ICMCTF1998 Session E4-F1-2: Mechanical Characterization - Micromechanical Testing & Modeling (2)

Wednesday, April 29, 1998 1:30 PM in Room California
Wednesday Afternoon

Time Period WeA Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF1998 Schedule

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1:30 PM E4-F1-2-1 Use of Pulsed High Power Ion Beams to Enhance Tribological Properties of Stainless Steel, Ti, and Al
D.C. Senft, T.J. Renk, M.T. Dugger (Sandia National Laboratories); K.S. Grabowski (U.S. Naval Research Laboratory); M.O. Thompson (Cornell University)

Enhanced tribological properties have been observed after treatment with pulsed high power ion beams, which results in rapid melting and resolidification. We have treated and tested 440C and 15-5 steel. Ti and Al samples were also treated after sputter coating to produce surface alloying. The samples were treated at the RHEPP-1 facility at Sandia National Laboratories (0.5 MV, 0.5-1 μs at sample location, <10 J/cm2, 1-5 μm ion range). The tribological properties of the samples were determined using a linear reciprocating tribometer with ball-on-flat geometry. Changes in the treated layers were characterized by nanoindentation hardness testing, X-ray diffraction, microprobe cross-section analysis, SEM, and topographical analysis. The thickness of the treated layers ranges from 2-5 microns. Concentration profiles of the surface alloyed Ti samples were determined by RBS.

Increases in hardness and durability were found after treatment. We have observed a reduction in size of second phase particles and other microstructural changes in 440C. The hardness of treated 440C increases with ion beam fluence and varies with the ion species used for treatment. Ion beam treatment of Ti-Pt and Ti-Nb co-sputtered overlayers on Ti substrates increases the durability of these surfaces over untreated Ti and treated bare Ti. The surface alloyed layers show improvements in hardness up to a factor of 3 over untreated Ti. Al was coated with a Al-Si co-sputtered overlayer and treated, resulting in a hardness increase of a factor of two over untreated Al, along with increased durability. The magnitude of the changes in surface topography and roughness depend on the ion beam species used in the treatment.

This work was supported by the United States Department of Energy under Contract DE-AC04-94AL85000. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy.

1:50 PM E4-F1-2-2 Characterisation of the Failure of Thin Hard Coatings Under Pure Bending
M. van der Meer, M.D. Tran, A.H.L. Hoeben, W.P. Vellinga, J.H. Dautzenberg (Eindhoven University of Technology, The Netherlands)

Thin, hard ceramic layers are widely applied as tool coatings to increase resistance to wear and corrosion. An important property characterising the quality of coatings for these applications is their strain-to-failure, at which cracks appear in the coating. We have used pure bending to apply a large controlled strain to the coatings, while monitoring the formation and propagation of cracks in the coating. Experiments were performed using two different methods of failure detection.

The first method uses an electrochemical signal to determine the strain-to-failure of non-conducting coatings. During the experiment a constant electric potential is applied to the thin-film-and-substrate system, with the thin-film in contact with an electrolyte. The current of corrosion is measured, and is seen to change dramatically when the coating cracks and the electrolyte contacts the substrate (in our case stainless steel). This is a quick, easily performed and well reproducing method, and therefore suitable as a quality control instrument. To investigate if it is possible to extract more information from such measurements, eg. on the exact moment of crack initiation, crack density and evolution, we have performed additional similar experiments using in-situ SEM.

In these experiments identical pure bending conditions are applied inside a SEM allowing to obtain visual information on the same phenomena. The initiation and propagation of cracks, and the crack density can be studied and registered in this way, and the electrochemical curve can now be interpreted in these terms.

Numerous coatings of titaniumnitride (TiN) and titaniumcarbide (TiC) produced with PVD (unbalanced magnetron sputtering) have been investigated in this way. In this paper the relation between the electrochemical method and the in-situ SEM visual observations is presented and discussed.

