Process Window for Nd:YAG Laser Welding of Super Duplex Stainless Steel

Super duplex stainless steel (SDSS), an advanced duplex stainless steel with higher alloying concentration, is employed widely in acidic atmospheres. In this study, we make an attempt to develop a process window for the pulsed mode Nd:YAG laser welding of SDSS, as reference maps, to identify the range of process parameters viz., laser power, welding speed, defocusing distance, and pulse frequency for obtaining a defect free full penetration welds. The eminence of the welds, based on the macrostructure, microstructure, and tensile strength, is reported. We obtain a complete penetration weld devoid of undercut, crating at the top and minimum heat affected zone (HAZ) with a overlapping factor of 80–90% and heat input at 100–200 J/mm. The experimental settings prevailing inside the preferred region of the process window exhibit a higher tensile strength as well.     

脉冲Nd:YAG激光熔覆修复塑料模具工艺参数的优化

 激光器的电压、电流、脉冲宽度、脉冲频率与激光的扫描速度、光斑直径等工艺参数直接影响着脉冲Nd:YAG激光熔覆质量。为了简化工艺调整过程，提出了重叠率的概念，并进行了理论推导，建立了重叠率与脉冲频率、激光扫描速度、激光光斑直径相互关系的方程式。利用预置法在低碳钢基体上熔覆Ni基合金粉末,获得了2组最佳工艺参数，即单脉冲能量、重叠率分别为6.7 J,97.4%和21 J,69.4%。研究表明：在单脉冲能量和重叠率一定的条件下，改变电流、脉宽、脉冲频率及熔覆速度不会影响熔覆质量。     

Dissimilar autogenous full penetration welding of superalloy K418 and 42CrMo steel by a high power CW Nd:YAG laser

Experiments of autogenous laser full penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 3.5 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser welding velocity, flow rate of side-blow shielding gas, defocusing distance were investigated. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. Results show that high quality full penetration laser-welded joint can be obtained by optimizing the welding velocity, flow rate of shielding gas and defocusing distance. The laser-welded seam have non-equilibrium solidified microstructures consisting of γ-FeCr_0.29Ni_0.16C_0.06 austenite solid solution dendrites as the dominant and very small amount of super-fine dispersed Ni₃Al γ′ phase and Laves particles as well as MC needle-like carbides distributed in the interdendritic regions. Although the microhardness of the laser-welded seam was lower than that of the base metal, the strength of the joint was equal to that of the base metal and the fracture mechanism showed fine ductility.     

Characterization of Kovar-to-Kovar laser welded joints and its mechanical strength

For the packaging of a pump laser in butterfly package, the most crucial assembly step is the fiber-to-laser diode coupling and attachment. The use of laser welding as the joining method offers several advantages if compared with the adhesive joints: strong joining strength, short process time and less contamination. This paper reports on laser welding process characteristics; weld strength and its fracture mode. The penetration depth and melt area of laser spot welds were found to be complicated functions of laser pulse energy, intensity, and beam diameter. Effects of pulse width, input power and size of the focal spot on the rate of energy input to the workpieces and consequently, the weld strength were reported. The weld strength was found to be dependent on the overlapping area between the two joining materials. Surface roughness, R_a, has influence on the fraction of energy absorbed, A, and therefore, affecting the penetration depth. Thermal analysis was carried out on the laser-welded joints and its heat-affected zone (HAZ) induced by various power densities was examined. These data are important in order to optimize and utilize the laser welding process as an effective manufacturing tool for fabrication of reliable pump laser.     

Characteristics of deep penetration laser welding of dissimilar metal Ni-based cast superalloy K418 and alloy steel 42CrMo

Experimental trials of autogenous deep penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 5.0 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser output power, welding velocity and defocusing distance on the morphology, welding depth and width as well as quality of the welded seam were investigated. Results show that full keyhole welding is not formed on both K418 and 42CrMo side, simultaneously, due to the relatively low output power. Partial fusion is observed on the welded seam near 42CrMo side because of the large disparity of thermal–physical and high-temperature mechanical properties of these two materials. The microhardness of the laser-welded joint was also examined and analyzed. It is suggested that applying negative defocusing in the range of Raylei length can increase the welding depth and improve the coupling efficiency of the laser materials interaction.     

