Structure Evolution of Ni36Al27Co37 Alloy in the Process of Mechanical Alloying and Plasma Spheroidization

In this paper, a novel approach to obtain a ferromagnetic material for smart applications was implied. A combination of mechanical alloying (MA) and plasma spheroidization (PS) was applied to produce Ni36Al27Co37 spherical powder. Then its structure was systematically studied. It was shown that homogenization of the structure occurs due to mechanism of layered structure formation. The dependence of the lamella thickness on the energy dose input at MA was defined. It was found that 14.7 W⋅h/g is sufficient to obtain lamella thickness of 1 μm and less. The low-energy mode of a planetary mill with rotation speeds of the main disk/bowl of 150/−300 rpm makes it possible to achieve a uniform element distribution upon a minimal amount of impurity. During MA in an attritor Ni3Al-type intermetallic compounds are formed that result in more intensive degradation in particle size. Plasma spheroidization of the powder after MA allowed obtaining Ni36Al27Co37 spherical powder. The powder had a fine β + γ-structure. The particle size distribution remains almost unchanged compared to the MA stage. Coercivity of the powder is 79 Oe. The powder obtained meets the requirements of selective laser melting technology, but also can be utilized as a functional filler in various magnetic composites.

Crystalline structure and reinforcement in hybrid PP composites

Hybrid composites were prepared from a PP homopolymer, talc and PVA fibers by twin-screw extrusion and injection molding. Talc was added to improve stiffness, while the fibers serve to increase impact resistance. Mechanical properties were characterized by tensile and impact testing, while structure was studied by SEM and optical microscopy. The results showed that talc has a strong nucleating effect in the PP used in spite of the fact that the grade contained a nucleating agent inherently. PVA also nucleated the PP slightly, with trans-crystallization occurring around the fibers. The effect of the two components was independent of each other on lamella thickness, but crystallinity decreased with increasing PVA content in the hybrid composites. The results clearly showed that crystalline structure changes considerably upon the addition of the two components, both lamella thickness and crystallinity increasing. However, somewhat contradictorily, the effect of these changes on the mechanical properties of the composites is small. Model calculations have shown that stiffness increases by about 0.5 GPa due to nucleation, while moduli as large as 7 GPa are reached by the addition of talc. Impact resistance is completely independent of lamella thickness or crystallinity; this property is determined mainly by local deformation processes initiated by the PVA fibers. Dispersed structure and the direct effect of the additive determine properties in the hybrid composites studied, and the role of crystalline structure is of secondary importance.

Nomogram for Single-pass Two-speed Automated Microkeratome Graft Preparation for Ultrathin Descemet Stripping Automated Endothelial Keratoplasty

PurposeTo create a nomogram including the translational speed of the microkeratome blade, microkeratome head size and precut tissue thickness to predict the postcut thickness for Descemet stripping automated endothelial keratoplasty (DSAEK) to obtain the thinnest possible graft.MethodsThis prospective study incorporated 48 grafts for DSAEK from March 2017 to June 2020. Corneal tissue for DSAEK was prepared by 3 experienced physicians using the Moria Evolution 3E (Moria Inc, Antony, France) microkeratome with 400, 450 and 500 mm head sizes. Precut central corneal thickness was measured with a DGH 550 handheld pachymeter (Pachette 2), taking an average of 3 readings. The microkeratome head was selected according to precut tissue thickness. The target donor lamella thickness ranged from 70 to 120 μm, and the selected microkeratome head size was 150μm less than the donor cornea thickness. Two translational speeds were used for the microkeratome cuts. One month after surgery, the central lenticular thickness was measured with a Visante® Optical Coherence Tomography caliper (Carl Zeiss Meditec Inc, Germany). A descriptive analysis was performed.ResultsForty-eight donor grafts were prepared. Mean graft thickness was 97.58 ± 29.84 μm (range 39-176 μm). Of the 48 samples, central graft thickness was <120µm (81.3%) in 39, <100 µm (58.3%) in 28 and <80µm (37.5%) in 18 at 1-month follow-up. There were no statically significant differences between translational speeds. ConclusionsA nomogram with an automated microkeratome to obtain thin grafts for DSAEK provided good graft thickness results without donor waste.

The Copper-Arsenic Eutectic and the Cu3As Phase

In ancient bronze ingots Cu3As was observed beside other impurities like Sb. Moreover, the Cu-As bronzes were studied concerning the decrease in As during melting respectively remelting. To verify the microstructure and hardness of the eutectic and Cu3As phase appropriate mixtures were produced by melting pure Cu and As. The eutectic point in the Cu-As system is at 685 °C and 20.8 wt. % As and the Cu3As phase with 29.56 wt. % As melts at 827 °C. In the sample´s core the microstructure is a homogeneous eutectic, but near the surface it becomes hypoeutectic, i.e. an As loss took place. The lamella thickness of the eutectic was in the range of about 1 µm. The sample with a Cu3As composition showed a proeutectic microstructure with mainly Cu3As and a small amount of eutectic. In the large Cu3As crystals twin lamellae were observed. Additionally, by Vickers indents new twins were introduced. The microhardness of the Cu-As solid solution is 78 HV0.025, of the eutectic 125 HV0.025 and of the Cu3As phase 158 HV0.025. On some surfaces of the Cu3As sample a Cu-rich phase was observed. We are not able to explain this phenomenon, but it is definitively no “inverse segregation”.

