Laser Surface Texturing

"A target of Fe-40 at.-%Al intermetallic alloy with ordered B2 structure was subjected to laser melting processing by a high energy XeCI excimer pulse (wavelength 308 nm, pulse length 120  ns) in low pressure air. The total thickness of the laser affected zone (LAZ) was ∼ 150 nm. The modified surface showed an increased roughness and the presence of cracking. The X-ray photoelectron spectroscopy (XPS) measurements revealed a strong enrichment in the aluminium concentration within the LAZ, as well as relatively high contents of oxygen and nitrogen incorporated in the near surface region. Both angle resolved and depth profile XPS analyses suggested that oxides, nitrides, and oxynitrides were mainly present within the LAZ as discrete particles in the metallic matrix rather than as surface layers. Significant surface hardness reduction was observed after laser treatment, which has been interpreted to be due to partial suppression of B2 lattice ordering. Electrochemical measurements  in borate buffer solution showed a reduced anodic activity of the laser processed aluminide in the potential range between the open circuit potential and 0.1 V saturated calomel electrode, whereas at higher anodic overpotentials no substantial differences in behaviour were observed with respect to the untreated Fe–40Al surfaces. Such consequences of the excimer laser treatment may be explained by mechanisms involving aluminium enrichment and nitride formation processes inside the LAZ."

The effect of micro patterning of cemented carbide surface using nanosecond diode pumped solid-state pulsed laser on the strength of induction brazed carbide and steel joints has been investigated. Surface patterns increase the total surface area of the joint and, for an originally hydrophilic surface, increase the wettability of a liquid on a solid surface such that, instead of building droplets, the liquid spreads and flows on the surface. Microcomputed tomography (µ-CT) was used to observe the filler/carbide interface after brazing and to analyze the presence of porosity or remnant flux in the joint. Microstructures of the brazed joints with various surface patterns were analyzed using scanning electron microscopy. The strength of the joints was measured using shear tests. Results have shown that the groove pattern on the surface of carbide increases the joint strength by 70-80%, whereas, surface patterns of bi-directional grooves (grid) reduced the joint strength drastically. Dimples on the carbide surface did not show any improvement in the strength of the brazed joints compared to samples with no surface pattern.

A B S T R A C T Textured surfaces have been shown to provide enhanced tribological performance in a variety of contacts. Numerical analysis and optimisation methods are combined for application-oriented texture optimisation. However, an analytical approach is advantageous in providing more generic in-depth understanding of the nature of the relationships between texture parameters and objective functions, such as enhanced load carrying capacity and reduced friction. The paper outlines such an approach to obtain a set of global optimum design parameters for partially textured surfaces. The optimised results are expressed in dimensionless form, which enables their use for a variety of applications. The performance of optimised partially textured sliding surfaces is compared with the other conventional bearing geometries in their optimum state.

Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions.
Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined
numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused
by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved microwedge
flow. The results show good agreement between numerical predictions and experimental measurements using a
precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for
given conditions, dependent on the intended application under laboratory conditions. The translation of the same into
practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain.
This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue
than that obtained under ideal laboratory conditions.

All those who study Hadrian’s Villa know that most of the sculptures, mosaics, architectural
elements and other pieces which decorated this extraordinary villa are currently preserved in many public
and private collections in Italy and elsewhere (in Europe). Although many well-known statues can be found in
the principal Roman museums, at the Villa there is still a large number of fragments of statues, architectural
elements and so on. After long and painstaking work, most of the materials have been reorganized in the socalled
Cento Camerelle complex. Among the materials stored are some figured friezes, referring to
architectural decoration, with a characteristic curved shape: the only buildings at the Villa with figured and
curved friezes are the Teatro Marittimo and Piazza d’Oro, where we can see the remains of curved masonry
and porticos. Our aim is to illustrate the first results obtained from the integrated data treatment processing of
laser scanner surveys called IBDP (image-based data processing). This has facilitated versatile data storage
and cataloging, as also the development of specific studies on the former shape of ancient buildings (virtual
anastylosis), based on scientific criteria and not just for dissemination.

Along with the pursuit of coatings to enhance tribological performance and development of formulated lubricants with appropriate additive packages, surface texturing techniques have also been developed to guard against direct interaction of contacting surfaces. We have already shown (chapter 1) that mixed and boundary regimes of lubrication occur as the result of any direct interaction of rough surfaces. This increases the generated friction and reduces the system efficiency, as well as giving rise to wear and other forms of surface damage. The surface textures act as small reservoirs of lubricant, under conditions which retention of a coherent film of lubricant would not be expected, such as in cessation of rolling and/or sliding motion or in the presence of high contact loads. In chapter 12 we show the role of surface textures in piston-cylinder system and its beneficial effect in terms of reduced friction, thus power loss. In chapter 12 we provided results of some numerical analysis for textured surfaces as well as some experimental benefit of their effect in terms of reduction of power loss. However, the numerical predictive approach is quite complex and leads to long computation times. Furthermore, not everyone has access to such complex numerical models. Therefore, here we provide some representative analytical methods.

