ICMCTF2005 Session F1/E3-2: Mechanical Properties and Adhesion

Monday, May 2, 2005 1:30 PM in Room California

Monday Afternoon

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1:30 PM F1/E3-2-1 Nanotribological Testing of Nickel and DLC Coated Nickel for Microdevice Applications
J.M. Jung (University of Minnesota); N.R. Moody (Sandia National Laboratories); M.S. Kennedy (Washington State University); S.V. Prasad, T.E. Buchheit (Sandia National Laboratories); D.F. Bahr (Washington State University); W.W. Gerberich (University of Minnesota)

Strength, friction, and wear are dominant factors in the performance and reliability of materials and devices fabricated using nickel based LIGA and silicon based MEMS technologies. However, the effects of frictional contacts and wear are not well-defined especially with respect to wear resistant coatings. We have therefore begun a program employing nanoscratch and nanoindentation on electrodeposited LIGA nickel and DLC coated nickel samples proposed for use in microdevice applications. Nanoscratch techniques were used to generate wear patterns as a function of load and number of passes. Nanoindentation was then used to measure properties in each wear pattern. The results on nickel show a systematic increase in hardness with applied load with surprisingly little effect of repeat passes on sample deformation. The results on DLC coated nickel show debris generation but no significant effect on properties at the loads tested. In this presentation, performance of nickel and DLC coated nickel will be compared under identical wear conditions. We will further use measured nickel hardness values and a model for plasticity to show how flow stress and the extent of plasticity evolve under sliding contacts.

The authors gratefully acknowledge the support of Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

