Michael J. Lukitsch

Effects of the ratio of hardness to Young's modulus on the friction and wear behavior of bilayer coatings

We present a study of the effects of the ratio of hardness to Young’s modulus on the friction and wear behavior of layered composite coatings. Layered coating structures with the same surface coating but different interlayers were prepared by physical vapor deposition. We found that the ratio of hardness to Young’s modulus plays an important role in determining the friction coefficient and wear resistance of layered composite coatings. A low friction coefficient and high wear resistance can be achieved in structures with high ratio of hardness to Young’s modulus and moderately high hardness.

Stress-induced growth of bismuth nanowires

We report a method of making nanowires of bismuth (Bi) with diameters ranging from 30 to 200 nm and lengths up to several millimeters. The nanowires are extruded spontaneously at the rate of a few micrometers per second at room temperature from the surfaces of freshly grown composite thin films consisting of Bi and chrome–nitride. The high compressive stress in these composite thin films is the driving force responsible for the nanowire formation. This mechanism can also be used to create nanowires of other materials.

Nano‐Indentation Studies of Twinned Magnesium Single Crystals

Nano-indentation measurements have been performed on {10–12} twin and adjacent matrix regions of deformed magnesium single crystals and the hardness values were analyzed by the Oliver-Pharr method. Although the hardness difference between the twin regions and the adjacent matrix was insignificantly small, the hardness values showed orientation dependence regardless of the twins’ size and variants. This observation can be interrupted by texture- softening resulting from the lattice reorientation in the twin regions. In contrast, the experimental evidence for the Basinski hardening mechanism in {10–12} twins, which is an increase in strength/hardness as a result of dislocation contributions within twin area, was not obtained from this experiment. This presentation provides framework for the discussion of the hardening/softening effect of {10–12} twinning on the plastic flow in single crystalline magnesium and quantitative values for hardening parameters used in the crystal plasticity modeling.

Microstructure and Mechanical Properties of Combinatorially Prepared Thin Film Aluminum-Silicon Nanocomposites

e have undertaken the exploration of the Al x Si 1-x systems to discover new alloys with enhanced properties. We describe the mechanical properties of thin film Al x Si 1-x alloys determined through indentation experiments. Combinatorial methods were used to systematically control thin film microstructure through variations in composition and growth temperature. Discrete libraries of compositionally graded films have been sputter deposited onto silicon substrates to produce two structural phase regions: amorphous Al-Si and amorphous Si plus crystalline Al. The mechanical properties of the thin films were determined by analyzing the load-displacement traces based on the Oliver-Pharr method. X-ray diffraction was used to investigate the microstructures and determine the crystallite sizes.