Short-time processing route has been designed to manufacture cost-affordable and high-quality powder metallurgy (PM) metastable β titanium alloy, containing rapid powder consolidation (modified ...thermomechanical pressing), one-step thermomechanical processing (simple open die uniaxial hot forging by industrial press) and fast heat treatment (one-step annealing at various temperatures for only one hour). Based on comprehensive microstructure characterizations and mechanical property examinations, underlying microstructural evolution mechanism and microstructure-property relationship of the produced alloys were uncovered and elucidated thoroughly. Homogeneous macrostructure and fine-grain microstructure without undissolved particles and large pores are obtained for the alloy after thermomechanical powder consolidation as a result of the concurrent effect of external deformation and high-temperature diffusion. One-step open-die forging is verified to produce full-dense and sound PM alloy pancake with large-scale and high strength. Attributed to the harmonious concurrence of hierarchical α precipitation and heterogeneous grain structure, synergistic strength-ductility combinations are achieved for the alloy after specific processing and heat treatment with the tensile strength and strain at failure values of 1386.5 MPa/7.3% and 1252.3 MPa/9.0%, respectively. These strength-ductility combinations are comparable and/or even better than other metastable β titanium alloys prepared by some PM and ingot metallurgy approaches with relatively high cost and time consumption.
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•Short-time processing route is designed to produce cost-affordable and high-quality powder metallurgy titanium alloy.•Rapid consolidation, one-step processing and fast heat treatment are applied to minimize the manufacturing cost and time.•Superior strength-ductility combinations are achieved for the alloy after specific processing and fast heat treatment.•The excellent mechanical properties are comparable to other expensive and time-consuming metastable β titanium alloys.
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•A toughened ZrO2/MgO nanocomposite coating is in-situ synthesized during the plasma electrolytic oxidation process (PEO).•The ZrO2/MgO toughening behavior occurs with dislocation ...slipping and pinning caused by semicoherent interface lattice distortion.•The toughness (KIC) of the ZrO2/MgO nanocomposite coating is 2.7 times that of the traditional PEO coating.
Ceramic coatings are in general a kind of brittle material because they are predominantly made up of ionic crystals that avoid dislocation motion caused by lattice distortion. In this regard, a remarkable toughened ZrO2/MgO nanocomposite coating is obtained by the plasma electrolytic oxidation (PEO) process and in-situ synthesized ZrO2 with quantitative control approach. It is revealed that the toughening behavior of the ZrO2/MgO coating is related to the coordination and diversion of lattice distortion at the metallic oxide interface, which induces distinct dislocation motion at the interface. The semicoherent interface between m-ZrO2 and MgO is verified to act as a buffer to realize toughening of the nanocomposite coating through dislocation slipping induced by lattice coordinated distortion. Simultaneously, significant interfacial lattice distortion transfer and dislocation pinning are discovered at the semicoherent interface between t-ZrO2 and MgO, which are beneficial to toughness enhancement of the nanocomposite coating. The results indicate that the toughening effect occurs along with dislocation slipping and pinning caused by lattice distortion of the ZrO2/MgO semicoherent interface, which enables the toughness of novel nanocomposite coating to reach 2.7 times of the traditional PEO coating.
Titanium alloys are widely used in aerospace, chemical, biomedical and other important fields due to outstanding properties. The mechanical behavior of Ti alloys depends on microstructural ...characteristics and type of alloying elements. The purpose of this study was to investigate the effects of different Cu contents (2.5 wt.%, 7 wt.% and 14 wt.%) on mechanical and frictional properties of titanium alloys. The properties of titanium alloy were characterized by tensile test, electron microscope, X-ray diffraction, differential scanning calorimetry, reciprocating friction and wear test. The results show that the intermediate phase that forms the eutectoid structure with α-Ti was identified as FCC Ti2Cu, and no primary β phase was formed. With the increase of Cu content, the Ti2Cu phase precipitation in the alloy increases. Ti2Cu particles with needle structure increase the dislocation pinning effect on grain boundary and improve the strength and hardness of titanium alloy. Thus, Ti-14Cu shows the lowest elongation, the best friction and wear resistance, which is caused by the existence of Ti2Cu phases. It has been proved that the mechanical and frictional properties of Ti-Cu alloys can be adjusted by changing the Cu content, so as to better meet its application in the medical field.
A CoCrCuFeNiTi0.8 high-entropy alloy was prepared using directional solidification techniques at different withdrawal rates (50 μm/s, 100 μm/s, 500 μm/s). The results showed that the microstructure ...was dendritic at all withdrawal rates. As the withdrawal rate increased, the dendrite orientation become uniform. Additionally, the accumulation of Cr and Ti elements at the solid/liquid interface caused the formation of dendrites. Through the measurement of the primary dendrite spacing (λ1) and the secondary dendrite spacing (λ2), it was concluded that the dendrite structure was obviously refined with the increase in the withdrawal rate to 500 μm/s. The maximum compressive strength reached 1449.8 MPa, and the maximum hardness was 520 HV. Moreover, the plastic strain of the alloy without directional solidification was 2.11%, while the plastic strain of directional solidification was 12.57% at 500 μm/s. It has been proved that directional solidification technology can effectively improve the mechanical properties of the CoCrCuFeNiTi0.8 high-entropy alloy.
