Wave CO2 Research Articles

Friction and wear behavior of laser composite surfaced aluminium with silicon carbide

The present study concerns the wear behavior of laser composite surfaced Al with SiC and Al + SiC particulates. A thin layer of SiC and Al + SiC (at a ratio of 1:1 and dispersed in alcohol) were pre-deposited (thickness of 100 μm) on an Al substrate and laser irradiated using a high power continuous wave (CW) CO 2 laser. Irradiation leads to melting of the Al substrate with a part of the pre-deposited SiC layer, intermixing and followed by rapid solidification to form the composite layer on the surface. Following laser irradiation, a detailed characterization of the composite layer was undertaken in terms of microstructure, composition and phases. Mechanical properties like microhardness and wear resistance were evaluated in detail. The microstructure of the composite layer consists of a dispersion of partially melted SiC particles in grain refined Al matrix. Part of the SiC particles are dissociated into silicon and carbon leading to formation of the Al 4C 3 phase and free Si redistributed in the Al matrix. The volume fraction of SiC is maximum at the surface and decreases with depth. The microhardness of the surface improves by two to three times as compared to that of the as-received Al. A significant improvement in wear resistance in the composite surfaced Al is observed as compared to the as-received Al. The mechanism of wear for as-received vis-à-vis laser composite surfaced Al has been proposed.

Compositionally graded SiC dispersed metal matrix composite coating on Al by laser surface engineering

The present study concerns development of a hard SiC dispersed composite layer on an Al substrate to improve its wear resistance property. A thin layer of SiC (dispersed in alcohol) is pre-deposited (thickness of 100 μm) on an Al substrate and laser irradiated using a high power continuous wave (CW) CO 2 laser. Irradiation of the pre-deposited Al substrate leads to melting of the substrate with a part of the pre-deposited SiC layer, intermixing and rapid solidification to form the composite layer on the surface. Following laser irradiation, a detailed characterization of the composite layer is undertaken in terms of microstructure, composition and phases. Mechanical properties like microhardness and wear resistance are evaluated in detail. The microstructure of the composite layer consists of a dispersion of partially melted SiC particles in a grain refined Al matrix. SiC particles are partly dissociated into silicon and carbon leading to formation of a low volume fraction of Al 4C 3 phase and free Si redistributed in the Al matrix. The volume fraction of SiC is maximum at the surface and decreases with depth. The microhardness of the surface is improved by two to three times as compared to that of the as-received Al. A significant improvement in wear resistance in the composite surfaced Al is observed as compared to the as-received Al. The pitting corrosion property (in a 3.56 wt.% NaCl solution) is marginally deteriorated by laser composite surfacing.

Laser cladding of Ni-based alloy on copper substrate

The laser cladding of Ni1015 alloy on Cu substrate was prepared by a high power continuous wave CO 2 laser. Its microstructure was analyzed by optical microscope (OM), scanning electron microscope (SEM), and X-Ray diffraction (XRD). The average microhardness of the cladding coating was Hv 280, which was almost three times of that of the Cu substrate (Hv 85). OM and SEM observations showed that the obtained coating had a smooth and uniform surface, as well as a metallurgical combination with the Cu substrate without cracks and pores at the interface. With the addition of copper into the nickel-based alloy, the differences of thermal expansion coefficient and melting point between the interlayer and cladding were reduced, which resulted in low stresses during rapid cooling. Moreover, large amount of (Cu, Ni) solid solution formed a metallurgical bonding between the cladding coating and the substrate, which also relaxed the stresses, leading to the reduction of interfacial cracks and pores after laser cladding.

Laser composite surfacing of AISI 304 stainless steel with titanium boride for improved wear resistance

The present study concerns development of a hard in situ boride-dispersed composite layer on the surface of AISI 304 stainless steel substrate to improve the wear resistance property. Laser processing was carried out by melting the surface of sand-blasted AISI 304 stainless steel substrate using a continuous wave CO 2 laser and simultaneous deposition of a mixture of K 2TiF 6 (potassium titanium hexafluoride) and KBF 6 (potassium hexafloroborate) (in the weight ratio of 2:1) using Ar as shrouding environment. Powder feed rate was maintained constant at 4 g/min. Irradiation results in dissociation of a pre-deposited mixture along with a part of the stainless steel substrate, intermixing and rapid solidification to form the composite layer on the surface. The micro-structure of composite layer consists of dispersion of titanium boride particles in AISI 304 stainless steel matrix. Volume fraction of particles is found to be uniform throughout the composite layer, though varied with laser parameters. The micro-hardness of the surface was improved 250–350 VHN as compared to 220 VHN of the AISI 304 stainless steel substrate with a significant improvement in wear resistance property. The mechanism of wear was found to be a combination of adhesive and abrasive in as-received stainless steel. However, it was predominantly abrasive for laser composite surfaced stainless steel.

