Ultrasonic nondestructive materials characterization

A brief review of ultrasonic wave propagation in solid materials is presented with consideration of the altered behavior in anisotropic and nonlinear elastic materials in comparison with isotropic and linear elastic materials. Some experimental results are described in which ultrasonic velocity and attenuation measurements give insight into materials microstructure and associated mechanical properties. Recent developments with laser beam non-contact generation and detection of ultrasound are presented. The results of several years of experimental measurements using high-power ultrasound are discussed, which provide substantial evidence of the inability of presently accepted theories to fully explain the interaction of ultrasound with solid materials. Finally, a special synchrotron X-ray topographic system is described which affords the possibility of observing direct interaction of ultrasonic waves with the microstructural features of real crystalline solid materials for the first time

Microstructure and properties of single crystal BaTiO3 thin films synthesized by ion implantation-induced layer transfer

Single crystal BaTiO3 thin films have been transferred onto Pt-coated and Si3N4-coated substrates by the ion implantation-induced layer transfer method using H+ and He+ ion coimplantation and subsequent annealing. The transferred BaTiO3 films are single crystalline with root mean square roughness of 17 nm. Polarized optical and piezoresponse force microscopy (PFM) indicate that the BaTiO3 film domain structure closely resembles that of bulk tetragonal BaTiO3 and atomic force microscopy shows a 90degrees a-c domain structure with a tetragonal angle of 0.5degrees-0.6degrees. Micro-Raman spectroscopy indicates that the local mode intensity is degraded in implanted BaTiO3 but recovers during anneals above the Curie temperature. The piezoelectric coefficient, d(33), is estimated from PFM to be 80-100 pm/V and the coercive electric field (E-c) is 12-20 kV/cm, comparable to those in single crystal BaTiO3

Local Phenomena in Oxides by Advanced Scanning Probe Microscopy

In the last two decades, scanning probe microscopies (SPMs) have become the primary tool for addressing structure and electronic, mechanical, optical, and transport phenomena on the nanometer and atomic scales. Here, we summarize basic principles of SPM as applied for oxide materials characterization and present recent advances in high-resolution imaging and local property measurements. The use of advanced SPM techniques for solutions of material related problems is illustrated on the examples of grain boundary transport in polycrystalline oxides and ferroelectric domain imaging and manipulation. Future prospects for SPM applications in materials science are discussed

Advanced optical microscopies for materials: new trends

Podeu consultar el llibre complet a: http://hdl.handle.net/2445/32166This article summarizes the new trends of Optical Microscopy applied to Materials, with examples of applications that illustrate the capabilities of the technique

Investigation of metallurgical coatings for automotive applications

Metallurgical coatings have been widely used in the automotive industry from component machining, engine daily running to body decoration due to their high hardness, wear resistance, corrosion resistance and low friction coefficient. With high demands in energy saving, weight reduction and limiting environmental impact, the use of new materials such as light Aluminum/magnesium alloys with high strength-weight ratio for engine block and advanced high-strength steel (AHSS) with better performance in crash energy management for die stamping, are increasing. However, challenges are emerging when these new materials are applied such as the wear of the relative soft light alloys and machining tools for hard AHSS. The protective metallurgical coatings are the best option to profit from these new materials\u27 advantages without altering largely in mass production equipments, machinery, tools and human labor. In this dissertation, a plasma electrolytic oxidation (PEO) coating processing on aluminum alloys was introduced in engine cylinder bores to resist wear and corrosion. The tribological behavior of the PEO coatings under boundary and starve lubrication conditions was studied experimentally and numerically for the first time. Experimental results of the PEO coating demonstrated prominent wear resistance and low friction, taking into account the extreme working conditions. The numerical elastohydrodynamic lubrication (EHL) and asperity contact based tribological study also showed a promising approach on designing low friction and high wear resistant PEO coatings. Other than the fabrication of the new coatings, a novel coating evaluation methodology, namely, inclined impact sliding tester was presented in the second part of this dissertation. This methodology has been developed and applied in testing and analyzing physical vapor deposition (PVD)/ chemical vapor deposition (CVD)/PEO coatings. Failure mechanisms of these common metallurgical hard coatings were systematically studied and summarized via the new testing methodology. Field tests based on the new coating characterization technique proved that this methodology is reliable, effective and economical

