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Effects of Low-Temperature Tempering on Microstructure and Properties of the Laser-Cladded AISI 420 Martensitic Stainless Steel Coating
摘要： Post-treatment is crucial to improve the comprehensive performance of laser-cladded martensitic stainless steel coatings. In this work, a low-temperature tempering treatment (210 ?C), for the ?rst time, was performed on the laser-cladded AISI 420 martensitic stainless steel coating. The microstructure and properties of the pre- and post-tempering specimens were carefully investigated by XRD, SEM, TEM, a micro-hardness tester, a universal material testing machine and an electrochemical workstation. The results show that the as-cladded AISI 420 stainless steel coating mainly consisted of martensite, austenite, Fe3C and M23C6 carbides. The phase constituent of the coating remained the same, however, the martensite decomposed into ?ner tempered martensite with the precipitation of numerous nano-sized Fe3C carbides and reverted austenite in the as-tempered specimen. Moreover, a slight reduction was found in the micro-hardness and tensile strength, while a signi?cant increase in elongation was achieved after tempering. The fractography showed a transition from brittle fracture to ductile fracture accordingly. The as-tempered coating exhibited a striking combination of mechanical properties and corrosion resistance. This work can provide a potential strategy to enhance the overall properties of the laser-deposited Fe-based coating for industrial applications.
关键词： microstructure,laser cladding,low-temperature tempering,properties,stainless steel coating
更新于2025-09-19 17:15:36
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Dependance of Poly(acrylic acid) Interfacial Adhesion on the Nanostructure of Electrodeposited ZnO Films
摘要： Understanding the impact of the intricate morphology and surface chemistry of ZnO nanorod arrays on their interactions with polyelectrolyte polymers is crucial for the development of nascent ZnO-based adhesion-promoting materials. AFM based Single Molecule Force Spectroscopy (SMFS) was applied for the analysis of the adsorption of poly(acrylic acid) (PAA) on zinc oxide (ZnO) film covered stainless steel substrates in aqueous electrolytes at pH 7. Based on the electrodeposition process, the morphology of zinc oxide films could be varied ranging from platelet-like crystals to nanorods. This approach allowed for the morphology dependent analysis of macromolecular adsorption processes on complex ZnO nanostructures which have diverse applications in the field of adhesion-promoting thin films. The surface chemical composition, as determined by X-ray photoelectron spectroscopy, could be correlated to the AFM-based desorption studies. Only equilibrium desorption events (plateaus), centered at 42 pN, were observed on mirror polished, preconditioned stainless steel. However, for platelet-like ZnO films, the poly(acrylic acid) desorption showed a mixture of rupture events (mean rupture forces of about 350 pN) and equilibrium desorption, while ZnO nanorod structures showed solely rupture events with mean rupture forces of about 1300 pN. These results indicate that simultaneous multiple ruptures of carboxylate-zinc bonds occur due to the macromolecular coordination of poly(acrylic acid) to the ZnO nanorods. The analysis of the interfacial adhesion processes is further supported by the dwell time dependence of desorption processes.
关键词： poly(acrylic acid),Single Molecule Force Spectroscopy (SMFS),worm like chain (WLC) model,stainless steel,zinc oxide (ZnO),electrochemical deposition,molecular adhesion,adsorption free energy
更新于2025-09-19 17:15:36
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Study of expanded austenite formed in plasma nitrided AISI 316L samples, using synchrotron radiation diffraction
摘要： AISI 316L stainless steel samples nitrided at different conditions of temperature and time, showing different properties, such as nitrogen concentration (CN) and nitrided layer thickness, were studied. Expanded austenite (gN) diffraction peaks up to the (222) reflection were observed using suitable wavelength synchrotron radiation. XRD patterns were fitted by Le Bail method, using a special triclinic crystal structure (with a lattice distortion η) for gN, whose peaks were decomposed in a few subpeaks, to consider CN gradient across the nitrided layer. Our results indicate that regarding gN magnetic behavior, which was observed for the samples nitrided at 450 °C, it seems to be correlated not only to high CN (≥31at.%), but also to higher η (≥2.4°), which reaches up to 5.6°. This distortion η decreases when CN increases, consequently, with its minimum close to the surface. On the other hand, for paramagnetic samples (350 °C), η increases up to 1.4° when CN increases up to 30 at.%.
