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Micro-arc oxidation (MAO) technology, as an efficient and widely used technology, can fabricate a ceramic film on magnesium (Mg) alloys in situ to significantly improve corrosion resistance. The study aims to investigate the effect of voltage modes on the preparation and performance of MAO coating on Mg alloys. The scanning electron microscope, X-ray diffractometer, potential dynamic polarization, and electrochemical impedance spectroscopy measurements were applied for characterizing the microstructure, composition, and corrosion resistance of the MAO film, respectively. The results revealed that employed 300/350 V step-up mode, the MAO film showed a more uniform distribution of surface micro-pores, fewer micro-cracks and denser inner layer, lower corrosion current density (1.871 × 10−3 mA·cm−2), and higher electrochemical impedance value, compared to other voltage treated parameters. Therefore, it could be concluded that the step-up voltage parameters are conducive to the optimization of microstructure, improvement of corrosion resistance of MAO coating, and reduction of the energy consumption during processing. [ABSTRACT FROM AUTHOR]

Low cycle fatigue (LCF) crack initiation, propagation and damage behaviors of TC21 alloy with basketweave microstructure were investigated. The process of LCF damage was observed by a long-focus optical microscopic imaging system, and fatigue crack propagation was analyzed through in-situ SEM fatigue. The results indicated that LCF crack damage displayed different sensitivity to cyclic stress. LCF microcracks initiated from slip bands and propagated through the microcrack coalescences at high stress, while LCF cracks tended to initiate at the αL/β interface and connect with these interface microcracks. Furthermore, the LCF damage model was established on the basis of Lemaitre damage theory. When the maximum stress exceeded yield stress, LCF damage increased sharply and fatigue life decreased significantly, which agreed with experiment data. [ABSTRACT FROM AUTHOR]

Low cycle fatigue (LCF) behaviors of TC21 alloy with a bi-lamellar basketweave microstructure were investigated in this paper. The strain fatigue tests were carried out at total strain amplitudes of 1.4% to 2.0%. The cyclic stress response showed the cyclic softening behavior. In addition, the shape of the hysteresis rings exhibited a non-Masing model behavior. The cyclic stress–strain as well as the strain-life equations were obtained. The fatigue life decreased significantly with an increasing total strain from 1.4% to 2.0%. The cyclic softening behavior was interpreted by cyclic back stress and friction stress. Low cycle fatigue cracks were predominantly initiated on the surface of the samples. The relationship between the fatigue sub-critical crack and microstructure was also discussed. The cyclic deformation behavior and crack initiation mechanism were revealed on the basis of the deformation microstructure under different strain amplitudes. [ABSTRACT FROM AUTHOR]

Recent experiments have proven that the 9R phase can dramatically improve the mechanical properties of Al alloys. This work aims to investigate the effects of solute atoms on 9R phase stabilization in Al alloys through first-principles calculations. Based on two distribution models of solute atoms, namely, the uniform distribution and the Fermi–Dirac distribution models, we discuss the influences of solute concentrations and finite temperatures on the increments of intrinsic stacking fault energy in the 9R phase structure. The results reveal that high-concentration solute atoms (Ga, Ge, Sc, Si, Sn, Sr, and Y) can promote 9R phase stabilization. Among them, the Sr atom shows the highest performance, but its stabilization can be disrupted by high temperature. These findings serve as a valuable guidance for designing and using high-performance Al alloys with the 9R phase structure. [ABSTRACT FROM AUTHOR]

In this work, diphasic mullite (3Al 2 O 3 ·2SiO 2) nanofibers with good homogeneity were prepared by electrospinning method. Aluminum nitrate (AN) and aluminum isopropoxide (AIP) were used as alumina sources, commercial colloidal silica as silica source, and polyvinyl alcohol (PVA) as polymer additive. Precursor nanofibers with continuous and uniform structures were acquired at mass ratio of PVA to precursor sol from 0.06 to 0.09. γ- Al 2 O 3 phase was obtained at 878 °C and mullite phase formed at 1322 °C upon heating of the precursor under air atmosphere. Calcined samples suggested mullite as dominant phase at 1300 °C and amorphous SiO 2 could even exist at 1400 °C. As-prepared nanofibers possessed continuous structures with subequal average diameters at 900–1200 °C. However, such morphological characteristics were lost at temperatures above 1300 °C due to rapid growth of crystal grains. Al and Si elements were uniformly distributed in fibers and mixed at nanoscale, confirming homogeneity and diphasic features of nanofibers. [ABSTRACT FROM AUTHOR]

The β-type Ti35NbxCu alloys (x = 0, 1, 3, 5, and 7 wt%) were produced by laser powder bed fusion (LPBF) and the influence of Cu content on the microstructure and mechanical properties was studied. The results indicate that when the content of Cu is less than 3 wt%, Cu can diffuse completely into the Ti matrix to form solid solution without element segregation. Moreover, the elastic modulus of Ti35Nb1Cu alloy (49.1 ± 1.6 GPa) is reduced by 33 % compared to that of Ti35Nb alloy (73.2 ± 1.4 GPa). When the content of Cu exceeds 3 wt%, the eutectoid reaction is activated during the cyclic heating and rapid cooling of LPBF, and the partially supersaturated β phase is transformed into nano-scale α and Ti 2 Cu phases (β→α+Ti 2 Cu). Nano-scale Ti 2 Cu particles precipitated along β grain boundary results in a pinning effect, which inhibits the growth of β grain, hinders dislocation movement, and improves the strength of the alloy. However, when the content of Cu is 7 wt%, the dislocation density (4.179 × 1015 m−2) and the ratio of brittle phase Ti 2 Cu (8.5 %) are too high, and the stress concentration caused by the initiation of inherent micro-cracks are the main reason for the tensile brittle fracture of Ti35Nb7Cu alloy. As such, the Ti35Nb5Cu alloy has the highest tensile strength of 867.3 ± 24 MPa and the elongation reaches 11.7 ± 0.5 %. Therefore, solution strengthening of Cu, fine grain strengthening of β, dislocation strengthening, and precipitation strengthening of Ti 2 Cu are the main reasons for the excellent comprehensive mechanical properties of Ti35Nb5Cu alloy. • LPBF-produced Ti35NbxCu alloys have uniform distribution of elements. • Adding Cu to Ti–Nb alloy can refine grains and reduce elastic modulus. • LPBF-produced Ti35NbxCu alloys have only half the elastic modulus of Ti6Al4V alloy. • Ti35Nb5Cu alloy exhibits an enhanced strength-ductility synergy. [ABSTRACT FROM AUTHOR]

