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60NiTi alloy is considered to be a promising material for specialized bearing and gear applications due to its high hardness, strength, and low modulus. However, fabricating 60NiTi through conventional processing methods is challenging due to the brittleness and poor workability. In this study, 60NiTi with high relative density was successfully fabricated directly from pre-alloyed powder through hot isostatic pressing. The effects of solution and aging treatments on microstructure and mechanical properties were systematically studied by advanced characterization techniques. The hot-isostatic-pressed 60NiTi showed low average hardness and elastic strain due to the formation of a soft Ni3Ti phase and B2 NiTi matrix. Solution treatment above 1000 °C dissolved the Ni3Ti phase and promoted the formation of nanoscale Ni4Ti3 precipitates, which significantly improved the hardness, strength, and elastic strain of 60NiTi. The formation of the Ni4Ti3 phase can be mainly attributed to the driving forces induced by the chemical supersaturation and mechanical stress concentration. Finally, the phase transformation mechanisms during heat treatment and compression test were discussed.

This article reports, for the first time, the application of Nb4C3Tx in the MXene series satisfying the formula of M4C3Tx in the field of hydrogen evolution reaction (HER). New etching parameters are proposed to obtain Nb4C3Tx with the largest c-lattice constant (3.165 nm) to date. Notably, Nb4C3Tx shows higher catalytic activity under the alkaline condition. Consequently, Nb4C3Tx has an overpotential of 398 mV at a current density of 10 mA cm−2, which is considerably less than that of other reported MXenes. Moreover, Nb4C3Tx has superior cycling performance and long-term stability in both acidic and alkaline environments. After 1000 cycles of CV, the overpotential of Nb4C3Tx clearly decreased by approximately 30 mV, and the current density significantly increased after the timing current test up to 50 h. This work demonstrates the excellent electrochemical performance that Nb4C3Tx can provide to benefit broad application prospects in energy fields.

Quasi-equiatomic CoCrFeMnNi high entropy alloy (HEA) has been in-situ alloyed by selective laser melting (SLM) from a blend of CoCrFeNi pre-alloyed powder and Mn elemental powder. The blended powder shows good printability with various SLM parameters and the as-built HEA samples achieve a reliable forming quality. Despite the slight evaporation of Mn, energy dispersive spectrometer mapping and X-ray diffraction results show that the as-built HEA has a homogeneous chemical distribution and presents a single face-centred-cubic (fcc) phase, indicating successful in-situ alloying. The study has verified the feasibility of using blended powder to prepare high-quality HEA by SLM.

To realize near net-shaping of hard-to-process intermetallics is an often challenging but critical issue to their wider industrial applications. In this work, we report that an intermetallic Ti–22Al–25Nb has been successfully fabricated by selective laser melting (SLM). The as-printed samples show a high room-temperature ultimate tensile strength ∼1090 MPa and excellent ductility ∼22.7%; both values are higher than most conventionally fabricated Ti–22Al–25Nb intermetallic. We clarify the mechanical performance achieved by detailed microstructure analysis, including dislocation and phase constitution. It is proposed that high-density dislocation networks significantly contribute to the strength and ductility, which are further enhanced by the favorable phase constitution, including the nano-scale O phase precipitates within the disordered β phase and disappearance of the brittle α2 phase in the microstructure. Phase evolution during solidification, particularly regarding the O phase's formation, has also been clarified using in-situ laser heating, high-temperature synchrotron X-ray diffraction and Scheil simulation. It is demonstrated that the O phase formation involves both displacive transition (B2 → B19) and chemical ordering (B19 → O). The metastable B19 phase (as an intermediate stage) may be formed by shearing cubic B2 phase along (110) [ 1 − 11 ] direction into an orthorhombic structure under high residual stress. Furthermore, a demonstrative part of turbine blade has been fabricated to highlight the importance of SLM in fabricating critical structural part like the hard-to-process intermetallics.