Localized CO 2 laser bonding process for MEMS packaging

The packaging poses a critical challenge for commercialization of MEMS products. Major problems with the packaging process include degraded reliability caused by the excess stress due to thermal mismatch and altered performance of the MEMS device after packaging caused by thermal exposure. The localized laser bonding technique for ceramic MEMS packaging to address above-mentioned challenges was investigated. A continuous wave CO 2 laser was used to locally heat sealing material for ceramic MEMS package lid to substrate bonding. To determine the laser power density and scanning speed, finite element analysis thermal models were constructed to simulate the localized laser bonding process. Further, the effect of external pressure at sealing ring on the bonding formation was studied. Pull testing results show that the scanning speed and external pressure have significant influence on the pull strength at the bonding interface. Cross-sectional microscopy of the bonding interface indicates that the packages bonded with relatively low scanning speed and external pressure conditions have higher bonding quality. This research demonstrates the potential of localized laser bonding process for ceramic MEMS packaging.

Investigating laser rapid manufacturing for Inconel-625 components

This paper presents an investigation of laser rapid manufacturing (LRM) for Inconel-625 components. LRM is an upcoming rapid manufacturing technology, it is similar to laser cladding at process level with different end applications. In general, laser-cladding technique is used to deposit materials on the substrate either to improve the surface properties or to refurbish the worn out parts, while LRM is capable of near-net shaping the components by layer-by-layer deposition of the material directly from CAD model. In the present study, a high-power continuous wave (CW) CO 2 laser system, integrated with a co-axial powder-feeding system and a three-axis workstation were used. The effect of processing parameters during LRM of Inconel-625 was studied and the optimum set of parameters for the maximum deposition rate was established employing Orthogonal L9 array of Taguchi technique. Results indicated that the powder feed rate and the scan speed contributed about 56% and 26%, respectively to the deposition rate, while the influence of laser power was limited to 10% only. Fabricated components were subjected to non-destructive testing (like—ultrasonic testing, dye-penetrant testing), tensile testing, impact testing, metallographic examinations and micro-hardness measurement. The test results revealed defect-free material deposition with improved mechanical strength without sacrificing the ductility.

In situ dispersion of titanium boride on aluminium by laser composite surfacing for improved wear resistance

The present study concerns development of a hard in situ titanium boride-dispersed Al matrix composite layer on Al substrate with an objective to improve wear resistance property. Laser composite surfacing was carried out by melting the surface of sand blasted commercially pure Al substrate using a continuous wave CO 2 laser and simultaneous deposition of a mixture of K 2TiF 6 and KBF 6 (in the weight ratio of 2 : 1) through an external feeder (at a feed rate of 4 g/min) using Ar as shrouding environment. The process variables used in the present study were applied laser power and scan speed. Following laser irradiation, a detailed characterization of the composite layer was undertaken in terms of microstructure, composition and phases. Important mechanical properties like microhardness and wear resistance were evaluated in details. Irradiation results into melting of the substrate along with the delivered powder mixture, intermixing and rapid solidification to form the composite layer on the surface of the substrate. The microstructure of the composite layer consisted of uniformly dispersed TiB 2 and TiB particles in Al matrix. The microhardness of the surface was improved (to a maximum of 3 times) as compared to that of as-received Al substrate. There was a significant improvement in wear resistance in composite surfaced Al as compared to as-received one. However, corrosion property in a 3.56 wt.% NaCl solution was marginally deteriorated because of the presence of boride phase in the matrix.

