1,720,967 research outputs found
Microstructure and mechanical properties of a Zn-0.5Cu alloy processed by high-pressure torsion
No full textThe microstructure, texture and mechanical properties of a quasi-single-phase Zn-0.5Cu (wt. %) alloy processed by high-pressure torsion (HPT) for up to 10 turns were investigated using electron backscatter diffraction (EBSD), Vickers hardness measurements and uniaxial tensile tests. The results show that during torsional straining there is dynamic recrystallization, subgrain refinement, a dissolution of ε – Zn4Cu precipitates and solid-solution strengthening. Monotonic deformation develops a strong {0001}〈112ത0〉 local texture instead of the characteristic basal fiber texture. Sharp texture and misorientation angles for all grain boundaries of < 30° causes significantly higher yield stress and ultimate tensile stress compared to processing of the alloy by equal-channel angular pressing
Crack initiation, small crack growth, and stress intensity factor in the very high cycle fatigue (VHCF) of wire arc additive manufactured (WAAM) nickel aluminum bronze (NAB)
No full textWire arc additive manufacturing (WAAM) has emerged as a favorable method for industrial manufacturing due to its high productivity and cost-effectiveness in producing large metal components. This study employs a fracture mechanics approach to investigate the very high cycle fatigue (VHCF) behavior of WAAM nickel aluminum bronze (NAB) alloy, a material prized for its high strength and corrosion resistance, making it ideal for marine and naval applications. WAAM NAB specimens were fabricated using optimized process parameters, followed by annealing to minimize residual stresses and enhance mechanical properties. Ultrasonic fatigue testing (USF) at 20 kHz was utilized to evaluate fatigue life up to 109 cycles. Advanced fractography analysis enabled the quantification of small crack growth, facilitating fatigue life prediction through detailed assessments of stress intensity factors (SIF) at critical crack initiation sites. The study also investigates the influence of WAAM-induced volumetric defects on crack initiation and propagation in the VHCF regime. A comparison with conventional S-N data (limited to 5 × 106 cycles) revealed a distinct step in the S-N curve, indicating a transition to secondary fatigue strength when moving from the high cycle fatigue (HCF) to the VHCF domain. This research offers valuable insights into the long-term fatigue durability of WAAM NAB, reinforcing its potential for high-frequency cyclic load applications in marine and industrial environments
Microstructure, mechanical properties, and fatigue performance of a PBF-LB Al2139ZrTi alloy
Full text linkThis study investigates the microstructure, tensile, and fatigue behavior of post-aged powder bed fused-laser
beam (PBF-LB) Al2139ZrTi alloy, developed by EOS North America. The microstructure exhibits an equiaxed
grain structure with an average grain size of approximately 1.5 μm and lacks any strong crystallographic texture.
It also contains a dense dispersion of fine, uniformly distributed precipitates including: (i) Al3(Zr,Ti) dispersoids
with L12-type structure, acting as semi-coherent nucleation sites that contribute to grain refinement; (ii) a unique
Al3(Zr,Ti) plate-like phase, further confirming Zr–Ti-driven modification of precipitation pathways; (iii) Al
(CuFeMn) and Al(MnCu) intermetallics, notably Al7Cu2 (Fe,Mn) and Al20Cu2Mn3(T-phase), and (iv) Mg oxides,
pointing to minor oxidation during processing. Notably, Al2Cu-based θ′ and Ω phases are sparse, with only coarse
θ-phase particles (~0.5–1 μm) at grain boundaries and fine plate-like Ω-phase (~tens of nm thick) along the
[100] zone axis. Mechanical properties were evaluated via tensile testing, yielding ~ 470 MPa yield stress (YS),
~570 MPa ultimate tensile strength (UTS), and ~ 6.5 % elongation. Conventional (servo-hydraulic) and ultrasonic fatigue tests were performed to cover high cycle and very high cycle fatigue responses spanning up to 109
cycles. Fractographic analyses, including optical and electron microscopy techniques, were carried out to
quantify the crack initiation mechanisms in the mentioned regime
Microstructure and very high cycle fatigue characteristics of powder bed fused – laser beam (PBF-LB) scandium-free Al-Mg-Zr alloy
No full textFatigue characteristics of a newly developed laser powder bed fused scandium-free Al-Mg-Zr-Mn alloy
