Structural metallic nanolaminates (coatings consisting of alternating layers of different metals) are being explored for applications ranging from high strength foils to wear resistant coatings due to their relatively high hardness. This study seeks to explore how the nanolaminate structure evolves after deposition due to sliding contact. Using two-component Cu-Nb and Cu-Ag model systems (with 20 and 100 nm individual layers), the scratch and wear behavior was characterized using linear reciprocating deformation testing. It was shown that the damage due to sliding (depth of wear track) and coefficient of friction both increased with increasing layer thickness

Economy, D. Ross

Jiminez, Emilio

Kennedy, Marian S.

Ranjbaran, Bobak

Schultz, Brad M.

English

Clemson University: TigerPrints

Clemson UniversityTigerPrintsGraduate Research and Discovery Symposium(GRADS) Research and Innovation MonthSpring 2013Effect of Sliding Contact on the Structure of Cu-XNanolaminatesD. Ross EconomyEmilio JiminezBobak RanjbaranBrad M. SchultzMarian S. KennedyFollow this and additional works at: https://tigerprints.clemson.edu/grads_symposiumThis Poster is brought to you for free and open access by the Research and Innovation Month at TigerPrints. It has been accepted for inclusion inGraduate Research and Discovery Symposium (GRADS) by an authorized administrator of TigerPrints. For more information, please contactkokeefe@clemson.edu.Recommended CitationEconomy, D. Ross; Jiminez, Emilio; Ranjbaran, Bobak; Schultz, Brad M.; and Kennedy, Marian S., "Effect of Sliding Contact on theStructure of Cu-X Nanolaminates" (2013). Graduate Research and Discovery Symposium (GRADS). 73.https://tigerprints.clemson.edu/grads_symposium/73Effect of Sliding Contact on the Structure of Cu-X Nanolaminates D. R. Economy1, E. Jimenez2, B. Ranjbaran3, B. M. Schultz1, M. S. Kennedy1 1Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634 2Department of Engineering, James Madison University, Harrisonburg, VA 22807 3School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164  Poster Presented at the Inaugural Graduate Research and Discovery Symposium, Clemson, SC: 4/8/2013  Introduction: Metallic nanolaminates consist of alternating nano-scale metallic layers and have increased resistance to dislocation flow due to high density of interfaces when compared to other composites.  They have potential as both freestanding high-strength foils1 and wear-resistant coatings2.  Their mechanical properties (strength) can be tailored by controlling the component layer thicknesses1,3,4.                         Cu/Ag and Cu/Nb were chosen as model systems due to their ability to form semi-coherent and incoherent interfaces1,3,4, this is due to their various crystal structures (Cu: FCC, Ag: FCC, Nb: BCC). Experimental Methods: Fabrication of Cu/Nb and Cu/Ag: •  Substrate: (100) P-type silicon (Ra < 2 nm). •  Deposition rates: 4.0 nm/min (Cu), 2.8 nm/min (Ag), and 2.8 nm/min (Nb).  •  Total coating thickness: 1 µm (1000 nm). •  Individual layer thickness: 20 or 100 nm. •  Kurt J. Lesker magnetron sputter deposition system (COMSET).  Characterization of Sliding Deformation:               Hardness: •  Measured with a Hysitron Triboscope nanoindentation system. •  Three-sided diamond Berkovich tip.  •  Displacement-controlled indentation mode to maximum depths between 100 and 50 nm, to minimize effects of the underlying substrate. •  Oliver-Pharr indentation analysis used to determine mechanical properties. •  Hardness is defined by:                               where P is maximum load and Ac is contact area Grain Size: •  Measured with a Digital Instruments Nanoscope IIIa atomic force microscope. •  Five areas (scan length: 750–1500 nm) measured. •  Grain size calculated using line intercept method. Results: Initial Properties of Nanolaminate Systems:            Scratch Damage of Cu/Ag Systems: Upon observing morphology of the scratch path, a shift from plowing abrasion in the thicker system to cutting abrasion in the thinner system was noted.  Additionally, a deeper scratch path on the 100 nm system shows that the thicker system underwent more damage due to the sliding contact.  These results are consistent with those described by previous work2,5.           Sliding Friction of Cu/Ag Systems: The coefficient of friction increases with the increase in bilayer thickness (Fig 6.), similar to trends described by previous researchers2.            Scratch Damage of Cu/Nb Systems: When sliding contact was imposed on the 100 nm Cu/Nb systems, the films buckled due to compressive stress.  Additionally, when viewed in cross-section, plastic deformation was observed.  This deformation in the upper surface of the film was due to the scratching and not the delamination.  Also, it was seen that the deformation was localized to the uppermost layers and did not permeate through the thickness of the film.           Results (continued): Microstructure Evolution of Cu/Nb Systems: Sliding friction causes localized heating at the point of contact.  In order to understand implications of that heating on long term stability, additional work has sought to examine microstructural evolution.                