Dissimilar Metal Joining of 304 Stainless Steel to SMA490BW Steel Using the Filler Metal Powders with a High-Entropy Design

Metals and Materials International - High-entropy alloys having excellent properties are particularly suitable for the application as the filler metals in welding. In the present study,...     

B对FeCoCrNiSiBx高熵合金激光熔覆层组织和硬度的影响

采用激光熔覆制备了FeCoCrNiSiB_x高熵合金熔覆层,利用光学显微镜、扫描电镜、X射线衍射仪和显微硬度计研究微量硼元素(摩尔比x=0、0.02、0.04、0.06、0.08)对FeCoCrNiSiB_x高熵合金熔覆层组织和硬度的影响。结果表明:无B高熵合金涂层组织主要为胞状晶。B的添加会促进枝晶的生成,逐渐形成鱼骨状树枝晶,但过量的B会破坏枝晶完整性,形成蠕虫状晶。此外,高熵合金熔覆层组织为FCC和BCC双相结构,B元素的添加会形成大量0.1~2.6 μm的Cr₂B第二相,有助于提高熔覆层硬度,其中x=0.06时激光熔覆层的硬度最高,约为537 HV0.2。     

A novel synthesis method for manganese ferrite nanopowders: The effect of manganese salt as inorganic additive in electrosynthesis cell

Manganese ferrite nanoparticles were electro-crystallized in an electrochemical cell containing two iron electrodes, and an electrolyte solution of sodium sulfate, sodium butanoate, and manganese sulfate hydrate. The samples were characterized by X-ray diffraction, electron microscopy, magnetometry, and Mössbauer spectroscopy methods. The crystal structure of the samples was studied using X-ray diffraction. Based on obtained results we found that the manganese ferrite nanoparticles are formed in the electrochemical cell containing 0.001 M manganese sulfate hydrate. Also, the formation of a paramagnetic secondary phase in the sample without manganese is suppressed by adding manganese salt in the electrochemical cell. The nanoparticle size, shape, and morphology were characterized using electron microscopy. Magnetization curves show that all samples are magnetically soft and their specific magnetization ranges from 15 A m² kg⁻¹ to 75 A m² kg⁻¹, depending on the growth conditions. Room temperature Mössbauer spectra confirm the formation of nonstoichiometric spinel ferrite of magnetite or manganese ferrite, again depending on the growth conditions. Based on Mössbauer analysis, reduction in the population of octahedral sites provides direct evidence for the presence of the manganese ions substitution in the octahedral sites.     

Metallic glass–steel composite with improved compressive plasticity

A Zr_52.5Cu₁₈Ni_14.5Al₁₀Ti₅ bulk metallic glass toughened with a commercially available spring-shaped steel wire has been produced by centrifugal casting. The addition of the steel spring significantly affects shear band nucleation and propagation through the blockage, deflection and multiplication of shear bands at the glass–spring interface. As a result of the more homogeneous distribution of the plastic strain, the room temperature plasticity increases from 0.9% for the monolitic glass to about 4% for the glass–spring composite. Given the low volume fraction of the spring used in the composite (4.2 vol.%), these results demonstrate the extreme effectiveness of the steel spring for improving the plasticity of the metallic glass.     

Theoretical and experimental study of fatigue growth of interacting cracks

Life assessment of structures weakened by interacting cracks represents an important and very challenging problem. Subsequently, the main objective of this paper is to address this problem by developing a new computational technique. It is based on the classical strip-yield model and plasticity-induced crack closure concept. It also utilises the 3D fundamental solution for an edge dislocation. The crack advance scheme adopts the cycle-by-cycle calculations of the effective stress intensity factors and crack increments. The modelling results are validated against an experimental study focusing on fatigue behaviour of two closely spaced collinear cracks in wide plates with different thicknesses. It is confirmed that non-linear effects associated with crack interaction have a significant influence on fatigue life and cannot be disregarded in life and integrity assessments of structural components.     

Synthesis of carbon–silica core–shell nanofibers from a dispersion of fluorinated carbon nanofibers in solvated polysiloxane

Carbon–silica core–shell fibers (which unusually consist of carbon nanofibers coated with silica) were synthesized using a two-step process. First, fluorination of carbon nanofibers (CNFs) allows their homogenous dispersion into a polysiloxane matrix. A longlife dispersion of nanofibers in solvated polysiloxane has been prepared. Second, the polysiloxane/fluorinated carbon was thermally treated in air until 700 °C. Defluorination and conversion of polysiloxane into silica occur and result in carbon–silica core–shell fibers. The thermal treatment of the polysiloxane/carbon and the resulting silica/carbon–silica core–shell nanostructures were investigated using solid state nuclear magnetic resonance using ¹⁹F, ¹³C ¹H, and ²⁹Si nuclei, X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopies.     

