YAG Disk Laser Research Articles

MICROSTRUCTURE AND PROPERTIES OF LASER-WELDED BUTT JOINTS OF AlSi1MgMn ALUMINIUM ALLOY

The process of autogenous laser welding of butt joints of aluminium alloy AlSi1MgMn plates with thickness of 3.0 mm was investigated. The Yb:YAG disk laser was used in the study. The aim was to determine the influence of the basic parameters of laser welding on the joint quality, fusion zone geometry, microhardness distribution across the butt joint, structure and microstructure of fusion zone (FZ) and heat affected zone (HAZ) was studied and determined. The chemical composition of the base metal was determined by spark emission spectroscopy, while the phase constituents were determined by XRD analysis. Results of the study have shown that the geometry of welds is proper without excessive imperfections. No voids were found the FZ. However, weld face of the joints are slightly convex, while the roots are slightly concave. Microscopic observations showed no discontinuities in the fusion zone of the welds. A significant decrease in hardness in the FZ was observed. The hardness in the FZ of the test joints is approx. 67÷70 HV0.1. The fracture of the samples during tensile tests occurred in the FZ or at the boundary FZ/HAZ, and the tensile strength was ranged from 200MPa to 220MPa.

Influence of ambient temperature on an Yb:YAG disk laser with anti-Stokes fluorescence cooling.

In general, the operating characteristics of solid-state lasers are significantly impacted by the ambient temperature, especially for Yb:YAG crystal with an anti-Stokes fluorescence cooling effect. In this Letter, the influence of the ambient temperature on the operating characteristics at the zero thermal load (ZTL) state is studied for an Yb:YAG disk crystal with a 1030 nm intra-cavity-pumped scheme. Theoretical analysis indicates that the output power of the laser at the ZTL state is significantly enhanced as the ambient temperature increases. Experimental results show that when the ambient temperature increases to 40°C, the output power of the laser at the ZTL state can reach 1.11 W, which is more than twice than that achieved at an ambient temperature of 25.5°C. This Letter provides a technical pathway for achieving a higher-power radiation-balanced laser (RBL).

MICROSTRUCTURE AND PROPERTIES OF LASER-WELDED BUTT JOINTS OF X2CRTINB18 STEEL

The process of autogenous laser welding of stainless steel X2CrTiNb18 was investigated. The Yb:YAG disk laser was used in the study for welding of 1.5mm thick butt joins. The influence of basic laser welding parameters on the joint quality, fusion zone geometry, microhardness distribution across the butt joint, structure and microstructure of fusion zone (FZ) and heat affected zone (HAZ) was studied and determined. The quality level of the test joints was determined according to the PN-EN ISO 13919-1 standard. The chemical composition of the base metal was determined by spark emission spectroscopy. Results of the study have shown that laser welding parameters have a significant influence on the quality of butt joints. However, it is possible to produce joints that meet the high requirements and criteria of quality. The width of HAZ of the butt joints welded in the investigated range of parameters was narrow and did not exceed 0.2 mm. It was found that the most common imperfections of the analysed joints are concavity of the weld face and insufficient penetration. The HAZ region of joints is characterized by mainly ferritic microstructure with complex carbides precipitates. In turn, the fusion zone is dominated by a ferritic microstructure but also precipitates were observed, which were identified as fine dispersion carbides. Hardness of the base metal is round 160÷170HV0.3. A tendency to increase in hardness in the HAZ and FZ was observed. The maximum hardness measured in HAZ was approx. 220HV0.3, while in the FZ 190HV0.3.

Amplified spontaneous emission intensity at the side surface of thin disk lasers

In the present research, amplified spontaneous emission (ASE) emerging from the lateral surface of a thin-disk laser is investigated. Through the method presented, an equation was derived to estimate the intensity of the ASE from the side surface of the disk. The equation results were compared with the findings of numerical approaches to validate the derived equation. Using this equation, the impact of the ASE on the reduction of the output power of a Yb:YAG disk laser was also explored. A comparison of the computational results with experimental findings indicated that the obtained equation could substantially enhance the estimation accuracy of the output power of the disk laser.

