Additive Manufacturing of Titanium Alloys by Electron Beam Melting: A Review

Electron beam melting (EBM), as one of metal additive manufacturing technologies, is considered to be an innovative industrial production technology. Based on the layer‐wise manufacturing technique, as‐produced parts can be fabricated on a powder bed using the 3D computational design method. Because the melting process takes place in a vacuum environment, EBM technology can produce parts with higher densities compared to selective laser melting (SLM), particularly when titanium alloy is used. The ability to produce higher quality parts using EBM technology is making EBM more competitive. After briefly introducing the EBM process and the processing factors involved, this paper reviews recent progress in the processing, microstructure, and properties of titanium alloys and their composites manufactured by EBM. The paper describes significant positive progress in EBM of all types of titanium in terms of solid bulk and porous structures including Ti–6Al–4V and Ti–24Nb–4Zr–8Sn, with a focus on manufacturing using EBM and the resultant unique microstructure and service properties (mechanical properties, fatigue behaviors, and corrosion resistance properties) of EBM‐produced titanium alloys.

     

Effect of Initial Annealing Temperature on Microstructural Development and Microhardness in High‐Purity Copper Processed by High‐Pressure Torsion

The effect of the initial annealing temperature on the evolution of microstructure and microhardness in high purity OFHC Cu is investigated after processing by HPT. Disks of Cu are annealed for 1 h at two different annealing temperatures, 400 and 800 °C, and then processed by HPT at room temperature under a pressure of 6.0 GPa for 1/4, 1/2, 1, 5, and 10 turns. Samples are stored for 6 months after HPT processing to examine the self‐annealing effects. Electron backscattered diffraction (EBSD) measurements are recorded for each disk at three positions: center, mid‐radius, and near edge. Microhardness measurements are also recorded along the diameters of each disk. Both alloys show rapid hardening and then strain softening in the very early stages of straining due to self‐annealing with a clear delay in the onset of softening in the alloy initially annealed at 800 °C. This delay is due to the relatively larger initial grain size compared to the alloy initially annealed at 400 °C. The final microstructures consist of homogeneous fine grains having average sizes of ≈0.28 and ≈0.34 µm for the alloys initially annealed at 400 and 800 °C, respectively. A new model is proposed to describe the behavior of the hardness evolution by HPT in high purity OFHC Cu.     

Mechanical Properties and Interlaminar Fracture Toughness of Glass‐Fiber‐Reinforced Epoxy Composites Embedded with Shape Memory Alloy Wires

The effects of the content and position of shape memory alloy (SMA) wires on the mechanical properties and interlaminar fracture toughness of glass‐fiber‐reinforced epoxy (GF/epoxy) composite laminates are investigated. For this purpose, varying numbers of SMA wires are embedded in GF/epoxy composite laminates in different stacking sequences. The specimens are prepared by vacuum‐assisted resin infusion (VARI) processing and are subjected to static tensile and three‐point‐bending tests. The results show that specimens with two SMA wires in the stacking sequence of [GF₂/SMA/GF₁/SMA/GF₂] and four SMA wires in the stacking sequence of [GF₄/SMA/GF₂/SMA/GF₄] exhibit optimal performance. The flexural strength of the optimal four‐SMA‐wire composite is lower than that of the pure GF/epoxy composite by 5.76% on average, and the flexural modulus is improved by 5.19%. Mode‐I and II interlaminar fracture toughness tests using the SMA/GF/epoxy composite laminates in the stacking sequence of [GF₄/SMA/GF₂/SMA/GF₄] are conducted to evaluate the mechanism responsible for decreasing the mechanical properties. Scanning electron microscopy (SEM) observations reveal that the main damage modes are matrix delamination, interfacial debonding, and fiber pullout.

     

High Efficiency Poly(acrylonitrile) Electrospun Nanofiber Membranes for Airborne Nanomaterials Filtration

The potential of poly(acrylonitrile) electrospun membranes with tuneable pore size and fiber distributions were investigated for airborne fine‐particle filtration for the first time. The impact of solution concentration on final membrane properties are evaluated for the purpose of designing separation materials with higher separation efficiency. The properties of fibers and membranes are investigated systematically: the average pore distribution, as characterized by capillary flow porometry, and thermo‐mechanical properties of the mats are found to be dependent on fiber diameter and on specific electrospinning conditions. Filtration efficiency and pressure drop are calculated from measurement of penetration through the membranes using potassium chloride (KCl) aerosol particles ranging from 300 nm to 12 μm diameter. The PAN membranes exhibited separation efficiencies in the range of 73.8–99.78% and a typical quality factor 0.0224 (1 Pa^?1) for 12 wt% PAN with nanofibers having a diameter of 858 nm. Concerning air flow rate, the quality factor and filtration efficiency of the electrospun membranes at higher face velocity are much more stable than for commercial membranes. The results suggest that the structure of electrospun membranes is the best for air filtration in terms of filtration stability at high air flow rate.