2:10 PM E4-F1-2-3 A Laser-acoustic Method for Testing and Classifying Hard Surface Layers
B. Schneider, B. Schultrich, H.-J. Scheibe (Fraunhofer Institute - IWS, Germany); M. Griepentrog (BAM - Berlin, Germany)
The laser-acoustic technique is a promising method for determining Young's modulus of thin films. Wide-band surface wave impulses are generated by short laser pulses and are detected with a piezoelectric transducer. Fourier transforming the acoustic signal provides the dispersion curve. The measurement in the frequency range up to 200 MHz enables the Young's modulus of film with thickness less than 100 nm to be determined. The test is non-destructive, does not required a special preparation of the samples, and can be performed in some minutes. Young's modulus of hard films has been proved to be a valuable parameter for characterizing thin films. It is related to atomic structure of important covalent and ionic materials which can vary in a wide range depending on the deposition condition. It is a sensitive indicator for optimizing the deposition technology and for classifying the film quality. Results are presented for TiN, TiC, cBN , and diamond-like carbon which show the correlation of the film modulus with hardness, density, adhesion, and the microstructure of the film material.
2:30 PM E4-F1-2-4 Fatigue-Corrosion Behavior of a Heat Treated AISI 1045 Carbon Steel Coated with Ni-P Electroless
J.A. Chitty, A. Pertuz, M.H. Staia, H.E. Hintermann, E.S. Puchi (Central University of Venezuela, Venezuela)
Fatigue-corrosion tests under rotatory bending conditions have been conducted on Ni electroless coated and uncoated samples of an AISI 1045 carbon steel quenched and tempered to a final hardness of approximately 32 HRC. The effect of the coating on the fatigue-corrosion behavior of both notched and unnotched samples has also been investigated. The Ni-P coating was obtained employing a solution of NiSO4 as a source of Ni ions and sodium hypophosphite as a reducing agent in an acid medium. The fatigue-corrosion tests were conducted at 50 Hz, employing a solution of 3% NaCl as corrosive environment. Four stress levels were chosen corresponding approximately to 60, 70, 80 and 90% of the yield stress of the material. The results obtained indicate that in the unnotched samples the deposit increases the fatigue-corrosion life of the substrate and that this increment is more marked at the lowest stresss level. For the notched and coated samples a small increment in the fatigue-corosion life was observed only at the lowest stress level. For the remaining stress level the behavior was similar to the uncoated substrate.
2:50 PM E4-F1-2-5 Nanoindentation of Atomically Modified Surfaces
S.G. Corcoran (Hysitron, Inc.); S.R. Brankovic, N. Dimitrov, K. Sieradzki (Arizona State University)
Nanoindentation studies on metal and semiconducting surfaces often display instabilities in the load-displacement curves which have been attributed to phase transitions, oxide breakthrough, surface contamination effects, and dislocation nucleation under the indenter tip. We present our recent nanoindentation results which have been aimed at understanding the effects of surface modification at the atomic scale on load instabilities. The mechanical properties of a Au surface with a single electrochemically deposited metal monolayer (Pb or Ag), and with an electrochemically deposited oxide monolayer will be presented. Detailed results of indentations performed on electrochemically reconstructed versus unreconstructed Au surfaces will also be presented. These experiments are unique in that the indentations were carried out while the Au surface was under electrochemical control. Strict control of the electrochemical environment was maintained to eliminate extraneous electrochemical reactions, e.g. gas evolution, corrosion reactions, and oxidation reactions.
3:30 PM E4-F1-2-7 Mechanical Properties of SiO2 and Si3N4 Coatings: A BAM-NIST Cooperative Project
U. Beck (Bundesanstalt für Materialforschung und-prüfung, Germany); D.T. Smith, S.J. Dapkunas (National Institute of Standards and Technology); G. Reiners (Bundesanstalt für Materialforschung und-prüfung, Germany)
Mechanical properties, i.e., hardness and modulus, of amorphous SiO2 and Si3N4 PE-CVD coatings have been studied for two coating thicknesses (0.1 µm and 1.0 µm) and two substrate materials (fused silica, i.e., Herasil; and borosilicate glass, i.e., BK 7) using low load instrumented indentation. Single layers of SiO2 and Si3N4 and a multilayer stack consisting of five double layers of SiO2/Si3N4 (individual layer thickness: 0.1 µm) were investigated on both substrate materials. A special plasma pre-treatment of the substrates prior to deposition ensured that layer adhesion exceeded inner film stress for all systems considered. The applied indentation load ranged from 700 mN down to 0.1 mN and resulted in indentation depths from more than 1 µm to about 15 nm. The influence of layer thickness and the effect of the substrate on the measurement of hardness and modulus of the films are discussed. The necessity for a system approach to the indentation of layered systems is demonstrated for both single- and multi-layer systems. Only one layer-substrate system (1.0 µm Si3N4 on Herasil) out of ten was found to be overcritical, with tensile cracks occuring both prior to, and as a result of, indentation. It is shown that Berkovich indentation may used to determine the hardness and modulus of thin layers and to investigate film stresses and adhesion.
3:50 PM E4-F1-2-8 Modelling Microhardness of Electroplated Nickel on Copper Substrates
A.M. Korsunsky, S.J. Bull (University of Newcastle, United Kingdom)

