Andrew J. Birnbaum

Functionally grading the shape memory response in NiTi films: Laser irradiation

A new process and mechanism are presented for controlling the shape memory response spatially within monolithic NiTi thin film structures. This technique is shown to effectively control the martensitic phase transformation temperature and exhibits control over aspects of the mechanical and shape memory responses as well. Specifically, the martensitic phase transformation temperature decreases with incident laser energy density. Concomitant modifications are observed in both the mechanical and shape memory responses in laser processed films. Analysis and characterization are performed via temperature controlled optical microscopy, x-ray diffraction, atomic force microscopy, and nanoindentation.

Substrate temperature effects on laser crystallized NiTi thin films

Amorphous sputter-deposited NiTi thin films were subjected to pulsed, melt-mediated laser crystallization techniques to engineer their microstructure. The effects of laser processing of preheated films are examined. Laser processing of films at an elevated substrate temperature has a significant effect on the rate with which solidification occurs. It is observed that the preheating temperature at which processing is carried out has significant implications for the resulting phase and microstructure, and therefore mechanical properties. Furthermore, the microstructural effects of varying incident laser energy density are examined via atomic force microscopy, scanning electron microscopy, and x-ray diffraction, and mechanical/shape memory properties are characterized via nanoindentation.

Annealing Effect on the Shape Memory Properties of Amorphous NiTi Thin Films

Thin film shape memory alloys have recently become a promising material for the actuation of devices on the microscale such as micropumps and microvalves. Their utilization, however, has been limited due to the difficulty in tailoring their properties for different applications. Control over the transformation temperatures as well as mechanical and shape memory properties is required to enable their widespread use. This study examines the effects of heat treatment time and temperature on the properties of amorphous, Ti-rich NiTi thin films on silicon substrates. The effects on the transformation temperatures are investigated through the use of temperature dependent optical microscopy and temperature dependent X-ray diffraction. The indentation modulus and hardness, as well as dissipated energy and depth recovery, are obtained through nanoindentation and atomic force microscopy. The role of microstructure and composition in altering both the mechanical and shape memory properties of the films is discussed.

On the lateral crystal growth of laser irradiated NiTi thin films

This letter demonstrates the ability to induce laterally grown, large-aspect crystals via pulsed, melt-mediated laser crystallization in NiTi thin films. Sputter-deposited 200 nm NiTi films were pulse irradiated utilizing a homogenized 308 nm excimer beam over a series of varying incident laser energy densities. Solidification occurred via two distinct pathways: nucleation and growth occurred away from the boundary of irradiation, while lateral growth of unmelted seeds into the undercooled melt developed at the boundary of irradiation. The potential for exploiting this technique to produce rolling direction texture for anisotropic properties is also discussed.

Effects of Clamping on the Laser Forming Process

Although considerable effort has gone into characterizing the laser forming process in terms of process parameters and conditions, there has been little emphasis on the effects of the mechanical and thermal constraints introduced by the clamping method utilized for a desired application. This research suggests means for investigating and predicting the resulting geometry of a specimen due to laser operation in close proximity to an array of imposed thermo-mechanical constraints for both the single and multiple scan cases; specifically, the resulting average bending angle as well as bending angle variations throughout the part. This is accomplished by initially only considering these effects on the thermal field. Conclusions are then drawn about the nature of the mechanical effects. These conclusions are validated through numerical simulation as well as physical experimentation. An analytical solution of the thermal problem is also presented for further validation of the temperature field as a constrained edge is approached.

Mechanism and Prediction of Laser Wet Cleaning of Marble Encrustation

During the removal of encrustation from marble with 355 nm laser pulses, the effects of the thin liquid layer covering the encrustation are experimentally and numerically investigated. The working mechanism of the liquid layer is analyzed. A two-dimensional axial symmetric model is proposed to simulate the changes in the temperature, liquid volumetric fraction, and vapor pressure in the irradiated encrustation. To model the conservation of mass, momentum, and energy, three coupled nonlinear partial differential equations are numerically solved. The measured porosity of the encrustation is incorporated into the model. Marble cleaning with three different liquids having different thermodynamic properties, distilled water, ethanol, and acetone, are compared in terms of the cleaning efficiency at different fluence levels. With the liquid layer, the surface color of cleaned marble is also studied. In addition, surface-enhanced raman spectroscopy and a chromameter are used to identify the chemical constituents and measure the color of the cleaned marble, respectively.