Generation of nanosecond pulsed azimuthally and radially polarized beams with an actively Q-switched rotating disk laser

We have directly generated two kinds of vector polarized beam pulses from an end pumped rotating Nd:YAG disk laser design acousto-optic Q-switch pulse modulation. About 20 ns pulse width with peak power 29 kW and stable pulse vector polarized beams are achieved at the continuous absorbed pump power. The laser crystal rotary effectively alleviates thermal effect that affects the power scaling with high beam quality. The output state is controlled by an intra-cavity polarization selector birefringent crystal. The polarization degrees of the azimuthally and radially polarized beams are 98.6% and 98.2%, respectively. The study suggests that this new method would constitute a laser light source for producing power and single pulse energy scaling, short pulse width, and high-purity structured vector beams and serve this function.

Laser Welding of Laser Powder Bed Fusion (LPBF) Manufactured 316L Stainless Steel Lap Joint

The aim of the study was to determine the static strength of laser welded lap joint in laser powder bed fusion (LPBF) printed stainless steel material and also a joint formed of printed and commercial sheet metal. Printed 316L test pieces with a thickness of 2 mm and a similar commercial 2 mm thin plate were used as test material. A laser welded lap joint made of a commercial sheet metal was used as a reference. Yb:YAG disk laser with wavelength 1030 nm and maximum output power 4 kW was used in welding tests. All test sets were welded with the same welding parameters and argon shielding gas. One fully penetrated keyhole weld was made to the lap joint. The static strength of the lap joints was determined by tensile tests. The measured shear strength was highest in the reference joint. In other cases, shear strength was only 8-11% lower compared to the reference joint. The cross-sections of the welds were analyzed on the basis of images taken with an optical microscope. Based on the results, the printed 316L is highly laser weldable material.

Pulsed azimuthally polarized beam from passively Q-switched rotating Nd:YAG disk laser

A azimuthally polarized laser pulse was produced from a passively Q-switched rotating Nd:YAG disk laser with a Cr4+:YAG crystal as the saturable absorber and a uniaxial YVO4 crystal as the polarization selection. The averaged laser power reached 5.04 W with a slope efficiency of 40%. The laser pulse had a maximum peak power of 4.3 kW, minimum pulse duration of 31.07 ns, and a 37.3 kHz repetition rate at absorbed pump power 15.93 W. The polarization degree of the azimuthally polarized beam was measured to be about 97.3%. Such an azimuthally polarized laser pulse is important to numerous applications.

Up conversion and excited state absorption analysis in the Tm:YAG disk laser multi-pass pumped by 1 μm laser

Abstract We present a 2 μm Tm:YAG disk laser multi-pass pumped by a 1 μm laser. The transitions in competition of up conversion (UC) and excited state absorption (ESA) are analyzed in detail based on a numerical model that considers stimulated emission, fluorescence, non-radiative decay, UC, andESA, showing good agreement with experiments. The proportions and fractional thermal loads of all transitions are derived quantitatively. The results show that UC and ESA are critical in Tm:YAG disk lasers, resulting in a decrease in the absorbed pump power and temperature after lasing for two different disk thicknesses. In addition, although the absorbed pump power of the 0.5 mm disk is lower than in the 1 mm case, its relatively weak UC and ESA and low total fractional thermal load can improve laser performance. A 0.5 mm Tm:YAG disk laser thus delivered the maximum output power of1.05 W with beam quality of Mx2 = 2.02 and My2 = 2.03.

Laser cladding process of Fe/WC metal matrix composite coatings on low carbon steel using Yb: YAG disk laser

The paper presents the studies of selected properties of Fe/WC metal matrix composite coatings produced using different laser beam power values and different powder feeding rates. Coatings were produced using the Yb: YAG disk laser by laser cladding method. Laser beam powers equal to 600 W, 700 W and 800 W were used. Scanning speed of laser beam was the same for all the coatings and was equal to 600 mm/min. Laser beam spot diameter was 1.64 mm. Two powder feeding rates (6.25 g/min and 12.50 g/min) were applied. In this study macroscopic observation, microstructure and microhardness examination as well as XRD and EDS analysis were carried out. Corrosion resistance was also investigated. In Fe/WC coating produced using slower powder feeding rate dendritic carbides that nucleated on the primary tungsten carbide particles were observed. In the coatings produced using an increased powder feeding rate, a changed type of secondary carbide was observed, which was bar-shaped or plate-shaped. The results of the XRD and EDS analysis of the composite Fe/WC coatings showed the presence of WC, W2C phases as well as M23C6 and (Fe,W)3C complex phases. The mechanism of formation and growth of composite coatings was described on the basis of microstructures obtained. The highest microhardness and corrosion resistance were observed for coatings produced at a powder feeding rate of 12.50 g/min.

