This PDF file contains the front matter associated with SPIE Proceedings Volume 11892, including the Title Page, Copyright information, and Table of Contents.

The balanced two-phase microstructure of austenite and ferrite endows duplex stainless steels (DSSs) excellent mechanical properties and high corrosion resistance. Additive manufacturing (AM) has been applied to the fabrication of DSS structures with the increased use of DSSs in corrosive environment. Direct energy deposition (DED) technologies, including laser metal deposition (LMD) and wire arc additive manufacturing (WAAM), have been regarded as the promising AM processes considering the industrial requirement of cost and size. The formation quality, microstructure evolution, mechanical properties and corrosion resistance largely depends on the heat sources used in AM processes. Super DSS 2594 powder and wire were used as feedstocks respectively for LMD and WAAM. A single-wall body of multiple layers was built with few defects. The chemical composition and microstructure were characterized. The effect of heat sources on mechanical and electrochemical properties was compared. The LMD samples exhibited relatively lower mechanical properties and weaker corrosion resistance than WAAM samples, which was resulted by more element loss due to the higher energy intensity during the LMD process. The results indicated that a proper content and uniform distribution of alloying element is critical to AM DSS parts.

With the development of additive manufacturing technology, it provides an efficient method for preparing complex structured NiTi alloy specimens. Different additive manufacturing technologies have different requirements for powder particle size. In order to satisfy the requirements of additive manufacturing technology for powders. This study aimed to produce spherical NiTi powders suitable for additive manufacturing by electrode induction melting gas atomization (EIGA). Scanning electron microscopy, X-ray diffractometry and differential scanning calorimetry were used to investigate the surface and inner micro-morphology, phase constituent and martensitic transformation temperature of the surface and inner of the NiTi powders with different particle sizes. The results show that the powder mean particle size D50 was 75 μm, flowability was 19.3 s/50 g, apparent density was 3.40 g·cm^–3, and the oxygen content of the powder only 0.005% higher than the raw materials. That the grain of powder becomes finer gradually with decreasing particle size. Ingot and all the powders exhibit a main B2 phase. Particles with different particle sizes have experienced different cooling rates during atomization. Various cooling rates cause different grain size inside the powder; in particular, the transformation temperature decreases with decreasing particle size. This study provides a basis for preparing high quality AM NiTi parts.

Laser welding was used to conduct autogenous welding of AlSi10Mg alloy fabricated by laser selective melting (SLM) technology and lap welding of the as-cast cover plate and SLM plate with similar composition. After welding, the weld was treated by three heat treatment processes (T5 single aging +T6 solution aging + annealing), and the microstructure as well as mechanical properties of the weld in each heat treatment state was analyzed. The results show that the microstructure of overlapped SLM welds is finer than that of autogenous welds, and the properties of overlapped SLM welds are better and more sensitive to heat treatment. After annealing and T5 single aging treatment, the dendritic structure with acicular eutectic silicon as network distribution at the edge of α-Al matrix of typical weld microstructure does not change, and the grain is coarsened to a certain extent. After solid solution treatment in T6 state, the Si network breaks, spheroidize and grows, and the eutectic Si distribution is more uniform, the number of pores in the weld increases and the volume of pores increases. After single aging treatment, the weld microhardness is increased, while annealing and solid solution treatment will reduce the weld microhardness.

Due to the formation of protective borosilicate scale during high-temperature oxidation, Mo-62Si-5B (at.%) alloy is deemed to be the promising candidate of high-temperature oxidation resistant coatings. Nevertheless, it faces the challenges on the application on surface engineering due to the difficulty of powder fabrication. In the present study, the pre-alloyed powder was obtained by mechanical crushing from Mo-62Si-5B bulk alloy fabricated by vacuum induction levitation melting. Subsequently, the original powder was further sieved by 60 mech sifter for the compatibility of laser cladding. The size distribution, morphology, oxygen content and phase composition of the powder were characterized. The results show that the D(50) of the powder is 130.55 μm and the average particle size is 124.65 μm. There are MoSi2 and MoB2 phases distributed in the powder with irregular morphologies, which is accord with the bulk Mo-62Si-5B alloy. The oxygen content of the powder is lower than 0.11%, meeting the requirements of the powder for laser cladding. A laser cladded layer was prepared on Nb-Si based alloy substrate by using the powders, which exhibits dense structure free of voids and cracks. The study proves the feasibility of pre-alloyed Mo-62Si-5B powder, which may give guidance for producing Mo-Si-B system oxidation-resistant coating by laser cladding or thermal spraying.

