Equal channel angular pressing (ECAP) is used to investigate the influence of microstructural evolution on mechanical properties and corrosion resistance of an extruded Mg alloy (ZFW MP) via route BC ...at 579 K. The transmission electron microscope (TEM) and the optical microscope (OM) are used to observe the microstructure. Tensile testing and hardness measurement are used to investigate the mechanical properties at room temperature, and electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements are used to examine the corrosion properties in Hank's solution at 37 °C. The ECAPed samples show the enhanced mechanical properties as compared with the extruded sample. The ECAPed ZFW MP alloy possesses a homogeneous microstructure due to dynamic recrystallization (DRX), as indicated by the resulting microstructures. However, the electrochemical measurements show that a reduction in the corrosion resistance is caused by the ECAP processing. A broader grain size distribution and a continuous network of the oxide layers along grain boundaries result in an improvement in the corrosion resistance in the extruded sample as compared with the ECAPed sample. However, better mechanical properties are observed with a further homogeneous microstructure in the ECAPed sample as compared with the extruded counterpart.
The ECAPed Magnesium alloy with a homogenized microstructure and a narrow grain size distribution show better mechanical strength than the as‐extruded counterpart used as a degradable biomaterial in medical implants. The increase in strength is accompanied by a reduction in uniform corrosion resistance. However, the increase of ECAP pass number decreases the tendency toward localized corrosion.
Abstract
In this study, we analyze the influences of carbon nanotube (CNT) addition on the martensite transformation and internal friction of Cu–Al–Ni shape-memory alloys (SMAs). X-ray diffraction ...and differential scanning calorimetry results demonstrate that Cu–13.5Al–4Ni–
x
CNT (
x
= 0, 0.2, 0.4, 0.6, and 0.8 wt%) SMA/CNT composites exhibit a
$${\upbeta }_{1}({\mathrm{DO}}_{3})\rightleftarrows {\upbeta }_{1}^{\mathrm{^{\prime}}}(18\mathrm{R})$$
β
1
(
DO
3
)
⇄
β
1
′
(
18
R
)
martensitic transformation. The martensitic transformation temperatures and transformation enthalpies of the martensitic transformation peaks for the Cu–13.5Al–4Ni–
x
CNT (
x
= 0–0.8 wt%) composites gradually decrease with the increase in the amount of CNT addition. Compared to the Cu–13.5Al–4Ni SMA, the Cu–13.5Al–4Ni–
x
CNT (
x
= 0.2–0.8 wt%) SMA/CNT composites exhibit significant improvements in the amount of dissipation of energy (storage modulus (
$${E}^{\prime}))$$
E
′
)
)
and mechanical strength. However, the tan δ of the internal friction peak gradually decreases with the increase in the CNT content above 0.6 wt%. The reduction in tan
δ
is attributed to the decrease in the magnitude of the austenite-to-martensite transformation and precipitation of γ
2
(Cu
9
Al
4
) phase particles, which impede the interface motion in between the parent/martensitic phase and martensitic phase.
This study investigates the damping properties of Cu–Al–Mn shape memory alloys (SMAs) with various chemical compositions and the effects of the addition of quaternary alloying elements Ag and Nb on ...the microstructure, martensitic transformation behavior, and damping capacity of SMAs. Compared to other Cu–12Al–xMn (x = 4–7 wt%) SMAs, Cu–12Al–5Mn has a more significant inherent and intrinsic internal friction (IFPT + IFI) peak above room temperature. The addition of Ag or Nb to Cu–12Al–5Mn reduced the grain size, thereby increasing the hardness of the alloys; however, the damping capacity and temperature of the IFPT + IFI peak decreased simultaneously. The addition of Ag to Cu–12Al–5Mn significantly reduced the damping capacity (IFPT+IFI peak) because of the notable decrease in the amount of transformed martensite. Moreover, the addition of Nb to Cu–12Al–5Mn caused the AlNb3 phase to precipitate, limiting the mobility of the martensite variant interfaces and slightly decreasing the damping capacity (IFPT + IFI peak). Among the Ag- and Nb-doped Cu–12Al–5Mn SMAs, Cu–12Al–5Mn–1 Nb showed not only a significantly higher hardness but also a higher IFPT + IFI peak, with tan δ exceeding 0.01 at approximately 50 °C.
