Magnesium (Mg) alloys are popular among structural materials due to their high specific strength and good machinability. However, poor corrosion resistance limits its application in harsh ...environments, which requires ceramic coating to overcome the shortage of corrosion sensitivity. In this work, ZrO2/MgO ceramic coating was in situ synthesized by plasma electrolytic oxide (PEO) technology, coatings with different pore structures were fabricated by adjusting the pH of the electrolyte, and X-ray computed tomography (XCT) is used to quantitatively investigate the pore structure in ceramic coating. As the pH of the electrolyte increases from 3 to 12, the Zr(OH)4 colloidal particles from electropositive to electronegative charges. Electropositive Zr(OH)4 moves to the anode by diffusion, while electronegative Zr(OH)4 participates in the growth of the coating by electromigration. Due to the electromigration mode at pH = 12, the ZrO2 deposited around the pores caused a change in the pore structure from interconnected to isolated, which resulted in a reduction of the overall porosity to 8.06%. Isolated pores effectively prevent the penetration of corrosive media, resulting in the corrosion current density (icorr) being nearly 46 times lower than the coating with pH = 3. This study presents a novel strategy of adjusting pore structure to enhance the corrosion resistance of ZrO2 ceramic coating, which may have implications for various applications.
In this work, the microstructure evolution characteristics after 3% pre-strained at different strain rates are elaborated to reveal the effect on the mechanical behavior of dual-phase steel. The ...results showed the strain field simulated by the representative volume element model shows obvious strain heterogeneity, and the degree of strain localization intensifies with the increase of the strain rate. There is sufficient time to complete the dynamic transition among geometrically necessary dislocations (GNDs)-low-angle grain boundaries (LAGBs)-middle angle grain boundaries (MAGBs)-high angle grain boundaries (HAGBs) at low strain rates (10−4 s−1∼10−3 s−1), thereby releasing strain distortion energy. As the strain rate increases, the transformation process from LAGBs to HAGBs is hindered due to the shortened strain response time. It can promote the accumulation of high-density GNDs and LAGBs inside the grains, which intensifies strain localization. The incomplete evolution of the microstructure caused by the pre-strain history becomes a resistance to dislocation motion during re-deformation, and more importantly, the higher the strain rate, the more severe the hardening rate loss. This leads to an increase in yield strength and a decrease in uniform elongation, which drastically deteriorates the mechanical stability of the steel.
Tensile tests were carried out on X80 steel girth welds with four different parameters (no deviation of welding parameters, inadequate number of welding layers, inadequate preheating temperature and ...inadequate interpass temperature) under automatic welding technology. The strain distribution behavior, strain hardening law and the influence of welding parameter deviation on mechanical properties were studied during tensile deformation. The results show that the strain localization occurs at the interface of the weld filler layer when the preheating temperature of the weld is inadequate and the interpass temperature of the weld is inadequate, and the strain localization occurs at the maximum thickness of the filler layer when the number of welding layers is inadequate. The deviation of welding parameters significantly reduces the strength of girth weld. The yield strength and tensile strength are the lowest when the interpass temperature is inadequate. When the interpass temperature is inadequate, the strain hardening ability deteriorates rapidly. When there is no deviation of welding parameters, the fracture is dimple shaped, which is typical ductile fracture. When the welding parameters deviate, the fracture of the girth weld is a mixed fracture of toughness and brittleness; When the number of welding layers is inadequate, it is mainly brittle fracture; When preheating temperature and interpass temperature are inadequate, ductile fracture is the main mechanism.
This work aims to improve the properties of aluminum foams including the mechanical properties and corrosion resistance by electrodepositing a SiC/TiN nanoparticles reinforced Ni–Mo coating on the ...substrate. The coatings were electrodeposited at different voltages, and the morphologies of the coating were detected by SEM (scanning electron microscope) to determine the most suitable voltage. We used XRD (x-ray diffraction) and TEM (transmission electron microscope) to analyze the structure of the coatings. The aluminum foams and the substrates on which the coatings were electrodeposited at a voltage of 6.0 V for different electrodeposition times were compressed on an MTS (an Electro-mechanical Universal Testing Machine) to detect the mechanical properties. The corrosion resistance before and after the electrodeposition experiment was also examined. The results showed that the coating effectively improved the mechanical properties. When the electrodeposition time was changed from 10 min to 40 min, the Wv of the aluminum foams increased from 0.852 J to 2.520 J and the σs increased from 1.06 MPa to 2.99 MPa. The corrosion resistance of the aluminum foams was significantly improved after being coated with the Ni–Mo–SiC–TiN nanocomposite coating. The self-corrosion potential, pitting potential, and potential for primary passivation were positively shifted by 294 mV, 99 mV, and 301 mV, respectively. The effect of nanoparticles on the corrosion resistance of the coatings is significant.
Strain hardening remains challenging for maintaining the plasticity of metals, especially those of high strength. The hetero-deformation induced (HDI) stress can effectively alleviate the problem, ...specifically with a large mechanical response mismatch. Accordingly, the strain localization and hardening in dual-phase steel consisting of ductile ferrite (F) and almost undeformed bainite (B) were investigated by calculating HDI stress (σh) based on the tensile load-unload-reload (LUR) hysteresis loop and modified equation. Of particular note is that strain localization first appears in the ferrite, and then transfers to the F/B interface during tensile LUR. The generated σh by the accumulation of geometrically necessary dislocations (GNDs) inhibits the mobile dislocation, thereby reducing the strain difference, which promotes the transfer of strain localization. The transformation of strain localization changes the hardening behavior from ferrite hardening to F/B interfacial hardening. The results state clearly that the σh enhances strain hardening while induced strain localization maintains tensile plasticity. Eventually, with the increase σh, the failure of dual-phase steel tends to transition from initial ductile fracture to brittle fracture.