Selective laser melting (SLM) is a laser-based additive manufacturing technique that can fabricate parts with complex geometries and sufficient mechanical properties. However, the optimal SLM process windows of metallic materials are difficult to predict, especially when exploring new metallic materials. In this paper, a universal and simplified model has been proposed to predict the energy density suitable for SLM of a variety of metallic materials including Ti and Ti alloys, Al alloy, Ni-based superalloy and steel, on the basis of the relationship between energy absorption and consumption during SLM. Several important but easily overlooked factors, including the surface structure of metallic powder, porosity of powder bed, vaporization and heat loss, were considered to improve the accuracy of the model. Results show that, to achieve near-full density parts, the energy absorption (Qa) by the local powder bed should be approximately 3–8 times greater than the energy consumption (Qc), and this finding applies to all materials investigated. The value of Qa/Qc highly depends on material properties, particularly laser absorptivity, latent heat of melting and specific heat capacity. Experiments on high-entropy alloy (CrMnFeCoNi) and Hastelloy X alloy, new metallic materials for SLM, have been further conducted to verify the model. Results confirm that the model can predict suitable laser energy densities needed for processing the various metallic materials without tedious trial and error experiments. Indications and uncertainty of the model have also been analyzed.

Correlation between the feedstock powder and the as-printed products is well expected in laser powder bed fusion (LPBF). However, the inheritance/heredity relationship between the feedstock powder and the products remains broadly overlooked since most atomized powders are printed without any modification. This study addresses the inheritance issue through comparing the hydrogenation/dehydrogenation (HDH) Ti powder with the ball-milled (BM) Ti powder, as well as the respective as-printed samples. Rietveld refinement, focused ion beam, electron backscatter diffraction, and transmission electron microscopy are employed to characterize the microstructure; uniaxial tensile tests and fractographic observation are performed for the mechanical analysis; single-track finite element simulations are conducted to reveal the varied powder-bed properties. A “core-shell” powder structure has been generated through the ball milling modification. Nano-crystallites in the “shell” and stress-induced twins have brought significant grain refinement to the BM powder. A β-to-αm massive transformation has been observed in the samples printed using HDH powder, whereas the microstructure changes to fully-martensitic when using BM powder as the feedstock. Excellent mechanical performance (∼1000 MPa tensile strength with ∼20% ductility) have been achieved through inheriting the fine microstructure and oxygen content from the BM powder, which are induced by the powder modification process. This study has therefore unveiled the comprehensive correlation between the feedstock powder and the as-printed Ti, highlighting a novel methodology for developing additively-manufactured, cost-effective, and high-performance materials through tailoring the feedstock powder.

Iron (Fe) is a potent β-stabaliser, capable to replace costly alloying elements such as V and Mo in forming cost-affordable, biomedical Ti alloys. Selective Laser Melting (SLM) is a mainstream additive manufacturing (AM) technology, competent in realizing near-net shaping of complex, quality parts. In this study, Ti-5Fe alloy was prepared by SLM using elemental powders of Fe and modified hydrogenated-dehydrogenated (HDH) Ti, aiming at providing a cost-affordable candidate biomedical Ti alloy. It is found that, under the “optimum printing parameters”, homogeneous distribution of Fe is possible by the in-situ alloying process. After further efforts in terms of impurity scavenging and heat treatment, the in-situ alloyed Ti-5Fe shows a combination of high strength, good ductility and good biocompatibility. The best mechanical properties achieved are ~865 MPa for tensile strength and ~12% for elongation. This study demonstrates the capability of laser in-situ alloying additive manufacturing in developing cost-affordable and high quality biomedical Ti materials.

Carbon/carbon (C/C) composite and Ti6Al4V alloy (wt%) were successfully brazed with graphene nanosheets strengthened AgCuTi filler (AgCuTiG). Graphene nanosheets (GNSs) with low CTE and high strength were dispersed into AgCuTi filler by ball milling. The interfacial microstructure was systematically characterized by varieties of analytical means including transmission electron microscopy (TEM). Results show that typical interfacial microstructure of the joint brazed at 880 °C for 10 min is a layer structure consisting of (Ti6Al4V/diffusion layer/Ti2Cu + TiCu + Ti3Cu4 + TiCu4/GNSs + TiCu + TiC + Ag(s,s) + Cu(s,s)/TiC/C/C composite). The interfacial microstructure and mechanical properties of brazed joints changed significantly as temperature increased. High temperature promoted the growth of TiCu and TiC phases, which were attached to GNSs. Meanwhile, the diffusion layer and primary reaction layers thickened as temperature increased, while the thickness of brazing seam decreased. The maximum shear strength of 30.2 MPa was obtained for the joint brazed at 900 °C for 10 min. GNSs decreased the thickness of brittle reaction layers and promoted the formation of TiCu and TiC phases in brazing seam, which caused the strengthening effect and decreased the CTE mismatch of brazed joints. The fracture modes are also discussed in this paper.