1:50 PM F1/E3-2-2 Phase Transformation and Hardness of the Ni-P-Al Ternary Coatings under Thermal Annealing
F.B. Wu, J.G. Duh (National Tsing Hua University, Taiwan)
Ternary Ni-P-Al coating was fabricated by dual-gun r.f. magnetron sputtering technique. The asdeposited Ni-P-Al coating exhibited a major Ni(111) nanocrystalline phase with Al and P doping. After 400°C heat treatment, various NixPy compounds, including Ni12P5, Ni5P2, and Ni3P, formed within the recrystallized Ni matrix. Accordingly, the hardness of the coating increased to 10 GPa due to the NixPy precipitation. For heat treatment temperature higher than 500°C, NimAln hard phases were observed in the ternary Ni-P-Al coating. A further increase in coating hardness from 10 to 12 GPa was revealed. The strengthening for annealed Ni-P-Al coating was attributed to precipitation of Ni-P and Ni-Al compounds formed around 400 and 500°C, respectively. A two-stage hardening in Ni-P-Al coating through heat treatment was then concluded. The effect of indentation displacement on resulted hardness was also revealed through continuous-stiffness-measurement (CSM). Furthermore, the Youngs modulus was evaluated to be around 200 GPa.
2:10 PM F1/E3-2-3 Ageing Under Mechanical Stress of a Silver Based Multilayered Mirror
A. Lalo (CNES, France); G. Ravel (CEA, France); M. Ignat (CNRS (lTCPM - INPG), France)
Improving materials and devices reliability is a major concern to the spatial industry. Results are reported for satellite mirrors-like specimens consisting in oxide-protected metal systems. Optical coatings were deposited by electron beam evaporation. Mechanical stress fields in multi-layered materials play an important role. The stress state can have far-reaching implications both in kinetics and thermodynamics. Therefore an integrated apparatus with four-point bending equipment was designed. The technique allowed us to exert stress into a film or a system of films on a substrate concurrently with thermal treatment. In order to achieve the first tests performed with the help of the apparatus, various preliminary characterizations were required. The article reports the preliminary micro-mechanical testing of the materials (ultra micro-indentation to evaluate the elastic modulus of the samples materials and wafer curvature technique to determine the specimen residual stress) and the first ageing experiment. Experimental evidence of accelerated ageing under stress is successfully reported.
2:50 PM F1/E3-2-5 Indenter Surface Area and Hardness Determination by Means of a FEM-Supported Simulation of Nanoindentation at Low Penetration Depths
K.-D. Bouzakis (Aristoteles University of Thessaloniki, Greece); N. Michailidis (Laboratory for Machine Tools and Manufacturing Engineering, Greece)
Through a developed finite elements method (FEM) simulation of the nanoindentation, the stress-strain curves of coatings and other materials can be defined. The actual indenter tip form deviations are detected by means of appropriate experimental and FEM supported procedures. At low indentation depths, the determined specimen mechanical properties are strongly affected by the indenter tip form finishing errors, thus rendering their consideration obligatory, in evaluation procedures of nanoindentation measurement results. In the frame of the described investigations the area functions of Vickers and Berkovich indenters are determined versus indentation depths of few nanometers, where the contact area is mainly between the transitional indenter tip area and the specimen. Taking into account the detected indenter area functions, the actual surface and projected contact areas during the loading phase of nanoindentation, as well as the occurring impression surface geometry after unloading were determined, by means of the mentioned FEM-supported simulation of the nanoindentation. Hereupon, the indenter elastic deformation during loading was also considered. Applications of the developed procedure are presented in the cases of thin coatings and other materialsâ?T, for which stress-strain curves as well as hardness courses after various methods versus the indentation load and depth, are defined. In this way, the hardness and the mechanical properties of coatings with thickness values less than 1 um can be accurately determined, without affecting the extracted results, by the indenter tip form deviations from their ideal geometry.
3:10 PM F1/E3-2-6 The Effects of Pulse Frequency and Substrate Bias to the Mechanical Properties of CrN Coatings Deposited by Pulsed DC Magnetron Sputtering
J.W. Lee, S.-K. Tien (National Tsing Hua University, Taiwan); Y.C. Kuo (Tung Nan Institute of Technology, Taiwan); J.G. Duh (National Tsing Hua University, Taiwan)
The chromium nitride coatings have been deposited on SUS 420 stainless steels by the bipolar symmetric pulsed DC magnetron reactive sputtering process at 2 KHz and 20 KHz pulse frequencies, respectively. The substrate bias was applied with different DC bias power and constant pulse frequency of 50 KHz. Oscilloscope traces of the target voltage and current waveforms were recorded during symmetric bipolar pulsed mode. The surface morphologies of the coatings were analyzed by the atomic force microscopy. The nanoindentation, scratch and Daimler-Benz Rockwell-C adhesion strength tests were adopted to evaluate the mechanical properties of CrN coatings. It was concluded that the nanohardness of the CrN coating increased with pulse frequency and the bias power. The scratch tests of the CrN coatings showed that almost no chipping failure was occurred. Only conformal cracking and buckling failure were observed besides the scratch track. A similar tendency was also found for the adhesion strength quality of the coating.
3:30 PM F1/E3-2-7 Use of Certified Reference Materials in Instrumented Indentation: Improved Methods for Indirect Calibrations
G. Aldrich-Smith, N.M. Jennett (National Physical Laboratory, United Kingdom)

Nanoindentation is one of the very few techniques that can measure both the elastic and plastic properties of very small volumes of materials, but considerable errors can be introduced when the indenter area function and instrument frame compliance are not known with sufficient accuracy. Frame compliance is a key uncertainty when measuring stiff materials (metals), at high forces (ultra-hard materials), and at high indentation depths (polymers).

Direct measurements of frame compliance are discussed and compared to indirect measurements using certified reference materials. Frame compliance was determined using the two reference material method, and a variation of this technique using reference indents in a stiff material and an AFM derived area function.

An improved calibration method is used using modulus certified reference materials, as specified by the EU project DESIRED. This allows the uncertainty in frame compliance to be reduced by a factor of three when compared to the Oliver and Pharr method of plotting total compliance against 1/√AC.

Frame compliance is strongly dependant on the technique, range of data used and on the modulus reference value. Recommendations are made for the use of certified reference materials in the determination of frame compliance and indenter area function for low uncertainty results.

