As-received Value Research Articles

Analysis of interfacial characteristics in polymer nanocomposites via visual particle recognition methodology and micromechanical predictive models

This study examines the morphological features of nano-zeolite nanoparticles incorporated into ultra-high molecular weight polyethylene nanocomposites, known for their excellent biocompatibility and significant potential in structural biomedical applications. The analyses involved qualitative assessments and a statistical approach based on visual particle recognition technique. Scanning electron microscopy was adopted for morphological assessments of impact-fractured surfaces. The scanning electron microscopy observations unveiled the improved dispersion of nanoparticles within the polymer matrix following nano-zeolite incorporation. In the quantitative approach, the nanoparticles size and distribution were systematically determined through tailored histograms, utilizing the customized particle recognition strategy applied to images. This analysis yielded average particle sizes for each composite, further used for calculating the effective elastic moduli of nanocomposites by employing a two-fold micromechanics-based homogenization technique, accounting for interfacial effects. The computation of average particle size based on visual measurements substantially improved the accuracy regarding the quantitative analysis of interphase effects on macroscopic properties, marking a departure from the conventional practice of conducting such calculations by relying on unrealistic particle sizes based on their as-received values before compounding with the polymer.

Nanograined Ti–Nb microalloy steel achieved by Accumulative Roll Bonding (ARB) process

Over the last decade, nanocrystalline and ultra-fine grained (UFG) materials with grain size less than 1μm have aroused considerable interest due to their superior mechanical properties compared to conventionally grained materials. In this work Ti–Nb microalloy steel was processed by the severe plastic deformation (SPD) technique called Accumulative Roll Bonding (ARB) in order to produce an ultra-fine grained microstructure and improve the mechanical properties. After initial preparation to achieve good sheet bonding, 8 cycles of ARB at 550°C were successfully performed. Observation of optical microstructure, scanning electron microscopy (SEM) micrographs, and X-Ray Diffraction (XRD) peak broadening analysis were used for the characterization of grain structure of the ARB processed sample. The mechanical attributes after rolling and cooling were examined. It was calculated that metal's yield and tensile strength increased by 334% and 215% respectively, while the ductility dropped from as-received value of 34% to 2.9%. Microhardness of the material was studied at room temperature. There was a continuous enhancement of hardness by increasing the pass number of the ARB process. At the 8th pass, the hardness values increased by 230%. The rolling process was stopped at 8th cycle when cracking of the edge became pronounced.

Comparison of Single-Step Recovery Anneal Processing and a Single-Step Recrystallization Processing on the Generation of Special Boundaries in Commercially Pure Nickel

The strain recovery route to generate a significant increase in special boundaries nominally involves a strain level of less than about 10%, plus a recovery anneal at a temperature–time combination sufficient to cause grain boundary migration, but insufficient cold work/time/temperature combinations to cause recrystallization of the material being processed. In the present communication using a simple material to avoid complications from industrial alloys, commercially pure (C.P.) Ni was processed using a single low strain value of 6% and a temperature of 800–1000 °C for time up to 38 min. The fraction of special grain boundaries, Fsp, based on a Σ3–29 as evaluated by Orientation Image Microscopy was then compared with the as-received C.P. Ni and Ni strained 25% and annealed at 800 °C to give a recrystallized structure. For the single low strain route, a 6% deformation at a temperature of 800 °C and a time of 8–10 min resulted in an Fsp value of close to 80%, as well as a grain size of about 25–35 μm compared to the as-received value of about 25 μm. Thus, while grain boundary migration occurred under these processing conditions, the increase in grain size was not excessive and would not result in a large reduction in tensile properties. The single 25% rolled and 800 °C recrystallized test samples however resulted in no major increase in Fsp relative to the as-received material, both being in the range 35–40% over a range of times. Therefore, compared to the optimized Fsp low strain recovery values of close to 80%, the fully recrystallized Fsp values were approximately half. It should be noted however that multiple cycles of higher strain values rather than a single strain value, coupled with a recrystallized anneal, have been shown in the literature to result in increase in the Fsp levels.