Characterization of W-Cr Metal Matrix Composite Coatings Reinforced with WC Particles Produced on Low-Carbon Steel Using Laser Processing of Precoat.

The paper presents the study results of laser processing of precoat applied on C30 steel. The precoat consisted of powder mixtures with a binder in the form of water glass. Tungsten powder, chromium, and tungsten carbide (WC) were used to produce the precoat. The laser processing was carried out using a Yb:YAG disc laser with a rated power of 1 kW. Constant producing parameters (power of laser beam, 600 W; laser beam scanning rate, 400 mm/min) were applied. Chemical composition of the precoat was a variable parameter in coating production. A mixture consisting of 50% W and 50% Cr as a metal matrix was prepared. Subsequently, WC particles in weight ratios of 25%, 50%, and 75% were added to matrix. As a result, W–Cr metal matrix composite coatings reinforced with WC particles were formed. This study focused on investigation of microstructure, microhardness, phase, and chemical composition as well as corrosion and wear resistance, of the newly formed W–Cr/WC coatings. An instrumented nanoindentation test was also used in this study. As a result of laser beam action, the newly formed coatings had an interesting microstructure and good properties which were improved in comparison to substrate material. It is anticipated that the resulting coatings, depending on the treatment parameters (e.g., W–Cr/WC powder mixture) used, can be successfully applied to metal forming or foundry tools.

Copper Oxides on a Cu Sheet Substrate Made by Laser Technique

This paper presents results from the production of copper oxide layers on a Cu sheet substrate using diode and Yb:YAG disc lasers operating in the wavelength ranges of 808–940 nm and 1030 nm. The parameters of these layers were compared with the layer obtained in the thermal process of copper oxidation at 300 °C in an infrared (IR) furnace in a natural atmosphere. Investigations into the layers mentioned above, concerning their topography, chemical composition and roughness, were made using scanning electron microscopy (SEM) and atomic force microscopy (AFM). A hot-point probe was used to determine and check the type of conductivity of the copper oxide layers formed. The optical band gap energy was estimated by applying the Kubelka–Munk method based on spectrophotometric data. Cross-sections and the element distribution maps were made using transmission electron microscopy (TEM). The phase analysis was investigated by the X-ray diffraction method (XRD). In sum, controlled laser oxidations of copper sheets allow for the formation of a mixture of Cu2O and CuO phases. The diode laser allows the production of a layer of copper oxides with a phase composition comparable to the oxides produced by the thermal oxidation method, while the distribution of high phase uniformity in the cross-section of the layer enables the process using a Yb:YAG disc laser.

Influence of Laser Cladding Parameters on Microstructure, Microhardness, Chemical Composition, Wear and Corrosion Resistance of Fe–B Composite Coatings Reinforced with B4C and Si Particles

The paper presents the study results of a laser cladding process of C45 steel using powder mixtures. The aim of this study was to investigate the microstructure, X-ray diffraction (XRD), chemical composition (EDS), microhardness, corrosion resistance and wear resistance of the newly obtained coatings. Modified coatings were prepared using laser cladding technology. A 1 kW continuous wave Yb:YAG disk laser with a powder feeding system was applied. Two different powder mixtures as well as various laser beam parameters were used. The first powder mixture contained Fe–B, and the second mixture was Fe–B–B4C–Si. Two values of laser beam power (600 and 800 W) and three values of scanning speed (600, 800, and 1000 mm/min) were applied during the studies. As a result of the influence of the laser beam, the zones enriched with modifying elements were obtained. Based on the results of XRD, the presence of phases derived from borides and carbides was found. In all cases analyzed, EDS studies showed that there is an increased content of boron in the dendritic areas, while there is an increased silicon content in interdendritic spaces. The addition of B4C and Si improved properties such as microhardness as well as wear and corrosion resistance. The microhardness of the coating increased from approx. 400 HV to approx. 1100 HV depending on the laser parameters used. The best corrosion resistance was obtained for the Fe–B–B4C–Si coating produced using the highest laser beam scanning speed. An improvement in wear resistance can be seen after wear tests, where the weight loss decreased from about 0.08 g to about 0.05 g.

