Thermally-induced microstructure and property alteration of nano-multilayer (NML) coatings are of principal importance for industrial applications. The phenomenon of surface outflow of confined metal ...is highly promising for the development of NML-based brazing fillers for joining technology. Annealing conditions, such as temperature and atmosphere, are the principal factors defining the brazing filler outflow characteristics besides the NML design. The present study addresses the microstructure evolution of Ag/AlN NMLs during thermal treatment in various atmospheres (Ar, air, vacuum). The mechanisms of the NML bulk microstructure modification do not change with the annealing atmosphere. Channels in the NML volume are formed at each annealing atmosphere by grain boundary grooving, which act as pathways for Ag atoms transport to the NML surface, causing metal outflow. However, a significant effect of the atmosphere on the metal outflow and shape of the particles formed was observed. Annealing in an inert atmosphere and vacuum results in a moderate surface outflow of Ag atoms. On the contrary, heat treatment in air results in a chemical interaction of nanolayers with oxygen, substantially intensifying the outflow. This interaction is rationalized by considering the surface energies of Ag/AlN and Ag/Al2O3 interfaces, where the latter are formed upon annealing. Based on grooving angles, the upper bound Ag(111)/AlN(0001) interface energy estimate of 0.54 J/m2 at 650 °C was derived, which is significantly lower than the average magnitude of Ag/Al2O3 interface energy (~ 2 J/m2 for crystalline phases). Besides, the annealing atmosphere has an impact on the shape (elongated whiskers, bulk faceted crystals) of Ag particles formed on the NML surface by modifying silver surface energies.
The proper choice of a heat treatment atmosphere provides an innovative pathway for controlling the Ag surface outflow in Ag/AlN NMLs for novel low-temperature joining applications.
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•Annealing in air results in a larger Ag outflow than annealing in Ar or vacuum•At each annealing atmosphere, channels in the nano-multilayer volume are formed•The annealing atmosphere affects the shape of Ag particles formed on the surface•Chemical driving forces and stress relaxation are at the basis of Ag outflow•The estimate of Ag(111)/AlN(0001) interface energy at 650 °C is 0.54 J/m2
Surface templating of nano-multilayers is a promising step for the advanced industrial application of these nanomaterials. In the present work, the effect of focused ion beam modification of Ag/AlN ...nano-multilayer near-surface region on the Ag surface outflow is revealed. Surface patterning by ion beam irradiation leads to the formation of a higher amount of Ag crystals in relation to the intact surface region. Heat treatment initiates grooving of Ag grain boundaries, resulting in the formation of channels in the nano-multilayer volume. These channels act as pathways for mass transport of Ag to the film surface. Ion bombardment creates regions of high concentration of non-equilibrium defects, which locally increase the driving force for grooving and channeling, thereby promoting creation of more pathways for Ag surface migration. The obtained experimental results indicate that surface modification by focused ion beam can be used for production of nano-multilayers with designed templates of surface outflow.
•Ag crystals are formed on the nano-multilayer surface upon high-vacuum annealing.•The HeFIB surface modification results in a higher density of Ag crystals.•Annealing induces formation of channels in the nano-multilayer volume.
Cashew Nut Shell Liquid (CNSL) has been explored in several applications within the sustainability principles and circular economy of agro-industrial product waste. To understand the anticorrosive ...and lubricant properties of CNSL solutions, a multi-faceted approach, incorporating electrochemical analyses, immersion test, tribological measurements, and tribochemical characterization was carried out for mild steel AISI 1012, stainless steel AISI 420 and Aluminium Alloy 6061. Electrochemical analyses reveal a positive impact of CNSL, inducing a shift in corrosion potential to more positive values and a decrease in corrosion current, indicating effective corrosion inhibition for stainless steel and aluminium alloy. In mild steel, CNSL exhibits a mixed-type inhibition with efficiency increasing in correlation with oil concentration. The lubricating properties of CNSL are evident according to the coefficients of friction (COF) obtained and the elastohydrodynamic lubrication regime observed during tribological tests. Tribochemical tests demonstrate a reduction in wear and an improvement in tribocorrosion behavior under sliding conditions. CNSL emerges as a promising tribocorrosion mitigator, demonstrating multifaceted benefits. The concentration-dependent effects highlight the need for optimization in specific applications, particularly for passive materials. CNSL not only inhibits corrosion through film formation but also provides effective lubrication, reducing friction, wear, and chemical-mechanical degradation. This research contributes valuable insights to corrosion science. It proposes practical applications for CNSL in diverse industrial contexts, showcasing its potential as an environmentally friendly and sustainable solution for tribocorrosion challenges.
