis of these materials. TaN_x layers were grown on MgO(001) and oxidized Si(001) by ultrahigh vacuum reactive magnetron sputtering in mixed Ar/N₂ discharges. The phase composition was determined as a function of the growth temperature T_s (100 - 800 °C) and N₂ fraction (0-1). We find a wide single-phase field at T_s < 650 °C corresponding to the growth of metastable B1 NaCl-structure δ-TaN_x with x ranging from 0.94 to 1.37 while the thermodynamically-stable hexagonal ε-TaN phase is formed at higher growth temperatures. High quality epitaxial films of δ-TaN_x were obtained on MgO(001) under high-flux (J_i/J_Me = 11), low-energy (E_i = 30 eV) ion irradiation. The room-temperature resistivity (ρ = 225 µΩ-cm), hardness (H = 30.9 GPa), and elastic modulus (E = 455 GPa) of δ-TaNx(001) are independent of x over the range 0.94-1.22. However, changes in the electronic structure associated with increasing x > 1.22 lead to an increase in ρ with a decrease in H and E. Increasing E_i above 50 eV results in superhardness values (H = 40-45 GPa) due to the formation of a coherent nanolayered structure consisting of cubic δ-TaN_x (001) and hexagonal TaN_x (either γ-Ta2N or ε-TaN, depending on the N₂ fraction).
9:50 AM		B3-1-5 Multilayer Oxide Coatings by Closed Field Unbalanced Magnetron Sputter Ion Plating K.E. Cooke (Teer Coatings Ltd, United Kingdom); J. Bassas (Univesitat Autonoma de Barcelona, Spain); D. Boscarino (Thin Films srl, Italy); A. Figueras (Univesitat Autonoma de Barcelona, Spain); V. Rigato (Instituto Nazionale de Fisica Nucleare, Italy); D.G. Teer (Teer Coatings Ltd., United Kingdom) A ceramic multilayer oxide coating of the type Al_xZr_yO_z has been successfully deposited onto tool and die steels and other substrates by Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUBMSIP). A graded metal-nitride-oxynitride bond layer has been developed to maximise the adhesion of the multilayer coating. The mechanical properties of the resulting coatings, including adhesion and hardness, have been evaluated by micro- and nano-indentation techniques, scratch testing etc. H_plast hardness up to 17 GPa has been achieved. The detailed micro-structure of the coatings, including their respective nm-scale multilayer repeat distance, λ, has been studied by advanced analytical techniques including High Resolution Transmission Electron Microscopy (HRTEM), Rutherford Back Scattering (RBS), and Glancing Angle X-ray Diffraction (GAXRD), etc. The coating properties are reviewed and correlated with the analytical data. Potential applications for, and some limitations of, the selected coatings are discussed.
10:10 AM		B3-1-6 The B-C-N Triangle - a Suitable System for the Production of Thin Films with High Load Carrying Capacity V. Linss, N. Schwarzer, I. Hermann (TU Chemnitz, Germany); U. Kreissig (Research Centre Rossendorf, Germany); F. Richter (TU Chemnitz, Germany) A special coating design, characterised by a certain depth profile of Young's modulus, for higher load carrying capacity was suggested by one of us [1] (see also [2]). Therefore a material system with an adjustable Young's modulus is needed. This was found in the B-C-N system. Thin films of varied stoichiometry were deposited by reactive DC magnetron sputtering of targets with different B/C ratio (B, B4C, BC, BC4, C) in an Ar/N₂ mixture. The portion of N₂ in the gas was varied with the substrate at floating potential. For 50% N₂ a negative substrate potential was applied for ion bombardment of the films. The film composition was measured by elastic recoil detection analysis. The mechanical properties hardness and Young's modulus were determined from nanoindentation using a UMIS-2000 system (CSIRO, Australia) [3]. All films were investigated by Fourier-transformed infrared spectroscopy (FTIR). The mechanical properties of the films depend on their composition on one hand and on ion bombardment on the other. With increasing amount of N hardness and Young's modulus decrease to a saturation level. This effect is much more pronounced for films made with the B-rich targets. Here the Young's modulus can be varied up to a factor of 3. FTIR spectra show changes even for 2% N₂ in the gas. For the ion bombarded films the mechanical properties change in dependence on the intensity of the bombardment: Hardness and Young's modulus increase up to 100%. For these films changes in the FTIR spectra can be seen. Films containing carbon show a decrease in the typical peak for the C-N triple bond. It is supposed that the ion bombardment changes the bonding characteristics and leads to a stronger atomic network. [1] N. Schwarzer: paper E2-10, ICMCTF 2000, San Diego, USA, April 2000, published in Surf. Coat. Technol. 133 -134 (2000) 397 - 402. [2] F. Richter et al., this conference [3] I. Hermann et al., this conference.