Ti2448 alloy fabricated by powder metallurgy using elemental powders of Ti, Nb, Zr and Sn exhibits good ductility but a high content of oxygen, and very limited work hardening in the tensile test. Its deformation mechanism is investigated by in-situ EBSD test conducted in an SEM equipped with a dynamic tensile stage. The results indicate that both dislocation slide and stress-induced phase transformation contribute to the plastic deformation of the alloy. Subsequent to yielding (after 3% of strain), β phase grains with preferential orientation " open=" 113 β / / X - a x i s tend to be transformed into α" martensite phase, which significantly reduces the plastic deformation caused by the dislocation slide and therefore leads to low work hardening.

Intermetallic γ-TiAl alloy has been considered as a promising structural material for high temperature use, owing to their advantages such as low density, high creep strength and good toughness. However, due to its intrinsic brittleness, γ-TiAl alloy could not accommodate the high thermal stress generated by fast cooling during laser-based additive manufacturing (LAM) process, resulting in cracking and distortion. To surmount the roadblock of low processability associated with γ-TiAl alloy, grain refinement technology was integrated to LAM. In the present work, LaB6 nanoparticles were identified and experimentally verified, for the first time, as an effective inoculant for LAMed γ-TiAl alloy. The results showed that the grain size of the as-printed alloy drastically decreased from 39.81 ± 9.12 µm to 1.5 ± 2.07 µm through 0.5 wt% LaB6 addition. Accordingly, the microstructural morphology transformed from coarse near-lamellar colonies into equiaxed and fine grains. The LaB6 inoculation treatment not only led to the fabrication of crack-free alloy but concurrently increases in compressive yield strength, ultimate strength and strain to fracture by 29%, 12.4% and 61.9%, respectively. Such an enhanced performance is comparable with or even better than the γ-TiAl alloys produced using conventional processing techniques.

Ti2AlNb (Ti–22Al–25Nb at.%, nominal composition) intermetallic is essential to aerospace industry from a weight reduction perspective, and brings a possibility of replacing some Ni-based superalloys. Despite evaporation of element Al (from its original composition 22.8 at.% to 18.5 at.%), selective laser melting (SLM) technology offers distinct advantages in fabricating Ti2AlNb intermetallic with superior room-temperature properties. A full understanding of corresponding heat treatment mechanism is the key to utilize well the SLM-prepared Ti2AlNb at high temperatures. This study aims to clarify the relationship between the microstructure and mechanical propensities of SLM-prepared then heat-treated Ti2AlNb, to ultimately achieve promising mechanical performances at high temperatures. For this research purpose, a series of heat treatments were conducted, and the corresponding microstructures, mechanical properties were systematic studied by advanced characterization techniques. Results show that the mechanical properties at both room and high temperatures depend on heat treatment adopted. The samples solution-treated at 950 °C and then aged at 700 °C show promising room and high temperature strengths due to the formation of acicular O, α2 and grain boundary α2 phases. However, their ductility was poor. Aging at 830 °C reduces the strength, but significantly improves the ductility due to the appearance of rodlike O phase and the increase of B2/β phase proportion. The alloy possesses promising strength and ductility (611 MPa, 10.0%) and high thermal stability at 650 °C. It is further demonstrated that the heat-treated Ti2AlNb possesses promising specific strength, even higher than that of as-cast Inconel 718 superalloy. The developed alloy, therefore, has a high potential for the industries requiring high-temperature performance and weight reduction.