No full textThis study investigates the fully reversed force-controlled fatigue response of a newly developed laser powder bed fused (LPBF) Al-Mg-Zr-Mn alloy (EOS Al5X1) in the post-aged condition. The fatigue behavior revealed a defect-driven response with a fatigue strength of approximately 140 MPa at 5 million cycles. Comprehensive microstructural analyses, including grain size, texture, and precipitate characterization, were performed using advanced microscopy techniques. Additionally, X-ray computed micro-tomography (XCT) was employed to assess defect size and distribution, yielding a relative density of 99.93 %. Fracture surfaces of all fatigue-failed specimens were examined using optical and scanning electron microscopy to determine the primary failure mechanisms, with a focus on distinguishing between defect-driven and microstructural causes. The results indicated that nearly all specimens, tested across seven stress levels, exhibited crack initiation from process-induced volumetric defects, such as pores and lack of fusion. At lower stress levels (up to 195 MPa), single crack initiation sites driven by defects were identified at either surface or subsurface locations. In contrast, at higher stress levels (234 to 351 MPa), multiple crack initiation sites were observed, also at the surface or subsurface
Fatigue behavior of powder bed Fused–Laser beam (PBF-LB) 70/30 Copper-Nickel (CuNi30)
Full text linkThe 70/30 Cu–Ni alloy (CuNi30) is widely employed in marine systems due to its excellent corrosion resistance
and mechanical reliability. Despite its industrial relevance, its behavior under additive manufacturing (AM),
particularly powder bed fusion–laser beam (PBF-LB) processing, has received limited attention in the context of
fatigue-critical applications. This study presents the first systematic assessment of the microstructure, defect
population, mechanical properties, and fatigue performance of PBF-LB 70/30 Cu–Ni in both the as-built and
heat-treated conditions, with specific attention to the role of build orientation using horizontally and vertically
fabricated specimens. The applied heat treatment increased mechanical strength and produced a marked
improvement in the stress–life (S–N) response of the alloy. Detailed microstructural characterization and postmortem fractography showed that fatigue cracks predominantly initiated from surface or subsurface crystallographic facets induced by local embrittlement in the matrix. The results provide essential guidance for designing
fatigue-resistant Cu–Ni components and support the broader adoption of PBF-LB 70/30 Cu–Ni in demanding
marine and naval environments. Furthermore, this work establishes a foundation for future investigations into
the corrosion-fatigue behavior of the alloy
Abnormal grain growth in a Zn-0.8Ag alloy after processing by high-pressure torsion
No full textAbnormal grain growth (AGG) in a Zn-0.8Ag (wt%) alloy, produced through the application of high-pressure torsion (HPT), was systematically investigated using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), high-resolution transmission electron microscopy (HR-TEM) and microhardness testing. The HPT-deformed alloy exhibits AGG at room temperature without any additional heat treatment. Analysis by EBSD revealed oriented grain nucleation in a {112¯0}〈0001〉 direction from the initial (0001) fibre texture which agrees with the maximum energy release model. New grains were oriented according to the minimal Young's modulus direction (c-axis), parallel to the shearing direction. The strain-induced dissolution of nanocrystalline Zn
3Ag precipitates was identified as the main driving force for AGG in this alloy. The strains necessary for the initiation and termination of AGG were determined as ~4.0 and ~5.0, respectively. The increase in solid-solution strengthening caused an increase in hardness from ~47 HK in the fine-grained centre to ~84 HK in the coarse-grained region. A Hall-Petch investigation revealed grain refinement softening below a grain size of 23 µm. These results provide the first comprehensive description of AGG in metallic materials processed by a severe plastic deformation method at room temperature.
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A novel high-strength Zn-3Ag-0.5Mg alloy processed by hot extrusion, cold rolling or high-pressure torsion
No full textA novel Zn-3Ag-0.5Mg alloy was plastically deformed using 3 processing paths: hot extrusion (HE), HE followed by cold rolling (CR) and high-pressure torsion (HPT). The processed samples consisted of the η-Zn phase, ε-Zn3Ag precipitates within the matrix, and nanometric Zn2Mg precipitates within the Zn11Mg2 phase located at the grain boundaries. Both the η-Zn phase and Mg-rich phases were enriched in Ag. Electron backscattered diffraction was used to examine the effects of grain size and texture on mechanical behavior with tensile tests performed at room temperature (RT) at different strain rates. The coarsegrained (~6 μm) samples after HE exhibited high strength with brittleness due to dislocation interaction with dispersed precipitates and, to some extent, with twinning activation. Significant grain refinement and processing at RT gave an increase in elongation to over 50% in CR and 120% in HPT. Ductile CR samples with an average grain size of ~2μm and favorable rolling deformation texture gave a yield strength of ~254 MPa, a tensile strength of ~456 MPa and a reasonable strain rate sensitivity. These values for the CR samples meet the mechanical requirements for biodegradable stents in cardiovascular applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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