Experimental study on the CO2 laser cutting of carbon fiber reinforced plastic composite

Promotion of massive application of carbon fiber reinforced plastics (CFRPs) in the industry can be accomplished by using faster and more flexible technologies such as laser cutting. The anisotropic and heterogeneous features of the CFRP make laser processing very challenging.A comprehensive study on the cut performance of a CO₂ laser to process sheets (3 mm thick) of a CFRP composite is presented. A high-beam quality CO₂ laser has been used in order to ascertain the capabilities of CO₂ laser cutting machines, widely used in metalworking applications, on the machining of this material. On the other hand, the influence of processing parameters, in both CW and pulsed mode, on the cut quality was studied.Cuts with a minimum heat affected zone, about 540 μm, were achieved using a high-beam quality CO₂ laser working in pulsed mode. In consequence, the CFRP strength remains practically unaffected compared to more conventional mechanical machining.     

CO2- Laserschneiden von Siliziumnitrid – Möglichkeiten und Grenzen

CO₂-Laser Cutting of Silicon Nitride - Possibilites and Limits Silicon nitride (Si₃N₄ · Y₂O₃) in different thicknesses was cutted with a CO^2? laser beam (1500 W). The reaction products on the cut surface by cutting with oxygen, air, nitrogen and argon as processing gases have been analysed by scanning electron microscopy, optical microscopy and x-ray. Moreover, the 4-point bending strength of cutted ceramics was examined to determine the grade of material damage. The parameter studies show that the highest bending strength and the optimal surface structure appear by cutting of silicon nitride with extremly short laser pulses and only with oxygen as processing gas.     

Dual-beam CO2 laser cutting of thick metallic materials

A dual-beam technique involving two CO₂ gas lasers with a power capacity of 1.5 kW each, was used to cut steel and superalloy. A comparison with single-beam CO₂ laser cutting showed that dual beams were capable of enhancing the cutting thickness and speed without deteriorating the quality of cut. Heat-conduction models, assuming the laser beams as line sources, were used to estimate the cutting thickness and speed as a function of distance between the two laser beams. Experimental data, coupled with theoretical modelling, have provided a new concept, namely stretching the width of the laser beam in the direction of cutting to cut thicker section solids at moderate speeds.     

Deactivation in Sub- and Supercritical Carbon Dioxide

Solutions of hexafluoroacetylacetone and a modifier such as, e.g., pyridine in supercritical CO₂ allow 97-99% removal of actinides from the stainless steel surface. The deactivation efficiencies were compared for liquid and supercritical CO₂. Single treatment run with solutions of HDEHP and DCH18C6 in liquid CO₂ removes 70-80% of transuranium elements and over 50% of strontium and cesium from the stainless steel surface. Deactivation of real contaminated radioactive samples was studied. Methods such as supercritical fluid extraction and extraction with liquid CO₂ are suitable for deactivation of surfaces and porous materials.     

High-temperature thermal barrier coating formation by laser alloying of CP-Ti with pre-placed Ni-SiC coating

High-temperature thermal barrier coating was created on CP-Ti using a pre-placed Ni-SiC layer by laser alloying technique. The coating was developed using 80% Ni + 20% SiC, 50% Ni + 50% SiC and 60% Ni + 40% SiC, and the latter two compositions are found to be efficient in producing a uniform layer. The 100% SiC pre-placement was also used. A flaw-less coating of 0.4–0.6 mm thickness was produced at a lower power density of 1.3 to 1.9 × 10⁵ W cm^–2. Very high power density of 2.5–3.0 × 10⁵ W cm^–2 is inefficient to produce uniform coating. The laser alloyed coating consists of dendrites and intermetallic precipitates. The degree of dendrite population depends upon the coating composition and laser processing conditions. The coating hardness was 600–1200 HV, which is three to six times higher than the base titanium. Uniform hardness was obtained for the coatings produced at a laser power density of 1.3 × 10⁵ W cm^–2. The titanium silicide (TiNiSi, Ti₅Si₃, TiSi) and nickelide (NiTi₂) phases formed on the laser-alloyed coating surface was confirmed by X-ray analysis. These intermetallic phases can improve high-temperature properties of titanium and its alloys. The effect of laser power density and coating composition on the alloying depth alloying width, hardness and microstructure are discussed. The present work investigated the microstructure evolution, hardness and compound phases by means of optical and scanning electron microscopy, Vickers hardness testing, EDXRD and SIMS analysis. A 5 kW CW CO₂ laser was used for laser alloying experiments.     