关键词： magnetic character,layer depth,AISI 316L stainless steel,expanded austenite,synchrotron diffraction,plasma nitriding
更新于2025-09-19 17:15:36
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Preparation and deposition of Pr-Fe-B permanent magnet powder using pulsed laser
摘要： We have already prepared a thin permanent magnet with the thickness of sub millimeter by obtaining magnet powders using a PLD (Pulsed Laser Deposition) method. In the study, the PLD followed by a flash annealing enabled us to deposit isotropic Pr-Fe-B magnet powders with coercivity (Hcj) > 1000 kA/m on a stainless thin shaft applicable to a miniaturized motor. Observation on the surface of Pr-Fe-B magnets and evaluation on mechanical behavior was carried out. Since the surface of a Pr-Fe-B magnet was coated by a Pr oxide through an annealing process, their magnetic properties didn’t degrade after one year. We also confirmed that the Pr-Fe-B magnet has possibility to be applied to a micro magnetization process. It was clarified that the powder technology using the PLD is useful to propose a thin magnet applicable to a next generation small motor.
关键词： stainless shaft,coating,Pr-Fe-B permanent magnet powder,PLD (Pulsed Laser Deposition)
更新于2025-09-19 17:13:59
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Effect of laser shock peening on high cycle fatigue characteristics of 316LN stainless steel
摘要： The influence of ‘laser shock peening’ (LSP) on fatigue behavior of 316LN stainless steel has been studied at 298 K by conducting fully reversed stress controlled fatigue tests in the range 200–300 MPa. A triangular wave form with a constant frequency of 5 Hz was employed for all the tests conducted below 107 cycles on the virgin and laser shock peened samples. The run out tests at 107 cycles were performed at a frequency of 60 Hz. The studies have clearly revealed that the fatigue life is dependent on surface condition of the material and stress amplitude employed. A comparison is made of cyclic stress-strain hysteresis loops and fatigue lives between virgin and peened material. The peened material showed better fatigue strength and life at low stress amplitudes pertaining to high cycle fatigue regime, and exhibited lower density of surface microcracks. The improved fatigue resistance of peened material is attributed to the presence of residual compressive stresses to a depth of ~100 μm from the surface. The beneficial effect of compressive stresses is perceived both in the reduction in number density of Stage-I microcracks and retarded stage-II crack growth in the initial stages (that revealed striations with lesser spacing compared to un-peened samples).
关键词： Laser shock peening,Stainless steel,High cycle fatigue,Compressive residual stresses
更新于2025-09-19 17:13:59
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Comparison between Shot Peening, Cavitation Peening, and Laser Peening by Observation of Crack Initiation and Crack Growth in Stainless Steel
摘要： The traditional technique used to modify the surface of a metallic material is shot peening; however, cavitation peening, a more recent technique in which shot is not used, was developed, and improvements in the fatigue strength of metallic materials were demonstrated. In order to compare the fatigue properties introduced by shot peening with those introduced by cavitation peening, crack initiation and crack growth in specimens of austenitic stainless steel (Japanese Industrial Standards JIS SUS316L) treated using these techniques were investigated. With conventional cavitation peening, cavitation is produced by injecting a high speed water jet into water. In the case of submerged laser peening, bubbles are generated using a pulsed laser after laser ablation, and the impact produced when the bubbles collapse is larger than that due to laser ablation. Thus, in this study, cavitation peening using a water jet and submerged laser peening were investigated. To clarify the mechanisms whereby the fatigue strength is improved by these peening techniques, crack initiation and crack growth in specimens with and without treatment were examined by means of a K-decreasing test, where K is the stress intensity factor, and using a constant applied stress test using a load controlled plane bending fatigue tester. It was found that the improvement in crack initiation and the reduction in crack growth were roughly in a linear relationship, even though the specimens were treated using di?erent peening methods. The results presented here show that the fatigue strength of SUS316L treated by these peening techniques is closely related to the reduction in crack growth, rather than crack initiation.
关键词： crack,stainless steel,fatigue,shot peening,cavitation peening
更新于2025-09-19 17:13:59
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KEYHOLE DYNAMICS AND MORPHOLOGY VISUALIZED BY IN-SITU X-RAY IMAGING IN LASER MELTING OF AUSTENITIC STAINLESS STEEL
摘要： In-situ X-ray observation was used to investigate the effect of process conditions on keyhole behavior in laser melting with austenitic stainless steel. It was confirmed that the keyhole depth and width increased, and the fluctuation in the keyhole depth decreased as laser power increased. With no shielding gas, there was a large fluctuation in keyhole depth. This is presumed due to the attenuation of laser power and change in laser beam quality by the interaction between laser and metal vapor. We found that when the laser traverse speed increased relative to the keyhole-forming speed, the inclination of the keyhole decreased, and the width and opening of the keyhole expanded. As the defocus distance increased, the inclination of the keyhole decreased and the fluctuation in the keyhole depth increased. As a result of decreasing the laser power for a predetermined time, the penetration depth of the laser melting portion did not change and the keyhole depth was maintained at a laser power reduction time of 1 ms. These results will contribute to the improvement in quality and efficiency of the laser-melting process regarding keyhole formation such as additive manufacturing and laser welding and cutting.