Passive Q-switching of Pulsed and CW Nd: YAG Lasers with Cr~(4 ): YAG

Ｐａｓｓｉｖｅ　Ｑ－ｓｗｉｔｃｈｉｎｇ　ｏｆ　Ｐｕｌｓｅｄ　ａｎｄ　ＣＷ　Ｎｄ：ＹＡＧ　Ｌａｓｅｒｓ　ｗｉｔｈ　Ｃｒ￣（４＋）：ＹＡＧＰａｓｓｉｖｅＱ－ｓｗｉｔｃｈｉｎｇｏｆＰｕｌｓｅｄａｎｄＣＷＮｄ：ＹＡＧＬａｓｅｒｓｗｉｔｈＣｒ￣（４＋）：ＹＡＧ...     

LD端面泵浦Cr4:YAG被动调Q激光器输出特性研究

对激光二极管端面泵浦Cr⁴⁺:YAG被动调QNd:YAG激光器输出特性进行了实验研究.实验研究发现,激光器输出功率及脉冲重复频率随谐振腔长度增大而增大.为解释这一实验现象,测量了泵浦光斑在激光晶体内尺寸,同时计算了激光晶体及Cr⁴⁺:YAG晶体内的基模激光光斑半径随谐振腔长度变化.分析结果表明:激光晶体内泵浦光斑尺寸远小于激光晶体内基模光斑半径,腔模间交叠效率较低;当腔长增加时,激光晶体内的基模激光光斑减小,腔模间交叠效率增加,从而导致输出功率及脉冲重复频率随腔长增加而增加;另外,Cr⁴⁺:YAG晶体内光斑半径也随谐振腔长度减小,引起Cr⁴⁺:YAG晶体漂白时间缩短,导致脉冲重复频率随腔长增加而增加.     

Quantitative visualization of the laser induced plume behavior using quasi-heterodyne holographic interferometry

It is very important that we understand the dynamic behaviors of the laser induced plume in welding, because the laser induced plume has considerable effects on welding efficiency and the quality of materials. Many experimental studies have been performed in order to observe the plume behaviors using a visualization method. In this paper, we describe the visualization and quantification of the laser induced plumes by pulse holographic interferometry. A pulsed Nd:YAG laser was used for the generation of laser induced plume and a Q-switched Ruby laser was employed to record the weld plume. For qualitative visualization of the laser induced plume, we used the double-exposure holographic interferometry. Then, we chose the quasi-heterodyne holographic interferometry with the dual-reference-beam and phase shifting in order to visualize the plume quantitatively. The experimental results show the visible behavior of the laser induced plume according to a change in the output power of the pulsed Nd:YAG laser and the time delay of Q-switched Ruby laser. Finally, we obtained the quantitative results by using the dual-reference-beam.     

Pulse width compression and enhancement of peak power in a diode-pumped doubly Q-switched Nd:GdVO<Subscript>4</Subscript> 1.34 μm laser with AO and V<Superscript>3+</Superscript>:YAG saturable absorber

By using both acousto-optic (AO) modulator and V³⁺:YAG saturable absorber, a diode-pumped doubly Q-switched a-cut Nd:GdVO₄ laser at 1.34 μm is realized. The average output power and the pulse width for different AO repetition rate f have been measured. The experimental results show that the doubly Q-switched laser can compress the pulse width and improve the pulsed peak power in comparison to the singly Q-switched laser with AO or V³⁺:YAG saturable absorber. At the pump power 10.34 W and f = 10 kHz, the greatest pulse width compression ratio 72% and the highest peak power improvement 8.8 times have been obtained, respectively.     

