Properties and Characterization of Hard Coatings and Surfaces

Thursday, May 1, 2014 1:30 PM in Room Royal Palm 1-3

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1:30 PM B4-4-1 Nanostructural Analysis of Magnetron Sputtered HfAlN Thin Films Grown on MgO(001) by Atom Probe Tomography
David Engberg (Linköping University, IFM, Thin Film Physics Division, Sweden); Lars Johnson (Sandvik Coromant, Sweden); Mattias Thuvander (Chalmers University of Technology, Department of Applied Physics, Sweden); Lars Hultman (Linköping University, IFM, Thin Film Physics Division, Sweden)

Thin films of transition metal nitrides are a field of great interest for academia and industry alike. TiAlN films exhibit high hardness, thermal stability and wear resistance, making them suitable for metal cutting applications. One major mechanism for maximizing hardness of such films is based on self-organized compositional modulations on the nanometer scale through spinodal decomposition and phase separation of immiscible components. All group IV transition metal nitrides are expected to phase separate when combined with AlN, owing to their immiscibility due to volumetric, electronic, and/or magnetic mismatch. Calculations have predicted that the mixing enthalpy of HfAlN is approximately twice that of TiAlN [1], yielding a stronger driving force for phase separation in HfAlN than in TiAlN. Previously, laser assisted atom probe tomography (ATP) methods were developed for TiAlN thin films [2,3]. In this study, Hf1-xAlxN (x = 0.17, 0.29, and 0.48) thin films deposited by magnetron sputtering on MgO(001) substrates have been analyzed using ATP. We observe the very onset of compositional modulations in samples with x > 0.2, but with less discrimination than initially seen by scanning transmission electron microscopy (STEM) [4]. Differences in the results from tomography and microscopy evaluation are discussed with respect to the choice of field evaporation and reconstruction parameters, and the contrast-forming mechanisms (atomic number contrast vs. strain-field contrast), respectively.

[1] B. Alling, A. Karimi, I. A. Abrikosov, Surf. Coat. Technol. 203 (2008) 883.

[2] R. Rachbauer, E. Stergar, S. Massl, M. Moser, P.H. Mayrhofer, Scr. Mater. 61 (2009) 725.

[3] L.J.S. Johnson, M. Thuvander, K. Stiller, M. Odén, L. Hultman, Thin Solid Films 520 (2012) 4362.

[4] B. Howe, J. Bareño, M. Sardela, J.G. Wen, J.E. Greene, L. Hultman, A.A. Voevodin, I. Petrov, Surf. Coat. Technol. 202 (2007) 809.

1:50 PM B4-4-2 Investigations on the Diffusion Behaviour of Fe, Cr, and C in Arc Evaporated TiN- and CrN-based Coatings and Their Influence on the Thermal and Mechanical Properties
Corinna Sabitzer, Christian Steinkellner, Benjamin Larrieu (Vienna University of Technology, Austria); Peter Polcik (Plansee Composite Materials GmbH, Germany); Mirjam Arndt, Richard Rachbauer (Oerlikon Balzers Coating AG, Liechtenstein); Jörg Paulitsch, Paul Heinz Mayrhofer (Vienna University of Technology, Austria)

Hard materials like CrN, TiN, CrAlN, and TiAlN are well established as protective coatings for tools used in various machining and forming applications. Even though the thermal stability and thermo-mechanical properties of such coatings have already been investigated in numerous studies only little information is available concerning the influence of transfer-material-diffusion during e.g. machining applications. Therefore, thin layers of Fe, Cr, and C ─ which are common transfer-elements during machining ─ were deposited on arc evaporated CrN, TiN, Al0.7Cr0.3N as well as on Ti0.5Al0.5N coatings. The concentration-depth profiles after vacuum annealed for 30 min at 600, 800, and 1000 °C were evaluated by cross-sectional EDX line-scans as well as by secondary ion mass spectroscopy. Additional to the determination of the diffusion coefficients at high temperatures, low temperature annealing treatments at 600 °C for 10, 100, and 1000 min were carried out to investigate in more detail the in-depth diffusion behaviour of Fe, Cr, and C. These results serve as a basis for a better understanding of the complex interaction between coated tool and work-piece as well as the influence of impurities on the thermal and mechanical behaviour of ceramic-like protective coatings.

