Dimitrios A. Dragatogiannis

Plasma micro-nanotextured, scratch, water and hexadecane resistant, superhydrophobic, and superamphiphobic polymeric surfaces with perfluorinated monolayers.

Superhydrophobic and superamphiphobic toward superoleophobic polymeric surfaces of polymethyl methacrylate (PMMA), polyether ether ketone (PEEK), and polydimethyl siloxane (PDMS) are fabricated in a two-step process: (1) plasma texturing (i.e., ion-enhanced plasma etching with simultaneous roughening), with varying plasma chemistry depending on the polymer, and subsequently (2) grafting of self-assembled perfluorododecyltrichlorosilane monolayers (SAMs). Depending on the absence or not of an etch mask (i.e., colloidal microparticle self-assembly on it), random or ordered hierarchical micro-nanotexturing can be obtained. We demonstrate that stable organic monolayers can be grafted onto all these textured polymeric surfaces. After the monolayer deposition, the initially hydrophilic polymeric surfaces become superamphiphobic with static contact angles for water and oils>153°, for hexadecane>142°, and hysteresis<10° for all surfaces. This approach thus provides a simple and generic method to obtain superamphiphobicity on polymers toward superoleophobicity. Hydrolytic and hexadecane immersion tests prove that superamphiphobicity is stable for more than 14 days. We also perform nanoscratch and post nanoscratch tests to prove the scratch resistance of both the texture and the SAM and demonstrate lower coefficient of friction of the SAM compared to the uncoated surface. Scanning electron microscope observation after the nanoscratch tests confirms the scratch resistance of the surfaces.

Microstructural Study and Mechanical Properties of Dissimilar Friction Stir Welded AA5083-H111 and AA6082-T6 Reinforced with SiC Nanoparticles

Dissimilar friction stir welds were produced in 3 mm thick plates of AA6082-T6 and AA5083-H111 aluminum alloys using SiC as reinforcing material. The optimum weld presents a good distribution of nanoparticles in the weld nugget and mechanical mixing of the two alloys as well as further grain refinement compared to the one without nanoparticles. Higher hardness in the weld nugget is also evidenced, followed by enhanced ultimate tensile strength and elongation values. All specimens, after the tensile test, were lead to fracture at the heat affected zone of AA6082-T6 and specifically at the region of the lowest hardness.

Dissimilar Friction Stir Welding Between 5083 and 6082 Al Alloys Reinforced With TiC Nanoparticles

Dissimilar friction stir welding between aluminum alloys thick plates reinforced with TiC nanoparticles was conducted. The defect-free welds are characterized by good mechanical mixing between the joined materials as well as by good nanoparticle distribution and further grain refinement in comparison with the unreinforced weld. The local mechanical behavior of the produced metal matrix composites was studied and compared with their bulk counterparts and parent materials. Specifically, the measured mechanical properties in microscale and nanoscale (namely hardness and elastic modulus) are correlated with microstructure and the presence of fillers. The hardness, elastic modulus, ultimate tensile strength, percentage of elongation, and yield values increase with the presence of TiC nanoparticles.

Finite element analysis, stress‐strain distribution and size effects rise during nanoindentation of welded aluminum alloy

Purpose – The purpose of this paper is to investigate the use of nanoindentation with a Berkovich indenter as a method of extracting equivalent stress‐strain curves for the base metal and the welded zone of a friction stir welded aluminum alloy.Design/methodology/approach – Friction stir welding is a solid‐state joining process, which emerged as an alternative technique to be used in high strength alloys that were difficult to join with conventional joining techniques. This technique has a significant effect on the local microstructure and residual stresses combined with deformation. Nano‐ and micro‐indentation are the most commonly used techniques to obtain local mechanical properties of engineering materials. In order to test the reliability of nanoindentation technique and to connect nanoscale with macroscale, the indentation hardness‐depth relation established by Nix and Gao was applied on the experimental values.Findings – The predictions of this model were found to be in good agreement with classica...

A study on time dependent properties of aluminum alloy by nanoindentation technique

Purpose – Lightweight alloys are of major concern, due to their applicability, in transport and industry applications. The purpose of this paper is to perform a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique, through investigation of creep behavior. Additionally, possible explanations on the time dependent behavior and the influence of the hold period at maximum load and the loading rate on the elastic modulus and hardness results are also analyzed and discussed.Design/methodology/approach – In this work, a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique was performed, by varying the loading rate, the maximum applied load and the loading time. The stress exponent values are derived from the displacement‐holding time curves. The present experimental setup includes three different approaches: variation of loading rate, maximum applied load and loading time. The creep deformation mechanisms of the alloy, wh...