The mechanism of remote cutting of metals by CO2-laser radiation

A thermal model is suggested of remote cutting (without a gas jet) of vertically positioned steel plates by a horizontally moving beam of a CO₂ laser. It is based on the assumption of instantaneous removal of melt, when the melt zone size reaches its critical value. The stable cutting region is calculated depending on the cutting speed, laser power, and thickness of specimens. It is shown that the initiation of the cutting operation at limiting parameters is accompanied by instability.     

Structural modifications induced by ion implantation in metals and polymers used for orthopaedic prostheses

Abstract

Ti–6Al–4V titanium alloy, AISI 316L stainless steel, and UHMW (ultrahigh molecular weight) polyethylene are commonly used as friction materials in orthopaedic joint prostheses. The most interesting property of the titanium alloy is its high corrosion fatigue resistance. However, its friction and wear behaviour is unsatisfactory, even when rubbing against a soft material such as polyethylene; it cannot be used without a surface treatment. The 316L stainless steel has superior friction and wear characteristics, but its mechanical properties are inferior and crevice corrosion is often associated with wear. The UHMW polyethylene wears and flows. Wear is related to the surface properties, whereas creep is linked to the bulk mechanical properties. Ion implantation is a surface treatment mainly used in industry for increasing the wear resistance of metals, such as in cutting tools, and for changing the electrical or optical properties of ceramics and polymers. In the present work, the technique is applied to orthopaedic materials, to improve their surface properties and to increase the lifetime of the prostheses. The treatment does not deteriorate the bulk characteristics of the materials. As far as metals are concerned, structural modifications are produced in a thin layer of <1 μm thickness. They depend on the implantation parameters, namely, nature of the ions, energy, dose, and temperature, and are analysed using glow discharge spectrometry and grazing incidence X-ray diffraction. For polymers, ion implantation leads to two different effects: a modification of the first atomic layers, which induces an increase in wettability, and a variation of the structure at greater depths, which influences the mechanical properties. These effects are analysed using specific methods such as electron spectroscopy for chemical analysis, electron spin resonance, and attenuated total reflectance infrared spectroscopy.

MST/1689     

Electrochemical deposition of carbon films on titanium in molten LiCl-KCl-K2CO3

Electrodeposition of carbon films on the oxide-scale-coated titanium has been performed in a LiCl-KCl-K₂CO₃ melt, which are characterized by scanning electron microscopy, Raman spectroscopy and X-ray diffraction analysis. The electrochemical process of carbon deposition is investigated by cyclic voltammetry on the graphite, titanium and oxide-scale-coated titanium electrodes. The particle-size-gradient carbon films over the oxide-scale-coated titanium can be achieved by electrodeposition under the controlled potentials for avoiding codeposition of lithium carbide. The deposited carbon films are comprised of micron-sized ‘quasi-spherical’ carbon particles with graphitized and amorphous phases. The cyclic voltammetry behavior on the graphite, titanium and oxide-scale-coated titanium electrodes shows that CO₃^2 − ions are reduced most favorably on the graphite for the three electrodes. Lithium ions can discharge under the less negative potential on the electrode containing carbon compared with titanium electrode because of the formation of lithium carbide from the reaction between lithium and carbon.     

Sondermetalle und ihre Anwendung im Chemieapparatebau

Refractory Metals and their Application in the Chemical Process Industry Special metals, such as titanium, zirconium and tantalum, are being used increasingly for chemical plant. The exceptional resistance of special metals to many corrosive chemicals - they show it even at high temperatures and pressures - arises not from natural immunity but from the formation of a protective oxide passive layer on the metal surface. Special metals are well suited for welding. Their reactions with gases of the atmosphere must be taken into account though. Welding is therefore possible only under inert gas or a high vacuum. Similarly, alloying with iron-based materials during welding must be avoided under all circumstances. It should be taken into consideration that the melting point of tantalum, for example, is about twice as high as that of steel. Tantalum and niobium are machined with high-speed cutting steels; the cutting speed and cutting angle are similar to those used for stainless steels. In detail, the outstanding properties of special metals in chemical plant are as follows:

• — the stability of titanium under oxidizing conditions
• — the stability of zirconium under reducing and alkaline conditions
• — the resistance of molybdenum to hydrofluoric acid and fluoride
• — the stability of tantalum under oxidizing and reducing conditions.

In pure mineral acids the passive behaviour generally improves in the order titanium - zirconium - tantalum. Except where molybdenum is concerned, the medium should not contain fluoride. The material with the widest range of applications is tantalum. The addition of niobium as an alloying element leads to favourably priced but similarly resistant materials whose prospects of becoming established in the chemical industry and playing a part similar in importance to that of tantalum itself are good.     

