Rapid surface microstructuring of porous alumina ceramic using continuous wave Nd:YAG laser

Laser surface microstructuring of porous alumina ceramic is investigated using a continuous wave Nd:YAG laser. The surface microstructure development is based on the rapid surface melting and subsequent solidification resulting in the evolution of crystallographic and morphological textures. The results indicated that surface microstructure is greatly influenced by the laser processing parameters. Detailed investigations of the influence of laser fluence on the thermal history and microstructural parameters are presented. Such investigations are intended to facilitate the tailoring of surface microstructures by controlling the laser processing parameters.     

Nano-second pulsed DPSS Nd:YAG laser striation-free cutting of alumina sheets

Lasers are extensively employed in cutting alumina sheets in the electronic industries. An important quality factor of laser cutting is striation (periodical lines) formation on the cut surfaces, which affects the surface roughness and geometry precision of laser cut products. The elimination of striation is important for laser cutting of alumina since it is necessary for denser circuit patterns and device miniaturisation. The present study demonstrates, for the first time, striation-free cutting of alumina sheets with 1 mm thickness using a 400 W high repetition rate nano-second pulsed DPSS Nd:YAG laser. The short pulse duration minimises heat damages. The effects of gas type, gas pressure, nozzle standoff distance, average laser power, cutting speed, and pulse repetition rate on striation characteristics were studied. The specific operating conditions for nano-second pulsed laser striation-free cutting were presented. The present study supports one of the existing theories for continuous wave (CW) laser striation-free cutting of metallic materials and further extends it to the pulsed laser striation-free cutting of ceramic materials. A mechanism of pulsed laser striation-free cutting was proposed, by which a model to predict the operating window for the nano-second pulsed laser striation-free cutting of alumina sheets was developed. The operating window predicted by the model was in agreement with the experiment.     

铝合金脉冲固体Nd：YAG激光切割及其对比试验

利用高功率脉冲固体Nd:YAG激光和空气等离子弧分别对4mm厚的5A06铝合金板材进行了切割试验.探讨了工艺参数对激光切割质量的影响,得出结论,激光功率、脉宽、频率和离焦量对切缝宽度影响较大,而切割速度、辅助气压的影响很小.通过光学显微镜和扫描电子呈微镜观察分析切缝宏观形貌及微观组织,结果表明,激光切缝窄钿平直,垂直度0.28mm,切面波纹浅,没有明显的热影响区;与空气等离子弧的切割效果进行对比,后者切缝较宽,大约是激光切缝的4倍,切面易氧化,波纹较深,且切割面有大量微裂纹存在.     

Effects of the cladding parameters on the deposition efficiency in pulsed Nd:YAG laser cladding

The purpose of the present study is to analyze the effects of the cladding parameters on the deposition efficiency in cladding of Co alloy powder by a low power pulsed Nd:YAG laser, and to optimize the cladding parameters for maximizing the deposition efficiency. Experiments were designed, conducted and analyzed by the Taguchi experimental method using a L18 orthogonal array. It was found that the powder feed position, powder feed angle, powder feed rate and travel speed had significant effects on the deposition efficiency, but the shielding gas type, laser pulse shape and focal position had nearly no effects. The optimal cladding conditions in the experimental range were obtained at 0 mm of the powder feed position, 50° of the powder feed angle, 0.62 g/s of the powder feed rate and 6.7 mm/s of the travel speed. From the confirmation experiment, the average deposition efficiency of 12.3% was achieved at the optimized cladding conditions as statistically predicted.     

Characterisation of solidification cracking in pulsed Nd:YAG laser welding of 2024 aluminium alloy

Abstract

Aluminium alloy AA2024 is one of the most susceptible alloys to solidification cracking. The influence of Nd:YAG laser welding parameters on cracking severity of AA 2024 alloy was studied. Welding was performed in two modes: single spot welding and overlap spot welding. In single spot welding mode, the formation of columnar zone increases cracking severity in the fusion zone. In overlap spot welding mode, the solidification cracks were characterised as: cracks propagated from previous spot, cracks initiated from the fusion line with the previous spot, and cracks initiated from the fusion line with the base metal. It was established that in comparison there is very limited tendency for initiation of new cracks from the fusion line with the weld metal of a previous spot.     