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.
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.
By introducing ceramic SiC particles, AlxCoCrFeNiTi1-x/SiC (x = 0.5,0.8 in molar ratio) high entropy alloy coatings (abbreviated as Al0.5, Al0.8, Al0.5/SiC, and Al0.8/SiC alloy coating respectively) ...were fabricated by laser cladding (LC) on the AISI1045 steel in this work. The microstructures, phase constitutions, mechanical and corrosion-resisting behaviors of the as-prepared coatings with and without SiC particles were investigated and compared intensively. It was found that the added SiC particles decomposed into the Si and C during the LC processing, which was verified to have a significant influence on constructing microstructures of the alloy coatings. The cuboidal L21 precipitates within the disordered BCC matrix in Al0.5 alloy coating transformed to the coarse lath-like microstructures composed by the L21 and FCC matrix in Al0.5/SiC. Simultaneously, the more refined braided network structures were obtained in Al0.8/SiC alloy coating, corresponding to the increased volume fraction of the B2 phase. The microhardness of the Al0.8/SiC alloy coating improved from 637 HV0.2 in Al0.8 to 718 HV0.2, and the coefficient of friction decreased from 0.40 to 0.31 with the SiC addition. In contrast, the SiC particles showed a negative effect on the microhardness of Al0.5/SiC alloy coating from 743 HV0.2 to 679 HV0.2, as a result of coarsened microstructure and increased fraction of the supple FCC solid solution. The friction coefficient reaches its lowest value of 0.29 in Al0.5 alloy coating, and there is a mixture wear mechanism of wear and delamination wear. Furthermore, the pitting potentials of both the Al0.5/SiC and Al0.8/SiC were lower than that of the SiC-free alloy coating. With the dissolution of SiC particles, the prompted spinodal decomposition and enlargement of lattice misfits between phases reduced the coatings' resistance to pitting corrosion.
•Ceramic-reinforced composites of AlXCoCrFeNiTi1-X HEA coatings without cracks were successfully prepared on the AISI1045 steel.•The added SiC particles are verified to have a significant influence on constructing microstructures of the alloy coatings.•Considerably enhanced microhardness and wear resistance were obtained in a SiC-added alloy coating, resulting from the more refined microstructure.
In this work, Ni-Mo-SiC-TiN composite coatings were prepared by pulse electrodeposition. Through analyzing the effect of particle content on the phase structure and morphology of Ni-Mo coatings, the ...relationship between nanoparticles co-deposition amount and the mechanical properties and corrosion resistance of Ni matrix composite coatings was evaluated. The results show that the coating prepared at an electrolyte concentration of 20 g/L is flat and dense presenting the highest particle content. The crystallite size ranging from 28.27 nm to 11.85 nm is affected by different nanoparticle concentrations. As shown by the Tafel polarization and wear test, the incorporation of two hard particles improved the coating performance, and the corrosion current density was reduced by 74% to 1.84 μA/cm2. The wear rate decreased from 10.196 × 10−4 mm3/N·m to 2.65 × 10−4 mm3/N·m, and the average friction coefficient decreased to 0.11. The duplex hard particles play a bearing and hindering role during friction and corrosion. Based on the co-deposition kinetic model, a five-step pulse deposition model referring to nanoparticles was established. It is found that SiC/TiN particles co-deposited to the preferential Ni (111) crystal face and subordinate Ni (200) face. And the good binding ability between the matrix and the nanoparticles results in a high load transfer effect, thus enhancing the tribological properties of the coating. Moreover, the interaction between the duplex nanoparticles was further discussed.
In this work, mechanical properties, microstructure evolution mechanism, texture variation process and deformation mechanism of a near-α CT20 titanium alloy with different hot and cold rolling ...reductions are investigated and uncovered comprehensively. The tensile strength of the alloy gradually increases, and the ductility decreases as the rolling reduction grows along both rolling direction (RD) and transverse direction (TD) due to the increase in grain boundary and dislocation density, while the mechanical properties along RD are better than those along TD. The high strain carried in α phases reduces the proportion of high-angle grain boundaries and increases the content of low-angle grain boundaries, with growing dislocation density in α phase. During cold rolling process, basal slip shifts {0001} pole toward ND, and prismatic slip inclines {11 2‾0} pole and {10 1‾ 0} pole toward TD. The intragranular orientation is enhanced with increasing rolling reduction, and the texture intensity of α and β phase is weakened as rolling reduction gradually grows. It is also noteworthy that prismatic slip dominates the slip mode along RD, while basal slip and pyramidal slip are activated along TD during cold rolling. The work-hardening rates of cold-rolled alloys are higher than that of the hot-rolled alloy as a large number of dislocations and grain boundaries were introduced by severe plastic deformation. The different work-hardening rates and mechanical properties of the rolled alloy along RD and TD are verified to be associated with the preferred orientation of α phase and the slip distances of dislocation during deformation.
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