Corrosion behaviour of some stainless steel alloys in molten alkali carbonates (I)

In the present work it is aimed to study the corrosion behaviour of two types of stainless steel alloys (one ferritic and two austenitic) in molten Li₂CO₃- Na₂CO₃- K₂CO₃ mixture. This mixture is of interest in corrosion studies because of its low melting point (397°C) and good electrical properties. In this investigation the following techniques of measurements are used: (i) open circuit-potential, (ii) galvanic current, (iii) impedance, (iv) atomic absorption spectroscopy for the determination of the amount of metals dissolved in the melt (v) corrosion tests, carried out on the oxide scales formed during the oxidation of stainless steel alloys in carbonate melt. In this melt the electrode Ag/AgCl was used as a reference electrode. In molten carbonates, the oxide ions originate by self-dissociation according to the equilibrium CO₃ ^2– CO₂ + O^2–. The oxide ions, O^2–, and carbonate ions, CO₃ ^2–, play an important role in the oxidation process of these alloys and their passivation in the carbonate melt. As previously mentioned in references it can be assumed that the oxide scales formed on the alloy surface consist mainly of LiCrO₂ and LiFeO₂. The cathodic path of the corrosion process may be the reduction of CO₂ and/or CO₃ ^2–. The resistance of alloys against corrosion in melt increases with the increase of temperature. This may be due to the increase of concentration of O^2– and CO₂, enhancing both the anodic and cathodic reactions. The activation energy was calculated and found to be 91.496, 23.412 and 37.956 kJ/mol for the alloys 1, 2 and 3 respectively. The above mentioned techniques of measurements showed that the oxide scales of the austenitic stainless steel alloys (2, 3) are more passive and protective than of ferritic stainless steel alloy (1). This means that the resistance against corrosion, in the carbonate melts, of austenitic stainless steel alloys is higher than that of ferritic one.     

Morphology and phase changes in laser-ablated TiO2 particles during thermal annealing

A method for obtaining titanium dioxide (TiO₂) nanoparticles by laser ablation has been developed. Pulsed laser irradiation at an intensity of 10⁹ W/m² leads to sputtering of titanium dioxide in the form of particles with dimensions within 10?C50 nm. The phase composition and morphology of obtained nanoparticles have been studied by the methods of transmission electron microscopy and X-ray diffraction. Thermal annealing above 600°C leads to an increase in the average particle size and induces the structural transition of titanium dioxide from anatase to rutile modification. Quantitative dependences of the particle size and phase composition on the annealing temperature are established. It is established that, using the laser ablation method, it is possible to obtain the anatase phase of TiO₂ with increased thermal stability.     

Investigation on photogenerated radicals of some carboxylates in solution and in aqueous dispersions of AgBr

Abstract

The photogenerated free radicals from formate, oxalate and acetate in aqueous solutions without and with dispered AgBr grains under illuminations of 355 nm laser light, natural light and monochromatic red, green or blue light were detected by electron spin resonance with spin-trap DMPO. The results showed that: (a) ·CO₂^? radicals were produced in the formate solution by all of these illuminations; (b) the signals of ·CO₂^? radicals were greatly intensified when an AgBr dispersion was present in the formate solution; (c) the signals of ·CO₂^? radicals in the oxalate solution were also detected and intensified when an AgBr dispersion was present, but only after illumination by the 355 nm laser; (d) ·CH₃ radicals, instead of ·CO₂^?, were weakly detected in the acetate solution, but only in the presence of AgBr under illumination by the 355 nm laser. The photochemical behaviour of these carboxylates, particularly formate and oxalate, perhaps implies their capability for trapping photogenerated holes and their potential for acting as a hole converter to an effective electron carrier.     

Laser-induced synthesis,deposition and etching of materials

The field of laser-induced synthesis, deposition and etching of materials is reviewed with an emphasis on the emerging trends and novel adaptations of the basic laser processing concepts. A number of examples are cited to illustrate the issues involved. These include rapid synthesis of titanium nitride by pulsed laser induced reactive quenching at Ti:liquid NH₃ interface, laser deposition of good quality thin films of such materials as hot oxide superconductors, zinc ferrite, iron oxide, stainless steel, etc. and laser etching of superconductor films.     