Laser treatment of plasma-sprayed ZrSiO 4 coatings

Self-supported zircon (ZrSiO 4) coatings have been deposited by means of atmospheric pressure plasma spraying, a high rate deposition method. Zircon is one of the technologically important oxide ceramic material known for its refractoriness, its low thermal expansion and low thermal conductivity. However, it is well known that ZrSiO 4 dissociates into ZrO 2 and SiO 2 in the high temperature plasma torch during plasma spraying, the rapid quenching preventing reverse combination of both components into ZrSiO 4. Usually, high temperature annealing (about 1500 °C) is applied in order to combine SiO 2 and ZrO 2 into ZrSiO 4. In this contribution, we investigate an attractive technological alternative to recombine SiO 2 and ZrO 2 into ZrSiO 4 by laser treatment with a scanning continuous wave CO 2 laser. We also investigate the addition of SiO 2 rich glassy particles to the plasma spray powders in order to facilitate the recombination of ZrO 2 and SiO 2 into ZrSiO 4 during laser treatment. By carefully adjusting the CO 2 laser treatment parameters (laser power density, scanning speed) we show that the SiO 2 and ZrO 2 phases indeed recombine into ZrSiO 4. It appears in this contribution that the addition of low melting point SiO 2 rich particles strongly benefits the reaction of zirconia and silica into zircon.

Laser rapid manufacturing of Colmonoy-6 components

This paper introduces a new manufacturing technique for the fabrication of Colmonoy-6 components using laser rapid manufacturing (LRM). LRM is a upcoming rapid manufacturing technology, being developed at various laboratories around the world. It is similar to laser cladding at the process level with different end applications. In general, laser cladding technique is used to deposit material on the substrate either to improve the surface properties or to refurbish the worn out parts, while LRM is capable of near net shaping the components by layer-by-layer deposition of the material directly from CAD model. In the present study, a high power continuous wave (CW) CO 2 laser system, integrated with a co-axial powder-feeding system and three-axis workstation was used. The effect of processing parameters during multi-layer deposition of Colmonoy-6 has been studied and optimized to fabricate about a dozen bushes. Thus fabricated bushes were finally machined and ground to achieve the desired dimensions and surface finish. These bushes were tested for non-destructive testing (like-ultrasonic testing, Dye-penetrant testing), metallographic examinations, micro-hardness measurement, X-ray diffraction and thermal ageing. Results compared well with those fabricated by deposition of Colmonoy-6 on austenitic stainless steel rods using gas Tungsten arc welding (GTAW). Thus, the new manufacturing technique not only produced quality product, but also minimized machining of hard-faced material and brought significant saving of time and costly Colmonoy-6 material.

Apatite formation on CO 2 laser irradiated titanium oxide films

Biomimetic apatite-forming ability on CO 2-laser-irradiated titanium oxide films was examined. Sol–gel-derived amorphous titanium oxide films were crystallized after irradiation of a continuous wave CO 2 laser at the power of 5 W. The irradiation induced crystallization of anatase. The apatite-forming ability on the irradiated titanium oxide film was investigated by soaking in a solution with ion concentration 1.5 times those of simulated body fluid (1.5SBF). X-ray diffractometry showed that apatite formed on the laser-irradiated titanium oxide film within 5 days in 1.5SBF, while no apatite formed on the non-irradiated (amorphous) film. The apatite forming ability can be enhanced and given at a desired position by using the CO 2 laser-irradiation.

Effect of sintering atmosphere and carbon content on the densification and microstructure of laser-sintered M2 high-speed steel powder

In the present work, the role of graphite addition and sintering atmosphere on the laser sintering of M2 high-speed steel (HSS) powder was studied. The test specimens were produced using a continuous wave CO 2 laser beam at power of 200 W and at varying scan rate ranges from 50 to 175 mm s −1 under nitrogen and argon atmospheres. It was found that laser scan rate and sintering atmosphere strongly influence the densification of M2 HSS powder. Opposite to the conventional sintering that the sinterability of HSS is improved by graphite addition, the result of this work demonstrated that graphite addition decreases the sintered density of M2 HSS at relatively low laser scan rates, i.e. <100 mm s −1, whilst at higher scan rates the effect is not very conspicuous. Furthermore, sintering under argon atmosphere yielded better densification compared to nitrogen atmosphere, particularly at higher scan rates. The microstructure of laser-sintered parts consisted of large and elongated pores and a heterogeneous metal matrix. The matrix structure includes martensite, high carbon austenite and inter-cellular or inter-dendrite carbide network. Addition of graphite to the M2 HSS powder increases the heterogeneity of the microstructure, as it was noticed from the variation in the micro-hardness throughout the sintered specimens.

Effects of CO 2 laser conditioning of the antireflection Y 2O 3/SiO 2 coatings at 351 nm

Y 2O 3/SiO 2 coatings were deposited on fused silica by electron beam evaporation. A continuous wave CO 2 laser was used to condition parts of the prepared samples at different scanning speeds in the air. LAMBDA 900 spectrometer was used to investigate the changes of the transmittance and residual reflection spectrum. A Nomarski microscope under dark field was used to examine the changes of the micro defect density. The changes of the surface roughness and the microstructure of the film before and after conditioning were investigated by AFM and X-ray diffraction, respectively. We found that laser-induced damage threshold (LIDT) of the films conditioning at 30 mm/s scanning speed was increased by more than a factor of 3 over the thresholds of the as-deposited films. The conditioning effect was correlated with an irradiation-induced decrease of the defect density and absorption of the films.