     

Enhanced Thermal Conductivity of 5A Molecular Sieve with BNs Segregated Structures

5A molecular sieves have been widely used as adsorbents in cryogenic distillation for hydrogen isotope separation in fusion reactor engineering, but its low thermal conductivity is detrimental to the process stability. Improving the thermal conductivity of 5A molecular sieves is one of the most important goals for high‐performance devices. Here, firm segregated structures with boron nitride sheets (BNs) are constructed around 5A molecular sieve particles. SEM results show 30 µm BNs tend to form the better networks in comparison with that of 0.12 µm BNs at 40 wt% loadings. It is further verified that BNs with the larger size promote the thermal conductivity. Meanwhile, the thermal conductivity increases with the increasing amounts of BNs. XRD and specific surface area results indicate that the sintering and the addition of BNs exert negligible effects on the structure of 5A molecular sieve. These results indirectly show 5A molecular sieve with BNs segregated structures is very likely to be used for the application of hydrogen isotopic separation. Besides, this work provides new insight into the construction of segregated structure in inorganic porous materials.

     

3‐D Printing and Development of Fluoropolymer Based Reactive Inks

Engineering reactive materials is an ever present goal in the energetics community. The desire is to have energetics configured in such a manner that performance is tailored and energy delivery can be targeted. Additive manufacturing (3‐D printing) is one area that could significantly improve our capabilities in this area, if adequate formulations are developed. In this paper, fluoropolymer based reactive inks are developed with micron (mAl) and nanoscale aluminum (nAl) serving, as the fuel at high solids loading (up to 67 wt%) and their viscosity required for 3‐D printing is detailed. For the pen‐type technique and valves used in this work, it is required to have viscosities on the order of 10⁴–10⁵ cP. For printed traces with apparent diameters under <500 μm, the combustion velocities for both micron and nano scale aluminum formulations, are approximately identical: 30 ± 3 versus 32 ± 2 mm s^?1, respectively. Further increasing the apparent diameter is shown to increase the combustion velocity in the case of the nanoscale aluminum formulation by four‐fold over that of the micron scale aluminum formulation, but it plateaus as it approaches an apparent diameter of 2 mm. The results suggest with proper architecture that tailorable combustion rates and energy delivery are feasible.

     

Impact of arteriovenous fistula cannulation on the quality of dialysis

Introduction: Adequate hemodialysis directly improves health. Puncturing an arteriovenous fistula (AVF) and the amount of blood recirculation greatly affect the quality of dialysis. Few studies have assessed the method to cannulate a fistula and its influence on efficiency of hemodialysis. Methods: This prospective pilot study included 14 patients with end‐stage renal failure receiving regular intermittent hemodialysis. Patients received three consecutive treatments with both needles directed upstream then three consecutive treatments with the venous needle directed upstream and the arterial needle directed downstream. With both techniques, the distance between the needles was kept constant at 2.5 cm. Recirculation rate and Kt/V ratio were measured during each treatment using thermodilution and a diascan Fresenius generator. Findings: The 14 patients received 84 hemodialysis sessions: i.e., 8 (57.1%) males and 6 (42.8%) females, mean age 62.3 ± 15.57 years. Results showed that mean recirculation rates and Kt/V did not significantly differ between the two techniques. Discussion: Because no significant difference was found between the two techniques, the direction of insertion of needles should be decided upon on a case‐by‐case basis depending on the anatomy of the AVF and the feasibility of the puncture.     

Research Advances in Microfiber Humidity Sensors

An overview of the numerous latest research in microfiber humidity sensors is carried out with a specific focus on measurement methods, humidity sensitive materials, probe structures, and sensing properties of different sensors. First, five mainstream measurement structures, including taper, fiber grating, coupler, resonator, and interferometer are reviewed. It is concluded that these measurement structures sense the physicochemical property variations of microfibers or sensitive films and exhibit the change of optical signal when exposed to environment. Second, the basic preparation methods, humidity‐sensing properties, and their advantages and disadvantages as humidity sensitive material are addressed. Then, the advantages and disadvantages of all the above sensing structures are also discussed and compared. Finally, the main existing problems and potential solutions of microfiber humidity sensors are pointed out.