10:30 AM		B3-1-7 Mechanical and Tribological Properties of CrBN Coatings T.Z. Gorishnyy, S.M. Aouadi, S. Varma, S.L. Rohde (University of Nebraska-Lincoln) The goal of this work is to investigate the hardness and wear resistance of CrBN coatings as a function of chemical composition and substrate temperature. To achieve this coatings were deposited by reactive unbalanced magnetron sputtering on a variety of substrates including: Si (100), A2 steel and 2024 Al substrates. The chemical composition was deduced from XPS measurements, and the phase composition was determined using XRD in conjunction with spectroscopic ellipsometry. These coatings consisted of an amorphous matrix with Cr_xB_1-x, Cr_xN_1-x, and in some cases BN nanoparticles incorporated in it. AFM measurements were utilized to determine surface roughness and average grain size. The grain size was found to be controlled by deposition temperature, bias voltage and boron content. The nanohardness of each sample was measured and was found to decrease with increasing the nitrogen content. Wear rates for several films were measured and the results are discussed in terms of coating composition and morphology.
10:50 AM		B3-1-8 Ir-base Multi-element Coating on Tungsten Carbide by RF Magnetron Sputtering Process J.G. Duh, F.B. Wu (National Tsing Hua University, Taiwan, ROC); Y.Y. Tsai (Industrial Technology Research Institute, Taiwan); W.Y. Chen (National Tsing Hua University, Taiwan, ROC) Ir-base noble metal hard coatings were deposited onto tungsten carbide (WC) substrate by r.f. magnetron sputtering process. Films were prepared by multi-target sputtering with iridium, rhenium and chromium as the sources. Argon and nitrogen were inlet into chamber to be the plasma and reactive gases. The relationship between contents of each component in the noble metal alloy films and the control parameter of the input powers of sputtering guns was investigated. The content of Cr and N ranged from 3.2 to 33.5 at.% and 7.3 to 21.0 at.%, respectively, as the power of Cr was controlled from 50 to 250 watt. The atomic ratio of Ir/Re remained constant at 2.0, regardless of the amount of Cr and N co-deposited. The coating microstructure and morphology were also studied by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. It was shown that the surface roughness (Ra) values of uncoated substrate and Ir-Re-CrN protective thin film were in the same order around 2~ 6 nm. The film hardness was measured by a Knoop microhardness tester and it is shown that the multi-element coatings exhibited superior hardness than the single noble metal hard films.
11:10 AM		B3-1-9 Tribological Behavior of Candidate Coatings for Al Die Casting Dies O. Salas (ITESM, Mexico on sabbatical to Colorado School of Mines); K. Kearns, S. Carrera, J.J. Moore (Colorado School of Mines) Candidate coatings on H13 steel substrates aimed at improving the tribological performance of Al die casting dies have been extensively characterized. The coating systems considered were: CrC, CrN, ZrN, MoNx, MoZrN, TiAlN, TiN/TiC and a control sample that was subjected to a carbonitriding thermochemical treatment. The characterization included: scratch testing, wear testing, nanoindentation, optical and scanning electron microscopy and x-ray diffraction. The results from the present work are part of a comprehensive study to design coating systems considering all aspects involved in the performance of the coating.
11:30 AM		B3-1-10 Deposition and Characterization of Ti(CNO) Coatings Deposited by Unbalanced Magnetron Sputtering J.H. Hsieh (Nanyang Technological University, Singapore); C. Li (School of MPE, Nanyang Technological University, Singapore) Several TiCNO coatings were deposited by a unbalanced magnetron sputtering system. The coating properties as a function of oxygen flow rate were studied using GDOS (glow discharge optical spectrometer), XRD, Raman spectroscopy, scratch testing and nano-indentation measurement. The tribological properties were then carried out using a ball-on-disk setup with M50 steel and alumina balls. The results show that coating properties and performance are greatly affected by the amount of oxygen. With oxygen flow rate at four sccm during deposition, the TiCNO coating had the lowest wear rate among all. Further increase in oxygen flow rate resulted in decreasing hardness, adhesion, and wear resistance, together with the increase of friction coefficient. Also found is that the color of these coatings changed as a function of oxygen flow rate, indicating that these coatings can be used as decorating thin films.
11:50 AM		B3-1-11 The Physical Properties of Titanium Aluminium Chromium Nitride Coatings Deposited by Closed Field Magnetron Sputter Ion Plating S. Yang, D.G. Teer (Teer Coatings Ltd., United Kingdom) TiAlCrN coatings have been deposited by closed field magnetron sputter ion plating on to M42 high speed steel, stainless steel and alumina substrates. The Ti and Al content was kept constant and a series of coatings was deposited while varying Cr content. The nitrogen was controlled using an optical emission monitor with feed back control. Some of the coatings were heat treated in air at 600°° C and 900°C. The hardness and adhesion of the coatings were measured and the wear properties were studied using a pin on disc tester running dry and with water lubrication. The properties of the as deposited and the heat treated samples were compared. Those coatings with the most promising properties as revealed by these simple tests were selected and used to coat high speed steel twist drills. The coated drills were tested under severe accelerated conditions with flood coolant and the results were compared with those from a range of commercially available coated drills. It has been shown that the coatings with optimised Cr contents have excellent wear properties, good thermal stability and give good drilling performance.