YAG Disk Research Articles

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.

Disk laser heads based on Yb : YAG for multikilowatt average power lasers

The main factors affecting the cooling efficiency of Yb : YAG disk active elements have been investigated, and key technologies for designing disk lasers with high average power and efficiency have been developed. The main parameters of a disk active element operating in the cw regime are optimised using numerical calculation. Disk laser heads are fabricated based on calculations and developed technologies, and lasing with optical efficiency up to 50 % is demonstrated. An average power at the kilowatt level is obtained in a cavity with two laser heads, and a possibility of its further increasing is demonstrated.

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.

Laser Welding of Titanium Alloys with an Yb: YAG Disk Source

In this paper, the laser welding of thin titanium sheet in a butt joint configuration are investigated using a continuous Yb: YAG disk source, with high beam quality and a particular fiber configuration, enable to provide a broad range of beam diameters with different intensity distribution. The thermal efficiency of the laser process is discussed as a function of the fiber type. The weldability results for the CP Ti grade 2 and the Ti-6Al-4V titanium alloy are expressed in terms of full penetration, and correct bead geometry (NF L06-395-2000). Full penetration welds are easily achieved with the core fiber, but the outer fiber produces welds with limited geometric defects. Butt joints microstructure consists of an acicular α phase in the fusion zone for CP Ti, and a martensitic α’ phase for the Ti-6Al-4V alloy. Tensile test results confirm a similar or slightly higher joint strength for the full penetration welds, compared with the parent metal.

Microstructure and selected properties of Fe-B coatings reinforced with B4C and Si particles produced by laser cladding using Yb:YAG disk laser

Microstructure and selected properties of Fe-B coatings reinforced with B4C and Si particles produced by laser cladding using Yb:YAG disk laser

1 kW, 200 mJ picosecond thin-disk laser system.

We report on a laser system based on thin-disk technology and chirped pulse amplification, providing output pulse energies of 200 mJ at a 5 kHz repetition rate. The amplifier contains a ring-type cavity and two thin Yb:YAG disks, each pumped by diode laser systems providing up to 3.5 kW power at a 969 nm wavelength. The average output power of more than 1 kW is delivered in an excellent output beam characterized by M2=1.1. The output pulses are compressed to 1.1 ps at full power with a pair of dielectric gratings.

Resonance spiking by periodic loss in the double-sided liquid cooling disk oscillator

A double-sided liquid cooling Nd:YAG disk oscillator working at a pump repetition rate of 20 Hz is demonstrated. The output energy of 376 mJ is realized, corresponding to the optical–optical efficiency of 12.8% and the slope efficiency of 14%. The pump pulse width is 300 µs and the laser pulse width is 260 µs. Instead of being a damped signal, the output of laser comprises undamped spikes. A periodic intra-cavity loss was found by numerical analysis, which has a frequency component near the eigen frequency of the relaxation oscillation. Resonance effect will induce amplified spikes even though the loss fluctuates in a small range. The Shark–Hartmann sensor was used to investigate the wavefront aberration induced by turbulent flow and temperature gradient. According to the wavefront and fluid mechanics analysis, it is considered that the periodic intra-cavity loss can be attributed to turbulent flow and temperature gradient.

High-power Yb:GGG thin-disk laser oscillator: first demonstration and power-scaling prospects.

We present the first demonstration of a thin-disk laser based on the gain material Yb:GGG. This material has many desirable properties for the thin-disk geometry: a high thermal conductivity, which is nearly independent of the doping concentration, a low quantum defect, low-temperature growth, and a broadband absorption spectrum, making it a promising contender to the well-established Yb:YAG for high-power applications. In continuous wave laser operation, we demonstrate output powers above 50 W, which is an order of magnitude higher than previously achieved with this material in the bulk geometry. We compare this performance with an Yb:YAG disk under identical pumping conditions and find comparable output characteristics (with typical optical-to-optical slope efficiencies >66%). Additionally, with the help of finite-element-method simulations, we show the advantageous heat-removal capabilities of Yb:GGG compared to Yb:YAG, resulting in >50% lower thermal lensing for thin Yb:GGG disks compared to Yb:YAG disks. The equivalent optical performance of the two crystals in combination with the easy growth and the significant thermal benefits of Yb:GGG show the large potential of future high-power thin-disk amplifiers and lasers based on this material, both for industrial and scientific applications.

Wear resistance in the soil of Stellite-6/WC coatings produced using laser cladding method

The paper presents the study results of macro- and microstructure, microhardness, phase composition and practical application of Stellite-6/WC metal matrix composite (MMC) coatings produced using laser cladding technology. For the preparation of MMC coatings the Yb:YAG disc laser with a rated power equal 1kW was used. The laser beam was controlled using a 5-axis CNC machine. The powder mixture was fed to laser beam by three-streams powder feeding system. Composite coatings were prepared to increase the durability of agricultural tools. The coatings were prepared on B27 boron steel. This steel grade is most often used into produce the tools for soil cultivation. Stellite-6/WC coatings were produced using laser beam power 550W, feed rate 400mm/min and powder feed rate 10g/min. Durability tests of agricultural tools were carried out by two methods. Measurement the mass loss was the first method, while measurement the tools shape using GOM ATOS II optical scanner was the second method. It was found that Stellite-6/WC coatings contributed to increase durability of agricultural tools applied for soils cultivation.