Characteristics of Ni-Ir and Pt-Ir hard coatings surface treated by pulsed Nd:YAG laser

The subjects of the presented paper are to develop a laser surface treatment technology for the protective coatings of glass-molding dies and to better understand the interaction between laser beam and materials coated on the die surface. A variety of alloy films, including Ir-25 at.% Pt, Ir-50 at.% Pt, Ir-75 at.% Pt, Ir-25 at.% Ni, Ir-50 at.% Ni, and Ir-75 at.% Ni compositions are deposited by the ion source assisted magnetron sputtering system (ISAMSS). A Cr layer that functioned as a buffer layer is deposited between the alloy film and die surface. After an alloy film and the buffer Cr layer were sequentially coated on tungsten carbide (WC) surface, Nd:YAG laser was directly applied in the writing process. The temperature profile of the film stack structure is simulated by ANSYS software. The surface roughness was analyzed by atomic force microscopy (AFM) to compare the coating surface roughness before and after the laser surface treatments. The treated coatings for oxidation prevention test were examined by energy dispersive x-ray spectrometry (EDS). Nanoindentation instrument was performed to evaluate microhardness and reduced modulus of the coatings. The cross-sectional structures between the hard coating layer and buffer layer were also inspected by a scanning electron microscope (SEM). The Pt-Ir and Ni-Ir film coatings are unable to withstand the working temperature over 1500 °C, which is considered for quartz molding process and hot embossing process. The films showed high roughness, low microhardness and low reduced modulus because the film oxidation occurred in a high working temperature process.     

Nd:YAG激光+脉冲GMAW复合热源焊接参数对焊缝熔宽的影响

通过试验研究了Nd:YAG激光 脉冲GMAW复合热源焊接过程中焊接工艺参数对焊缝熔宽的影响.结果表明,复合热源焊缝熔宽随电弧功率和激光功率的增大而增大,随焊接速度的提高而减小,而光丝间距和离焦量对复合热源焊缝熔宽影响相对较小.复合热源焊缝熔宽远大于激光焊缝熔宽而仅稍大于脉冲GMAW焊缝熔宽,说明在复合热源焊接过程中脉冲GMAW决定焊缝熔宽,这主要是由于激光束加热区域远小于电弧加热区域造成的.试验结果的分析比较还表明,在激光 电弧复合热源焊接过程中激光功率的增大还极大地提高了焊接速度.     

High-speed deposition of Y-Si-O films by laser chemical vapor deposition using Nd:YAG laser

Y-Si-O films were prepared by laser chemical vapor deposition (LCVD) with a Nd:YAG laser using TEOS (tetraethyl orthosilicate) and Y(dpm)₃ precursors. The effects of laser power (P_L), deposition temperature (T_dep) and total chamber pressure (P_tot) on the phase, microstructure and deposition rate of Y-Si-O films were investigated. At P_L < 102 W (T_dep < 1140 K), amorphous Y-Si-O films were obtained independent of P_tot. At P_tot = 0.6 kPa, mixture phase films of Y₂SiO₅ (the X1 phase) and Y₂Si₂O₇ (the α, β, δ and y phases) were obtained at P_L = 102 W (T_dep = 1210 K), while single phase X1-Y₂SiO₅ films were prepared at P_L > 139 W (T_dep > 1280 K). Y₂Si₂O₇ mixture phase films were obtained at P_tot = 3.5 kPa and Y₂Si₂O₇ and Y₂SiO₅ (the X2 phase) mixture phase films were obtained at P_tot = 7.5 kPa independent of T_dep. Amorphous Y-Si-O films showed a dense, glassy microstructure. Faceted columnar grains grew on the Y-Si-O films at P_tot = 0.6 kPa, whereas rounded cauliflower-like grains grew at P_tot = 7.5 kPa. The R_dep increased with increasing P_L and T_dep and reached a maximum of 430 μm h⁻¹ at P_tot = 0.6 kPa, P_L = 186 W and T_dep = 1310 K.     

