ICMCTF2014 Session B4-5: Properties and Characterization of Hard Coatings and Surfaces

Friday, May 2, 2014 8:00 AM in Room Royal Palm 1-3

Friday Morning

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8:00 AM B4-5-1 Bias Effect on Structure and Mechanical Properties of Magnetron Sputtered Nanocrystalline Zirconium Tungsten Nitride Thin Films
Paritosh Dubey, Ramesh Chandra (Indian Institute of Technology Roorkee, India)

Nano-crystalline zirconium tungsten nitride (Zr-W-N) thin films have been deposited on Si (100) substrates by magnetron sputtering at 200°C substrate temperature. The effect of substrate bias on structure and mechanical properties of deposited films has been studied in details using X-ray diffraction, field emission scanning electron microscopy, atomic force microscopy and nano-indentation. All Zr-W-N films exhibit a crystalline fcc phase with (111) and (200) preferred crystallographic orientations of grains. Increasing substrate bias decreases the crystallite size and increases the roughness of the Zr-W-N films. The lattice parameter and thickness of Zr-W-N films varies non-monotonically with increasing substrate bias. The Zr-W-N films have columnar structure which becomes finer at high substrate bias. Nano-indentation hardness and reduced elastic modulus of the films increases as the substrate bias goes up. Maximum wear resistance (H/Er~0.22) and maximum resistance to fatigue fracture (H3/E2~1.1 GPa) have been achieved for the film deposited at -80 V bias voltage.

8:20 AM B4-5-2 Structural, Mechanical and Electronic Properties of 3d Transition Metal Nitrides in Cubic Zincblende, Rocksalt and Cesium Chloride Structures: a First-Principles Investigation
Z.T.Y. Liu, Xiuquan Zhou, Sanjay Khare (University of Toledo, US); Daniel Gall (Rensselaer Polytechnic Institute, US)
In the quest for super-hard materials widely used in cutting and coating industries, research attention has been drawn by transition metal nitrides. The existing literature is either limited to singular compounds or does not present the mechanical properties and their connection to electronic properties. We thus report systematic results from ab initio calculations with density functional theory on three cubic structures, zincblende (zb), rocksalt (rs) and cesium chloride (cc) of the ten 3d transition metal nitrides. We computed lattice constants, elastic constants, their derived moduli and ratios that characterize mechanical properties. Experimental measurements exist in the literature of lattice constants for rs-ScN, rs-TiN and rs-VN and of elastic constants for rs-TiN and rs-VN, all of which are in good agreement with our computational results. Similarly, computed Vicker’s hardness values for rs-TiN and rs-VN are consistent with earlier experimental results. Several trends in our rich data set of 30 compounds were observed. All nitrides, except for zb-CrN, rs-MnN, rs-FeN, cc-ScN, cc-NiN and cc-ZnN, were found to be mechanically stable. A clear correlation in the atomic density with the bulk modulus (B) was observed with maximum values for B for FeN in zb, MnN in rs, and CrN in cc. The shear modulus, Young’s modulus, Vicker’s hardness (HV) and indicators of brittleness showed similar trends and all showed maxima for cc-VN. The calculated value of HV for cc-VN is above 30 GPa, while the next highest values are for rs-ScN and rs-TiN, above 24 GPa. A relation (HV ~(θD)2) between HV and Debye’s temperature (θD) was investigated and verified for each structure type. A tendency for anti-correlation of the elastic constant C44, which strongly influences stability and hardness, with the number of electronic states around the Fermi energy, was observed.
8:40 AM B4-5-3 Local Residual Stress Measurement on Amorphous Plasma-sprayed Single-splats
Marco Sebastiani (University of Rome "Roma Tre", Italy); Giovanni Bolelli, Luca Lusvarghi (University of Modena and Reggio Emilia, Italy); Edoardo Bemporad (University of Rome "Roma Tre", Italy)

Residual stress was measured on plasma sprayed Nickel-Aluminum (Ni-Al), Alumina (Al2O3) and Alumina-Titania (Al2O3-TiO2) single splats, by using the incremental focused ion beam micron-scale ring-core method (IµRCM). Results showed a tensile residual stress for polycrystalline Ni-Al, where the quenching stress is only partially relaxed by edge curling, through-thickness yielding and interfacial sliding. Conversely, a significant compressive stress for the amorphous Al2O3-TiO2 splats and a relatively lower compressive stress for the large micro-cracked crystalline Al2O3 splats were measured.

The observed differences between the Al2O3 and Al2O3-TiO2 splats suggest that, for these materials, a complex interaction exists between the stress component due to different thermal contraction and the quenching stress one, which is supposed to be reduced by different relaxation mechanisms, also correlated to the microstructural evolution and during splat formation.

The experimental methodology developed provided a unique way for the study of the residual stress build-up mechanisms in amorphous and crystalline single splats obtained by plasma spraying, and gave further insights into the actual micro-scale phenomena that give rise to adhesion and nano-mechanical behavior of thermally sprayed coatings.

9:00 AM B4-5-4 Oxidation Behavior of TiC0.81N0.48 Coating and TiC0.61N0.44O0.15 Coating Deposited by Chemical Vapor Deposition
Lihui Zhu, Yumeng Zhang, Tao Hu (Shanghai University, China); Peter Leicht, Yixiong Liu (Kennametal Incorporated, US)
This paper aims to investigate the effect of oxygen addition on the oxidation resistance of Ti(C,N) coating prepared by chemical vapor deposition (CVD). TiC0.81N0.48 coating and TiC0.61N0.44O0.15 coating were deposited by CVD, and their oxidation behavior at 600°C and 700°C was compared. At 600°C, the TiC0.61N0.44O0.15 coating oxidizes with a linear growth rate at the beginning of the oxidation. Nevertheless, the oxidation kinetics of TiC0.81N0.48 coating follows a linear law initially, and then changes to a parabolic law. The oxidation kinetics of TiC0.81N0.48 coating and TiC0.61N0.44O0.15 coating is similar and obeys a parabolic law at 700°C. The oxidation resistance of the TiC0.61N0.44O0.15 coating is inferior to that of the TiC0.81N0.48 coating. The reduced oxidation resistance of the TiC0.61N0.44O0.15 coating is ascribed to the formation of more gas holes, fissures and cracks.
9:20 AM B4-5-5 Modulus and Compressive Stress Graded Ti-C Coating on Ti-6Al-4V Aerospace Alloy
Thulasi Raman Kamalakshi Hemachandran, Mohan Rao Gowravaram (Indian Institute of Science, India)
In this study, to accommodate higher interfacial shear stress between Ti-C coating system and Ti64 substrate, coating modulus and compressive stresses are graded from interface to 4.5 µm thickness. The modulus gradient is achieved by varying Ti to C ratio by tuning the methane flow and compressive stress gradation from 0.1GPa to 3.5GPa by changing bias voltage during the reactive sputtering process. Micro tensile testing revealed that modulus and compressive stress graded coatings failed at 1.2% tensile strain, which is higher tensile load bearing capacity than the monolithic stoichiometric TiC coating. Hardness and modulus of the 4.5 µm thick film are 30GPa and 290 GPa respectively. At higher strain, coating started cracking and post-microscopy analysis shows variation of crack width at different zones of the tensile specimen. The gradation technique has shown that higher thickness films could be deposited without adhesion problems as compared to monolithic coatings.
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