郑州机械研究所有限公司

Objective Laser micromachining technology refers to the machining of microstructures with certain sizes, shapes, and arrangements on the surface of workpieces, which can endow the material surface with characteristics such as superhydrophobicity, superhydrophilicity, wear resistance, and friction reduction. Laser micromachining has enormous application prospects and value in fields such as aerospace, automobiles, energy, and materials. In general, the application environment of microstructures is extremely harsh, with relatively high speeds, wide temperature ranges, and severe vibrations. Therefore, the requirements for processing quality are extremely stringent. Laser micromachining technology has excellent characteristics, such as high precision, no contact or pollution, high energy density, wide adaptability to various materials, and a small heat-affected zone, thus gradually becoming the mainstream in fine machining technology research. In this study, a nanosecond pulse laser is used for micromodeling experimental research on the surface of stainless steel. By adjusting different process parameters such as scanning speed, laser power, repetition frequency, and pulse width, the material removal effects under different laser processing parameters as well as the change laws of surface morphology and wettability are analyzed. The optimal parameter group is obtained through process optimization. This provides a technical reference and a theoretical basis for research on the surface states and wettability-related aspects of laser-processed materials. Methods The material selected for the experiment is 304 stainless steel. The sample dimensions are 50 mm >< 50 mm >< 1 mm. The nanosecond pulsed laser processing equipment used in the experiment is equipped with a field lens. The incident spot radius is calculated to be approximately 20 m. The microtexture morphology of the surface of the 304 stainless steel is observed using a laser confocal microscope. Wettability is measured using a contact angle tester. Roughness is measured using a contact roughness meter, and the surface profile is fitted using DataView TIME3200 software. In this study, the processing time is set to 30. By changing parameters such as the laser processing power, scanning speed, repetition frequency, and pulse width, a 7 mm>< 7 mm rectangular texture is processed to study the changes in microtexture depth, morphology state, and wettability. Results and Discussions In analyzing the experimental results, when the processing parameters are laser power of 6 W, scanning speed of 800 mm/s, repetition frequency of 30 kHz, and pulse width of 20 ns, a micro-texture depth of 18-22 m is obtained, and the microstructure surface is uniform. Therefore, the influence of the filling direction on the processed surface morphology is studied using these parameters. Unidirectional, cross, four-way, and six-way fillings are selected to process the microtextures and explore the improvement effect of the filling direction on the surface morphology state (Fig. 17). As shown in the figure, the surface morphology of the one-way filling has a furrow-like morphology formed by the successive microchannels, whereas cross-filling produces a grid-like microstructure. Increasing the filling direction further gradually flattens the surface morphology. This is because as the number of changes in the scanning direction increases, the energy absorbed by the material surface becomes more uniform, reducing the influence of the characteristics of the Gaussian distribution of the laser energy. The surface roughness after six-way filling is the lowest obtained by a contact roughness meter (Fig. 18), reaching about 0.301 mu m. In unidirectional filling, the roughness is 0.380 mu m. The roughness in cross filling is the largest, reaching 1.151 mu m, and that in four-way filling reaches 0.601 mu m. Microchannels are observed to have a lower impact on surface roughness. The generation of the microchannel morphology is mainly due to the line spacing of laser scanning. In this experiment, the scanning line spacing is uniformly 10 mu m. Therefore, the distance between the pulse centers of two adjacent channels is less than the spot radius; thus, the height difference of the generated microchannel structure is not obvious. For cross filling, owing to the interaction of energy, the ablation effect is not obvious on the area with energy deficiency, resulting in the accumulation of molten matter, which has a very serious impact on surface morphology. As the filling direction continues to increase, the surface ablation coverage effect increases; the area of the energy-deficient regions is significantly reduced; and the surface state is improved. The microtexture obtained by the cross filling method has the worst hydrophilicity (Fig. 19), and the contact angle of the left droplet is 80.74 degrees. In the above figure, when cross filling is used, the internal structure height of the texture is observed to be relatively high and evenly distributed. There are more gaps at the bottom to accommodate the droplet, and more microstructures significantly hinder the spreading of the droplet. With other filling methods, the low surface roughness reduces the internal height undulations of the texture. Therefore, the droplet spreading on the textured surface is less hindered, and the droplets exhibit better hydrophilicity. In particular, when processing microtextures by six-way filling, because of the large number of filling directions and more uniform pulse distribution, the texture surface is relatively flat, and the obtained droplet has the smallest contact angle of 56.2 degrees. Conclusions The surface state is mainly regulated by the pulse overlap rate and energy density. When the pulse overlap rate and energy density are relatively high, the surface appears charred black, and a recasting effect is evident. As the pulse overlap rate and energy density continue to decrease, the color of the microgroove surface changes from deep to light; the surface gradually becomes uneven; and pulse ablation traces become obvious. When the pulse overlap rate and energy density are low, the Gaussian distribution of the laser energy is manifested as volcanic morphology on the microgroove surface. Wettability is mainly affected by the surface micromorphology and surface energy of the microtextures. This paper focuses on discussing the influence of micromorphology changes on wettability under different laser parameters. The wettability gradually increases with an increase in processing power and gradually weakens with an increase in scanning speed. However, the repetition frequency and pulse width do not directly affect the energy distribution of the laser pulses; therefore, the change in wettability is not significant. In experimental research and analysis of the filling direction, the more the filling directions, the more uniform the surface energy distribution of the material, which improves surface morphology and wettability of the microgroove. Considering the requirements of processing efficiency, processing quality, and processing depth, when the processing time reaches a certain value, the influence on the depth gradually weakens. Therefore, in the experiment, a laser power of 6 W, scanning speed of 800 mm/s, pulse width of 20 ns, repetition frequency of 30 kHz, six-way filling method, and processing times of 30 are selected, thereby obtaining a microgroove with a depth of 18-22 mu m and good wettability.

