In this article results from earlier studies have been compiled in order to compare the protection efficiency of self-assembled monolayers (SAM) of alkanethiols for copper, zinc, and copper–zinc ...alloys exposed to accelerated indoor atmospheric corrosion conditions. The results are based on a combination of surface spectroscopy and microscopy techniques. The protection efficiency of investigated SAMs increases with chain length which is attributed to transport hindrance of the corrosion stimulators in the atmospheric environment, water, oxygen and formic acid, towards the copper surface. The transport hindrance is selective and results in different corrosion products on bare and on protected copper. Initially the molecular structure of SAMs on copper is well ordered, but the ordering is reduced with exposure time. Octadecanethiol (ODT), the longest alkanethiol investigated, protects copper significantly better than zinc, which may be attributed to the higher bond strength of Cu–S than of Zn–S. Despite these differences, the corrosion protection efficiency of ODT for the single phase Cu20Zn brass alloy is equally efficient as for copper, but significantly less for the heterogeneous double phase Cu40Zn brass alloy.
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•Alkanethiols are efficient corrosion inhibitors for copper surfaces exposed indoors.•The protection efficiency for copper increases with alkanethiol chain length.•Corrosion protection of octadecanethiol increases as Zn<Cu40Zn<Cu20Zn≈Cu.
•Effect of ESR process on microstructure of Cu–Cr–Zr alloy was investigated.•The hardness, strength and electrical conductivity are sensitive to thermomechanical treatment.•The microstructure of the ...alloy can be optimized for obtaining the best combination of mechanical and electrical properties.
Effect of thermomechanical treatment (TMT) on aging behavior of electroslag remelted Cu–Cr–Zr alloy was investigated. The relationship between microstructure, mechanical and electrical properties was clarified using hardness, tensile and electrical conductivity testing methods and optical and scanning electron microscopy techniques. The results showed that an appropriate processing and aging treatment may improve the properties of the alloy due to the formation of fine, dispersive and coherent precipitates within the matrix. Indeed, the optimum condition for electrical conductivity and mechanical properties was obtained after cold working of 40% followed by aging at 500°C for 150min.
The effect of the preliminary high strain-rate deformation, performed via the method of dynamic channel-angular pressing (DCAP), and subsequent annealings on the tribological properties of a ...dispersionhardened Cu–0.092 wt % Cr–0.086 wt % Zr alloy has been investigated. It has been shown that the surfacelayer material of the alloy with a submicrocrystalline (SMC) structure obtained by the DCAP method can be strengthened using severe plastic deformation by sliding friction at the expense of creating a nanocrystalline structure with crystallites of 15–60 nm in size. It has been shown that the SMC structure obtained by the high strain-rate DCAP deformation decreases the wear rate of the samples upon sliding friction by a factor of 1.4 compared to the initial coarse-grained state. The maximum values of the microhardness and minimum values of the coefficient of friction and shear strength have been obtained in the samples preliminarily subjected to DCAP and aging at 400°С. The attained level of microhardness is 3350 MPa, which exceeds the microhardness of the alloy in the initial coarse-grained state by five times.
•Thermal analysis of copper alloys valve seat was investigated.•Engine cylinder head is subdivided into several boundary condition zones.•Thermal data in the zones are extracted to assess the ...transient thermal simulation.•Copper alloys valve seat shows improvement in the thermal characteristics.•Thermal data enable to identify zones subjected to highest temperatures.