Advances in laser-induced plastic deformation processes

Abstract: Although myriad laser processes take advantage of the ability to convert photon energy into thermal energy resulting in a local increase in temperature, e.g. laser cutting, drilling, welding, in a sense these processes represent a direct energy conversion from laser energy to task. However, when converting laser energy to desired, controllable mechanical deformation, there exist what may be thought of as intermediate steps that arise in the process. This chapter aims to give a brief background and review recent advances for three processes: laser forming, laser shock-peening and laser peen forming. All three of these processes utilize laser energy in order to induce plastic deformation resulting in either a desired final part geometry, desirable material properties/performance or both.

SHAPE MEMORY PROPERTY ALTERATION OF AMORPHOUS NITI THIN FILMS THROUGH AGING HEAT TREATMENT

Thin film shape memory alloys have recently become a promising material for actuation of devices on the micro scale such as micro-pumps and micro-valves. Their utilization, however, has been limited due to the difficulty in tailoring their properties for different applications. Control over the transformation temperatures as well as mechanical and shape memory properties is required to enable their widespread use. This study examines the effects of heat treatment time and temperature on the properties of amorphous, Ti-rich NiTi thin films on silicon substrates. The effects on the transformation temperatures are investigated through the use of temperature dependent optical microscopy. The modulus and hardness, as well as dissipated energy and depth recovery are obtained through nano-indentation and atomic force microscopy (AFM). The role of microstructure and composition in altering both the mechanical and shape memory properties of the films is discussed.© 2009 ASME

Mechanism and prediction of laser wet cleaning of marble encrustation

During the removal of encrustation from marble with 355 nm laser pulses, the effects of the thin liquid layer covering the encrustation are experimentally and numerically investigated. The working mechanism of the liquid layer is analyzed. A two-dimensional axi-symmetric model is proposed to simulate the changes of the temperature, liquid volumetric fraction and vapor pressure in the irradiated encrustation. To model the conservation of mass, momentum, and energy, three coupled nonlinear PDEs are numerically solved. The measured porosity of the encrustation is incorporated into the model. Marble cleaning with three different liquids has different thermodynamic properties, that is, distilled water, ethanol and acetone, are compared in terms of the cleaning efficiency at different fluence levels. With the liquid layer, the surface color of cleaned marble is also studied. In addition, Surface-enhanced Raman spectroscopy (SERS) and the Chromameter are used to identify the chemical constituents and measure the color of the cleaned marble, respectively.During the removal of encrustation from marble with 355 nm laser pulses, the effects of the thin liquid layer covering the encrustation are experimentally and numerically investigated. The working mechanism of the liquid layer is analyzed. A two-dimensional axi-symmetric model is proposed to simulate the changes of the temperature, liquid volumetric fraction and vapor pressure in the irradiated encrustation. To model the conservation of mass, momentum, and energy, three coupled nonlinear PDEs are numerically solved. The measured porosity of the encrustation is incorporated into the model. Marble cleaning with three different liquids has different thermodynamic properties, that is, distilled water, ethanol and acetone, are compared in terms of the cleaning efficiency at different fluence levels. With the liquid layer, the surface color of cleaned marble is also studied. In addition, Surface-enhanced Raman spectroscopy (SERS) and the Chromameter are used to identify the chemical constituents and measure the...

Effect of Fluence on the Discoloration of Marble Cleaned With UV Lasers

The effect of fluence level on the discoloration of marble surfaces after the removal of the encrustation by 355nm laser pulses is comparatively studied. Considering the thermochemical reaction possibly occurring in the encrustation during laser irradiation, the mechanism responsible for the discoloration of the cleaned marble surface is analyzed. The reduction of iron oxides by graphite plays a key role in determining the final color of the cleaned marble surface. A two-dimensional laser ablative cleaning model including the reaction heat is applied to calculate the temperature distribution during laser heating. The kinetics of the thermochemical reaction is estimated based on the simulated temperature field. The occurrence of the thermochemical reaction is also verified indirectly with experiments. The marble surfaces before and after laser irradiation are characterized in term of the chemical components through surface enhanced Raman spectroscopy. The surface color is measured with a chromameter using a 1976 CIE Lab color system. The proposed mechanism is also applied to numerically analyze the severer discoloration of marble cleaned with laser pulses at 1064nm.Copyright