Comparison of Titanium Metal Matrix Composite Surface Layers Produced During Laser Gas Nitriding of Ti6Al4V Alloy by Different Types of Lasers

Abstract The article presents the results of a comparative study of the nitriding process of titanium alloy substrate using two lasers with different characteristics of laser beams. One of the applied lasers was a high power diode laser emitting at a dominant wavelength of 808 nm, with a rectangular laser beam spot, and multimode energy distribution across the spot. The second laser was a solid state Yb:YAG disk laser emitting at a wavelength of 1.03 μm, with a circular beam spot, characterized by near Gaussian energy distribution across the spot. In a case of both lasers single stringer beads with a similar width and at similar energy input were produced. As a result of melting of the substrate with a laser beam in a pure gaseous nitrogen atmosphere composite surface layers with in situ precipitated titanium nitrides embedded in the metallic matrix of titanium alloy were produced, in both cases. However, the surface topography and structure is different for the surface layers produce by different lasers at the same processing parameters and width of laser beams.

Modified Twin-Spot Laser Welding of Complex Phase Steel

Abstract The work addresses modified methods of twin-spot laser welding of complex phase steel sheets and investigates the effects of laser beam distribution on the macrostructure, microstructure and hardness. The research-related results were obtained for the beam power distributions of 50%-50%, 60%-40% and 70%-30%. Test joints were made using a Yb:YAG disc laser with a maximum power of 12 kW and a welding head by means of which it was possible to focus a laser beam on two spots. It was found that the change in the laser beam distribution affects geometrical features of the joint. The application of the second beam of lower power enables obtaining tempering-like effects, which finally lead to the beneficial hardness reduction both in the fusion zone and in heat-affected zone. The identification of various microstructural constituents in different zones of the joint was performed using light microscopic micrographs and scanning electron images.

Effect of dual beam laser welding on microstructure–property relationships of hot-rolled complex phase steel sheets

The work addresses microstructure–property relationships of hot-rolled complex phase steel sheets subjected to various conditions of dual beam laser welding. The article also contains a comparison between single-spot and twin-spot laser welding. Test-related joints were made using a Yb:YAG disc laser having a maximum power of 12kW and a welding head enabling the focusing of a laser beam on two spots. The tests involved investigating the effect of power distribution on the macrostructure, microstructure and mechanical properties of joints. Microscopic investigations revealed the stabilisation of some fraction of retained austenite in the intercritical heat affected zone (ICHAZ) of joints. The application of the second beam resulted in tempering-like effects in the martensite of the fusion zone and in the HAZ, favourably reducing the hardness of the joint. The use of bifocal welding enabled the obtainment of a 10% hardness reduction in the fusion zone as against single-spot laser beam welding.

340 W average power output of diode-pumped composite ceramic YAG/Nd:YAG disk laser

We report on a diode-pumped composite ceramic disk laser in this paper. The composite ceramic YAG/Nd:YAG disk consists of 4 mm thick pure YAG and 2 mm thick Nd:YAG with 1.0 at.% doping concentration. The slope efficiency of the composite ceramic disk laser is 36.6% corresponding to the maximum optical–optical efficiency of 29.2%. Furthermore, 340 W average power output was achieved at the absorbed pump power of 1290 W.

Two side liquid-cooled and passively Q-switched disk oscillator with nanosheets in flowing CCl4

A passively Q-switched and two side liquid-cooled Nd:YAG disk oscillator is demonstrated, which is operated at a pump pulse width of 300 μs and a pump repetition rate of 10 Hz. The coolant flows over the two large surfaces of the disk and will be passed through by laser beam, so it can also serve as a saturable absorber. For the unmodulated laser, the pure CCl4 was employed as coolant and a plane output mirror of 15 % transmission was employed. The maximum output energy of 795 mJ is realized corresponding to the optical–optical efficiency of 27.4 % and the slope efficiency of 30 %; for the graphene Q-switched laser, the CCl4 with graphene nanosheets was employed as coolant and a plane output mirror of 40 % transmission was employed. The maximum output energy of 376 mJ is realized corresponding to the optical–optical efficiency of 13 % and the slope efficiency of 18 %. The maximum average Q-switching repetition rate is 385 kHz, and the minimum average pulse width is 116 ns; for the MoS2 Q-switched laser, the CCl4 with MoS2 nanosheets was employed as coolant and a plane output mirror of 30 % transmission was employed. The maximum output energy of 486 mJ is realized corresponding to the optical–optical efficiency of 17 % and the slope efficiency of 22 %.The maximum average Q-switching repetition rate is 470 kHz, and the minimum average pulse width is 137 ns.

Low temperature diode pumped active mirror Yb3+:YAG disk laser amplifier studies.

An experimental study of a static helium gas gap heat switch concept for laser amplification is presented. High single pass gains with large co-sintered ceramic Yb:YAG disks are recorded in the 80-200K temperature range on a diode pumped active mirror amplifier.

Microstructural Aspects of Twin-Spot Laser Welding of Dp-Hsla Steel Sheet Joints

Abstract The article presents the possibility of using twin-spot laser welding (i.e. laser welding with focusing a laser beam on two spots) for making overlap joints made of 0.8-1 mm thick HSLA and DP type high strength steel sheets. Joints were made using a Yb:YAG disc laser having a maximum power of 12 kW and a welding head by means of which it was possible to focus a laser beam on two spots, 0.6 mm and 1 mm away. The angle between focuses amounted to 0° or 90°, whereas the power distribution was 50%-50%. With settings as presented above it was possible to obtain high-quality overlap joints. The geometrical parameters of the joints were primarily affected by beams positions (in relation to each other) and, to a lesser degree, by the distance between the focuses. It was possible to obtain a 10% hardness reduction in the fusion zone of the DPHSLA steel joints if the angle between the beams amounted to 90°. The tests also involved microstructural examinations of individual zones of the joints