The valve seat insert is a component of the engine cylinder head, whose primary function is to seal the combustion chamber and absorb the valve's heat, releasing it to the engine cylinder head. The valves experience high temperatures owing to high thermal loading and low heat absorption in the valve seat, which can potentially damage the engine. Therefore, the thermal characteristics of the valve seat must be optimised to increase the heat transmission between the valve and its seat. Here, three copper alloy valve seats, brass, beryllium copper, and bronze copper, were tested against the existing sintered iron valve seat, and their temperature maps were determined using actual engine operation conditions. The instantaneous heat transfer coefficients of the valves, seats, and engine cylinder head during the four-stroke cycle were evaluated using a one-dimensional thermal simulation analysis. The values obtained were used to assess the finite-element model using a three-dimensional thermal simulation in the Ansys software. The results show that the brass, beryllium-, and bronze-copper valve seats increased the overall heat flux by 4.46%, 4.16%, and 2.06%, respectively, compared to those for sintered iron. Thus, the results are essential to improve the thermal characteristics of the copper alloy valve seat imposed on the cylinder head. For validation, an experimental engine thermal survey and uncertainty magnification factors were used to validate the model. The results indicate that the maximum difference between the simulation and experimental values is 8.42%. Therefore, this approach offers a direct and comprehensible application for evaluating the temperature distribution, heat gradient, and heat flux of the cylinder head of air-cooled spark-ignition moped motorcycle engines using copper alloy valve seat materials at intermediate engine speeds. Furthermore, this method is applicable as a platform for the automotive industry to improve the heat transfer of the structural parts of internal combustion engines.
Herein, we have investigated the structural, mechanical, magneto-electronic and thermoelectric properties of Vanadium-based Heusler alloy
V
2
FeGe
via the full-potential linearized augmented plane ...wave (FP-LAPW) method. The calculated equilibrium ground states of properties reveal that the compound favor the XA-type configuration with a ferromagnetic state. Due to the strong
d
-electron correlations, we have used the GGA
+
U approach to improve the magneto-electronic properties. The magneto-electronic calculation shows a half-metallic behavior with an integer magnetic moment and large band gap in majority spin channel. The calculated elastic properties show that the compound satisfied the criteria stability and the elastic moduli indicated that the studied compound was ductile and anisotropic material. Finally, the thermoelectric responses were computed to explore the potential of this compound and their analysis results are discussed in detail.
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In the wide group of thermoelectric compounds, the half-Heusler ZrNiSn alloy is one of the most promising materials thanks to its thermal stability and narrow band gap, which open it to the ...possibility of mid-temperature applications. A large variety of defects and doping can be introduced in the ZrNiSn crystalline structure, thus allowing researchers to tune the electronic band structure and enhance the thermoelectric performance. Within this picture, theoretical studies of the electronic properties of perfect and defective ZrNiSn structures can help with the comprehension of the relation between the topology of defects and the thermoelectric features. In this work, a half-Heusler ZrNiSn alloy is studied using different defective models by means of an accurate Density Functional Theory supercell approach. In particular, we decided to model the most common defects related to Ni, which are certainly present in the experimental samples, i.e., interstitial and antisite Ni and a substitutional defect consisting of the replacement of Sn with Sb atoms using concentrations of 3% and 6%. First of all, a comprehensive characterization of the one-electron properties is performed in order to gain deeper insight into the relationship between structural, topological and electronic properties. Then, the effects of the modeled defects on the band structure are analyzed, with particular attention paid to the region between the valence and the conduction bands, where the defective models introduce in-gap states with respect to the perfect ZrNiSn crystal. Finally, the electronic transport properties of perfect and defective structures are computed using semi-classical approximation in the framework of the Boltzmann transport theory as implemented in the Crystal code. The dependence obtained of the Seebeck coefficient and the power factor on the temperature and the carrier concentration shows reasonable agreement with respect to the experimental counterpart, allowing possible rationalization of the effect of the modeled defects on the thermoelectric performance of the synthesized samples. As a general conclusion, defect-free ZrNiSn crystal appears to be the best candidate for thermoelectric applications when compared to interstitial and antisite Ni defective models, and substitutional defects of Sn with Sb atoms (using concentrations of 3% and 6%) do not appreciably improve electronic transport properties.