Clinical study on laser therapy of the venous malformations and hemangioma in oral and maxillofacial regions

To try to find the best method of laser therapy for the management of venous malformation and hemangioma in oral and maxillofacial regions. From June, 1999 to July, 2002, 2 481 cases of venous malformations and hemangiomas were treated by several kinds lasers in our department. The lesions included port-wine stains, venous malformations, telangiectasia and hemangioma. The lasers used were continuous wave CO(2), Nd:YAG and Krypton lasers, pulsed dye laser and ultra-pulsed CO(2) lasers. The treatment modalities were direct irradiation, irradiation after surgical flap raising and photodynamic therapy. Follow up between 2 - 5 years revealed the treatment results as follows: excellent is 79.24%, good is 14.31% and poor is 6.45%. Laser therapy is one of the best method to treat venous malformations and hemangiomas. The key point is to apply different lasers properly.

Corrosion behaviour of laser-melted magnesium alloys

The present paper reports studies of the corrosion behaviour of magnesium alloys, AZ31, AZ61 and WE43 following laser surface melting (LSM) with a 2 kW continuous wave CO 2 laser to depth about 1 mm. The laser-melted samples were immersed in 5 wt.% sodium chloride solution of pH 10.5 for 10 days, with open circuit potential measurements recorded in the initial 24 h. LSM resulted in improvement of the corrosion resistance of the alloys, with weight losses reduced by about 30, 66 and 87% for the AZ31, AZ61 and WE43 alloys, respectively. Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) revealed that the average compositions of the alloys, following removal of surface oxide, were relatively unaffected by laser melting, indicating that any losses of magnesium or gains of oxygen only affected superficial layers. The improved corrosion resistance following LSM is associated with refinement of the alloy microstructure due to the rapid cooling of the melted layer, which results in increased concentration of alloying elements in solid solution in matrix regions and more uniform distributions of the corrosion-resistant β-phase that can accumulate as a protective layer.

Laser-assisted direct manufacturing of functionally graded 3D objects

Composition gradients of different types were produced in three-dimensional (3D) objects by means of a repetitive deposition process to manufacture functionally graded materials (FGMs). Each layer of about 30-μm thickness is created by coaxial powder injection into the working zone along with the laser beam through a specially designed nozzle. The influence of two different laser sources, pulse-periodic Nd:YAG (wavelength 1.06 μm) and quasi-continuous wave CO 2 (wavelength 10.6 μm), on the process has been studied. Since the former source provides better beam quality, the pulse-periodic Nd:YAG laser seems preferable for developing FGM components. The technique used allows developing predefined composition gradients by an appropriate change of the powder composition during the layer deposition process. The layered FGM samples were examined by metallography, microhardness measurements and SEM analysis. The compositional gradient can be smooth or sharp. This process also allows development of periodic multilayered structures. The SEM analysis showed that the minimal transition zone between two different alloys is only about 70 μm for a given condition. Thus, development of FGM structures by the above process seems feasible.

Studies on laser bending of stainless steel

Abstract In the present study, laser bending of AISI 304 stainless steel sheet has been attempted with a high power (2 kW) continuous wave CO 2 laser. Bending angle was measured as a function of laser/processing parameters including power density, scan speed, number of passes and sheet thickness. Following laser bending, microstructural evolution (using a scanning electron microscope) and phase analysis (by X-ray diffraction technique) were systematically carried out to study the effect of laser irradiation and thermal stress on the microstructure and phase transformation behavior of the sheet. Microhardness of the bent sheet at different position was carefully measured using a Vickers microhardness tester. Bending angle was found to vary from 0.5° to 70° under different processing conditions. The microhardness of the bend zone was found to increase (from 1.5 to 2 times) as compared to the as-received sample. The improved microhardness is attributed to grain refinement associated with rapid quenching during laser bending. Finally, the optimum processing zone for laser bending of stainless steel was derived.