•The influence of Cashew Nut Shell Liquid (CNSL) on the tribocorrosion behavior across three metallic alloys (mild steel, stainless steel, and aluminium) is explored.•Electrochemical analyses, immersion test, tribological measurements, and tribochemical characterization was carried out for AISI 1012, AISI 420 and AA6061.•CNSL exhibited a positive impact on corrosion inhibition for stainless steel and aluminium alloy, inducing a shift in corrosion potential to more positive values and a decrease in corrosion current.•CNSL demonstrated lubricating properties according to the coefficients of friction (COF) obtained and the elastohydrodynamic lubrication regime observed during tribological tests.•CNSL emerges as a promising tribocorrosion mitigator, demonstrating multifaceted benefits.
Second-phase hardening in refractory high-entropy alloys (RHEAs) has been recognized as one of the main routes to significantly improve their mechanical properties. However, their costbenefit should ...not be compromised. Thus, we designed second-phase strengthened RHEAs by a low-cost powder metallurgy method. We induced the formation of FCC (face-centered cubic) ZrC second phase, which has not been reported in Ti-Nb-Zr-Ta alloys before and may be easily confused with the FCC-Zr due to the complexity of identifying carbon by conventional methods. We used neutron diffraction and electron backscatter diffraction for microstructural studies, as well as hardness, ultrasonic and compression techniques for assessing mechanical properties. Our investigation centered on equiatomic and equimassic Ti-Nb-Zr-Ta alloys, both displaying similar grain morphology and porosity but differing in grain sizes and phases. The variation in grain size was attributed to the influence of Ta as a grain growth pinning element. Our second-phase ZrC hardened alloys revealed higher stiffness and hardness, surpassing those documented in the existing literature.
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•We produced ZrC-reinforced Ti-Nb-Zr-Ta alloys by mechanical alloying.•Neutron diffraction measurements characterized FCC-ZrC in new alloys.•Phase evolution elaborated by CALPHAD and experimental results.•FCC-ZrC hardened Ti-Nb-Zr-Ta alloys showed higher stiffness and hardness.
Al
2
O
3
-13%TiO
2
coatings were deposited on stainless steel substrates from conventional and nanostructured powders using atmospheric plasma spraying (APS). A complete characterization of the ...feedstock confirmed its nanostructured nature. Coating microstructures and phase compositions were characterized using SEM, TEM, and XRD techniques. The microstructure comprised two clearly differentiated regions. One region, completely fused, consisted mainly of nanometer-sized grains of γ-Al
2
O
3
with dissolved Ti
+4
. The other region, partly fused, retained the microstructure of the starting powder and was principally made up of submicrometer-sized grains of α-Al
2
O
3
, as confirmed by TEM. Coating microhardness as well as tribological behavior were determined. Vickers microhardness values of conventional coatings were in average slightly lower than the values for nanostructured coating. The wear resistance of conventional coatings was shown to be lower than that of nanostructured coatings as a consequence of Ti segregation. A correlation between the final properties, the coating microstructure, and the feedstock characteristics is given.
Abstract
Electrical conductivity (σ), relative dielectric permittivity (ε
r
) and dissipation factor (
D
) measured in graphene-alumina composites. Samples obtained by plasma spark sintering (SPS) ...from a mixture of raw powders: δ-alumina (36 nm average particle size) and graphene flakes (3 nm thickness and 2–3 μm length). Graphene content in samples was 0, 1 and 2% by weight. The study carried out for frequencies from 50 Hz to 100 kHz. Both c and ε
r
were higher for Al
2
O
3
–2% graphene: up to 90 μS/m and 19 respectively; while alumina with 1% graphene showed similar values to the pure alumina samples: 50 μS/m to electrical conductivity and 16 to relative permittivity. The dissipation factor was similar in the three materials tested.
D
increased with the frequency, reaching high values (0.7) at 100 kHz. Composites with 1 and 2% graphene content showed a dissimilar dielectric behavior with the frequency. Alumina reflected a classical behavior of the permittivity dependence with the frequency. Graphene composites also show the same behavior at frequencies above 100 Hz. Below this frequency, the presence of graphene increases the relative permittivity to exceed that from pure alumina. The graphene content leads to rise of relative permittivity, which means easier polarizability.
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