Microstructure and Wear Behaviour of SS420 Micron Layers on Ti–6Al–4V Substrate Using Laser Cladding Process

Ti–6Al–4V is commonly used material in automobile, aerospace, biomedical and marine due to its excellent properties. However, their uses are reduced because their its poor tribological performance. In the current study, stainless steel 420 alloy powder was cladded on Ti–6Al–4V base material using high-power Yb: YAG disc laser. Then, the cladded surfaces were evaluated to reveal their new phase formation, hardness changes and improved wear properties. Besides, the various wear mechanisms and their corresponding rough averages were studied. Results showed that the microhardness of laser cladded specimen is 613HV while base material shows 303HV. The wear rate of laser cladded specimen reduces remarkably compared to un-clad specimen. The identified major wear mechanisms are abrasive, adhesive and oxidation wear. The worn-out cladded surface shows lesser roughness than base material.

Cylindrical vector beam rotary Nd:YAG disk laser with birefringent crystal

A rotating neodymium-doped yttrium aluminum garnet (Nd:YAG) disk laser resonator for efficiently generating vector beams with azimuthal and radial polarization is demonstrated. In the study, the laser crystal rotary for thermal alleviation and polarization discrimination uses c-cut ytterbium vanadate (YVO4). The laser output could be switched between azimuthal and radial polarizations by simply adjusting the cavity length. The laser power reached 4.38 W and 4.64 W for azimuthally and radially polarized beams at the slope efficiencies of 45.3% and 48.5%, respectively. Our study proved that an efficient, high-power vector rotary disk laser would be realistic.

Characterization and tribological evaluation of NiCrMoNb and NiCrBSiC laser cladding on near-α titanium alloy

In the present study, two different types of coatings such as NiCrMoNb and NiCrBSiC were produced on titanium alloy using a high power Yb:YAG disk laser. Then the coatings were analysed to expose their phase characterization, microstructure and hardness using X-ray diffraction analysis (XRD), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), optical microscopy (OM) and Vickers microhardness machine (HV). Further, tribotest was performed through ball-on-plate machine to analyse the wear properties of coatings. In addition, worn surfaces of cladding and surface roughness were examined using FE-SEM and whitelight interferometer, respectively. The results showed that the both NiCrMoNb and NiCrBSiC cladding exhibited a dendrite homogeneous structure due to higher cooling rates. XRD results indicating that the solid solution of γ-Ni was mixed with chromium, boride, silicon and formed the structure of interdendritic eutectics on cladding region. Microhardness of the clad layer has remarkably been increased than substrate. The results of friction coefficient of specimen with NiCrBSiC are lower than that of specimens NiCrMoNb clad and substrate. Also, the wear resistance of NiCrBSiC clad has been increased than NiCrMoNb clad and substrate sample, which reveals that NiCrBSiC laser cladding plays a major role on wear resistance. The microstructures of NiCrMoNb and NiCrBSiC cladding layer are composed of Ni-rich austenitic, Cr, Mo, Nb and carbide, borides, respectively. The analysed wear track indicates that adhesion and abrasion was a major wear mechanism. The NiCrSiBC cladded worn-out surfaces exhibited reduction in surface roughness than NiCrMoNb clad and substrate.

Laser Welding of SLM-Manufactured Tubes Made of IN625 and IN718.