Overlapping rate effect on laser shock processing of 1045 steel by small spots with Nd:YAG pulsed laser

Lower power lasers operating at higher frequencies, which are much more reliable and economical, have been explored for laser shock processing to improve fatigue and wearing resistance of metals. Laser shock processing with a Q-switched Nd:YAG pulsed laser was attained by the overlap of small laser spots for the treatment of AISI 1045 steel. The changes of mechanical properties of the specimen treated by different overlapping rates were investigated by both experiments and numerical simulation. Surface quality was essentially unaffected after treatment. Plastic affected depth was much shallower than that obtained with larger spot sizes, due to rapid attenuation of shock waves. Induced residual stress field was uniform on the top surface and was enhanced with the increase of overlapping rate. Surface micro-hardness reached a larger value than that reached on the untreated region and was also improved with the increase of overlapping rates. A plastically deformed martensite transformation zone was found in an extremely thin layer near the top surface due to the heat effect.     

A study on the solderability of QFP outer lead using Nd:YAG laser

The solderability of QFP (Quad Flat Package) outer lead was investigated using the laser soldering process. An Nd:YAG laser system was constructed for this experiment, and the QFP outer lead was scanned by laser beam one by one. The process variables for the laser soldering were the scanning time of laser beam and the laser power. Sn-37%Pb and Sn-3.5%Ag pastes were chosen for solders, and the fluxes contained in the pastes were RMA (Rosin Mildly Activated). Experimental results showed that the molten solder of Sn-37%Pb wetted well on joints with a concave shape with a scanning time of over 400ms and the laser beam power of 5 and 5.9W. Under similar conditions, the molten solder of Sn-3.5%Ag also showed good wettability. The length of the solder joint was slightly increased with increasing laser beam power from 3 to 5.9W.     

Porosity and microstructure in pulsed Nd:YAG laser welded Ti6Al4V sheet

The overlapping factor of pulsed laser welding is used to help understand the correlation between welding parameters and the quality of Ti6Al4V welded joints. The number of porosity decreases with the increase in overlapping factor, and the welded joints are almost completely free of porosity when overlapping factor is greater than 75%. This can be attributed to the fact that the remelted volume of the spot region increases with the increase of overlapping factor, which assists porosity formed in the previous pulse wave in escaping from molten pool formed by the subsequent pulse. With the increase of overlapping factor, the weld microstructure becomes much coarser and the width of the fully transformed region of heat affected zone increases, which reduces the microstructure gradient and microhardness gradient from the fusion zone to heat affected zone. A method to evaluate the porosity susceptibility of a specific welding condition prior to actual welding process is presented.     

Microstructure and corrosion behavior of the AISI 304 stainless steel after Nd:YAG pulsed laser surface melting

Different laser energy densities were utilized to treat AISI 304 stainless steel via Nd:YAG pulsed laser surface melting (LSM). The surface composition and microstructure of the stainless steel were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM). In particular, the corrosion behaviors of the stainless steel surface without and with LSM were evaluated by the electrochemical polarization measurement in 3.5 wt.% NaCl aqueous solution at room temperature. The results showed that the stainless steel surface without LSM suffered severe localized pitting under the testing conditions. A thin surface oxide protective layer was produced on the stainless steel surface with LSM, which considerably improved the corrosion resistance properties of the stainless steel. The height differences of the corrosion regions on the stainless steel surface with LSM were measured to establish more corrosion resistant region, using scanning confocal laser microscopy. The underlying corrosion mechanism of the stainless steel with LSM was revealed.     

Fabrication and optical properties of a highly transparent Nd：YAG ceramic

A neodymium doped yttrium aluminum garnet (Nd:YAG) transparent ceramic was fabricated by a solid state reaction method using commercial α-Al₂O₃, Y₂O₃, and Nd₂O₃ powders as starting materials and tetraethyl orthosilicate (TEOS) as sintering aid. The morphology and microstructure of the nanopowders and the Nd:YAG transparent ceramic were investigated. The fully dense Nd:YAG ceramic with an average grain size of ∼20 μm was obtained by vacuum sintering at 1720°C for 12 h. Few pores and grain-boundary phases were observed. The in-line transmittance of the ceramic was 81.5% at 1064 nm.     