Laser Textured Calcium Phosphate Bio-Ceramic Coatings on Ti-6Al-4V for Improved Wettability and Bone Cell Compatibility

The interaction at the surfaces of load bearing implant biomaterials with tissues and physiological fluids is an area of crucial importance to all kinds of medical technologies. To achieve the best clinical outcome and restore the function of the diseased tissue, several surface engineering strategies have been discussed by scientific community throughout the world. In the current work, we are focusing on one such technique based on laser surface engineering to achieve the appropriate surface morphology and surface chemistry. Here by using a pulsed and continuous wave laser direct melting techniques we synthesize three dimensional textured surfaces of calcium phosphate (Ca-P) based surface chemistry on Ti-6Al-4V. The influence of each processing type on the micro texture and phase evolution and thereby its associated effect on wettability, in vitro bioactivity, and in vitro biocompatibility are systematically discussed. For samples processed using the pulsed laser, it was realized that with increasing laser scan speed and laser pulse frequency there was a transition from surface textures with sharp circular grooves to surface textures with radial grooves and thereby improved hydrophilicity. For CW laser processing the results demonstrated improved hydrophilicity for the samples processed at 100 μm line spacing as compared to the samples processed at 200 μm line spacing. Owing to the importance of Si for cartilage and hard tissue repair, a preliminary effort for synthesizing Ca-P-SiO2 composite coating on Ti-6Al-4V surface were also conducted. As a future potential technique we also explored the Laser Interference Patterning (LIP) technique to achieve the textured surfaces and developed understanding on their wetting behavior. In the current work, by adjusting the laser processing parameters we were able to synthesize textured coatings with biocompatible phases. The in vitro bioactivity and in vitro vi biocompatibility of the coatings were proved by the precipitation of an apatite like phase following immersion in simulated body fluid (SBF), and increased proliferation and spreading of the MC3T3-E1 like cells. The results and understanding of the current research is encouraging in terms of looking at other bio-ceramic precursor compositions and laser process parameter window for synthesizing better textured biocompatible coatings

Investigation of Transport Behavior in Two-Dimensional Ferroelectric Heterostructures

This dissertation summarizes an investigation of the polarization-related electronic transport behavior in the ferroelectric thin films and two-dimensional (2D) materials heterostructures using Scanning Probe Microscopy (SPM) techniques. The polarization-related resistive switching in hafnium oxide thin films-based ferroelectric tunnel junction has been demonstrated by employing semiconducting MoS2 as a top electrode. We explored a coupling between the semiconducting properties of MoS2 and the polarization of Hf0.5Zr0.5O2 resulted in an enhanced tunneling electroresistance effect of up to 3 orders of magnitude. These results provide a possible pathway for the fabrication of high-density non-volatile memory devices. These results are presented in Chapter 3. Resistive switching control using conducting domain walls as functional elements has been investigated using graphene/LiNbO3 heterostructures. One approach involves the modulation of resistance through the manipulation of domain wall density using super-coercive voltage. This approach requires higher energy to switch the polarization and can induce high leakage current that makes it deleterious. To overcome this drawback, we have developed a new approach that involves tuning of domain wall conductivity by a sub-coercive voltage without altering the domain configuration. These results are presented in Chapter 4. Chapter 5 describes modulation of the transport behavior of 2D MoS2 junctions by mechanical stress induced by the sharp probe of atomic force microscope (AFM). We show that the junction resistance can be reversibly tuned by up to 4 orders of magnitude by altering the mechanical force applied via AFM tip. Additionally, we show that AFM tip generates strain gradient inducing flexoelectric effect that leads to an enhancement of photovoltaic effect. Finally, we have discovered stable room temperature ferroelectricity with out-of-plane polarization in trigonally distorted 1T”-MoS2. Here, the polarization switching has been realized by the mechanical load applied via AFM probe. The piezoelectric and the electrical properties of MoS2 flakes are probed. Moreover, we show that flipped flakes of 1T”-MoS2 samples consist of monolayers of randomly oriented polarization, showing the possibility of head-head or tail-tail configuration. These results are presented in Chapter 6. Advisor: Alexei Gruverma