Abstract The hollow Fe p -reinforced Cu-matrix homogeneous immiscible alloys were successfully produced by the combination of Kirkendall effect and laser powder deposition. The microstructure and corrosion resistance depended not only on chemical composition, but also on cooling rate. When Fe content decreased from 30% to 12% and cooling rate decreased from ∼2 × 104 to ∼1 × 104 K/s, the demixing was eliminated, the mixed Fe p (α-Fe/γ-Fe) were uniformly embedded within ε-Cu matrix and the "single-void" Fe p transformed into the "multi-voids" Fe p. The "multi-voids" immiscible alloy exhibited higher corrosion resistance than the "single-void" immiscible alloy and Brass after immersing for 5 days. Highlights • Kirkendall-effect induces hollow Fe p within immiscible alloys of laser powder deposition. • Homogeneous immiscible alloys are obtained with decreasing of Fe content. • "Single-void" Fe p transforms into "multi-voids" Fe p with decreasing of cooling rate. • "Multi-voids" immiscible alloy exhibits higher corrosion resistance than Brass after immersion. [ABSTRACT FROM AUTHOR]

• The in-situ Ti-TiB composites are produced by selective laser melting. • TiB whiskers are in-situ synthesized due to the reaction of TiB 2 particles and Ti matrix. • α′-Ti grains are significantly refined with the increase in TiB 2 content. • Microhardness of the composites can be gradually enhanced with the increase in TiB 2 content. • Wear rate and worn depth of the composites decrease with increasing the TiB 2 content. In order to investigate the effect of TiB 2 contents on the microstructure and wear resistance of titanium matrix composites, commercial pure Ti (CP-Ti) powders with 0–7.5 wt.% TiB 2 particles were melted by selective laser melting (SLM) to produce the in-situ Ti-TiB composites. When the TiB 2 content increases from 2.5 wt.% to 7.5 wt.%, the microstructures of the Ti-TiB composites undergo a transition from the single phase of α′-Ti to the mixed phases of α′-Ti, TiB and TiB 2 , and the acicular α′-Ti is refined significantly from 1.03 ± 0.24 μm to 0.36 ± 0.05 μm, showing that increasing the TiB 2 content induces the formation of TiB and refines the microstructure. Moreover, large TiB 2 particles are not melted completely and they react with the Ti matrix liquid to form a TiB layer around the Ti matrix during SLM. However, small TiB 2 particles are completely dissolved into the Ti matrix liquid so that the eutectic TiB grains are precipitated at the boundaries of the Ti matrix after in-situ reaction of TiB 2 with Ti. The formation of α′ martensite in the titanium matrix and the addition of TiB 2 can induce the fine grain strengthening, the dispersion strengthening, the solid solution strengthening in the SLM-produced composites. The results indicate that the microhardness of the composites increases from 258 ± 10.3 HV 0.2 to 435 ± 14.7 HV 0.2. The wear process of the SLM-produced CP-Ti and TiB 2 reinforced Ti matrix composites is accompanied by adhesion wear, abrasive wear and oxidation wear. As a result, when the TiB 2 content increases to 7.5%, the wear resistance of the composites increases by 32.6% compared with that of the CP-Ti. These improvements are mainly due to strengthening and hardening effects induced by TiB 2 particles and refinement of Ti matrix. This study provides some basis for developing wear-resistant and high-strength titanium alloys. [ABSTRACT FROM AUTHOR]

In order to further improve the corrosion resistance of commercial pure titanium (CP–Ti), the ex-situ formed Ti-5 wt.% TiN composite was developed by selective laser melting (SLM) and the corrosion behavior of the SLM-produced CP-Ti and Ti-5 wt.% TiN composite in 0.5 M HCl solution was investigated. The results show that the Ti-5 wt.% TiN composite consists of α′-Ti, δ-TiN and ε-Ti 2 N, where the acicular α′ martensite (∼0.73 μm) is much smaller than that (∼1.37 μm) in the CP-Ti. The passive film formed on the surface of the Ti-5 wt.% TiN composite and CP-Ti is mainly composed of TiO 2. However, the Ti-5 wt.% TiN composite exhibits higher corrosion resistance than the CP-Ti, which is attributed to the fact that TiN as the micro-cathode preferentially induces the composite to enter the passivation state. The immersing tests also confirmed that the addition of 5 wt% TiN can efficiently improve the corrosion resistance of CP-Ti. Image 1 • Ti-5 wt.% TiN composite is successfully produced by selective laser melting. • SLM-produced Ti-5 wt.% TiN composite consists of Ti, δ-TiN and ε-Ti 2 N. • Addition of 5 wt% TiN can improve the corrosion resistance of CP-Ti in 0.5 M HCl solution. • SLM-produced CP-Ti mainly suffers from pitting in 0.5 M HCl solution. • Ti-5 wt.% TiN composite experiences from pitting to uniform corrosion with prolonged immersing. [ABSTRACT FROM AUTHOR]