GMAW电弧对Nd:YAG激光传输的影响

针对脉冲过渡熔化极气体保护焊(gas metal arc welding,GMAW)电弧和短路过渡GMAW 电弧,通过保持 GMAW 电弧正常态,Nd:YAG 激光水平逐层、逐点扫描穿过脉冲电弧区域的试验方式,获得了Nd:YAG 激光穿过GMAW 电弧后的激光折射和散射结果.试验发现,波长为1.064μm的Nd:YAG激光穿过脉冲GMAW 电弧激光光斑会略微变小,并且不同电弧区域对激光的影响能力基本相同;激光穿过短路GMAW电弧后激光光斑也会略微变小,不同电弧区域对激光的影响也基本相同.结果表明,GMAW电弧可以近似看作各项同性的激光传输介质,还可以近似认为GMAW电弧对波长1.064μm的Nd:YAG激光是透明的.

Abstract：

By keeping gas metal arc welding(GMAW)arc normal position and Nd: YAG laser parallel crossing GMAW arc,refrangibility of GMAW arc to Nd: YAG laser was measured.The results indicate that when Nd:YAG laser crosses pulse GMAW arc,laser radius will decrease slightly.And the influence of pulse GMAW arc of different part to Nd : YAG is almost same.Similarly,when Nd: YAG laser crosses short-circuiting pulse GMAW arc,the radius of the laser will decrease slightly too.By considering this phenomenon from welding point of view,GMAW arc can be regarded as transparent substance and optic isotropy to Nd:YAG laser.     

Study on the microstructure and mechanical properties of Nd:YAG pulsed laser beam weld of UNS-C17200 copper beryllium alloy

In this study, the microstructure of Nd:YAG pulsed laser welding of copper beryllium sheet has been investigated by tensile and hardness tests, optical and scanning electron microscopy (SEM) and X-ray diffraction (XRD). The SEM images reveals three distinct solidified structures due to various thermal gradients occurred in the fusion zone. The XRD patterns show that the preferred solidification directions are like other FCC materials. Tensile strength of the weld metal is lower than that of the base metal since the CuBe phase precipitates during solidification. The effects of pulsed laser parameters on the weld pool dimensions were also studied. The results show that by applying constant pulse energy, focused beam diameter should be kept as low as possible to obtain the weld pool with the highest penetration and the least width. Moreover, the effect of passive layer on the reflectivity of surface by incident beam was investigated. It was found that weld pool increases when the laser energy is high due to multiple internal reflections.     

GMAW脉冲电弧对Nd:YAG激光能量的吸收

揭示了激光-电弧复合热源焊接过程中GMAW电弧对Nd∶YAG激光的吸收作用,对深入分析激光和电弧的耦合机制具有重要意义.通过保持脉冲GMAW电弧正常态,Nd∶YAG激光水平逐层、逐点扫描穿过脉冲电弧区域的试验方式,获得了Nd∶YAG激光穿过脉冲GMAW电弧后的能量损失情况.结果表明,波长为1.064μm的Nd∶YAG激光穿过保护气成分为Ar/CO2=80/20的脉冲GMAW电弧的任何区域都几乎不损失能量,波长为1.064μm的Nd∶YAG激光穿过不同电流强度的脉冲GMAW电弧也几乎不损失能量.     

Nd:YAG脉冲激光作用溶胶与纳米粉复合层制备复合纳米氧化锆涂层

利用Nd：YAG脉冲激光技术对在不锈钢上涂敷的氧化锆凝胶涂层进行加工处理,使凝胶涂层受热结晶并与不锈钢基体牢固结合制得纳米氧化锆涂层;同时利用自制的氧化锆纳米粉与氧化锆溶胶复合,激光作用后,激光辐照熔化粉末材料,同时溶胶结晶与粉末复合在不锈钢表面形成复合纳米氧化锆涂层。研究了激光对氧化锆凝胶及其与氧化锆纳米粉复合物的热作用,并描述了氧化锆涂层的结晶过程。     

Nd:YAG laser welding of pure titanium to stainless steel

Electromagnetic compatibility (EMC) is often associated only with radio interference. But another significant component of EMC is generation of harmonic components of electric current and voltage by a device that has an impact on a mains circuit and that could be a reason for considerable losses of supplied energy. The acceptance limits of generated interruptions are specified in both Polish and European standards which, as a result of a quick development of electrical appliances, are frequently updated.

This paper presents comparative test results of interruptions generated by selected welding instruments ranging from transformer inverters for both hobby and workshop purposes, up to professional industrial devices.