Papers

ICMCTF2003 Session H1-2: Nanoengineered Structures for Applications

Tuesday, April 29, 2003 1:30 PM in Room San Diego

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		H1-2-1 Structure and Properties of Nanolayer Coatings for Cutting Tool Applications S. Kudapa (Valenite Inc.); K. Narasimhan (Valenite, Inc.); P. Boppana (Valenite Inc.) Multiphase nanolayered coatings can potentially provide significant improvements over conventional coatings for cutting tool applications. The structure, smoothness, hardness, abrasive wear resistance and diffusive wear resistance properties can be enhanced by nanolayered coatings that contain multiphases or composite structures depending on the thicknesses of the individual layers. Nanolayered coatings of nitrides, carbo-nitrides, and oxides of Al, Ti, Zr were deposited on cemented carbide substrates using CVD techniques in a hot-wall reactor. Several combinations were chosen for this study containing various nanolayered configurations. Structure, smoothness, friction coefficient, hardness, fracture toughness and elastic properties of these coatings were evaluated and compared with conventional coating designs. Machining performance of these coatings were compared with conventional coatings and correlated with structure, smoothness and mechanical properties.
2:10 PM		H1-2-3 Nanocomposite Tribological Coatings with "Chameleon" Surfaces for Extreme Environment Lubrication J.S. Zabinski, A.A. Voevodin (Air Force Research Laboratory) Hard coatings offer tremendous advantages for controlling wear at surfaces and, therefore, they can substantially increase the value of relatively inexpensive engineering components. New classes of hard coatings using nanocomposite architectures have evolved that provide even better hardness and toughness for increased wear resistance. However, these coatings are generally not designed to provide low friction and, as with most coatings, perform optimally within a limited environmental range. Now, nanocomposite chameleon coatings have been discovered that provide good wear resistance, and also have low friction over a wide range of environments. Chameleon coatings respond to changing conditions by self-adjustment of their surface properties to maintain good tribological performance in any environment. The term "chameleon" is borrowed from analogy to the reptile, which can change its skin color to avoid predators. Similarly, the coating changes its surface chemistry and structure ("skin") to avoid wear. A review of recent results in the development, preparation, and properties of these coatings is provided. The first "chameleon" coatings were made of WC, WS₂, and DLC; these coatings provide superior mechanical toughness and performance through dry/humid cycling. To address temperature variation, the second generation of "chameleon" coatings were made using oxides such as alumina and yttria stabilized zirconia (YSZ) in a gold matrix with encapsulated nano-sized reservoirs of MoS₂ and DLC. Developments of "chameleon" coatings with other chemistries are also discussed. Coatings were produced using laser ablation assisted magnetron sputtering and other techniques not requiring vacuum. The relationships among chemical, mechanical, and tribological properties will be discussed. It will be shown that coatings exhibited "chameleon" behavior resulting in good friction and wear performance during environmental cycling.
2:50 PM		H1-2-5 Study of Tribological Behavior of Surface Alloyed Pt and Hf layers on a Ti-6Al-4V Substrate¹ T.J. Renk, P.P. Provencio, S.V. Prasad (Sandia National Laboratories) This paper deals with the microstructure, friction, and wear performance of surface-alloyed Pt and Hf layers on a substrate of Ti-6Al-4V alloy. The surface layers were prepared by co-sputtering of either the Pt or Hf mixed with Ti (either 10 or 20 wt% Hf or Pt) in a 1 µm layer over the substrate. The layer is then subjected to a number of pulsed intense ion beam pulses (700 kV, 1-5 J/cm²). During the 200 ns pulse, the layer melts and diffuses into the substrate, producing a thicker layer of altered microstructure with reduction in grain size and formation of metastable phases. Friction and wear measurements were made on surface alloyed layers against a Si₃N₄ counterface using a linear wear tester in a ball-on-disk configuration. The tests were performed in dry nitrogen atmosphere. The improved wear performance of a surface-alloyed Pt-Ti layer has been previously investigated.1 The Pt is observed to form a metastable layer which is believed to help improve the wear performance. In the current study, we have investigated the effects of both Pt and Hf layers, the latter chosen because Hf is miscible in all phases of Ti. The surface-alloyed layers of both Pt and Hf were found to exhibit lower friction coefficient compared to the sputtered but untreated layer. Microcopy of the wear tracks, including cross-sectional Transmission Electron Microscopy (TEM), is being performed to relate the wear performance to the microstructure of the alloyed layer. ¹ Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Co., under US DOE Contract DE-AC04-94AL85000. ²T. J. Renk, R. G. Buchheit, N. R. Sorensen, D. Cowell Senft, M. O. Thompson, and K. S. Grabowski, Phys. Plasmas 5 (1998) 2144. .
3:10 PM		H1-2-6 Laser-Assisted Nanocoating for Engines N.B. Dahotre (University of Tennessee)
3:50 PM		H1-2-8 Analysis of Thermomechanical Damage from Laser Pulse Heating of Coated and Uncoated Gun Steel P. Cote, M. Todaro, S.L. Lee, G. Kendall (US Army Research Development and Engineering Center, Benet Labs) Laser pulse heating (LPH) was used to produce thermomechanical damage on coated and uncoated gun steel surfaces in order to obtain basic information on erosion mechanisms during gun firing. Earlier laser pulse heating studies[1,2], using inert and reactive gases, have shown that the laser method reproduces many of the erosion damage features seen in fired gun tubes. This damage includes generation of a heat affected zone (HAZ) in steel, plastic flow, recrystallization and grain growth in coatings, crack initiation and propagation, and surface chemistry modifications. In the present study, thermomechanical damage effects in the HAZ observed from LPH of coated and uncoated gun steel specimens are compared with data from vented combustor tests and from fired 120mm and 155mm gun tubes. The residual stresses in the HAZ of several specimens were measured using X-ray diffraction and found to be 200-300 Mpa compressive. Hot hardness data taken during a complete thermal cycle through the phase transformations are used to explain a variety of unusual features observed in the HAZ including the compressive residual stress, subsurface crack initiation, crack blunting and cavitation, and surface upheavals from compositional variations. Effects of thermal fatigue, superplasticity, and hydrogen thermal charging are also discussed. [1] P.J. Cote, G. Kendall, M. Todaro, Proceedings of ICMCTF 2001, April, 2001, San Diego, CA. [2] P.J. Cote, G. Kendall, M. Todaro, and M. Witherell, Proceedings of ICMCTF 2002, April 2002, San Diego,CA.