In order to further explore the application of W and W alloy fabricated by selective laser melting (SLM), W with different geometrical morphologies, support structure and second phase combination were prepared, and the corresponding microstructure characteristics were also investigated. The grain morphology and size distribution were significantly depend on the heat dissipation conditions caused by different geometrical morphologies, support structure and second phase combination. With the specimen size increases from 1D-2 to 3D, the average grain size increases, the percentage of large grains increases, and the dislocation density decreases. Because no remelting occurred in 2D specimen due to no overlap in the corresponding position, more prone to epitaxial growth and formed elongated cellular grains. Increase the height of support structure could decrease the cooling rate, especially the center area, which induced the grain size along with the reduction of cracks. The crack in pure W during SLM was related to the high thermal stress caused by high cooling rate as well as the recrystallization and epitaxial growth of W phase during SLM. Adding the second phase such as Cu or Cu10Sn could reduce the grain size of W phase remarkably, and crack was severely restrained in W phase simultaneously. This could be attributed to that grain refinement of W phase could decrease the DBTT and the second phase combination also breaks the epitaxial growth of W phase.

Laser powder bed fusion (LPBF) is a key metal additive manufacturing process and has attracted increasing attention both in academia and industry. However, it is not easy to achieve high formation quality and high dimensional accuracy meanwhile especially for magnesium alloy due to its high chemical reactivity, low boiling point, low surface tension and high coefficient of thermal expansion. We employed LPBF with various laser power and scanning speed to fabricate WE43 magnesium alloy porous scaffolds with strut sizes of 300, 400 and 500 μm. With a high laser energy input of 60 W and 600 mm/s, the relative density of the struts reached 99.77-99.79 %, while there was a big dimensional error about 33.78- 96.75 % between the designed and the fabricated values of the diameter of struts. With a low laser energy input of 60 W and 1200 mm/s, the dimensional error decreased to 8.13-9.38 %, but the relative density also decreased to 90.41-92.78 % due to lack of fusion. Preset size compensation was used to achieve high densification and accuracy. The offset value of 300, 400, and 500 μm strut was set in advance as 110.4, 92.7 and 89.2 μm respectively. After employing compensation scan strategies, the relative density was 99.64-99.79 % and the dimensional error was 7.16-9.27 % for all the struts. The compressive strength of porous scaffolds ranged from 4.37 MPa to 21.21 MPa with the strut size 300-500 μm, and the compressive strain reached approximately 50 %.

Selective laser melting (SLM) technology has received great attention in recent years for its application in the fabrication of Cu-Sn-based devices used in a wide range of industries, such as aerospace, ocean engineering, etc. However, the SLMed Cu-Sn alloys have different microstructure and properties, compared with the alloys made by traditional process, especially after heating treatments. In this paper, the effects of heat-treatment processing parameters on the microstructure and mechanical strength have been investigated for the SLMed Cu-10Sn alloy. A dense Cu-10Sn alloy bulk specimen was obtained by optimizing the SLM processing, and the relative density of the specimen reached above 99%. The grain morphology was mainly the columnar dendrite and inter-dendritic phases formed along the solidification direction. Tensile testing and detailed microstructural characterization were carried out on specimens in the as-SLMed and heat-treated conditions. The strength and plasticity of the SLMed specimen are much higher than that of the casted Cu-l0Sn alloy, mainly because of the grain refinement in the grain of the SLMed specimen. After the 800°C solution treatment, and the 400°C aging treatment, the microstructure of the specimen transformed from the columnar grain to equiaxed grain, the dislocations reduced, and a lot of twins generated obviously. Therefore, the yield strength (σ0.2) of the heat-treated specimen was decreased compared to the as-SLMed specimen. However, the UTS and the elongation were increased, due to the interaction between twins and equiaxed grain.

As the third-generation aluminum-lithium alloy developed by China, 2A97 is widely used in the aerospace field. However, the weak fine equiaxed zone (FEQZ) of weld severely limits its application. In this study, the macro- and microscopic characteristics of weld and the formation mechanism of the microstructure were investigated under the condition of large heat input non-autogenous laser welding (NLW) with ER2319 and ER4047 filler metals. The results showed that, the porosity imperfection in 2A97-T3 via NLW could be modified by using ER2319. The addition of Zr in the equiaxed zone resulted in effective refinement of equiaxed dendrites. The distribution of FEQZ concentrated at the four corners of the weld which was affected by the flow of weld pool. Furthermore, the morphology and distribution of FEQZ were influenced significantly by welding parameters and filler metals.