Laminated ZrB2–SiC ultra-high temperature ceramics (UHTCs) with different layer thickness ratios and strong interfaces were fabricated by hot-pressing. Residual stresses developed on the surfaces of laminated ZrB2-SiC ceramics were evaluated by X-ray diffraction (XRD) and indentation techniques. Results showed that the characteristic XRD peaks of the ZrB2 phase on the surface of the laminated ceramics presented a shift due to the residual surface stress existence. Both XRD and indentation tested results suggested that the surface residual stress increases with the increasing layer thickness ratio confirming the theoretical analysis and calculation reported by our previous work. The presence of a compressive residual stress in the external layer of the heterogeneous material is expected to improve the mechanical properties of laminated ZrB2-SiC ceramics.

This study presents a novel approach for the fabrication of commercially pure titanium (CP–Ti) components. The approach conferred superb strength to CP-Ti without sacrificing its ductility. A yield strength of 807 MPa combined with 19.15% elongation was realized through selective laser melting (SLM) by using a high-power laser and incorporating solute atoms from the Ar−N 2 reactive atmosphere. Mechanical properties and microstructures of the as-printed CP-Ti were systematically investigated. Transmission electron microscopy, electron backscatter diffraction, and atom probe tomography were employed to reveal the mechanism underlying the in-situ reaction between CP-Ti and the reactive atmosphere. Results suggest that nitrogen generally dissolved in the α′-Ti matrix as interstitial solute atoms. The beneficial N content has a critical limit of ∼0.43 wt%. The ductility of CP-Ti will decrease drastically if its N content exceeds this limit. A constitutive model was developed for describing the tensile deformation behavior of the in-situ strengthened CP-Ti over various solute contents and grain sizes. This work demonstrates a promising methodology for the fabrication of high-performance metallic components and extends the fundamental understanding of SLM process under the reactive atmosphere.

Ti-6Al-4V is the single most important Ti alloy, accounting for use in almost 60% of all the applications of Ti materials. Additive manufacturing (AM) offers design freedom with regard to Ti-6Al-4V for creation of high-quality, customized products. However, the large-scale development of this technology is constrained by the high raw material costs. In this study, a method based on ball milling powder modification was proposed to convert low cost, non-spherical hydrogenated-dehydrogenated Ti (HDH-Ti) powder into spherical, printable Ti powder. Following mechanical mixing, the ball-milled HDH-Ti powder was further blended with elemental powders of aluminum and vanadium to develop low-cost HDH Ti-6Al-4V. Simultaneously, the issue pertaining to high oxygen associated with HDH Ti-6Al-4V was addressed via introduction of yttrium. A cost-affordable, high-performance AM Ti-6Al-4V alloy was finally developed via laser-based powder bed fusion of metals (PBF-LB/M) after printing parameter optimization and heat treatment. The AM-prepared Ti-6Al-4V demonstrated a relative density of 99.3%, an ultimate tensile strength of ~1083 MPa, and an elongation of 9%, comparable to those obtained using costly pre-alloyed powders. Further, numerical simulation and detailed microstructural characterization were performed to reveal the underlying mechanism. Powder modification, compositional modulation, and laser in-situ alloying were the three essential techniques used as part of this approach for optimizing the mechanical properties of the Ti-6Al-4V alloy. Overall, this method demonstrates excellent potential in terms of mitigating the high cost. Moreover, it may further promote research on AM of a variety of Ti alloys besides Ti-6Al-4V.

The CVD nano-diamond film and Ti-6Al-4V alloy were successfully brazed with AgCuTi active brazing filler. The interfacial microstructure was investigated by SEM, EDS, XRD and TEM. Typical interfacial microstructure of brazed joint was conformed as Ti-6Al-4V/diffusion layer/Ti 2 Cu + TiCu + Ti 3 Cu 4 /Ag(s,s) + Cu(s,s) + Ti 2 Cu 3 /TiCu + TiC/nano-diamond film. The effects of brazing temperature on interfacial microstructure and mechanical properties of the brazed joints were analyzed. With the increasing brazing temperature, the thickness of reaction layers adjacent to Ti-6Al-4V substrate and nano-diamond film increased obviously. Moreover, the Ti 2 Cu 3 phase coarsened and aggregated in brazing seam at higher temperature. The joint was formed by the diffusion and reactions between atoms, and the microstructure evolution of brazed joint was discussed. In addition, a slight graphitization of nano-diamond film occurred during brazing process, and the highest shear strength can reach 25 MPa when the joint was brazed at 880 °C for 10 min. Finally, the fracture positions and fractographs of brazed joints were also discussed.