•Strain localization first appears in the ferrite, and then transfers to the ferrite/bainite interface.•The HDI stress by the accumulation of GNDs inhibits the dislocation motion, the hardening behavior from ferrite hardening to F/B interfacial hardening.•The HDI stress induces strain localization and hardening, which ameliorates the strength and tensile plasticity of the dual-phase steel.•The failure of heterogeneous structure tends to transiter from ductile fracture to brittle fracture.
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Superplastic behavior and deformation mechanism of Ti600 alloy Zhang, Xuemin; Cao, Leilei; Zhao, Yongqing ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
01/2013, Letnik:
560
Journal Article
Recenzirano
The superplastic deformation behavior and mechanism of Ti600 alloy at elevated temperature were investigated. Results show that Ti600 alloy exhibits excellent superplastic behavior in the temperature ...range of 840–960°C at 5×10−4s−1 and all of the tensile elongations exceed 220%. Optical microstructure shows that the grains still remain equiaxed and refined after deformation. However, primary α phase increases with the increasing of temperature. TEM observation indicates that the intragranular dislocation movement is very active and is accompanied by the occurrence of dynamic recrystallization, which is beneficial to promote the grainboundary sliding and to relieve the stress concentration. The superplastic deformation mechanism of Ti600 alloy is grainsgroup sliding accommodated by dislocation movement and dynamic recrystallization. The model of this mechanism is a corrected Ball–Hutchinson Model.
Fe-based amorphous powder and shell-core-structured composite powder prepared by ball-milling Fe-based amorphous powder with 10wt.% Ni/Al powder, were used to fabricate Fe-based amorphous coating and ...Fe-based amorphous composite coating by plasma spray process, respectively. X-ray diffraction (XRD) analysis results showed that the composite coating was comprised of multi-component amorphous Fe62.8Ni13.6Cr9.9Mo8.6Si1.6C2.3B0.9 layer and crystalline Ni3Al layer. Compared with Fe-based amorphous coating, the composite coating exhibited a more compact structure. The corrosion resistance of Fe-based amorphous coating, which was tested by potentiodynamic polarization method in 3.5wt.% NaCl solution, was significantly improved by using shell-core-structured composite powder. The composite coating showed lower corrosion current density (12.5μA/cm2) and passive current density (9.0mA/cm2) than Fe-based amorphous coating. The improved corrosion resistance of the composite coating is attributed to the dense structure and the formation of passivation film.
In this work, a CuCe alloy was prepared using a directional solidification method at a series of withdrawal rates of 100, 25, 10, 8, and 5 μm/s. We found that the primary phase microstructure ...transforms from cellular crystals to cellular peritectic coupled growth and eventually, changes into dendrites as the withdrawal rate increases. The phase constituents in the directionally solidified samples were confirmed to be Cu
Ce, CuCe, and CuCe + Ce eutectics. The primary dendrite spacing was significantly refined with an increasing withdrawal rate, resulting in higher compressive strength and strain. Moreover, the cellular peritectic coupled growth at 10 μm/s further strengthened the alloy, with its compressive property reaching the maximum value of 266 MPa. Directional solidification was proven to be an impactful method to enhance the mechanical properties and produce well-aligned in situ composites in peritectic systems.
Diffusion reaction was a crucial route to enhance the wear resistance of Ti-6Al-4V alloys surface. In this work, the Ni/Cu/Ni composite layers were fabricated on the surface of Ti-6Al-4V alloy by ...electroplate craft, and then different annealing temperatures were applied to further optimize its tribological properties. The diffusion behaviors at various temperatures were systematically analyzed to reveal the physical mechanism of the enhanced tribological properties of the coatings. It was demonstrated that Cu
Ti
and Ni
Ti
intermetallic compounds with high hardness and strength were produced in the Ni/Cu/Ni coating, which acted as the reinforcing phases and improved the microhardness, reduced the friction coefficient, and lessened the wear rate. Specially, this effect reached the maximum when the annealing temperature was 800 °C, showing excellent wear resistance. This work revealed the relationship between annealing temperatures and tribological properties of the Ni/Cu/Ni coating, and proposed wear mechanism, aiming to improve the surface performance of Ti-6Al-4V alloy by appropriate diffusion behavior.
In this paper, micro harmonic vibration was applied to the typical titanium alloys to clarify their damping performance at cryogenic temperatures. The effects of vibration modulus at different ...frequencies were elaborately analyzed, and the crack propagation mechanism was discussed. The increase of internal dislocations improves the damping performance and eventually leads to interface cracking, which is positively correlated with frequency. More importantly, dislocations of β phase aggregated at the interface, leading to interface cracks and transgranular fractures by stress concentration. Whereas, dislocations in the α phase are first activated and then glide toward the boundary to cause cracking, resulting in intergranular fracture. During harmonic vibration at 0∼−60 °C with 200 Hz, the crack propagation of α phase always has a hysteresis behavior compared with that of β phase. When ΔK = 0.137 MPa m1/2 (−60 °C, 200 Hz), the second crack tip of β phase is deflected in different directions, leading to higher harmonic vibration energy is consumption. As a result, the crack growth rate slows down and the damping performance reaches its peak. This contribution is expected to provide experimental data and theoretical support for the vibration damping behavior of typical titanium alloys at cryogenic temperature.
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