The considerable local dissolution of strengthening phases under gradient thermo-mechanical effects of friction stir welding leads to a noticeable decrease in material local hardness and tensile properties in friction stir welded Al-Li joints at the joint central area, known as the thermo-mechanical coupling zone, compared to its surrounding regions. Consequently, the resulting high gradient in joint local properties at borders of the joint center leads to high local stress concentration and tensile failure under relatively low loading values at this region. In this study, firstly, effects of joint center laser-peening-induced local compressive residual stresses evolution and work hardening are investigated on the enhancement in local hardness and tensile properties of AA2195-T6 friction stir welded joints. Then overall induced joint mechanical property homogeneity effects from these effects are evaluated on the improvement in joint global tensile properties. LP-induced local residual stresses are measured through the depth using the X-ray diffraction method. X-ray diffraction pattern peak broadening analysis is utilized to measure dislocation density local variations after LP which represent plastic work hardening effects. Local tensile properties are characterized by the digital image correlation technique with the corporation of the monotonic tensile test approach. Considerable increments in local material properties lead to the enhancement of overall joint tensile yield strength up to about 31% and ultimate tensile strength to 11% as a result of LP-induced compressive residual stresses, surface work hardening and joint tensile homogenization effects.

The purpose of the present study was to verify the effectiveness of dry laser peening (DryLP), which is the peening technique without a sacrificial overlay under atmospheric conditions using femtosecond laser pulses on the mechanical properties such as hardness, residual stress, and fatigue performance of laser-welded 2024 aluminum alloy containing welding defects such as undercuts and blowholes. After DryLP treatment of the laser-welded 2024 aluminum alloy, the softened weld metal recovered to the original hardness of base metal, while residual tensile stress in the weld metal and heat-affected zone changed to compressive stresses. As a result, DryLP treatment improved the fatigue performances of welded specimens with and without the weld reinforcement almost equally.

Laser peen forming (LPF) is a novel flexible forming process with remarkable advantages in complex shape forming. The distributed process planning model, which applies eigen-moment as the intermediate design variable, is an effective way to realize the process planning for complex shape forming. Due to the immaturity of the model, numerical instabilities such as checkerboards and intermediate densities commonly occurring in process planning. Therefore, it is difficult to apply the planning results as a forming scheme directly. This study utilizes the perimeter constraint method, re-drives the process planning model's mathematical expression to realize the aggregation control of the eigen-moment field. Effects of perimeter constraint and Tikhonov regularization term are verified and compared through the numerical method. Results show that perimeter constraint is more effective in preventing numerical instabilities. Then the improved model is applied to the LPF process planning of cylinder, saddle, and wave surface. LPF experiments are carried out based on the process planning results. Experimental surfaces are measured and compared with objective surfaces to verified the improved model. Because there still exists a specific error between the experimental surfaces and the objective surfaces. Reasons for the error are analyzed and discussed, and methods to improve the precision of LPF technology are further proposed.

Recently, highly regular thermochemical laser-induced periodic surface structures (TLIPSS) have become the subject of active studies. TLIPSS are formed in the interference maxima due to the local oxidation of the material irradiated with ultrashort laser pulses and are characterized by the elevation of the relief that forms parallel oxide protrusions. The gas surrounding is expected to affect the morphology and chemical composition of the resulting TLIPSS; however, such effects were rarely studied so far. Here we present the results of the TLIPSS fabrication on glass-supported Si-Ti bilayer films using an astigmatic Gaussian IR femtosecond beam both in air and a nitrogen-rich atmosphere. The formation of ordered TLIPSS with the period of ≈ 920 nm is observed at slow scanning speeds (∼1 μm/s) and low fluences in a nitrogen-rich atmosphere. Raman spectroscopy revealed the presence of TiO₂ (rutile) peaks, as well as bands centered at 280 cm^-1 and 320 cm^-1, which can be related to TiN in amorphous and polycrystalline phase.

Laser surface hardening is one of the effective methods to enhance the mechanical properties of localised surface area of engineering parts made of different types of steels and other metals like ultra-high strength steel etc. Laser surface hardening has many advantages over conventional hardening process like, self-quenching, very fast, control over energy input and localised hardening etc. In order to further improve the surface quality and mechanical properties of 30CrMnSiNi2A ultra-high strength steel parts fabricated by laser deposition manufacturing (LDM). The quenching modified layer was prepared on the surface of 30CrMnSiNi2A steel by laser quenching technology. This work presents the effect of different laser parameters on the surface morphology and mechanical properties of 30CrMnSiNi2A steel after laser hardening. The experimental data of OM morphology, microstructure, micro-hardness and wear property of hardened layer were analyzed by using the methods of range analysis. Effects of these parameters over the micro hardness of the surface are described. It has been found that, there is around 20% increase in hardness after laser hardening. It considerably debased the surface roughness and wear rate of LDM 30CrMnSi2A alloy parts, which has decreased by 53% and 57% than without laser surface hardening parts. Accordingly, industrial applications of laser deposition manufacturing 30CrMnSi2A alloy parts were supposed to be widened by this study.