The first-stokes pulse generation in Nd:KGW intracavity driven by a diode-pumped passively Q-switched Nd:YAG/Cr<Superscript>4+</Superscript>:YAG laser

The operation of an all solid-state pulsed Nd:KGW Raman laser pumped by compact passively Q-switched Nd:YAG/Cr:YAG laser is demonstrated. The first-Stokes radiation of stimulated Nd:KGW Raman scattering at the 1178 nm is generated. The average output power of 336 mW at Stokes wavelength was obtained under the laser diode pump power of 5.74 W. The corresponding optical efficiency from the diode light to the Raman output is 9.85%. The pulse width of 1.65 ns and a pulse repetition rate of 10 kHz were also obtained.     

Design and construction of a 110 W green laser for medical application

In this paper, the design and the construction of a high-power side-diode-pumped Nd:YAG solid-state laser at repetition rates of 6 and 10 kHz has been presented. Second harmonic of the Nd:YAG laser with green light at 532 nm, with an average power of 111.5 W at 10 kHz repetition rate, and with 90 ns pulse duration, has been obtained by the nonlinear crystal of KTP with 59% conversion efficiency and 12% diode-to-green optical–optical efficiency in the linear resonator. Beam spot size and divergence is 4 mm and 8 mrad, respectively. The laser stability is about 97%. As a medical application of this laser, investigation of degree of effectiveness and penetration depth of laser on adenomas of resected prostate after open prostatectomy has been done.     

Cr^4＋：YAG在对撞脉冲锁模的Nd：YAG激光器中实现被动锁模的研究

在理论上提出了Ｃｒ＾４＋：ＹＡＧ作为可饱和吸收体在Ｎｄ：ＹＡＧ激光器中实现被动锁模的可能性，运用速率方程组导出在强激光脉冲作用下Ｃｒ＾４＋：ＹＡＧ激发态吸收的恢复时间和饱和光强。实验上在带有抗共振环结构的接近于介稳腔的脉冲式Ｎｄ：ＹＡＧ激光器中用Ｃｒ＾４＋：ＹＡＧ作为可饱和吸收体实现被动锁模运转，得到能量１３．５ｍＪ、平均脉宽１８０ｐｓ的锁模脉冲序列。     

Numerical modeling and experimental investigation of TiC formation on titanium surface pre-coated by graphite under pulsed laser irradiation

A model for carbonization of titanium surface by pulsed Nd:YAG laser was developed. The Ti substrate was covered with a relatively thick graphite layer prior to be processed under the laser beam. The experiments were performed at 15 J pulse energy with various pulse durations and overlapping factor to validate the results obtained from the numerical calculations. The model results such as temperature gradient, surface temperature, and the cooling rate were correlated with the micro-hardness of the alloyed layer. Higher pulse durations and overlapping factors which lead to the heat input increasing will result in significant rising in the micro-hardness values. The hardness values of the processed layer partially containing TiC, increased up to 10 times of the Ti substrate.     

Spectroscopic characterization of low-nickel copper welding with pulsed Nd:YAG laser

Effects of various operating parameters of 400 W pulsed Nd:YAG laser on welding of nickel-alloyed copper have been investigated. The induced plume spectra in case of using different assist gases and preheat temperatures have been analyzed and the effects of these key factors on melt features such as penetration depth, porosity and spattering have been attributed to the spectroscopic behavior of the plume. Moreover, the CuI electron temperature and its standard deviation as the spectroscopic responses of the plasma plume to various laser process parameters have been quantitatively evaluated at different average and peak powers and pulse energies. Also, the mentioned responses were utilized to justify the weld bead profile features, involving weld depth, width and their stabilities, at similar process parameters. The operating conditions of welding were optimized, regarding the results of spectroscopic observations and attributing them to the qualitative aspects of the melt pool.     