The advantage of selective laser melting (SLM) is its high accuracy and geometrical flexibility. Because the maximum size of the components is limited by the process chamber, possibilities must be found to combine several parts manufactured by SLM. An application where this is necessary, is, for example, the components of gas turbines, such as burners or oil return pipes, and inserts, which can be joined by circumferential welds. However, only a few investigations to date have been carried out for the welding of components produced by SLM. The object of this paper is, therefore, to investigate the feasibility of laser beam welding for joining SLM tube connections made of nickel-based alloys. For this purpose, SLM-manufactured Inconel 625 and Inconel 718 tubes were welded with a Yb:YAG disk laser and subsequently examined for residual stresses and defects. The results showed that the welds had no significant influence on the residual stresses. A good weld quality could be achieved in the seam circumference. However, pores and pore nests were found in the final overlap area, which meant that no continuous good welding quality could be accomplished. Pore formation was presumably caused by capillary instabilities when the laser power was ramped out.

Tm:YAG Disk Laser Intra-Cavity Pumped by QCW $1 ~\mu$ m Yb:YAG Thin Disk Laser

We report a $2~\mu \text{m}$ Tm:YAG disk-laser intra-cavity pumped by a Yb:YAG thin-disk laser at 1030 nm. The result demonstrates that a thin-disk-shape Tm:YAG crystal can operate with $1~\mu \text{m}$ pumping sources having an extremely low absorption ( $ /mm). The slope efficiency of the $2~\mu \text{m}$ laser with respect to the 940 nm laser diode (pump source of the 1 $\mu \text{m}$ laser) was ~1.05%. We obtained a maximum average power of 760 mW, and a maximum peak power of 2.5 W. As far as we know, this is the first report of a $1~\mu \text{m}$ -laser-pumped disk-shape Tm3+ laser. Our work implied that a low-cost, high-power Tm:YAG thin-disk laser can be implemented by power-scaling through this intra-cavity pumping scheme.

Radiation-balanced Yb:YAG disk laser.

A radiation-balanced Yb:YAG disk laser is demonstrated in an intracavity pumping geometry. Detailed analysis of the data reveals the feasibility of using the multi-kilowatt level "athermal" disk lasers with minimal modal instabilities, which arise from thermal lensing.

A contribution to laser cladding of Ti-6Al-4V titanium alloy

A wear resistant coating was successfully made on an annealed Ti-6Al-4V titanium alloy by laser surface cladding using 60 wt.% WC + wt.% 40 NiCrBSi powder blends. Coaxial laser cladding was performed by means of Yb:YAG disk laser with a 3-KW continuous wave. Different laser interaction times were attempted to get the optimal conditions for promising mechanical properties. The new contribution was to accomplish larger clad layer thickness with applying the shortest possible laser interaction time that can achieve superior clad layer properties. This will decrease energy consumption with an expected money saving which is an essential factor for successful engineering solutions. A high powder flow rate of 20 g.min−1 was intended in order to obtain a thick, nonporous and crack free clad layer. The clad samples were subjected to thorough microstructure investigations, in addition to microhardness and wear evaluation. The coating so produced exhibits multiple hardness values and exceptional wear resistance under adhesive/sliding wear conditions. The obtained results expose clad layer with superior quality that was achieved at a laser interaction time of 0.3 s. An enhancement in the microhardness values of the clad layers by more than fourfold was attained and the wear resistance was thus significantly improved.

Laser welding of AlSi10Mg aluminium-based alloy produced by Selective Laser Melting (SLM)

Additive manufacturing can produce very complex and highly integrated parts that cannot be manufactured by traditional methods. In many of its applications, the AM-manufactured part may be a very small part of the whole, and therefore it has become increasingly important to find suitable attachment methods for printed parts. The aim of this study was to find out the laser weldability of the printed AlSi10Mg material without filler material. The laser used in these welding experiments was Yb:YAG disk laser. The laser wavelength was 1030 nm and the maximum output power on the workpiece surface was 4 kW. AlSi10Mg is a widely used material in parts that are produced utilizing the SLM technique. The material has very good corrosion resistance properties, good electrical conductivity and excellent thermal conductivity. AlSi10Mg has proven to be much easier to print than steel materials, so it is a popular material also in prototype production. Based on welding tests, laser welding without filler material is suitable for AlSi10Mg material and the static strength of the weld is reasonably good compared to the base material. However, AlSi10Mg can be found to be challenging due to its composition.