2:10 PM B4-4-3 Mechanical and Tribological Behavior of Nanocrystalline Ni-W Coatings: Importance of Grain Size and Grain Boundary State
Timothy Rupert (University of California Irvine, US)

The high strength of nanocrystalline metals suggests that these materials are promising for wear-resistant coatings, where protective films must be able to survive the repetitive application of high contact stresses. However, nanocrystalline metals also demonstrate novel grain boundary-dominated deformation mechanisms and a tendency for mechanically-driven structural evolution. This talk first addresses the tribological response of nanocrystalline Ni-W alloys across a range of grain sizes from 3 to 100 nm, with a focus on understanding how the extreme conditions produced during wear can lead to dynamic nanostructures and properties. Both experiments and simulations reveal evidence of grain growth and relaxation of grain boundary structure during tribological contact, which are actually beneficial to wear resistance. We next isolate the importance of atomic grain boundary structure on mechanical properties using small-scale uniaxial testing and molecular dynamics simulations. An ordered boundary structure is found to increase strength at the expense of ductility. Finally, we synthesize these results and identify strategies for metallurgical design of optimal nanocrystalline coatings.

2:50 PM B4-4-5 Microstructure-Related Depth-Gradients of Mechanical Properties in Thin Nanocrystalline Films
Rostislav Daniel (Montanuniversität Leoben, Austria); Angelika Riedl (Materials Center Leoben Forschung GmbH, Austria); Thomas Schöberl (Montanuniversität Leoben, Austria); Bernhard Sartory (Materials Center Leoben Forschung GmbH, Austria); Christian Mitterer, Jozef Keckes (Montanuniversität Leoben, Austria)
Physical and functional properties of nanocrystalline thin films are strongly dependent on their microstructure. Thermal (thermal expansion and conductivity), electrical and magnetic properties depend on the amount of structural defects, which affect the electron and phonon transport and magnetocrystalline anisotropy, thus controlling the macroscopic properties of nanostructured materials. The microstructure, however, also determines the mechanical properties of nanocrystalline films as the generation and motion of dislocations under mechanical loading may be effectively constrained by the presence of structural defects. This effect may be further promoted by compressive stress typically developed in PVD films. Due to inherent heterogeneous nature of nanocrystalline films related with non-equilibrium growth conditions, depth-gradients of microstructure, stresses, physical and functional properties are developed. In this paper, microstructure-related depth-gradients of mechanical properties will be discussed for nanocrystalline CrN films prepared under various growth conditions as single- and multilayers. Nanoindentation experiments performed on single layered films and at the small-angle cross-section of a multi-layered CrN film coupled with spatially resolved synchrotron nanodiffraction experiments will be shown to reveal changes of hardness and elastic modulus associated with a variation of the grain size and stress state across the film thickness.
3:10 PM B4-4-6 Corrosion Resistance of Zirconium Oxynitride/Zirconia Thin Film Growth by Spray Pyrolysis-nitruration and DC Sputtering Magnetron Unbalance
Gloria Cubillos, Daniela Posso, Jhon Olaya (Universidad Nacional de Colombia Bogotá, Colombia)

Were deposited ZrOxNy/ZrO2 thin films on stainless steel by two different methods ultrasonic spray pyrolysis-nitruration and DC sputtering magnetron unbalance technique. Using the first technique is initially deposited ZrO2 and subsequently nitrided in anhydrous ammonia atmosphere at 750 ºC atmospheric pressure [1]. By DC sputtering the film is deposited in atmosphere of air/argon, with a flow ratio Φair/ΦAr of 3.0. The ZrOxNy/ZrO2 films were obtained from a 4 in. ×1/4 in. Zr (99.9%) target (CERAC, Inc.). The parameter set used during the deposition process was: base pressure at 1.0×10−3 Pa, deposition time 30 min, target–substrate distance at 5 cm and argon (99.999%) flow at 9.0 sccm at room temperature (287 K) [2]. Structural analysis was carried out through X-ray diffraction (XRD); morphological analysis was done through scanning electron microscopy (SEM) and chemical analysis was determined using X-ray photoelectron spectroscopy (XPS). From spray pyrolysis-nitriding grows ZrOxNy rhombohedral polycrystalline film, whereas DC sputtering the oxynitride films were grown with cubic crystalline structures Zr2ON2 and preferentially oriented along the (222) plane. Chemical analysis determined that in the last 5.0 nm, the Zr coatings present the following spectral lines: Zr3d3/2 (184.6 eV) and 3d5/2 (181.7 eV), O1s (531.3 eV), and N1s (398.5 eV). SEM analysis presented the homogeneity of the films. Zirconium oxynitride films enhance the stainless steel’s resistance to corrosion by the two techniques. The protective efficacy has been evaluated using electrochemical techniques based on linear polarizations (LP). The results indicate that the layer provides good resistance to corrosion in chloride-containing media [3,4].

