Friction stir welding of thick section reduced activation ferritic–martensitic steel

Full penetration friction stir welding was conducted on 12?mm thick reduced activation ferritic–martensitic steel at tool rotational speeds of 500 and 900?rev?min^?1. Comparator welds at 500?rev?min^?1 were also produced in 6?mm thick reduced activation ferritic–martensitic steel plate to evaluate section thickness effects. Increase in section thickness led to an increase in heat input, which strongly influenced the microstructure evolution in stir zone (SZ), thermo-mechanical affected zone and the overall hardness in the SZ of this steel. In the as-welded condition, the base metal microstructure was significantly altered and resulted in carbide-free grain boundaries. The desirable microstructure and mechanical properties were achieved by subjecting the as-welded joints to appropriate post-weld heat treatments.     

Carbon nanohorn‐graphene nanoplate hybrid: An excellent electrode material for supercapacitor application

This study describes the capacitor behavior of carbon nanohorn (CNH)/graphene nanoplate (GNP) hybrid (CNGN). The well‐CNH‐decorated GNP‐plate electrode materials show high capacitance value (≈677 F/g) and can be extensively used in new generation for energy storage. In the hybrid (CNGN), two nanofillers jointly affect the capacitance behavior and increase the capacitance value of the CNGN hybrid. Homogeneous coating of CNH over the GNP plate plays an effective role to enhance the capacitance behavior of the composite. Field emission scanning electron microscopy and high‐resolution transmission electron microscopy analysis of the composite confirmed the CNH coating on the GNP plate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42118.     

Synthesis and kinetics of ascorbic acid initiated graft copolymerized delignified cellulosic fiber

Graft copolymerization of delignified Grewia optiva fiber with methyl methacrylate (MMA) as vinyl monomer was attempted using ascorbic acid/H₂O₂ as redox initiator. Different reaction conditions affecting the grafting percentage (P_g) were optimized to get the maximum P_g (32.56%) of MMA onto delignified Grewia optiva fibers. Grafted and ungrafted fibers were subsequently subjected to evaluation of physico‐chemical properties such as swelling behavior and acid and alkali resistance. The rate expression for the grafting reaction (R_g = k [ASC]^0.12 [H₂O₂]^0.53 [MMA]^0.05) was evaluated and a suitable mechanism for grafting was suggested. The overall activation energy of the copolymerization reaction was found as 11.97 kJ mol^?1 at temperature range 25–65°C. Further, morphological and structural analysis of raw, delignified, and grafted Grewia optiva‐g‐poly(MMA) were studied by using Fourier‐transform Infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, and thermogravimetric analysis.The tensile properties of grafted and ungrafted fiber samples were also reported. POLYM. ENG. SCI., 55:474–484, 2015. © 2014 Society of Plastics Engineers     

Hexagonally ordered arrays of metallic nanodots from thin films of functional block copolymers

We demonstrate a new and simple route to fabricate highly dense arrays of hexagonally close packed inorganic nanodots using functional diblock copolymer (PS-b-P4VP) thin films. The deposition of pre-synthesized inorganic nanoparticles selectively into the P4VP domains of PS-b-P4VP thin films, followed by removal of the polymer, led to highly ordered metallic patterns identical to the order of the starting thin film. Examples of Au, Pt and Pd nanodot arrays are presented. The affinity of the different metal nanoparticles towards P4VP chains is also understood by extending this approach to PS-b-P4VP micellar thin films. The procedure used here is simple, eco-friendly, and compatible with the existing silicon-based technology. Also the method could be applied to various other block copolymer morphologies for generating 1-dimensional (1D) and 2-dimensional (2D) structures.     

Heat conduction mechanisms in hot pressed ZrB2 and ZrB2–SiC composites

Thermal diffusivity and conductivity of hot pressed ZrB₂ with different amounts of B₄C (0–5 wt%) and ZrB₂–SiC composites (10–30 vol% SiC) were investigated experimentally over a wide range of temperature (25–1500 °C). Both thermal diffusivity and thermal conductivity were found to decrease with increase in temperature for all the hot pressed ZrB₂ and ZrB₂–SiC composites. At around 200 °C, thermal conductivity of ZrB₂–SiC composites was found to be composition independent. Thermal conductivity of ZrB₂–SiC composites was also correlated with theoretical predictions of the Maxwell–Eucken relation. The dominated mechanisms of heat transport for all hot pressed ZrB₂ and ZrB₂–SiC composites at room temperature were confirmed by Wiedemann–Franz analysis by using measured electrical conductivity of these materials at room temperature. It was found that electronic thermal conductivity dominated for all monolithic ZrB₂ whereas the phonon contribution to thermal conductivity increased with SiC contents for ZrB₂–SiC composites.     

