As a crucial branch for titanium industry, high-strength titanium alloys (HS-TAs, with UTS ≥ 1100 MPa) are indispensable structural materials for advanced engineering applications such as aerospace and marine fields. Along with the expansion of HS-TAs’ market, achieving satisfying synergies of high strength, high ductility (elongation ≥ 6%) and high toughness (KIC ≥ 50 MPa⋅m1/2) has been identified as the uppermost technical bottleneck for their research and development. To overcome the challenge, two primary strategies have been initiated by the titanium community, developing novel alloys and innovating processing technologies. For the former, a dozen of newly-developed alloys were reported to exhibit excellent strength-ductility-toughness combinations, including Ti-5553, BT22, TC21 and Ti-1300, for which the ideal mechanical performances were based on specific microstructures realized by low impurity rate (e.g. oxygen content ≤ 0.15 wt%), complicated processing and complex heat treatment. For the latter, several innovatory forging and heat treatment technologies were originated for the mature alloys to optimize their balanced property by extraordinary microstructural characteristics. In this review, we provide a comprehensive overview over the research status, processing and heat treatment technologies, phase transformation, processing-microstructure-property correlation and strengthening-toughening mechanism of HS-TAs for aerospace engineering applications manufactured via melting-forging process. Finally, the prospects and recommendations for further investigation and development are proposed based on this review. 

High-strength titanium alloys for aerospace engineering applications: A review on melting-forging process

Ti and Ti alloys have charming comprehensive properties (high specific strength, strong corrosion resistance, and excellent biocompatibility) that make them the ideal choice in orthopedic and dental applications, especially in the particular fabrication of orthopedic and dental implants. However, these alloys present some shortcomings, specifically elastic modulus, wear, corrosion, and biological performance. Beta-titanium (β-Ti) alloys have been studied as low elastic modulus and low toxic or non-toxic elements. The present work summarizes the improvements of the properties systematically (elastic modulus, hardness, wear resistance, corrosion resistance, antibacterial property, and bone regeneration) for β-Ti alloys via surface modification to address these shortcomings. Additionally, the shortcomings and prospects of the present research are put forward. β-Ti alloys have potential regarding implants in biomedical fields.

β-Ti Alloys for Orthopedic and Dental Applications: A Review of Progress on Improvement of Properties through Surface Modification

Investigation on surface roughness and hardness of β-Ti alloy by ball burnishing assisted electrical discharge cladding for bio-medical applications

A novel interfacial reaction nucleation mechanism for the preparation of water-soluble Ag-In-S quantum dots (AIS QDs) was proposed in which interfacial acid regulates the concentration of hydroxide ions outside the complex and sulfur sources attack cations at the interface of the complex, covalent bonds between cations and sulfur sources are formed at the interface of the complex, and the nucleation and growth of crystals is finished at room temperature. By bypassing the heating process normally necessary for crystal nucleation and growth, AIS QDs can be produced on a large scale under simple, mild conditions. At the same time, the characteristics of this mechanism enable AIS QDs to be directly synthesized in an organic pollutant solution. This study represents a significant advance in the mechanism of crystal synthesis and contributes to the photocatalytic decomposition of organic pollutants from theory to practice.

Interfacial Nucleation Mechanism of Water-Soluble Ag-In-S Quantum Dots at Room Temperature and Their Visible Light Catalytic Performance.

CdO stellated octahedra, octahedra, {100}-truncated octahedra, and Cd(OH)2 hexagonal plates with respective average sizes of 147 nm, 700 nm, 2 m, and 105 nm have been synthesized by progressively increasing...

Morphological evolution of cadmium oxide crystals showing color changes and facet-dependent conductivity behavior

Development and heat treatment of β-phase titanium alloy for orthopedic application

Formation of CsPbCl3 Cubes and Edge-Truncated Cuboids at Room Temperature

Semiconductor crystals generally exhibit notable facet-dependent electrical conductivity and photocatalytic activity properties. If semiconductor nanocrystals of different shapes are available, their light absorption and emission bands can also display facet dependence, although bulk plus surface absorption combines to give the recorded spectra. All these physical phenomena can be understood, assuming a thin surface layer exists with slight structural deviations as predicted by density functional theory (DFT) calculations to give dissimilar band structures and hence different degrees of band bending and barriers to charge transport across a particular crystal face. This layer thereby tunes light absorption. Recent X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) analyses begin to suggest the presence of the proposed surface layer. 

Origin and manifestation of semiconductor facet effects

CdSe nanocrystals with average sizes of 15, 24, and 32 nm have been synthesized from an aqueous solution of Na2SeSO3, HCl, and cadmium nitrate at 15, 45, and 70 °C, respectively, for about 1 h. Mixing aqueous CdCl2, HNO3, and Na2SeSO3 at 22 °C for 4 h yields 44 nm CdSe nanocrystals. X-ray and electron diffraction analyses indicate the possession of a zinc blende crystal structure for all the samples. Despite the large particle dimensions, their absorption band red-shifts significantly from 520 to 570 nm with increasing particle sizes, and band gap values decrease from 2.03 eV for 15 nm particles to 1.68 eV for 44 nm crystals. Although these nanocrystals are not emissive, introduction of the cetyltrimethylammonium chloride surfactant during crystal growth can restore their photoluminescence attributed to the improved crystal quality, and the similarly sized CdSe nanocrystals have an emission band red-shifting from 544 nm for 15 nm particles to 583 nm for 47 nm crystals. A band diagram was constructed for these CdSe nanocrystals using information from Mott-Schottky plots. While they have close conduction band positions, the notable size-related band gap variation means that their valence band energies differ considerably with implications of electrochemical and photocatalytic properties. The 44 nm CdSe particles also show the smallest electrochemical charge-transfer resistance.

Gautam Kumar

Papers

Development and heat treatment of β-phase titanium alloy for orthopedic application

Formation of CsPbCl3 Cubes and Edge-Truncated Cuboids at Room Temperature

Morphological evolution of cadmium oxide crystals showing color changes and facet-dependent conductivity behavior

Origin and manifestation of semiconductor facet effects

Synthesis of Zinc Blende-Phased CdSe Nanocrystals with Size-Tunable Optical Properties and Adjustable Valence Band Positions.