Nanomechanical Properties and Deformation Mechanism in Metals, Oxides and Alloys

Metals, oxides and alloys are widely used in transport and industry-engineering applications, due to their functionality. In this work, the nanomechanical properties (namely hardness and elastic modulus) and nanoscale deformation of metals, oxides and alloys (elastic and plastic deformation at certain applied loads) are investigated, together with pile-up/sink-in deformation mechanism analysis, subjected to identical condition parameters, by a combined Nanoindenter—Scanning Probe Microscope system. The study of discrete events including the onset of dislocation plasticity is recorded during the nanoindentation test (extraction of high-resolution load–displacement data). A yield-type pop-in occurs upon low applied load representing the start of phase transformation, monitored through a gradual slope change in the load–displacement curve. The ratio of surface hardness to hardness in bulk is investigated, revealing a clear higher surface hardness than bulk for magnesium alloys, whereas lower surface hardness than bulk for aluminium alloys; for metals and oxides, the behavior varied. The deviation from the case of Young’s modulus being equal to reduced modulus is analyzed, for all three categories of materials, along with pile-up/sink in deformation mechanism. Evidence of indentation size effect is found and quantified for all three categories of materials.

Dissimilar friction stir welding of aluminum alloys reinforced with carbon nanotubes

This chapter is devoted to studying the possibility of incorporating carbon nanotubes (CNTs) as reinforcing fillers in dissimilar metal matrices joints produced by friction stir welding (FSW), as well as the impact of this incorporation on the microstructural and mechanical properties of these joints. Carbon nanotubes are extensively used as a reinforcing material in nanocomposites, due to their high stiffness and strength. FSW is a solid-state welding process of joining aluminum and other metallic alloys and has been employed in the aerospace, rail, automotive, and marine industries. Recently, friction stir processing (FSP), a derivative method of FSW, has been employed as an alternative for the production of metal matrix composites (MMCs). In this work, the process parameters were optimized in order to achieve nondefective welds, with and without the addition of CNTs. Two main cases were studied: (1) FSP was optimized by changing the tool rotational and travel speed as well as the number and direction of FSW passes, and (2) a Taguchi design scheme was adopted to further investigate the FSP in relevance to three factors (number, direction of passes, and tool rotational speed). Mechanical behavior was studied, and the local mechanical properties of the produced MMCs were compared with their bulk counterparts and parent materials. More specifically, the measured mechanical properties in the micro- and nanoscale (namely hardness and elastic modulus) are correlated with the microstructure and the presence of fillers.

Deformation mechanism during nanoindentation creep and corrosion resistance of Zn

Purpose – The study of nanoindentation as a reliable method to extract creep properties as well as for fundamental understanding of deformation mechanisms at small length scales is an open interesting field. The observed creep behavior is attributed to time-dependent plastic deformation based on loading rates. There is a lot of work in the field of nanoindentation in order to understand the dynamic effects on nanomechanical properties. The paper aims to discuss these issues. Design/methodology/approach – The deformation mechanism is investigated under two experimental approaches (high and low loading rates, respectively) during nanoindentation. The effect of loading rate in the nanomechanical properties, during nanoindentation creep of zinc layer on hot dip galvanized (HDG) steel, is discussed through nanoindentation. Findings – Analysis of this research effort is emphasized on nanoindentation stress exponent, a critical parameter for the life time and reliability of nano/micro-materials and systems. The ...

Synthesis of hafnium nanoparticles and hafnium nanoparticle films by gas condensation and energetic deposition

In this work we study the fabrication and characterization of hafnium nanoparticles and hafnium nanoparticle thin films. Hafnium nanoparticles were grown in vacuum by magnetron-sputtering inert-gas condensation. The as deposited nanoparticles have a hexagonal close-packed crystal structure, they possess truncated hexagonal biprism shape and are prone to surface oxidation when exposed to ambient air forming core–shell Hf/HfO2 structures. Hafnium nanoparticle thin films were formed through energetic nanoparticle deposition. This technique allows for the control of the energy of charged nanoparticles during vacuum deposition. The structural and nanomechanical properties of the nanoparticle thin films were investigated as a function of the kinetic energy of the nanoparticles. The results reveal that by proper adjustment of the nanoparticle energy, hexagonal close-packed porous nanoparticle thin films with good mechanical properties can be formed, without any additional treatment. It is shown that these films can be patterned on the substrate in sub-micrometer dimensions using conventional lithography while their porosity can be well controlled. The fabrication and experimental characterization of hafnium nanoparticles is reported for the first time in the literature.

Nanomechanical properties of plasma treated polylactic acid

In this work, a radio frequency discharged plasma generated in air atmosphere by pressure has been used to modify polylactic acid (PLA) surface. The results were evaluated through nanoindentation testing. Contact angle measurements revealed a gradual transition to a more hydrophilic state with increasing polarity after plasma treatment, while partial recovery to their untreated state during 10 day storage in air was evidenced. The results were evaluated through nanoindentation testing. All PLA samples exhibited an almost hard-like surface area where hardness and elastic modulus are enhanced. The activity of the plasma creates a higher cross-linking density within the material in the surface region. For higher displacements, both H and E tend to reach pristine PLAs values. Hardness values reveal surface hardening due to plasma treatment except for 180 s etching time, where hardness is slightly decreased possibly due to surface deformation. The change of H/E slope reveals the strengthening of oxygen plasma etched PLA with 180 s of etching time with increasing displacement.