Enhanced Morphology-Dependent Tensile Property and Breakdown Strength of Impact Polypropylene Copolymer for Cable Insulation

The decrease in electrical properties caused by the toughening of polypropylene (PP) is a difficult problem for the modification of PP used for cable insulation. In this research, an isotactic PP, a cross-linked polyethylene (XLPE) and two impact PP copolymers (IPCs) with an ethylene–propylene rubber phase content of 15 and 30% were prepared to assess the possibility of IPCs to be used as cable insulating material. The tensile properties and breakdown strength were evaluated, meanwhile, the rubber phase content dependence of the crystalline structure, morphology and trap distribution were also investigated. Results show that IPCs with a 15% rubber phase content (IPC15) can achieve the simultaneous improvement of elongation at break and breakdown strength compared with isotactic PP, which can be attributed to the special crystalline structure. According to the results of differential scanning calorimetry (DSC) and FTIR, it is proposed that the lamella thickness of IPC15 is maximal and some ethylene segments exist in PP crystals of IPC15 as crystalline structure defects, which is responsible for this enhanced breakdown strength. The morphology results reveal that rubber microspheres are found to coexist with spherulites, which can promote the relative sliding among lamellas under external force and further results in the increase in the elongation at break.

Preparation of photochromic isotactic polypropylene filaments: influence of drawing ratio on their optical, thermal and mechanical properties

In this research, metallocene catalyst isotactic polypropylene (miPP) filaments were produced with different concentrations of photochromic pigments to develop ultraviolet (UV) sensing materials. The produced miPP filaments showed good photochromic response under UV irradiation. In this work, six drawing ratios were applied to get the final product (miPP filament). Resultant filaments showed significant photochromic responses, such as Kubelka–Munk values ( K/ S). The interesting observation was that the photochromic response was indirectly proportional to the applied drawing ratio. The photochromic color build was found to be maximum with the highest concentration of pigment as well as the lowest drawing ratio. Overall, it was observed that the thermal properties were significantly dependent on the drawing ratio. The changes in thermal properties, such as T m, ΔH m and ΔS m, for miPP filaments in dependence on photochromic pigment concentration was significantly less as compared to the drawing ratios. The thermal properties improved with the drawing ratio, which directly influenced the crystallinity of produced miPP filaments. The addition of photochromic pigment to the miPP filaments increased the crystallinity by 14%. Also, the lamella thickness increased with increasing the drawing ratio. However, there was no significant effect of pigment concentration on lamella thickness. In this experimental work, the impact of drawing ratio on the optical, thermal and mechanical properties of photochromic miPP filaments was investigated.

Preparation of boron nitride nanosheets using a chemical exfoliation method as a thermal conductive filler for the development of silicone thermal pads: Part II: Optimization of process parameter design on the development of a silicone thermal pad

This study developed a silicone thermal pad with high thermal conductivity and high mechanical properties. Boron nitride nanosheets (BNNSs) with different lamella thicknesses were prepared in Part I and Al2O3 was filled with silicone rubber to prepare silicone thermal pads. The silicone thermal pads were prepared using the Taguchi method and the elimination and choice translating reality method. BNNSs with different lamella thicknesses, BNNS loading level, and Al2O3 loading level were set as control factors for the experiment. The effect of the three sets of control factors on the thermal conductivity, tensile property, and hardness of the silicone thermal pads was discussed so as to determine the optimum product optimization process parameters. According to the experimental results, the optimum experimental combination was BNNSs with lamella thickness (B24), a BNNS loading level of 20 wt%, and an Al2O3 loading level of 60 wt%. The thermal conductivity of the silicone thermal pads prepared by thermosetting was 5.25 W/mK, the maximum tensile strength was 7.55 kg/cm2, and the Shore hardness was 65.2 (Shore A). Under identical conditions, the thermal conductivity and tensile strength were higher than that of commercially available silicone thermal pads by 34.48% and 20.26%, respectively. The control factor influencing the thermal conductivity and tensile strength of silicone thermal pads was the BNNS loading level, with contribution degrees of 34.66% and 50.13%, respectively. Accurate parameter settings could be obtained for silicone thermal pad processes.

Optimal Design of High-Strength Ti‒Al‒V‒Zr Alloys through a Combinatorial Approach

The influence of various Zr contents (0–45 wt.%) on the microstructure and mechanical properties of Ti6Al4V alloy was investigated through a combinatorial approach. The diffusion multiples of Ti6Al4V–Ti6Al4V20Fe–Ti6Al4V20Cr–Ti6Al4V20Mo–Ti6Al4V45Zr were manufactured and diffusion-annealed to obtain a large composition space. Scanning electron microscopy, electron probe micro-analysis, and a microhardness system were combined to determine the relationships among the composition, microstructure, and hardness of these alloys. The Ti–6Al–4V–30Zr alloy was found to contain the thinnest α lath and showed peak hardness. X-ray diffraction and transmission electron microscope results indicated that after quenching from the β-field, the metastable α″-phase formed; moreover, at the secondary aging stage, the metastable α″-phase acted as precursor nucleation sites for the stable α-phase. The bulk Ti6Al4V30Zr alloy was manufactured. After aging at 550 °C, the alloy showed excellent balance of strength and ductility, and the tensile strength was 1464 MPa with a moderate elongation (8.3%). As the aging temperature increased, the tensile strength and yield strength of the alloys rose, but the total elongation decreased. The lamella thickness and volume fraction of the α-phase were the major factors that had great impacts on the mechanical properties.