The Ti60 alloy was successfully vacuum-brazed with Ti2AlNb alloy by using TiZrNiCu amorphous filler metal.SEM,EDS,and other methods were used to analyze the interfacial microstructure of the brazed joint.The influence of brazing temperature on the interfacial microstructure and mechanical properties of the joint was studied.The results show that the typical interfacial microstructure of the brazed joint is Ti60/α+β/(Ti,Zr)2(Ni,Cu)/α+β/B2/β/Ti2AlNb.As the brazing temperature increases,the content of(Ti,Zr)2(Ni,Cu)compound decreases,and they distribute more evenly.A lower brazing temperature causes the thick brittle compound layer,making it prone to microcracks and becoming a weak link in the joint.Besides,the large-scale lamellar α+β microstructure is formed at the base metal of Ti60 when the brazing temperature is too high.With the increase in brazing temperature,the shear strength of the joint first increases and then decreases.The maximum average shear strength of 283.9 MPa is obtained at the brazing temperature of 980 ℃ for 10 min.Fracture analysis indicates that all fractures occur at the brazed joints and are brittle.

Ceramic/metal brazing connection faces problems such as poor wetting of the ceramic surface by brazing metal and difficulty in alleviating the residual stress of joints.The effects of Ag-Cu-Ti active filler metal and the interlayer on the shear properties of the sapphire/TC4 alloy brazed joints were studied.The results show that with the increase of Ti elements content,the melting temperature of Ag-Cu-Ti filler metals increased slightly,the solid-liquid temperature range remained unchanged.The melted phases of Ag-Cu-3Ti brazing metal mainly included Ag base phase,Ti base phase,crystal phase,etc.,the crystal phase included CuTi,Cu3Ti,CuO,TiO,Cu2O,Ti2O,TiAg,etc.A dense metallurgical reaction layer formed between the sapphire and filler metals,its structure was mainly composed of Ag based,Cu based solid solutions and various stable intermetallic compounds.The sapphire/TC4 alloy brazing was completed at 870℃/20 min using Ag-Cu-3Ti filler metal and adding 0.2 mm 4J29 sheet,Cu sheet,Mo sheet,titanium fiber porous material,and 2 mm Cu and Mo sheet as the interlayer.The shear strengths of brazed sapphire/TC4 alloy joints were 26.74 MPa,15.20 MPa,15.78 MPa,3.11 MPa,23.73 MPa,and 30.49 MPa,respectively.The shear strength of brazed sapphire/2 mm Mo sheet/TC4 alloy joints was ideal.

Two Inconel 625 Ni-based alloy surfacing layers were prepared on the inner wall of high-strength steel in oil pipeline by using double tungsten electrode TIG technology with hot wire that was controlled by independent power supply. The samples obtained from the oil pipeline were solution treated at the temperature of 800 ℃ and 900 ℃, respectively. The microstructure and composition of Ni/steel surfacing plates were analyzed by optical microscope (OM) and scanning electron microscope (SEM). Its hardness and electrochemical corrosion resistance were tested and its passive film was analyzed by X-ray photoelectron spectroscopy (XPS). The results showed that in the as-welded state, the first layer of Ni-based surfacing alloy grew upwards in order perpendicular to the steel, however, the second layer nucleated on the substrate and from precipitates in the substrate of the first layer alloy, and its growth sequence became chaotic. Meanwhile, the grain size of the first layer was smaller than that of the second layer owing to the heat effect of the second layer on the first layer. After solid solution treatment, the microstructure of HAZ became more uniform and refined compared to that in the as-welded state, and this could improve the strength and toughness of the Ni/steel interface. In the as-welded state, the microstructure of Ni/steel surfacing composite plate presents a gradient distribution, which shows that the Ni/steel surfacing layer (220 HV) is significantly higher than that of the high strength steel substrate (140 HV), and the steel matrix HAZ has the lowest hardness (100 HV) due to the microstructure softening caused by the welding heat cycle. The process of solid solution treatment can increase the corresponding hardness, especially, when the solid solution treatment temperature was 800 ℃, secondary Ni-based austenite γ" phase, whose dislocation density was large, started to form, thus the hardness value of Ni-based alloy was up to the maximum. Moreover, when the solution treatment temperature was 800 ℃, the dissolution of Nb and Mo elements increased, the Laves phase and carbide phase reduced, and the needle-like δ phase appeared, thus the corrosion resistance of Ni-based alloy reached the optimal value. The passivation film was composed of two layers that the inner layer consisted of Cr, Fe, Nb, Mo oxides and the outer layer consisted of Cr, Fe, Nb, Mo hydroxide.

Transient liquid phase（TLP）bonding is an optimised bonding process that joins nickel-based superalloys. The post-bond heat treatment（PBHT）refers to a heat treatment process for the joint after the connection. This article summarizes the adverse effects of TLP thermal cycling on the tissue properties of nickel-based superalloys and the harmful phase problems of joints after TLP joining. The article explains the mechanism， types and current status of the PBHT process， analyses and discusses the systems and effects of the PBHT process where it is applicable. Finally， the development prospects and future research directions are presented. For future PBHT process research， it is recommended to continue to develop in the direction of multi-level and multi-pass precision heat treatment， and explore the TLPB-PBHT integrated process.