Corrosion and stress corrosion cracking behavior of 316L austenitic stainless steel in high H2S–CO2–Cl− environment

In oil and gas production environments, H₂S and Cl^? can coordinate to cause pitting or stress corrosion cracking (SCC) of stainless steels. There has been limited work conducted on corrosion and SCC of autenitic stainless steels in high H₂S–CO₂–Cl^? environments. In this paper, by four-point bending test method and scanning electron microscopy analysis, SCC of 316L steel was investigated under high H₂S–CO₂ pressures with 150,000 ppm Cl^? at 60 °C. The effect of high H₂S–CO₂ pressure was discussed. The results indicated that the higher H₂S–CO₂ pressure can accelerate anodic dissolution process, deteriorate passive films, and aggravate SCC sensitivity. Using cyclic potentiodynamic polarization measurements, the corrosion behavior of 316L steel was studied in high H₂S–CO₂–Cl^? environments. The effect of pH on pitting corrosion was discussed. Lower pH can promote both cathodic and anodic actions on 316L steel and facilitate passive film breakdown.     

Lightweight lasers for industry

The low power CO₂ laser is described and its growing industrial applications to engineering processes such as cutting, drilling, soldering and marking are discussed.     

A Reflection Kinoform for Use with a CO2 Laser

The production of a binary reflection kinoform on stainless steel for use with a high-powered CO₂ laser is described. The kinoform focuses the laser beam into the letters LUT which may be burned onto a suitable material placed at its focus. A theoretical discussion of the reconstruction process from a binary kinoform is presented and the effects of phase quantization are considered.     

High strength electron beam welded titanium–stainless steel joint with V/Cu based composite filler metals

Composite V/Cu based filler metals for electron beam welding of titanium–stainless steel joint were designed, based on the element metallurgical compatibility. Powder metallurgy method was used to manufacture the filler metal. To determine the feasibility of these filler metals, microstructures were analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction. Mechanical properties of the joints were evaluated by tensile strength tests. The feasibility of the Cu/V filler metal was poor for the differences in physical properties between copper and vanadium, vanadium and titanium. A non-fusion defect was produced in the joint under low heat input, and cracking occurred in the joint under higher heat input due to the continuously distributed brittle TiCu, TiFe and τ₂ compounds. However, such defects were eliminated using a powder metallurgical V/Cu–V filler metal. A joint with a tensile strength of 395 MPa, 72% of that of the stainless steel was obtained. And almost no intermetallics were detected in Ti/V/Cu–V/Fe joint.     

Synthesis of rutile TiO2 powder by microwave-enhanced roasting followed by hydrochloric acid leaching

In this paper, the preparation of rutile TiO₂ powder from titanium slag by microwave-assisted activation roasting followed by hydrochloric acid leaching was investigated. The effects of the additive Na₂CO₃ on the crystal form, cell, crystallinity, phase transformation, surface functional groups and micro-surface structure of the calcined product were systematically studied using X-ray powder diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The results confirmed that the strongest characteristic Raman bands of rutile TiO₂ and the weakest FT-IR bands of (CO₃)⁻² were found when the Na₂CO₃ mass ratio was 0.4. Accordingly, the crystallinity for the product, namely short rod structure rutile TiO₂ powder, reached its peak value of 99.21% with a corresponding average grain size of 43.5 nm. The excessive Na₂CO₃ was found to be disadvantageous for the crystallinity of the product, since it formed a coverage on the surface of titanium slag which prevented the oxidation reaction for the decomposition of anosovite.     

Oxidation and corrosion behaviour of laser-alloyed mild steel with chromium

The oxidation and corrosion of mild steel coated with chromium powder followed by laser treatment has been investigated. Chromium powder was deposited on mild steel surface using atmospheric plasma spraying. The chromium-coated surface was irradiated separately using a pulsed Nd:YAG laser and a continuous CO₂ laser. The oxidation tests were carried out in air at 700°C and anodic polarization tests in 1N H₂SO₄ solution. There was significant difference in the morphologies of the surface alloys formed using CO₂ laser and Nd:YAG laser. Samples treated with CO₂ laser showed better oxidation resistance whereas the surface alloys formed using Nd:YAG laser showed poor oxidation resistance. Anodic polarization tests carried out on samples laser-treated with CO₂ laser showed improved corrosion resistance.     

Effect of laser heating on substructure of 0· 4%C steel

Abstract

It is expected that surface treatment by CO₂ laser will be useful for industrial applications in which improved wear resistance is required on selected areas of already accurately machined parts. Precision in the hardening of such surfaces using laser processes is an additional advantage. Moreover, it is possible to obtain these desirable properties for low cost construction steels. The microstructural changes within the laser heated zones of commercial grade medium carbon C45 steel were determined on thin foils from the treated regions using transmission electron microscopy. Components of the substructure are described and the influence of rapid laser heating on austenite formation and its transformation into martensite are discussed.

MST/563