The microstructure evolution in the as-cast pure Cu and Cu-(1.0–3.0)Fe-0.5Co and Cu-1.5Fe-0.1Sn (wt. %) alloys was characterised in the previous work. Herein, the plastic deformation characteristics ...were examined by uniaxial tensile tests at room temperature. Along with the microstructure evolution, the yield strength increased with increasing Fe content and reached a peak value at 1.5 wt % Fe, but thereafter decreased with the further addition of Fe in the Cu–Fe–Co alloys. Nevertheless, the tensile strength and elongation synchronously improve with increasing Fe content. In particular, the Cu-1.5Fe-0.1Sn alloy achieved the optimal strength–ductility combination. In terms of the strengthening mechanism, the (Fe, Co)- or (Fe, Sn)-doped copper encouraged impediment, trapping, and storage of dislocations by the iron-rich nanoparticles and grain boundaries, which enhanced the strength and sustained the work hardening and elongation. The evolution of mechanical properties under an alloying effect was quantitatively described by the strengthening models. The results indicate that the optimum balance between strength and ductility was achieved by designing a microstructure containing fine grains, intragranular smaller spherical nanoparticles, and a minor solute element with higher misfit and higher growth restriction effect. The necessities for engineering a microstructure to achieve simultaneously strong and ductile bulk metals were discussed.
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•Microstructure evolution involving grain and iron-rich nanoparticle was investigated.•Mechanical properties of copper were tailored by alloying with different Fe, Co, Sn content.•Mechanism of properties evolution was discussed.•Insight to optimize microstructure for optimum mechanical properties was proposed.
Micro-liquid floated gyroscopes are widely used in nuclear submarines, intercontinental missiles, and strategic bombers. The machining accuracy of micro-ball sockets determined the motion accuracy of ...the rotor. However, it was not easily fabricated by micro-cutting because of the excellent physical and chemical properties of beryllium copper alloy. Here, we presented a linear compensation of tool electrode and a proportional variable thickness method for milling micro-ball sockets in C17200 beryllium copper alloy by micro-electrical discharge machining. The machining parameters were systematically investigated and optimized to achieve high-precision micro-ball sockets when the
value was 0.98 and the initial layer thickness was 0.024 mm. Our method provided a new way to fabricate micro-ball sockets in C17200 with high efficiency for micro-liquid floated gyroscopes.
This work deals with the influence of gallium addition on the constitution and formation of the phases in the Al-rich corner of the Al–Mn system during casting. Al-rich binary Al–Mn and ternary ...Al–Mn–Ga alloys were cast into a copper mould with a cavity diameter of 5 mm. The microstructures of the produced alloys were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction and X-ray diffraction. The characterization revealed the presence of αAl, Al6Mn, λ-Al4Mn, L-Al4Mn, icosahedral quasicrystals (IQCs) and decagonal quasicrystals (DQCs). As the amount of gallium in the synthesized alloys increased, the proportion of the phases varied and IQCs and DQCs were formed. Microanalysis revealed that IQCs contained more gallium and less manganese than DQCs.
•Binary Al–Mn and ternary Al–Mn–Ga alloys were cast in a copper mould and characterized by SEM, EDS, EBSD and XRD.•Characterization of the alloys shows that αAl, Al6Mn, λ-Al4Mn, L-Al4Mn, IQCs and DQCs are present.•The EDS microanalysis shows that more gallium is present in the IQCs than in the DQCs.•The results reveal that with the addition of gallium to the binary Al–Mn system, L-Al4Mn, IQCs and in some cases DQCs form.
We report the structural disorder effect on magnetic and electric transport properties of
Ni
50
Mn
35
In
15
Heusler alloy (HA) films. Two sets of samples were investigated: disordered (partially ...amorphous) and ordered (crystalline with
L2
1
structure) samples. Electric transport measurements vs. temperature shows that the process of structural ordering is accomplished with a two-stage drop in resistivity at 570 and 630 K which are ascribed to crystallization and
L2
1
-type structural ordering, respectively. Ordered films show a metallic and magnetization behavior typical for
Ni
50
Mn
35
In
15
HA. By contrast, disordered films show ten times lower saturation magnetization with comparable effective magnetization determined from ferromagnetic resonance. We explain this difference as the unusual effect of the inhomogeneous microstructure of the disordered films consisting of Ni clusters embedded in a nonmagnetic matrix.
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