Mechanical Properties of Wear Tested LIGA Nickel
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Mechanical Properties of Wear Tested LIGA Nickel N. R. Moody1, J. M. Jungk2, M. S. Kennedy3, S. V. Prasad4, D. F. Bahr3, and W. W. Gerberich2 1 Sandia National laboratories, Livermore, CA 94550 2 University of Minnesota, Minneapolis, MN 55455 3 Washington State University, Pullman, WA 99164 4 Sandia National Laboratories, Albuquerque, NM 87158 ABSTRACT 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 on the mechanical performance of microdevices are not well-defined. To address these effects on performance of LIGA nickel, we have begun a program employing nanoscratch and nanoindentation. Nanoscratch techniques were used to generate wear patterns using loads of 100, 200, 500, and 990 µN with each load applied for 1, 2, 5, and 10 passes. Nanoindentation was then used to measure properties in each wear pattern correcting for surface roughness. The results showed a systematic increase in hardness with applied load and number of nanoscratch passes. The results also showed that the work hardening coefficient determined from indentation tests within wear patterns follows the work hardening behavior established from tensile tests, supporting use of a nanomechanicsbased approach for studying mechanical properties of wear tested material. INTRODUCTION Strength, friction, and wear are dominant factors in the performance and reliability of materials and devices fabricated using nickel based LIGA technologies. These technologies are of particular interest for microelectromechanical systems (MEMS) applications as they enable fabrication of miniature parts with extremely small feature size [1] with greater strengths than bulk Ni in the annealed or wrought conditions. [2] However, questions on friction, wear, and mechanical behavior of micromachines employing sliding contacts have not been addressed in any detail. Regions of contact are severely stressed and give rise to acute gradients of strain which may change topography, microstructure and properties. [1-3] In this study, nanoindentation, nanoscratch, and scanning probe-based measurement techniques were used to evaluate the mechanical behavior of wear tested LIGA nickel samples. MATERIALS AND PROCEDURE The samples used were fabricated in a previous study using a UV mask to create a 10 mm x 10 mm square array of micromolds in a 500 µm thick photoresist layer on a metallized silicon substrate. [1] Nickel was electroplated into the micromolds from a
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Figure 1. A 4x4 matrix of wear patterns on LIGA Ni using loads of 100, 200, 500, and 990 N with each load applied for 1, 2, 5, and 10 passes. Each pattern is 40 µm x 40 µm. sulfamate bath followed by a surface lapping procedure. The photoresist mold material was dissolved leaving Ni coupons on the substrate. The substrate was then diced to obtain individual test coupons. The resulting microstructure had a columnar structure with grains
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