Discussion and Conclusions: •  The same relationship between layer thickness and hardness were observed as in other groups1,3,4.   •  Decreased friction observed in thinner layered Cu/Ag system.  Similar to trends reported elsewhere2. •  Transition in abrasion morphology from plowing to cutting as layer thickness is decreased.  Similar to trends reported elsewhere2. •  Friction and wear morphology behavior is likely due to hardness of film systems5. •  Buckling and localized yielding observed along scratch path in Cu/Nb.  Deformation due to scratch did not penetrate through depth of nanolaminate. •  Effect of heating and aggressive species on microstructural development observed, possible pinning of grain growth by impurities. •  Non-uniform grain growth observed in system heated in vacuum. .  Acknowledgments: The authors would like to thank:  •  NSF Award #: DMR-1062873 •  The Center for Optical Materials Science and Engineering Technologies •  Dr. J. Hudson and the Clemson Electron Microscopy Facility Staff •  Dr. J. Harriss of the Clemson Electrical and Computer Engineering department References:  [1]  Misra, A. in Nanostructure Control of Materials (ed R. H. J. Hannick, Hill, A. J.) Ch. 7, 146-176 (Woodhead Publishing, 2006).  [2]  Wen SP, Zong RL, Zeng F, Gao Y, Pan F (2008) Investigation of the wear behaviors of Ag/Cu multilayers by nanoscratch. Wear 265 (11–12):1808-1813.  [3]  Misra, A., Hirth, J. P. & Hoagland, R. G. Length-scale-dependent deformation mechanisms in incoherent metallic multilayered composites. Acta Materialia 53, 4817-4824 (2005).  [4]  Verdier, M., Huang, H., Spaepen, F., Embury, J. D. & Kung, H. Microstructure, indentation and work hardening of Cu/Ag multilayers. Philosophical Magazine 86, 5009-5016 (2006). [5] Koji K, Koshi A (2000) Wear Mechanisms. In: Modern Tribology Handbook, Two Volume Set. Mechanics & Materials Science. CRC Press.   Future Work:           Aims:  •  Understand the effects of initial stress on mechanical behavior of model nanolaminate systems. •  Determine dislocation (and deformation zone) evolution of model nanolaminate systems as a result of dynamic loading. •  Elucidate residual stress evolution in nanolaminate films during thermal cycling. Table 1 Scratch test parameters used for this study. Future Work: •  Further examination of friction progression in nanolaminates using scratch and wear testing. •  Examination of Cu/Ni systems to complement Cu/Ag and Cu/Nb. •  Use of FIB and TEM to examine dislocation evolution in individual layers due to deformation. •  Correlation with theory in dislocation dynamic simulations. Metallic	  Nanolaminate	  Performance	  Structure	  and	  Design	  Environmental	  Evolu8on	  Mechanical	  Evolu8on	  Fig. 1 Concept map of major issues for stable and durable nanolaminate systems. Scratch	  Test	  Parameters	  Load	   Velocity	   Length	   #	  of	  Passes	  0.5	  N	   1	  mm/sec	   2	  cm	   20	  Passes	  •  Linear reciprocating wear tests conducted using CETR UMT-2.   •  Counterface: 440C SS 3/8” ball bearing. •  Table 1 shows parameters used for the scratch testing.  •  Plastic deformation observation using non-contact profilometry (Wyko white light interferometer) and field emission scanning SEM (Hitachi S-4800). Fig. 2 Linear reciprocating wear test of Cu/Nb nanolaminate and stainless steel counterface. Fig. 6 Coefficient of friction of Cu/Ag nanolaminates during scratch testing.  Thicker system shows higher steady state friction level. Fig. 5 Measured film profiles following scratch testing.  Thicker system (100 nm) shows more deformation in scratch path. Fig. 4 Plan-view of sliding wear deformation of 100 nm (A) and 20 nm (B) Cu-Ag nanolaminates. A B Sliding Direction Fig. 7 Cross-sectional views of sliding wear deformation of 100 nm (A) and 20 nm Cu-Ag (B) nanolaminates. A B Sliding Direction Fig. 8 Cross-sectional view of deformation in 100 nm Cu/Nb following sliding contact.  Buckling and localized scratch damage can be seen. Fig. 10 Non-uniform grain size observed by AFM in Cu/Nb system heated in vacuum. Fig. 9 Grain growth observed in 20 nm Cu/Nb systems in varying environments. Possible grain pinning due to impurities. Research	  Hypothesis	  It	  is	  hypothesized	  that	  as	  the	  disloca8on	  density	  and	  residual	  stresses	  within	  metallic	  nanolaminates	  increase,	  their	  wear	  mechanisms	  will	  change.	  Fig. 3 Hardness of nanolaminate systems increase with decreasing thickness (A), 20 nm nanolaminate geometry as seen in Cu/Nb TEM (B), initial XRD patterns for Cu/Nb (C), and Cu/Ag (D). Hardness of nanolaminate systems behave similar to description by the confined layer slip model1,2.  Decreased layer thickness shows elevated hardness (Fig. 3A).  Initial nanolaminate structures were formed (Fig. 3B, 3C, 3D). H = P / AcA B C D Fig. 11 Confined layer slip model, image taken from Misra1. 

Effect of Sliding Contact on the Structure of Cu-X Nanolaminates

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Effect of Sliding Contact on the Structure of Cu-X Nanolaminates

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