Conventional heat treatment of a component is performed in a furnace whereby the component is continuously heated to a high temperature and quenched to get a hardened material. The furnace heating and tempering process take several hours which is expensive over a long run and less flexible. Laser transformation hardening is an attractive heat treatment technology which can be used to enhance the surface properties of highly stressed components such as cams, gears, and bearings without altering its bulk properties. The highly intense laser beam rapidly heats up the irradiated surface above its austenitization temperature which cools down instantaneously (self-quenching) as the laser moves away from the spot producing a hardened surface. The fast heating and cooling generate a non-equilibrium phase transformation of which very little is understood. An attempt was made to improve the surface properties of steel through solid solution hardening and microstructure refinement using a 250 W fiber laser. To identify the effect of various parameters on laser hardening, scanning conditions such as beam spot size, scan rate, power input, surface condition and overlap ratio were controlled. The change in hardness and morphology of laser treated surface were carefully investigated. The results show the surface hardness increased above 800 HV after laser treatment compared to 260 HV of the as-received specimen. It is found that austenitization has the highest effect on hardness achieved and can be controlled by proper choice of laser parameters and scanning rates.
Laser texturing is extensively investigated for modifying surface properties. A continuous wave (CW) fiber laser (λ=
1090nm) was used to pattern a silicon wafer surface in ambient and O2 atmosphere respectively. The O2 gas stream was
delivered through a coaxial nozzle to the laser spot. Characterization of the patterned features was carried out by surface
profiling, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS or EDX), Raman
spectroscopy, and X-ray photoelectron spectroscopy (XPS). Formation of laser-induced silicon oxide sub-micron bumps
was observed, which were analyzed and shown to cause changes in surface wetability and reflectivity.
Yongqi Fu
School of Physical Electronics, University of Electronic Science and Technology of China, No. 4, Section 2, North Jianshe Road, Chengdu, Sichuan Province 610054 China
Wei Zhou
Precision Engineering and Nanotechnology Center, School of Mechanical and Aerospace Engineering, Nanyang Technological University and Institute of High Performance Computing, Singapore, 639798 Singapore
A hybrid Au-Ag subwavelength metallic zone plate-like structure was put forth for the purpose of preventing oxidation and sulfuration of Ag film, as well as realizing superfocusing. The Au film acts as both a protector and modulator in the structure. Focusing performance is analyzed by means of three-dimensional finite-difference and time-domain (FDTD) algorithm-based computational numerical calculation. It can be tuned by varying thicknesses of both Au and Ag thin films. Our calculation results show that thickness difference between the Au and Ag thin films plays an important role for transmission spectra. Ratio of Au to Ag film thicknesses, hAu/hAg is proportional to the relevant peak transmission intensity. In case of hAuhAg=50 nm, both transmission intensity and focusing performance are improved. In addition, the ratio hAu/hAg strongly influences position of peak wavelengths Au and Ag generated from beaming through the metallic structures.
An optical probe with a single aperture flanked by depth-tuned grooves is presented. It is employed as an example to investigate propagation properties of the plasmonic nanostructures with a nonparaxial Gaussian beam illumination. The propagation through the subwavelength aperture is the process that a near-field diffraction of the Gaussian beam interferes with the surface plasmon polaritons (SPP) wave induced wavelets on surface of the grooves. An enhanced optical transmission at the exit side of a subwavelength aperture and a degraded reflection at top side of the compound dielectric/metal nanostructure (air/glass/C/Ag/air) of the probe can be generated with this illumination. Characteristics of the Gaussian beam illumination have been studied numerically via analysis of the transmission and reflection issues. In contrast, the results for plane wave illumination were given as well. Two-dimensional (2D) finite-difference time-domain (FDTD) algorithm is employed for the 2D simulation.
We discuss a novel whole-field optical strain sensor termed the moiré interferometric strain sensor (MISS) for simultaneous measuring of multipoint strains and whole-field contours of in-plane displacement. A high-frequency grating, attached to the surface of a specimen, is used as the displacement and strain-sensing unit. When illuminated by two collimated beams at a prescribed angle, the interference of the diffracted beams gives the whole-field deformation contours. If, on the other hand, each of the individual beams is separately imaged using a multilens CCD sensor similar to a wavefront sensor, the separation between the spot centroids for each microlens is directly proportional to the normal or shear strain component at the corresponding position on the specimen. Applications are demonstrated for uniform rotation and simulated in-plane strains.
Design of an enhanced surface plasmon polaritons (SPPs)–based nanostructure for the purpose of beam shaping is discussed. An indentation with depth-tuned grooves is presented to realize the beam shaping and extraordinary transmission. The nanostructure is directly fabricated using focused ion beam (FIB) milling on an Ag thin film coated on quartz with a thickness of 200 nm. A large measurement error is found during geometrical characterization of the nanostructures by use of an atomic force microscope (AFM) working in tapping mode. Apex wearing and 34 deg full cone angle of the probe generate the measurement errors during the characterization of nanostructures with a feature size of 200 nm and below. To solve this problem, an FIB trimmed AFM probe is employed in the geometrical characterization. The results show that the error is improved greatly using the trimmed probe. The desired excitation of the SPPs is derived using an optical fiber coupled CCD spectrometer after the modified geometrical characterization. The designed structure can be used as an optical probe for future inspection and detection use.
In this paper, a novel interferometric method with a wide range of sensitivities, called holography quasi projection moire method, is presented. It combines the features of the varied double projection moire method and the holographic interferometry method. This technique has been used to study the various failure modes, such as spallation, delamination, 1D buckle, 2D buckle, and crush, in microelectronic packaging film/substrate modules. The experimental phenomenon and fracture mechanism for various failure modes are presented and analyzed.
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