ICMCTF2013 Session B4-1: Properties and Characterization of Hard Coatings and Surfaces

Tuesday, April 30, 2013 2:10 PM in Room Royal Palm 4-6

Tuesday Afternoon

Start	Invited?	Item
2:10 PM	Invited	B4-1-1 Low-temperature Plasma Surface Hardening of Austenitic and Martensitic Stainless Steels Mingkai Lei (Dalian University of Technology, China); X.M. Zhu (Dalian Jiaotong University, China) Plasma surface hardening of austenitic and martensitic stainless steels has been performed at low process temperatures below 450^o C by plasma-based low-energy ion implantation. A high nitrogen face-centered-cubic (f.c.c.) phase (γ_N) on the plasma-based low-energy nitrogen ion implanted Fe-Cr-Ni austenitic stainless steel and a high nitrogen hexagonal-close-packed (h.c.p.) phase (ε-Fe_2+xN) on the nitrogen-modified Fe-Cr martensitic stainless steel have a combined wear and corrosion resistance, respectively. The microstructure of the γ_N phase was constructed of the novel CrN_x and FeN_x bonds with a nitrogen concentration up to about 35 at.%. The metastable ε-Fe_2+xN phase was observed as a high supersaturated nitrogen concentration up to about 40 at.%. The hardening surface layers on the austenitic and martensitic stainless steels possessed high microhardness for the γ_N phase with HV_{0.10 N} 20.0 GPa and for the ε-Fe_2+xN phase layer with HV_{0.25 N} 15.7 GPa. The improved wear and corrosion behaviors of the γ_N phase and the ε-Fe_2+xN phase were respectively investigated by tribological test on a ball-on-disc tribo meter and by electrochemical test using a standard three electrodes system in 3.5 % NaCl solution. The wear and corrosion resistance mechanism of the γ_N phase and the ε-Fe_2+xN phase was explored based on dependence of the composition and microstructure on the wear and corrosion properties. The industrial application using the low-temperature plasma surface hardening has been carried out by the plasma-based low energy nitrogen ion implanted AISI 316L austenitic and AISI 420 martensitic stainless steels.
2:50 PM		B4-1-3 Microstructural Origins of Stress Gradients in Nanocrystalline Thin Films: the Dominant Role of Grain Evolution Against Texture Rostislav Daniel, Jozef Keckes, Christian Mitterer (Montanuniversität Leoben, Austria) The gradual development of microstructure is inherently characteristic for nanocrystalline thin films. It is controlled by competitive growth of adjacent grains and is responsible for the development of depth gradients of stresses if the structure develops from fine at the film/substrate interface to coarse in the film bulk [1]. Film growth is, however, typically also accompanied by the evolution of texture as the preferential orientation of grains may change in the course of film development as a consequence of competitive atomistic processes on the surface of the growing film. This phenomenon has been reported for almost every transition metal nitride thin film material [2, 3]. As soon as the change of the grain size during growth of nanocrystalline films is accompanied with a change of texture, it is not possible to isolate the effect of the individual phenomena on the development of residual stresses. The knowledge of the origin of stress gradients in thin films is, however, crucial in controlling the stress state of these materials. Thus, we discuss in this paper the exclusive effect of the grain size on the development of stress gradients in thin nanocrystalline films irrespective of the film texture. As examples, the stress gradients in TiN films having exclusively either (111) or (100) texture were studied. The effect of the varying film texture on the development of stress gradients is further discussed for TiN films exhibiting a crossover of texture from (100) to (111) with increasing thickness. As an evidence of the depth gradients of stresses in strongly textured film materials, stress measurements of the cross-section of a TiN(100) film by spatially resolved synchrotron nanodiffraction experiments is given. It will be shown that the development of stress gradients in nanocrystalline films is predominantly given by the variation of the grain size, whereas the contribution of the texture changes has only a minor effect. [1] R. Daniel, K.J. Martinschitz, J. Keckes, C. Mitterer, Acta Mat. 58 (2010) 2621-2633. [2] J.E. Greene, J.-E. Sundgren, L. Hultman, I. Petrov, D. B. Bergstrom, Appl. Phys. Lett. 67 (1995) 2928-2930. [3] I. Petrov, P.B. Barna, L. Hultman, J.E. Greene, J. Vac. Sci. Technol. A 21 (2003) 117-128.