In this paper, Ti6Al4V/AlSi10Mg multi-material specimens were fabricated by selective laser melting (SLM). The influence of process parameters on the interfacial crack was discussed and the formation mechanism of interfacial crack under different process parameters was expounded through the simulation of temperature field. The microstructure, element distribution, phase composition and microhardness of the Ti/Al interface were investigated. The cooling rate and temperature gradient increased with the increase of laser power and scanning speed, which easily led to the interfacial crack. Using chess scanning strategy and increasing the preheating temperature of the substrate could effectively reduce the cooling rate, so as to reduce the stress and avoid the interfacial crack. There was a good metallurgical bonding between titanium alloy and aluminum alloy, the typical molten pool morphology could be seen at the interface. In the heat affected zone near the interface, the grain size of aluminum alloy became coarsen, because the lower thermal conductivity of titanium alloy and heat accumulation in the process of forming aluminum alloy. There were needle-like intermetallic compounds (IMCs) at the interface. According to the results of SEM and EDS, the thickness of IMCs was about 2-4 μm, and the composition of IMCs was mainly TiAl and TiAl₃. The results of XRD showed that there were not only Ti₃Al, TiAl, TiAl₃ IMCs but also TiSi₂ ceramic phase at the interface, which made the microhardness of the interface reached as high as 679 HV.

Femtosecond laser direct writing via two-photon polymerization (TPP), which utilizes high intensity laser induced two-photon absorption to initiate polymerization, is a promising approach for 3D microstructure fabrication especially micro-optical devices. The traditional point-by-point direct writing TPP has high spatial resolution but usually timeconsuming[1], thus it is hard to fabricate large structures or arrays. Recently, several solutions have been proposed to facilitate the polymerization, for instance, the multi-focus generation for parallel processing but the interference between foci limits their density[2], the multi-beam interference for specific periodic structures[3], and the focal field engineering[4,5]. In this work, we fabricate arbitrary 3D structures with the focal field engineering (FFE) by inversely retrieving the incident beam profile from the target focal field to speed up the polymerization of the microstructures. Moreover, we anneal the structure as post heat treatment to improve its smoothness of the surface.

Laser cleaning has become a widely used cleaning technology in recent years. Currently, researchers are mainly engaged in the studies of laser cleaning process parameters. However, when the casing of oil tanks, wind turbines, and electronic equipment are cleaned, the high temperature generated by thermal deposition in the substrates will accelerate the aging of oil, reduce the performance of lubricants, and cause the damage of semiconductor devices. These will indirectly lead to mechanical or electronic failures of the devices and systems. To avoid these adverse effects, it is significant to investigate the temperature distribution of the substrate during the laser cleaning process. In this paper, the results of the temperature distribution measurement of the substrates covered with the rust, cooking oil, industrial lubricants and industrial primer has been presented.

In intelligent manufacturing system, a systematic method of constructing stereo vision using neural network is proposed, and the operation and control mechanism in practical operation is put forward. In particular, the concept of calculation process is established. And this method overcomes the complexity of a large number of calculations. And it has significant advantages in the system scientifically, the operation speed and the operability.

Laser drilling has been more and more widely used in laser machining process. Therefore, optimizing the quality of laser drilling becomes extremely important. We know that laser drilling can be achieved by using high power density of a laser. As light waves with different waveforms represent the different energy distributions in time domain, we believe that the quality of laser drilling should be related to the laser waveform. At present, a laser used in the laser processing usually hasthe waveform with a Gaussian or a Lorentzian distribution. In this study, we numerically simulated the punching quality of a pulsed laser with the Gaussian distribution and a pulsed laser with the top-flat distribution (we called it as a square-shaped laser pulse) at the same energy. It mainly refers to the changes of density, temperature, and pressure of the target materials under the same energy for different waveforms. The constrained interpolation profile algorithm has been used to simulate the machining process. Until now, there are few studies on the features of laser drilling with different waveforms in time domain. This paper provides a new method to optimize the quality of laser drilling.

Laser processing plays a key role in treating a lot of materials. The mechanism of laser stealth dicing (SD) is based on irradiation of a laser beam which is focused inside the brittle material. The laser beam scans along the predetermined path, so that the characteristics of the interior brittle material can be changed, the stress layer can be therefore formed. Finally, an external force is applied to separate the brittle material. Since only the limited interior region of a wafer is processed by the laser irradiation, the damages and debris contaminants can be avoided during the SD process. SD has the advantages of a high speed for thinner wafers without any chipping, the smooth section without dust and slag, and completely dry process, which has been widely used in large scale integrated circuits and microelectronic manufacturing systems. However, further studies on the simulation analyze and parameter optimization have kept to be rear for SD so far. In this study, an approach named as constrained interpolation profile (CIP) was adopted, which has the advantages of compactness, stability, and low dissipation in computational fluid dynamics compared with other simulation procedures. We have finished a theoretical simulation to obtain the physical features of the temperature, pressure, density of the silicon substrate at different focal depth where a nanosecond pulsed laser is irradiated, then we found a suitable focal depth with a good dicing quality by analyzing these physical features.