Nitrided Pressureless Sintering에 의해 제조된 Si3N4의 산화거동

Oxidtion behavior of ceramics with the different porosity by the Nitrided Pressureless Sintering (NPS) were investigated in pure oxygen gas atmosphere at 1000 to . The thickness of formed oxide film on the surface of silicon nitride ceramics was increased with oxidation time and temperature. The oxide film thickness of 5A5Y5Si and 5A5Y10Si specimens for 100 h at was about 10 m and 20 m, respectively. The oxidation of 5A5Y5Si and 5A5Y10Si specimens follows the parabolic behavior with an apparent activation energy of 215 kJ/mol and 104 kJ/mol, respectively. The flexural strength of 5A5Y5Si specimens after oxidation test for 500 h at 1300^{circ}C were maintained as-received value of 500 ma. On the other hand, that of 5A5Y10Si specimens were decreased about 100 MPa in as-received value.

Growth and decomposition of bulk GaN: role of the ammonia/nitrogen ratio

Gallium nitride crystals grown via vapor-phase transport processes that incorporate ammonia as the only source of nitrogen below atmospheric pressures experience significant surface roughening and the eventual cessation of growth. Investigations of these phenomena in this research, and in the context of the discovery of a non-ceasing process route to larger GaN crystals, showed that the RMS values of the surface roughness of single crystal GaN (0 0 0 1) films exposed to pure ammonia flowing at 60 sccm for 2 h at 1130°C increased from the as-received value of 3.7–6.8 nm, 21.4 and 32.6 nm at 100, 430 and 760 Torr, respectively. Quadrupole mass spectrometry revealed that the concentrations of H 2 and N 2 measurably increased at pressures above 400 Torr. The primary reason for the increased roughness above 430 Torr was the enhanced etching of GaN via reaction with atomic and molecular hydrogen derived from the dissociation of the ammonia. At lower pressures, the decomposition of the GaN via the formation and evaporation of N 2 and Ga increased in importance relative to etching for enhancing surface roughness. Dilution with nitrogen reduced the amount of hydrogen generated from the dissociation of the ammonia. The GaN surface annealed at 1130°C and 430 Torr in ammonia diluted with 33 vol% N 2 maintained the smoothest surface with a nominal RMS value of 10.4 nm. Mixtures with higher and lower percentages of N 2 showed enhanced roughness under the same conditions. Use of this optimum gas mixture also allowed the seeded growth of a 1.5×1.5×2.0 mm 3 GaN crystal and a 2.3×1.8×0.3 mm 3 thick platelet with neither observable decomposition nor cessation of the growth over periods of 36 and 48 h, respectively.

Influence of hydrogen on the magnetic properties of amorphous FeSiB fibres

The saturation magnetization and switching characteristics of amorphous Fe 77.5Si 7.5B 15 fibres were investigated after hydrogen incorporating by the electrochemical method. The switching field ( H ∗ ) increased from its as-received value (5.57 Am −1 to 18.62 Am −1 after charging with a current density ( I ch) of 30 mA cm −2 for 2 h. The saturation magnetization ( M s) decreased with hydrogen content up to a critical concentration corresponding to I ch = 60 mA cm −2 after 2 h of charging. At this critical current density, M s decreased from 1.57 T, its as-received value, to 0.89 T. The results are explained by considering various kinds of interaction of hydrogen with metals, such as electron exchange, volume dilation, etc.

Effect of low-dose reactor radiation on the dynamic mechanical behavior of pyrolytic graphite

The dynamic mechanical behavior of pyrolytic graphite (PG) (deposited at 2200°C) has been investigated as a function of reactor radiation dose up to 1.8 × 10 17 nvt (fast). Studies made from about 100°K to 800°K at frequencies near 2000 c/s indicate that the dynamic modulus of as-received PG decreases over this temperature range a few percent. A relaxation peak ( Q −1≈ 10 −3) appears near 240°K. Irradiation to 1.8 × 10 17 nvt (fast), results in a non-linear increase in modulus with dose to about 5.5 per cent and in a pronounced modulus inflection near 240°K. Relaxation processes are also evident near 380°K and 700°K in the irradiated samples. Upon retesting of irradiated samples, which had been exposed to temperatures of 700°K to 800°K during the prior test runs, the modulus recovered to approximately as-received values, but the 240°K inflection anomaly became more prominent. Annealing studies indicate that the modulus recovery depends upon temperature and time. Exposure to high test temperatures appears to eliminate the 380°K post-irradiation peak but leaves the 700°K process almost undisturbed. The 380°K peak also disappears with time at constant temperature (near 380°K). An attempt is made to interpret some of the experimental results and to correlate the observations with irradiation effects in graphite as reported in the literature.