星光Ⅱ装置激光能量测量实时采集和数据传输系统

介绍一套激光能量实时采集和多路传输通信系统。该系统兼容现有的不同型号和规格的激光能量计,具有峰值保持和功率积分功能,抗干扰能力强,可实现数据自动采集、处理及长距离多点传送。为实现激光能量测量精密化和自动化打下了技术基础。     

An investigation on capability of hybrid Nd:YAG laser-TIG welding technology for AA2198 Al-Li alloy

This paper surveys the capability of the hybrid laser-arc welding in comparison with lone laser welding for AA2198 aluminum alloy experimentally. In the present research, a continuous Nd:YAG laser with a maximum power of 2000 W and a 350 A electric arc were used as two combined welding heat sources. In addition to the lone laser welding experiments, two strategies were examined for hybrid welding; the first one was low laser power (100 W) accompanied by high arc energy, and the second one was high laser power (2000 W) with low arc energy. Welding speed and arc current varied in the experiments. The influence of heat input on weld pool geometry was surveyed. The macrosection, microhardness profile and microstructure of the welded joints were studied and compared. The results indicated that in lone laser welding, conduction mode occurred and keyhole was not formed even in low welding speeds and thus the penetration depth was so low. It was also found that the second approach (high laser power accompanied with low arc energy) is superior to the first one (low laser power accompanied with high arc energy) in hybrid laser-arc welding of Al2198, since lower heat input was needed for full penetration weld and as a result a smaller HAZ was created.     

A compact passively Q-switched intra-cavity frequency doubled Nd:YAG/Cr4+:YAG composite crystal green laser

A compact diode-end-pumped passively Q-switched intra-cavity frequency doubled Nd:YAG/Cr⁴⁺:YAG composite crystal laser was demonstrated. The pulsed laser at 532 nm was produced and the dependence of the average out power, pulse width and pulse repetition rate on incident pump power were measured. Under the pump power of 14 W, the minimum pulse width of 3.5 ns with repetition rate of 27.5 kHz was obtained, corresponding single-pulse energy of 18 μJ and peak power of 5.3 kW.     

LD端面泵浦Cr~4∶YAG被动调Q激光器输出特性研究

对激光二极管端面泵浦Cr4+∶YAG被动调Q Nd∶YAG激光器输出特性进行了实验研究.实验研究发现,激光器输出功率及脉冲重复频率随谐振腔长度增大而增大.为解释这一实验现象,测量了泵浦光斑在激光晶体内尺寸,同时计算了激光晶体及Cr4+∶YAG晶体内的基模激光光斑半径随谐振腔长度变化.分析结果表明:激光晶体内泵浦光斑尺寸远小于激光晶体内基模光斑半径,腔模间交叠效率较低;当腔长增加时,激光晶体内的基模激光光斑减小,腔模间交叠效率增加,从而导致输出功率及脉冲重复频率随腔长增加而增加;另外,Cr4+∶YAG晶体内光斑半径也随谐振腔长度减小,引起Cr4+∶YAG晶体漂白时间缩短,导致脉冲重复频率随腔长增加而增加.     

A keyhole volumetric model for weld pool analysis in Nd:YAG pulsed laser welding

This study presents a new model for analyzing the temperature distribution and weld pool shape in Nd:YAG pulsed laser welding. In the proposed approach, a surface flux heat transfer model is applied in the low laser energy intensity region of the weld, while a keyhole heat transfer model based on a volumetric heat source is applied in the high laser energy intensity region of the weld. The correlation between the intensity of the laser input energy and the geometric parameters of the volumetric heat source is derived experimentally. A series of MARC finite element simulations based on the proposed single pulse model are performed to investigate the shape and size of the weld pool given different laser energy intensities. A good agreement is observed between the simulation results and the experimental results obtained under equivalent single pulse welding conditions. Thus, the basic validity of the proposed model is confirmed.     

High energy and high stability Cr:YAG passively Q-switched laser with convex-ARR unstable resonator

A convex-ARR (Anti-resonant Ring) unstable resonator was introduced in a Cr⁴⁺:YAG passively Q-switched Nd:YAG pulsed laser. There are two novel features in this cavity, one is the unstable resonator increasing output energy and improving laser mode; the other is the ARR structure efficiently enhancing the laser stability. A high energy and high stability Q-switched pulse with a single pulse energy of 85.6 mJ, a pulse width of 38 ns and an energy stability of 99.6% was obtained. The experimental results were analyzed well by using the mechanism of transient grating and the properties of the unstable resonator.