3:30 PM B4-4-7 Structural Characterization of NbAlN Coating Deposited on AISI D2 Steel by TRD Method
Eray Abakay, Saduman Sen, Ugur Sen (Sakarya University, Turkey)
In this study, Nb-Al-N coating was applied on pre-nitrided AISI D2 steel by the thermo-reactive deposition technique in a powder mixture consisting of ferro-niobium, ammonium chloride and alumina at 1000°C for 1–4 h. The coated samples were characterized by X-ray diffraction, scanning electron microscope and micro-hardness tests. Nb-Al-N layer formed on the pre-nitrided AISI D2 steel was compact and homogeneous. X-ray diffraction analysis showed that the phases formed on the steel surfaces are NbN0.95, Nb2CN, Nb3Al2N and AlN. The depth of the Nb-Al-N layer ranged from 3.63 μm to 10.05 μm, depending on treatment time. The higher the treatment time the thicker the Nb-Al-N layer observed. The hardness of the Nb-Al-N layer was changing between 1708 HK0.01 and 2577HK0.01 .
3:50 PM B4-4-8 Surface Hardening of IF Steel by Plasma Nitriding and Pre-shot Peening
AnaPaula Manfridini (Universidade Federal de Minas Gerais, UFMG, Brazil); AntonioCesar Bozzi (Universidade Federal do Espírito Santo, UFES, Brazil); Junia Cristina Avelar-Batista Wilson (Tecvac, Ltd., UK); Marcos V. Auad (Auad Godoy Consultants, Brazil); Cristina Godoy (Universidade Federal de Minas Gerais, UFMG, Brazil)

Shot peening and plasma processes are widely used to improve the surface properties of metals and alloys. This work aims at broadening the applicability of interstitial free (IF) steels by combining both processes. In addition, we evaluate the influence of prior shot peening on the plasma nitriding process, as shot peening introduces non-equilibrium defects on the surface, which enhance the diffusions rates of nitrogen [1, 2]. The plasma nitriding was carried out for 4h at temperatures of 450°C, 475°C and 500°C on a Ti-stabilized IF steel, with and without pre-shot peening. The microstructure and structural phases were characterized by means of backscattered scanning electron microscopy (SEM) and x-ray diffraction (XRD); while mechanical properties were investigated using micro- and nanoindentation as well as dry sliding wear tests.

SEM showed that the morphology and distribution of the precipitates formed in the surface layers strongly depend on the pre-shot peening and plasma process temperature. Long nitride needles were only observed in the samples without pre-shot peening. For all samples the XRD patterns showed the presence of ε-Fe2-3N, γ’-Fe4N and the Fe-α matrix ferrite peak. Ultramicrohardness exhibits a two fold increase in hardness values near the surface relative to the substrate, and a hardened region, which extends up to a depth of 500µm in the IF steel treated at 500°C. For all test temperatures, a slight increase in hardness was observed for the shot peened samples compared to the ones without prior shot peening. Further investigation of the sample cross-sections by nanoindentation showed that shot peening caused a hardening effect up to a depth of 20 µm on the untreated substrate. It was also shown that for the plasma processed samples at 500°C, up to a depth of 70 µm, the shot peened samples had a higher average nanohardness than the samples which were not pre-treated. This suggests that an enhanced nitrogen diffusion due to the pre-mechanical treatment might have increased the nitrogen concentration in this region. The dry sliding wear tests showed an improvement of wear resistance of the IF steel after the different treatments, which was compared by the worn volume and measured using 3D profilometry. Characteristic undulation on the coefficient of friction versus sliding distance curves indicated a tribochemical wear process [3], which is confirmed by EDS compositional maps of the wear tracks.

[1] Hashemi et al., Material and Design. 3287-3292 (2011) 32.

[2] Shen et al., Surf. Coat. Technol . 3222-3227 (2010) 204.

[3] Zhang et al. Tribology International. 214-223 (2013) 61.

4:10 PM B4-4-9 Influence of Cu Additions on the Mechanical and Wear Properties of NbN Coatings
Kadri Ezirmik, Sina Rouhi (Atatürk University, Turkey)

The influences of increasing copper content in the NbN-Cu coatings on mechanical and tribological properties were studied. The coatings were deposited on M2 tool steel by using reactive magnetron sputtering method. Copper content of the coatings was varied from 1 to 24at.%. The microstructure, microhardness and wear properties of the coatings were examined. The addition of Cu into NbN coatings has modified the grain size and morphology. Mechanically, the microhardness values of the coatings other than NbN-1at% Cu were significantly reduced by Cu doping. The hardness of the films reached maximum level, 38GPa, at 1%at copper content and decreased with a further increase of the Cu content. Introduction of 1at % Cu into niobium nitride showed a beneficial effect on abrasive character of the coating. Wear of counter material increased at these coatings while others showed exact opposite behavior.