Making decisions and deducing control actions in manufacturing environments requires considering many uncertainties. The ability of fuzzy logic to incorporate imperfect information into a decision model has made it suitable for the optimization of both productivity and final quality. In laser surface texturing for wettability control, in fact, these aspects are governed by a complex interaction of many process parameters, ranging from those connected with the laser source to those concerning the properties of the processed material. The proposed fuzzy-based decision approach overcomes this difficulty by taking into account both the random error, associated with the process variability, and the systematic error, due to the modelling assumptions, and propagating such sources of uncertainties at the input level to the output one. In this work, the laser surface texturing was carried out with a nanosecond-pulsed laser on the surfaces of AISI 304 samples, changing the laser scanning speed, the hatch distance, the number of repetitions, and the scanning pattern. A significant change of the contact angle in the range 24–121° is observed due to the produced textures. The fuzzy maps highlight the inherent uncertainty due to both the laser texturing process and the developed model.

Laser surface texturing and through-mask electrochemical
micromachining (TMECMM) are some of the commonly
used methods which include multiple steps to achieve
micro-textures. However, for large-area applications, it is desirable
to have an economical single-step process. In this regard,
ECMM is expected to be a promising and economically
viable micro-texturing process for micro-manufacturing industries.
This paper proposes a novel maskless EC microtexturing
process using tool sinking technique with low voltage
and short pulses. Methodology of using edges (∼30 μm
each) of printed circuit boards (PCBs) for ECMM of microchannels
and micro-pillars is a unique one. Micro-pillars,
micro-dimples and micro-channels are produced through a
direct electrochemical cathode sinking process. Analysis of
current density and prediction of width and depth of microdimples
on a flat stainless steel surface are studied through 2D
numerical simulation carried out on COMSOL 4.3a. The proposed
method implies the use of less toxic electrolyte, low
voltage (1–6 V), short pulses (5 to 50 μs) and selective polymer
coating on the tool (cathode). A series of experiments of
EC sinking for creating various micro-patterns and microstructures
has been carried out on the flat as well as curved
metallic surfaces. This paper reports machining of microdimples
of 200–300 μm diameter, micro-channels of 150–
250 μm and square micro-pillars of 300–350 μm.
Comparison of the predicted geometrical dimensions of the
micro-dimples through the simulation shows reasonable
agreement with the experimental results for the given process
parameters of ECMM. The paper also reports a brief comparison
of laser surface texturing (LSTex) and electrochemical
surface texturing (ECSTex).

Using effective medium theory, spatial and angular Goos-Hanchen and Imbert-Fedorov reflection shifts of a graphene-coated granular substrate composed of non-spherical gold nanoparticles in a dielectric host are investigated. The numerical results indicate that the composite substrate can play a role in tunability of shifts similar to that of an electrically-controlled graphene layer does. It is realized that both shape and volume fraction of granular inclusions can bring about a broad shift modulation. This may provide applications in nano-optics as well as in characterizing the parameters of the composite.

The piston compression ring-bore contact accounts for 5-6% of input fuel energy [1]. This is significant for such a small conjunction. With ever-increasing costsand stricter emerging legislation much attention is directed towards reducing the parasitic losses.The piston ring is one of the most challenging tribological contacts on account of transient nature of the regime of lubrication during a typical engine cycle [2]. High friction occurs at piston reversals at the top and bottom dead centres, with highest friction at the beginning of the power stroke, where high pressures act behind the inner rim of the ring and with low piston sliding speed, inducing some Boundary interactions [2].
Laser texturing is used to reduce friction [3-7].This paper comprises direct measurement of friction from a reciprocating slider bearing test rig. It also presents numerical prediction of the same. The combined approach enables the study of possibleimprovements in tribological conditions similar to ring reversals in a piston system, but at a more fundamental level. It further reduces a plethora of other effects such as ring dynamics [8] and thermal distortions which make measurements difficult in an operating engine.

This paper presents the surface microstructure of Ti and Ti6Al4V alloy irradiated with a high output energy XeCl (λ = 308 nm) excimer laser. The treatments are carried out on both materials at two beam fluences and the effects of single- and multiple-pulse irradiation are compared. The results of the scanning electron microscopy and of the X-ray diffraction techniques suggest the possible influence of both time-behaviour and energy fluence of the laser pulse on the relative weight of the ablation rate and of the reaction product deposition rate at the sample surface.