Display omitted
•In Cu-based SMAs, damping capacity depends on microstructure and the volume fraction of the transformed martensite.•Alloying elements with different mechanisms affect the damping performance of Cu-based SMAs.•In Cu-based SMAs, both damping capacity and mechanical strength improve by optimizing chemical composition.
This study investigates the effect of Co additions on the damping properties of Cu-13.5Al–4Ni-xCo and Cu-14.0Al–4Ni-xCo (x = 0–2 wt%) shape memory alloys (SMAs). The Cu-14.0Al–4Ni SMA exhibits a ...higher inherent and intrinsic internal friction (IFPT + IFI) peak than the Cu-13.5Al–4Ni SMA, but its (IFPT + IFI) peak temperature is below 0 °C. Adding Co into the Cu-14.0Al–4Ni SMA can effectively increase the (IFPT + IFI) peak temperature and reduce the grain size of the alloys. The grain size of the Cu-14.0Al–4Ni-xCo SMAs decreases from approximately 300 μm to below 50 μm when the Co content increases from 0 to 2 wt%. The (IFPT + IFI) peak temperature for the Cu-14.0Al–4Ni-xCo SMAs increases from −0.1 °C to 77.7 °C when the Co content increases from 0 to 1 wt%, but their tan δ values decrease from 0.0402 to 0.0090 simultaneously. The Cu-14.0Al–4Ni–2Co SMA does not exhibit an observable (IFPT + IFI) peak. The tan δ values of the (IFPT + IFI) peaks decrease with increasing Co content because the movements of the parent/martensite phase interfaces and twin boundaries are impeded by the increased amounts of grain boundaries and γ2 phase precipitates. Among these Cu–Al–Ni–Co SMAs, the Cu-14.0Al–4Ni-0.5Co SMA is more suitable for high-damping applications as it possesses an (IFPT + IFI) peak with tan δ close to 0.02 at approximately 50 °C.
•Adding Co into Cu–Al–Ni SMAs can increase the (IFPT + IFI) peak temperature.•Adding Co into Cu–Al–Ni SMAs can reduce the grain size of the alloys.•The tan δ values of Cu–Al–Ni–Co SMAs decrease with increasing Co content.•Cu-14.0Al–4Ni-0.5Co possesses an (IFPT + IFI) peak with tan δ close to 0.02 at 50°C.
This study assessed the feasibility of using a plasma-modified Ni foam as an anode to improve the electrochemical performance of double-chamber microbial fuel cells (MFCs). Scanning electron ...microscopy results showed that Ni foam exhibited an open cellular structure and rough surface morphology, providing a large contact area between bacteria and anodes in the MFCs. N 2 plasma modification did not influence the surface morphology of the Ni foam, whereas the hydrophobic surfaces of the Ni foam became highly hydrophilic. X-ray photoelectron spectrometer results revealed that Ni–N and NH 3 functional groups, formed on the surface of the Ni foam during the N 2 plasma modification, were responsible for its highly hydrophilic surface. Electrochemical measurements demonstrated that the highest power density of the MFC configured with an unmodified Ni foam anode electrode (166.9 mW m −2 ) was much higher than those of the MFCs configured with dense Ni rod (5.1 mW m −2 ) or graphite rod (29.5 mW m −2 ) anodes because Ni foam combined the advantages of an open cellular structure and good electrical conductivity. The highest power density of MFC configured with Ni foam was further improved to 247.1 mW m −2 after 60 min N 2 plasma treatment owing to the high hydrophilicity of the N 2 plasma-modified Ni foam electrodes, which facilitated bacteria adhesion and biofilm formation.