Effects of process and source on elastic modulus of single cellulose fibrils evaluated by atomic force microscopy

A test method to measure cellulose fibril elastic modulus using atomic force microscopy was used to investigate the effects of process and source on the moduli of single cellulose fibrils. The cellulose fibrils were generated from cellulose by mechanical treatments. Individual fibrils were suspended over a micro scale groove etched on a silicon wafer. A nano-scale three-point bending test was performed to obtain the elastic moduli. The results indicated that the elastic moduli of cellulose fibrils were not significantly different between 30 min and 60 min of high intensity ultrasonic treatment for Lyocell fiber, between isolation methods of ultrasonic and homogenizer treatment for pure cellulose fiber, and between different cellulose sources of pulp fibers treated by homogenizer regardless the effects of sample size coupled with inherent variation in the raw material. The elastic modulus of Lyocell fibrils with diameters from 150 to 180 nm was evaluated to be 98 ± 6 GPa. Modulus values decreased dramatically when the diameter was more than 180 nm.     

Textile fiber-reinforced anionic polyamide-6 composites. Part I: The vacuum infusion process

In order to manufacture thicker, larger and more integrated thermoplastic composite parts than currently can be achieved by melt processing, a vacuum infusion process is currently being developed at the Delft University of Technology using a reactive thermoplastic polymer called anionic polyamide-6 (APA-6). In previous studies it was demonstrated that the anionic polyamide-6 (APA-6) resin that is used has excellent mechanical properties. The present study assesses infused thermoplastic composites and focuses on fiber-matrix interactions. Part I of this study focuses on the thermal effects, causes for deactivation of the initiator and the restriction caused by the low in-plane permeability of the fiber textiles on various transport phenomena. It will be shown that addition of pre-heated fibers not only shortens the infusion window, but also influences the matrix properties by reducing the exothermic heat production. In addition, the low in-plane permeability of the fiber textiles influences the infusion time and causes the entrapment of voids. Finally, reactions between the matrix and the fiber surface can lead to deactivation of the initiator and bond formation with the activator. Interfacial bonding, however, is discussed in more detail in Part II of this study, whereas the effect of adding a nucleating agent is discussed in Part III.     

Erosive wear properties of unidirectional carbon fiber reinforced PEEK composites

The erosive wear properties of unidirectional carbon fiber (CF) reinforced polyetheretherketone (PEEK) composites were studied. A semi-ductile erosive wear manner was found regardless of the CF orientation. Wear mechanism analysis revealed that both cutting and deformation mechanisms existed in the erosion of the composites, although different damaging forms were involved depending on the impingement angles and CF orientation. To give further support on the erosion mechanisms, a special procedure was designed to observe the cross-sectional surface of the eroded composites, and the surface temperature variation was registered. It increased with increasing impingement angle, indicating higher energy dissipation by deformation, which is consistent with the revealed shift of the main erosive wear mechanism from cutting to deformation and “wholesale” fiber fracture.     

Grain-orientation-dependent residual stress and the effect of annealing in cold-rolled stainless steel

Cold rolling leads to a residual stress that is dependent not only on the specimen directions but also on the orientation of the grain. Neutron diffraction was used to investigate residual stresses and the effect of annealing in cold-rolled stainless steel, a two-phase material consisting of 62 vol% austenite and the rest deformation-induced martensite. The specimens were prepared by cold rolling of AISI 301 stainless steel with 48% reduction. The grain-orientation-dependent residual stress, or inter-granular stress, was determined by constructing the stress orientation distribution function, a recently developed concept, from the residual strains measured along various crystallographic directions. For the cold-rolled sample, a strong grain orientation anisotropy was observed for residual stresses in both phases. Detailed analysis of the experimental stress and texture data indicates that the observed orientation anisotropy was caused by the selective phase transformation that occurred during cold rolling. Annealing at 500°C leads to recovery, which significantly reduces the orientation anisotropy of the residual stress. The experimental data show that the recovery dynamics in the austenite and martensite phases are quite different. It appears that the overall recovery behavior in this two-phase material is driven by the martensite phase.