3:50 PM F1/E3-2-8 Analysing Nanoindentation Unloading Curves using Pharr’s Concept of the Effective Indenter Shape
N. Schwarzer (Technische Universität Chemnitz, Germany)
In this paper an extended Hertzian approach will be used in order to develop a tool for the analysis of nanoindentation unloading curves of sharp indenters. The approach is based upon the concept of the effectively shaped indenter introduced by Pharr and co-workers. However, in contrast to the Sneddon formulae used by Pharr the extended Hertzian approach allows a complete evaluation of the elastic field produced by the effective indenter in closed and elementary form and thus a much more thorough discussion of the effects observed during the indentation experiment. Exemplary the new approach is used here to determine the critical yield stress of a variety of materials directly from the unloading curves of Berkowich indentations. The results are compared with those of other methods and the deviations are discussed.
4:10 PM F1/E3-2-9 The Effect of Heat Treatment on the Mechanical Properties and Microstructure of CrN/AlN Multilayer Coatings
J.G. Duh, K.L. Lin, S.-K. Tien (National Tsing Hua University, Taiwan)
Polycrystalline CrN/AlN multilayer coatings deposited on the stainless steel and silicon substrate were fabricated by rf magnetron sputtering technique. The CrN/AlN bilayer periods were controlled from 3 nm to 30 nm by the adjustment of deposition time. To evaluate the thermal stability of CrN/AlN multilayer coatings, the CrN/AlN films were annealed from 600°C to 1000°C for 1 h in the N2 purged environment. The phase transformation during thermal evolution was studied by X-ray diffraction (XRD). The microstructure of CrN/AlN multilayer coatings at as-deposited and annealed states was observed by transmission electron microscope (TEM). The hardness of as-deposited CrN/AlN coating with period of 5 nm was 31.5 GPa, which was much higher than those of CrN and AlN single layers. However, the hardness with large period was close to that by the rule of mixture. In addition, the thermal stability of CrN/AlN multilayer coatings with different bilayer periods was also investigated.
4:30 PM F1/E3-2-10 Mechanical Behaviour of Thin Films Deposited on Ductile Substrates: Cracking and Critical Parameters for Damage Evolution
M. Ignat (INP, Grenoble, France); M. Latella (ANSTO, Australia)
To perform advanced characterisation of coatings and thin films, nanoscale tools have been developed. This includes nanoindenters for mechanical parameter determinations and atomic force microscopes for accurate surface characterisation. Even though with these tools the characterisation of thin films and coatings is related to their microstructural properties and then compared with respect to the bulk material and/or substrate, it remains difficult to deduce directly, how a global film/substrate system will behave under external stresses. This aspect remains an open field of investigation, where the scratch test, the pull test and bending experiments have been developed to understand the mechanical behaviour of the mentioned systems. Anyhow, in all cases the results point out that not exclusively the intrinsic properties of the film will control a film/substrate response, but also the interface and the substrate properties will strongly participate to control the thermal and mechanical behaviour of the system. We present an analysis of the mechanical behaviour of thin films (titania), deposited on ductile substrates, when submitted to external tensile loading. The damage evolution (cracking and debonding) was observed and recorded. The critical parameters related to the observed mechanisms are discussed.
4:50 PM F1/E3-2-11 Combination of Normal and Lateral Force-Displacement Measurements as a New Technique for the Mechanical Characterization of Surfaces and Coatings
T. Chudoba, V. Linss (ASMEC GmbH, Germany)
Nanoindentation with Vickers or Berkovich tips has become an established technique for the measurement of hardness and Young's modulus. Also the use of spherical indenters has attracted more and more attention for the determination of the Young's modulus and yield strength. However, these techniques are still far away from the conditions in a real application where usually normal forces are combined with lateral forces in a tribological system. Therefore, often scratch and wear tests are used additionally to characterize the mechanical behavior. However, conventional techniques, which apply lateral forces, have the disadvantage that they normally do not deliver characteristic and comparable material parameters which are independent of the measurement conditions and which can serve as input parameters for the modeling with analytical or finite element models. This shall be overcome by a new technique, which will allow the measurement of lateral force-displacement curves with the same accuracy like conventional nanoindentation can do in normal direction. The realization of two independent measurements with the same tip at the same sample position will allow the calculation of more unknown material parameters than before. Beside that, mechanical anisotropy within the surface plane can easily be detected. The use of spherical indenters with forces at which elastic or beginning plastic deformation takes place makes it easier to combine the measurements with analytical stress calculations and to derive critical material parameters. As a first step towards the above mentioned characterization method, a new nanomechanical tester with a high-resolution measurement of force and displacement in normal and lateral direction was developed and tested. The working principle of the instrument will be explained and the parameters, which could be realized so far, will be given. The results of first measurements will be presented.
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