3:10 PM		B4-1-4 Effect of Tetramethylsilane Gas on the Fabrication of CrZrSiN Coatings by Cathodic Arc Deposition System Tzu-Chin Tseng, Jyh-Wei Lee (Ming Chi University of Technology, Taiwan, Republic of China); Sung-Hsiu Huang (National Chiao Tung University, Taiwan, Republic of China) The CrZrSiN coatings were deposited on Si wafer and tungsten carbide substrates by cathodic arc deposition system using CrZr target and tetramethylsilane gas. The tetramethylsilane gas flow rate was adjusted to fabricate the CrZrSiN coatings with different silicon contents. The crystalline structure of coatings was measured by a glancing angle X-ray diffractometer. Microstructures of thin films were examined by a scanning electron microscopy (SEM) and transmission electron microscopy (TEM) , respectively. The hardness, adhesion and tribological properties of thin films were measured by nanoindentation, scratch tester and ball-on-disk wear tests. It was found that the micro structure and mechanical properties were strongly influenced by the tetramethylsilane gas flow rate and Si content of the CrZrSiN thin films. The optimal silicon content for the Cr ZrSiN coating was proposed in this study.
3:30 PM		B4-1-5 Toughness Measurement of Nanocomposite Coatings by a Micro Double Cantilever Beam Method Shiyu Liu (University of Cambridge, UK); XingZhao Ding, Xianting Zeng (Singapore Institute of Manufacturing Technology, Singapore); William Clegg (University of Cambridge, UK) Toughness is one of the most important mechanical properties of protective thin films, especially those under erosive environments. In this paper, a method is presented for measuring the fracture toughness of hard coatings. Pre-cracked micro double cantilever beams of the coatings are fabricated using focused ion beam, which are subsequently compressed by nanoindentation with a flat diamond punch. The compression exerts a bending moment on the cantilever beams causing the pre- cracks to grow. Thus, the fracture toughness of the coating can be determined as a function of the compression load at the point of crack elongation. Crack growth has been studied experimentally and compared with FE simulations to evaluate effects such as friction between indenter tip and coating surface. This method has been demonstrated using materials of known toughness and found to be useful for materials with a large yield stress to toughness ratio. Finally, this technique was applied to determine the fracture toughness of different PVD hard coatings, which will also be compared and discussed here.
3:50 PM		B4-1-6 Microstructure and Characterization of TaN Protective Coatings Kun-Yuan Liu, Fan-Bean Wu (National United University, Taiwan, Republic of China) Tantalum-nitride, TaN, coatings were fabricated by magnetron sputtering technique. The microstructure of the TaN coatings was controlled by N₂/Ar+N₂ gas flow ratio. TaN coatings showed a columnar structure at a 0.1 N₂/Ar+N₂ gas flow ratio. With the increase of the N₂/Ar+N₂ gas flow ratio to 0.25, the microstructure of TaN coatings transformed to be nanocrystalline/amorphous . An amorphous structure was found under further increase of the flow ratio. The increase in reactive nitrogen content would suppress the crystallization of TaN coatings during sputtering. TaN multilayer coatings were fabricated by modulation of crystalline and amorphous TaN layers with N₂/Ar+N₂ gas flow ratio control. TaN single and multilayer coatings were characterized through thermal annealing, nano-indention and corrosion tests. With the introduction of amorphous/crystalline interface, the multilayer coatings exhibited superior mechanical properties and chemical stability than single layer TaN coatings.