Different heat treatments, including quenching and hot isostatic pressing, were conducted on the Ti–24Nb–4Zr–8Sn alloy fabricated by powder metallurgy, in order to improve its mechanical properties. As-sintered samples have high oxygen content over 3000 ppm, resulting in α phase precipitates and low ductility. But the mechanical properties can be improved by solution treatment at a suitable temperature and subsequent quenching. Although the treatment is only effective within a narrow temperature window ranging from 950 to 1000 °C, the treatment can completely eliminate the detrimental α phase and substantially improve the ductility of the alloy from 2% to 19.33%. In comparison, although the hot isostatic pressing can improve the density of the as-sintered alloy to nearly fully dense, it proves unable to remove the α phase from the material or improve its ductility alone.

Ti–22Al–25Nb (at.%) intermetallic is a light weight, high performance, high temperature material with density of merely ˜60% of Ni-based superalloys. The advent and rapid development of selective laser melting (SLM) enable direct fabrication of the Ti–22Al–25Nb intermetallic into complex geometry parts, promising for various critical applications. This paper is dedicated to better understanding the effects of hatch distance, an important but often underestimated processing factor, on microstructure and mechanical properties of the SLM-prepared Ti–22Al–25Nb. Along with analytical means such as transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD), finite element simulation has also been employed to explore the underlying mechanisms. It is determined that the highest mechanical properties are achieved at a hatch distance of 0.16 mm due to the following factors: (a) High density dislocation, (2) favorable phase features, and (3) high relative density. As-fabricated parts of micro-turbine engine using the optimized parameters are provided in the end of the study to demonstrate the capability of SLM to manufacture high quality and delicate structural parts of the Ti–22Al–25Nb intermetallic.

The enthalpy sensitivity of liquid fraction has been proposed as a novel criterion for assessing the semi-solid processability. Via experimental analysis and thermodynamic prediction, the enthalpy sensitivity turns out to be more reasonable than previous criterions. Based on criterion of enthalpy sensitivity, the effects of elements Si and Cu on semi-solid aluminium processability were analysed, indicating the approach to develop new alloys. Furthermore, the influences of heat exchange rate on semi-solid processability were investigated. It is suggested that increasing heat exchange rate would benefit the processability but with a sacrifice of the process time window in practice.

To realize near net-shaping of hard-to-process intermetallics is an often challenging but critical issue to their wider industrial applications. In this work, we report that an intermetallic Ti-22Al-25Nb has been successfully fabricated by selective laser melting (SLM). The as-printed samples show a high room-temperature ultimate tensile strength ~1090 MPa and excellent ductility ~22.7%; both values are higher than most conventionally fabricated Ti-22Al-25Nb intermetallic. We clarify the mechanical performance achieved by detailed microstructure analysis, including dislocation analysis and phase constitution analysis. High-density dislocation networks significantly contribute to the strength and ductility, which are further enhanced by the favorable phase constitution, including the nano-scale O phase precipitates within the disordered β phase and disappearance of the brittle α2 phase in the microstructure. Phase evolution during SLM has also been clarified using in situ heating, high-temperature synchrotron X-ray diffraction and Scheil simulation, particularly regarding the O phase's formation. It is demonstrated that O phase is formed by shearing primary cubic B2 phase along (110)[111] direction into an orthorhombic structure under high residual stress. Furthermore, a demonstrative part of turbine blade has been fabricated to highlight the importance of SLM in fabricating critical structural part like the hard-to-process intermetallics.

Herein, we present a systematic investigation of oil-in-water Pickering emulsions stabilized by the complex of polystyrene (PS) particles and chitosan (CS). The presence of both PS particles and CS resulted in a stable emulsion, in contrary to those prepared with PS particles or CS alone, and the adsorption of PS particles and CS on oil droplet surface was observed using SEM and fluorescence microscopy. In addition, the mechanism of the emulsifying ability of the complex has been studied by determining the wettability of PS particles modified by CS, as well as the flocculation of PS particles. Specifically, at the low concentration of CS, the emulsion was stabilized by the flocculated PS particles induced by the adsorption of CS molecules, whereas at the high concentration of CS, the emulsion was stabilized mainly by free CS.