Direct laser sintering of iron–graphite powder mixture

Abstract In the present work, the role of graphite addition on the laser sintering of iron powder was studied. Powder mixtures containing iron and 0.4, 0.8, 1.2, and 1.6 wt.% graphite were prepared by blending elemental powders. These powders were sintered layer-by-layer under nitrogen atmosphere using a continuous wave CO 2 laser beam. A laser power of 70–225 W, scan rate of 50–600 mm s −1 , scan line spacing of 0.1–0.3 mm, and layer thickness of 0.1 mm was used. It was found that the processing parameters play a key role on the densification of the iron–graphite powder mixtures. The addition of graphite enhances the densification of the iron powder and improves the surface quality of the laser sintered parts when optimized manufacturing conditions are applied. The graphite content has a significant influence on the internal pore structure of the sintered parts. They are gradually changed from interconnected networks to closed and spherical shaped pores with increasing graphite content. The metal matrix structure consists of different phases such as ferrite, austenite, and tempered martensite, which highlights the heterogeneous distribution of dissolved carbon in the iron matrix. This article presents the experimental details of the microstructural evolution in laser sintered iron–graphite powder mixtures. The role and key importance of graphite addition to iron powder in the laser sintering process is addressed.

Lack of difference in the rates of hypopigmentation with 90-microsecond pulsed and longer dwell time carbon-dioxide laser resurfacing

Background Hypopigmentation is an adverse outcome associated with carbon-dioxide (CO 2) laser resurfacing. A 90-microsecond pulse produces a more favorable postoperative course of healing, erythema, and pain compared with a 900-microsecond dwell time. The rate of hypopigmentation after 90-microsecond pulsed CO 2 resurfacing may also be reduced. To date, there have been no comprehensive reports on the effect of varying pulse duration on the occurrence of hypopigmentation. Objective We sought to investigate the relationship between pulse duration and the occurrence of hypopigmentation after CO 2 laser resurfacing. Methods We conducted a retrospective review of 447 consecutive patients who were treated with a 90-microsecond pulsed CO 2 laser (n = 229) or a continuous wave CO 2 laser with a modifiable dwell time (100-950 microseconds, n = 218). Follow-up ranged from 8 to 61 months (median: 27). Results A series of 4 threshold dwell times (range: 90-950 microseconds) were used to divide patients into 2 treatment groups (above and below) at each threshold. The rates of hypopigmentation between groups were similar (range: 6.37%-9.09%) and serial chi-square testing revealed no statistical differences between groups for each dwell time tested ( P < 1.0). Conclusion No significant relationship between pulse duration and the occurrence of hypopigmentation was observed.

Laser surface engineering of a magnesium alloy with Al+Al 2O 3

The present study concerns an attempt to improve the wear resistance of a commercial magnesium alloy, MEZ (rare earth 2 wt.%, Zn 0.5 wt.%, Mn 0.1 wt.%, Zr 0.1 wt.%) by dispersion of Al 2O 3 particles and alloying with aluminium on the surface by laser surface engineering. Laser processing was carried out with a 10-kW continuous wave CO 2 laser by melting and subsequent feeding of Al+Al 2O 3 particles (in the ratio of 3:1) on the surface of MEZ. Following laser processing, a detailed microstructural and phase analysis of the surface modified layer were carried out. The microhardness of the surface layer was measured as a function of laser parameters and wear resistance property was evaluated in details. Microhardness of the surface layer was significantly improved to as high as 350 VHN as compared to 35 VHN of the substrate. The optimum processing region for formation of a homogeneous microstructure and composition for laser surface modification of MEZ with Al+Al 2O 3 was established. The wear resistance of the laser surface modified samples was considerably improved as compared to the as-received specimen.

Impact wear behavior of laser hardened hypoeutectoid 2Cr13 martensite stainless steel

Impact assessment for laser hardened hypoeutectoid 2Cr13 martensite stainless steel was carried out on a specifically developed ball-on-flat impact tester. Results showed better impact behavior of 2Cr13 surfaces treated by a continuous wave CO 2 laser than those under conventional heat treatment. Micro-hardness measurement demonstrated that the surface hardness of the laser treated specimens varied with the operation parameters of laser hardening. Scanning electron microscope (SEM) analysis and surface profile measurement suggested that the size of the impact wear scars of 2Cr13 specimens decreases with the increase of the surface hardness. EDX analysis showed that the oxidation resistance of the laser-hardened surfaces was relatively superior to their conventionally heat-treated counterparts. Compared with conventionally-treated 2Cr13 steel, the superior impact wear resistance of laser surface-processed steel was attributed both to grain refinement and to the higher martensite content near the surface that resulted from rapid cooling.