4:10 PM		B4-1-7 Structure and Residual Stress Analysis of Titanium Nitride Coatings Produced by DC Magnetron Sputtering Gustavo Martinez, Chintalapalle Ramana (University of Texas at El Paso, US) Titanium nitride exhibits unique physical, chemical, optical and mechanical properties and find application in a wide variety of scientific and technological applications.^[¹^-3] Due to their excellent physical and mechanical properties, TiN films have been in use as protective and wear and corrosion resistant coatings for industrial machinery tools. TiN coatings exhibit beautiful lustrous color and are useful for decorative applications while protecting the components from wear and corrosion. TiN films are also attractive for applications in micro- and nano-electronics. These electronic applications typically take the form of metallization materials or diffusion barriers. The optical properties of films, such as selective spectral range optical transmission and reflection, make these materials interesting for application in solar cells, optical filters, and potentially plasmonics. The present work was performed to understand the effect of film thickness in the nano-scale regime (5-100 nm) on the properties and phenomena of TiN coatings with a special attention towards microstructure and residual stress evolution. TiN samples were grown using DC sputtering method onto Si and MgO substrates. Samples were analyzed employing X-ray reflectivity (XRR), Grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM) and ψ measurements. Increasing film thickness is found to induce the (111) texture development of TiN coatings. Residual stress calculated using a modified ψ non-destructive technique in Si and MgO substrates giving residual stress of 0.43 MPa and 2.229 MPa, respectively, both in compression. SEM data indicate that increased deposition time improves grain formation and size of the TiN coatings. Rutherford backscattering was used to accurately calculate the film thickness showing thickness in the range of 13.31nm to 119.87nm as well as the compositional percentage of titanium, nitrogen and oxygen in the films. The results are presented and discussed.
4:30 PM		B4-1-8 Surface Directed Spinodal Decomposition at TiAlN / TiN Interfaces Axel Knutsson, Isabella Schramm, Klara Grönhagen (Linköping University, IFM, Nanostructured Materials, Sweden); Frank Mucklich (Saarland University, Functional Materials, Germany); Magnus Odén (Linköping University, IFM, Nanostructured Materials, Sweden) Cubic (c)- Ti_1-xAl_xN coatings are unstable and isostructurally decompose to c-TiN and c-AlN at elevated temperature for compositions inside the spinodal. Both theoretical and e xperimental studies of this alloy have revealed the detailed characteristics of this decomposition. However, a the details of the early stage spinodal decomposition behavior and the resulting microstructure of Ti_1-xAl_xN /TiN multilayers remains unclear . Such study is of interest since the kinetics of the spinodal decomposition is seen to differ compared to monolithic TiAlN. The characteristic of an interface-controlled decomposition is the formation of a layered microstructure parallel to the interface, i.e. surface directed spinodal decomposition (SDSD). If present in TiAlN/TiN layers it could explain the improved high temperature properties observed in these multilayers. Hence, in this study we investigate if SDSD is present in arc evaporated c-Ti_0.33Al_0.67N/TiN and c-Ti_0.50Al_0.50N/TiN coatings and discuss the prerequisites for such decomposition. We have used DSC, XRD, STEM/TEM-EDX, and 3D atom probe tomography (APT) in combination with 2D phase field simulations to understand the decomposed morphology and the decomposition kinetics. The annealing procedure was chosen such that the spinodal decomposition was at an early stage, i.e. annealing at 700-900 °C with no isothermal period. DSC revealed that the isostructural spinodal decomposition, to c-AlN and c-TiN, in the multilayers has the same onset temperature regardless of composition. The onset is located ~100 °C lower compared to the monolithic coatings. Z-contrast STEM imaging confirms this by showing a decomposed structure of the multilayers at a temperature where it is not present in the monoliths. The APT shows an evolving AlN-rich layer followed by enrichment in TiN at the interfaces in the decomposed state. The phase field simulations also predict such SDSD. The simulations further show that the decrease of the total energy transpires over a longer time period in the multilayers compared to monoliths due to the SDSD. This is in line with the thermograms showing a broader spinodal decomposition peaks from the multilayers. We also note that the microstructure resulting from SDSD in TiAlN is highly dependent on the growth induced elemental fluctuations. The decomposition behavior of the coatings is discussed in terms of internal interfaces, elemental fluctuations, coherency stresses, and alloy composition. Understanding and controlling the evolving microstructure and the onset of the spinodal decomposition by interface architecturing, may facilitate optimization of the cutting performance of TiAlN coatings.