The formulation and verification of accurate and sufficiently general hardness models applicable both to soft-on-hard and hard-on-soft composite systems, which may exhibit either fracture or plasticity-dominated coating responses, is vital for improved understanding of mechanical properties of coated systems, as well as for practical design aspects of surface engineering for mechanical applications. A recently proposed energy-based model for hardness-load dependence is applied here to a series of samples of electroplated Ni on Cu substrates, in which the hardnesses of both the coating and the substrate were controlled by bath formulation, heat treatment, and annealing.

It was found that the model accurately describes the transition between the coating-only hardness response at very low loads, and at penetration depths below approximately one tenth the coating thickness, to substrate controlled response at larger loads, and depths comparable or greater than the coating thickness. When once the coating-only hardness is measured or estimated, the model contains a single non-dimensional 'composite response' parameter, which depends on certain combination of system properties. The series of microhardness measurements discussed in the paper is used in conjunction with least square fits to the model predictions. One of the purposes of this analysis is to clarify the physical meaning of the composite response parameter. The implications of the results are discussed in view of the possible engineering and design applications of this approach.

4:10 PM E4-F1-2-9 Finite Element Modeling of Contact Stresses in Monolayer Thin Films
R.M. Souza, J.J. Moore, G.G.W. Mustoe (Colorado School of Mines)
In this work, the finite element analysis was used to model situations of contact stresses in systems involving monolayer thin films. Different geometries related to the case where an indenter applies normal forces on the substrate or film/substrate were studied. The accuracy of the model was initially tested in systems without a film, using both the analytical solution for elastic substrates and the actual depth profile of Rockwell F indentations when considering elastic-plastic substrates. For the case of coated substrates, the influence of film thickness and film Young's modulus on the contact stresses was studied
4:30 PM E4-F1-2-10 Nano- and Micro- Tribology of Molybdenum Oxide Thin Films Having Controlled Microstructure
O.D. Greenwood, S.D. Dvorak, R.J. Lad (University of Maine)
Crystalline molybdenum trioxide (MoO3) is often a product of tribological processes involving lubricious MoS2 coatings, but MoO3 films themselves have received little attention as tribological coatings. The plate-like crystallite structure observed for MoO3 offers the potential for anisotropic tribological processes and for solid lubricant coatings which can withstand high temperatures and harsh oxidizing environments. We have synthesized MoO3 thin films using electron cyclotron resonance (ECR) oxygen-plasma-assisted electron beam evaporation of molybdenum onto r-cut and c-cut sapphire substrates. Surface microstructure was characterized by RHEED during film growth as a function of substrate crystal orientation and temperature. High quality epitaxial MoO3 films were obtained at temperatures between 873 K and 1073 K. Processing of these MoO3 films at temperatures up to 873 K in O2 caused no change in microstructure or composition as determined by RHEED, XPS and UPS measurements. A novel nanotribometer, which extends the AFM’s dynamic force range, and a pin-on-disk tribometer were used to test friction and wear of well characterized MoO3 thin films in the 10 μN to 0.6 N load range with sapphire sphere sliders. For an epitaxial microstructure, up to a load of approximately 0.2 N negligible pin-on-disk wear was observed and the friction coefficient remained constant at μ = 0.2 for 40 m sliding distance. At loads above 0.2 N, microscopic wear track topography suggests that wear mechanisms are directly correlated with the film crystalline microstructure.
Time Period WeA Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF1998 Schedule