This study assessed the feasibility of using a plasma-modified Ni foam as an anode to improve the electrochemical performance of double-chamber microbial fuel cells (MFCs). Scanning electron ...microscopy results showed that Ni foam exhibited an open cellular structure and rough surface morphology, providing a large contact area between bacteria and anodes in the MFCs. N
2
plasma modification did not influence the surface morphology of the Ni foam, whereas the hydrophobic surfaces of the Ni foam became highly hydrophilic. X-ray photoelectron spectrometer results revealed that Ni-N and NH
3
functional groups, formed on the surface of the Ni foam during the N
2
plasma modification, were responsible for its highly hydrophilic surface. Electrochemical measurements demonstrated that the highest power density of the MFC configured with an unmodified Ni foam anode electrode (166.9 mW m
−2
) was much higher than those of the MFCs configured with dense Ni rod (5.1 mW m
−2
) or graphite rod (29.5 mW m
−2
) anodes because Ni foam combined the advantages of an open cellular structure and good electrical conductivity. The highest power density of MFC configured with Ni foam was further improved to 247.1 mW m
−2
after 60 min N
2
plasma treatment owing to the high hydrophilicity of the N
2
plasma-modified Ni foam electrodes, which facilitated bacteria adhesion and biofilm formation.
Plasma-modified Ni foam electrodes are suitable for MFCs because they combine the advantages of high surface area structures and good electrical conductivity.
The main aim of the present research was to investigate the effects of a ternary nitrate salt (NaNO
3
-KNO
3
-LiNO
3
) on high-temperature corrosion behaviour of stainless steel 321 (SS 321) in a ...parabolic trough collector in a concentrating solar power system. The corrosion behaviour of SS − 321 was examined in a ternary salt (LiNO
3
(25 wt-%)-NaNO
3
(25 wt-%)-KNO
3
(50 wt-%)) at 400°C and 550°C for 250 h, 500 h and 1000 h, and the obtained findings were then compared with the results of a solar salt ((NaNO
3
(60 wt-%)-KNO
3
(40 wt-%)). In order to determine the quantitative corrosion behaviour of SS − 321, the results of immersion tests and microstructural investigations obtained through scanning electron microscopy and energy-dispersive X-ray microanalysis were also considered. It was found that the addition of lithium nitrate (LiNO
3
) to solar salt formed resistant oxide layers on the surface of SS 321 and subsequently, increased its corrosion resistance ability.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Ultrafine-grained (UFG) pure copper has been in the focus of materials scientists over the last two decades, however ultrafine-grained high-strength copper alloys have scarcely been processed or ...characterized so far industrially.In this contribution, UFG copper alloys, especially Cu-Ni-Si alloys, being well known as ideal materials for electromechanical connectors, springs and leadframes, are presented. Precipitation hardened Cu-Ni-Si alloys are a well established and technologically important class of materials for a wide range of applications where high strength and good conductivity are required. Yield strength and fatigue properties of metallic alloys can be significantly enhanced by severe plastic deformation methods. In contrast to other strengthening methods such as solid solution hardening, severe plastic deformation leads to a weaker decrease of electrical conductivity and is therefore a means of enhancing strength while maintaining acceptable conductivity for current bearing parts and components. Characterization of these materials after severe plastic deformation by swaging, wire drawing and subsequent aging was carried out using conductivity-, hardness-and tensile tests as well as highly-resolved microstructural characterization methods.The results reveal that UFG low alloyed copper alloys exhibit impressive combinations of properties such as strength, conductivity, high ductility as well as acceptable thermal stability at low and medium temperatures. By a subsequent aging treatment the severely plastically deformed microstructure of Cu-Ni-Si alloys can be further enhanced and thermal stability can profit from grain-boundary pinning by precipitated nanoscale nickel silicides.
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