关键词： X-ray observation,Keyhole,Laser melting,Stainless steel
更新于2025-09-19 17:13:59
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Analytical model for estimating bending angle in laser bending of 304 stainless steel/Q235 carbon steel laminated plate
摘要： Compared with the single-component metal plate, the stainless steel-carbon steel laminated plate (SCLP) combines the stainless steel layer and the carbon steel layer with a special preparation technique. In order to estimate the bending angle of laminated plates accurately, it is of great significance to establish an analytical model. Based on the temperature gradient mechanism, the temperature distribution equation of the SCLP is established by the piecewise function. Then, the depth of the plastic zone is calculated by the recrystallization temperature according to the temperature distribution along the thickness direction of the SCLP. Moreover, by fitting the yield strength curves of stainless steel and carbon steel, the average compressive stress of the plastic zone is calculated through the integral method. By optimizing the calculation of the plastic depth and the average compressive stress in the plastic zone, the analytical model is established based on mechanical equilibrium equations. The experimental verification shows that the average error of bending angle using the proposed model is 9.95%, while Liu’s model is 38.02%. The proposed model provides a calculation method for estimating the bending angle, which contributes to improving the accuracy of the analytical model in laser bending of SCLP.
关键词： stainless steel-carbon steel laminated plate,analytical model,bending angle,laser bending,depth of plastic zone
更新于2025-09-19 17:13:59
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Picosecond Laser-Induced Hierarchical Periodic Near- and Deep-Subwavelength Ripples on Stainless-Steel Surfaces
摘要： Ultrafast laser-induced periodic surface subwavelength ripples, categorized based on the ripple period into near-subwavelength ripples (NSRs) and deep-subwavelength ripples (DSRs), are increasingly found in the variety of materials such as metals, semiconductors and dielectrics. The fabrication of hierarchical periodic NSRs and DSRs on the same laser-irradiated area is still a challenge since the connection between the two remains a puzzle. Here we present an experimental study of linearly polarized picosecond laser-induced hierarchical periodic NSRs and DSRs on stainless-steel surfaces. While experiencing peak power density higher than a threshold value of 91.9 GW/cm2, in the laser-scanned area appear the hierarchical periodic NSRs and DSRs (in particular, the DSRs are vertically located in the valley of parallel NSRs). A large area of the uniformly hierarchical periodic NSRs and DSRs, with the spatial periods 356 ± 17 nm and 58 ± 15 nm, respectively, is fabricated by a set of optimized laser-scanning parameters. A qualitative explanation based on the surface plasmon polariton (SPP) modulated periodic coulomb explosion is proposed for unified interpretation of the formation mechanism of hierarchical periodic NSRs and DSRs, which includes lattice orientation of grains as a factor at low peak power density, so that the initial DSRs formed have a clear conformance with the metallic grains.
关键词： stainless steel,surface plasmon polaritons,coulomb explosion,laser induced subwavelength ripples
更新于2025-09-19 17:13:59
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Characterization of laser beam offset welding of titanium to steel with 38Zn-61Cu alloy filler
摘要： Laser welding of TC4 Titanium (Ti) alloy to 304 austenitic stainless steel (SS) has been applied using 38Zn-61Cu alloy as filler metal. A new welding process for SS-Ti alloy joint was introduced on the basis of the controlling the formation of Ti-Fe intermetallics in the joint. One pass welding involving creation of a joint with one fusion weld and one diffusion weld separated by remaining unmelted Ti alloy. When laser beam on the Ti alloy side was 1.5 mm, Ti alloy would not be completely melted in joint. Through heat conduction of unmelted Ti alloy, the atomic diffusion occurred at the SS-Ti alloy interface. A diffusion weld was formed at the SS-Ti alloy interface with the main microstructure of β-CuZn + Fe3Zn7, β-CuZn and Ti2Zn3 + Ti3Cu4. The joint fractured at the diffusion weld with the maximum tensile strength of 128 MPa.
关键词： Diffusion welding,Microstructure,TC4 Ti alloy,Filler metal,304 austenitic stainless steel,Laser welding
更新于2025-09-19 17:13:59