Low cycle fatigue and creep-fatigue interaction behavior of modified 9Cr-1Mo ferritic steel and its weld joint

The aim of the present paper is to study the low cycle fatigue and creep-fatigue interaction behavior of modified 9Cr-1Mo ferritic steel weld joint. Total axial strain controlled continuous cycling tests were conducted between 773 K and 873 K and at strain amplitudes ±0.25%, ±0.4%, ±0.6% and ±1%. Hold tests were also conducted at +0.6% and 823 K and 873 K temperatures to study the creep-fatigue interaction behavior of the weld joint. The alloy exhibited cyclic softening from first cycle onwards irrespective of the loading conditions. Failure location in the weld joint was correlated to the test parameters. Detailed replica study conducted on all the failed specimens revealed that most of the failures occurred in one side of the heat affected zone (HAZ) of the weld joint. Strain localization in the soft zone of the HAZ and subsurface creep cavity formation in this region and their linkage had caused enhanced crack propagation that translated into lower fatigue life of the weld joint at high temperatures. Type IV mode of failure was identified to be operative under tensile hold and high temperatures. The alloy was also found to be compressive dwell sensitive and it was ascertained that the lower life under compression hold compared to tension hold was due to the deleterious effect of oxidation.     

Comprehensive microstructural characterization in modified 9Cr-1Mo ferritic steel by ultrasonic measurements

Modified 9Cr-1Mo ferritic steel (T91/P91) has been subjected to a series of heat treatments consisting of soaking for 5 minutes at the selected temperatures, starting from the α-phase region (1073 K) to the γ + δ-phase region (1623 K), followed by oil quenching. Hardness measurements, microstructural features, and grain-size measurements by the linear-intercept method have been used for correlating them with the ultrasonic parameters. Ultrasonic velocity and attenuation measurements, and spectral analysis of the first backwall echo have been used for characterization of the microstructures obtained by various heat treatments. As the soaking temperature increased above Ac ₁, the ultrasonic velocity decreased because of the increase in the volume fraction of martensite in the structure. There were sharp changes in the ultrasonic velocities corresponding to the two critical temperatures, Ac ₁ and Ac ₃. Ultrasonic longitudinal- and shear-wave velocities were found to be useful in identifying the Ac ₁ and Ac ₃ temperatures and for the determination of hardness in the intercritical region. However, ultrasonic attenuation and spectral analysis of the first backwall echo were found to be useful to characterize the variation in the prior-austenitic grain size and formation of δ ferrite above the Ac ₄ temperature. The scattering coefficients have been experimentally determined for various microstructures and compared with the theoretically calculated value of the scattering coefficients for iron reported in literature.     

A critical assessment of the mechanistic aspects in HAYNES 188 during low-cycle fatigue in the range 25 °C to 1000 °C

The low-cycle fatigue (LCF) behavior of a wrought cobalt-base superalloy, Haynes 188, has been investigated over a range of temperatures between 25 °C and 1000 °C employing a triangular waveform and a constant strain amplitude of ±0.4 pct. Correlations between macroscopic cyclic deformation and fatigue life with the various microstructural phenomena were enabled through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), detailing the crack initiation and propagation modes, deformation substructure, and carbide precipitation. Cyclic stress response varied as a complex function of temperature. Dynamic strain aging (DSA) was found to occur over a wide temperature range between 300 °C and 750 °C. In the DSA domain, the alloy exhibited marked cyclic hardening with a pronounced maximum at 650 °C. Dynamic strain aging has been documented through the occurrence of serrated yielding, inverse temperature dependence of maximum cyclic stress, and cyclic inelastic strain developed at half of the fatigue life. Additionally, the alloy also displayed a negative strain rate sensitivity of cyclic stress in the DSA regime. These macroscopic features in the DSA domain were accompanied by the substructure comprised of coplanar distribution of dislocations associated with the formation of pileups, stacking faults, and very high dislocation density. Toward the end of the DSA domain, dislocation pinning by M₂₃C₆ precipitates occurred predominantly. The deformation behavior below and above the DSA domain has also been investigated in detail. The temperature dependence of LCF life showed a maximum at ≈300 °C. The drastic reduction in life between 300 °C and 850 °C has been ascribed primarily to the deleterious effects of DSA on crack initiation and propagation, while the lower life at temperatures less than 200 °C has been attributed to the combined influence of low ductility and larger cyclic response stress.     

Disparities in arteriovenous fistula placement in older hemodialysis patients

The benefits of an arteriovenous fistula (AVF) as the preferred vascular access for hemodialysis have been clearly demonstrated. However, only about 20% of patients in the United States initiate hemodialysis with an AVF. In this study, we assessed whether disparities exist in the type of first hemodialysis access placed prior to dialysis start (rather than that used at dialysis initiation), to detect whether certain disadvantaged groups might have lower likelihood of AVF placement. Study cohort of 118,767 incident hemodialysis patients ≥67 years of age (1/2005–12/2008) derived from the United States Renal Data System was linked with Medicare claims data to identify the type of initial access placed predialysis. We used logistic regression model with outcome being the initial predialysis placement of an AVF as opposed to an arteriovenous graft or a central venous catheter. Increasing age, female sex, black race, lower body mass index, urban location, certain comorbidities, and shorter pre–end‐stage renal disease nephrology care are all associated with a significantly lower likelihood of AVF placement as initial access predialysis. Our study suggests the presence of significant disparities in the placement of an AVF as initial hemodialysis vascular access. We suggest that additional attention should be paid to these patient groups to improve disparities by patient education, earlier referral, and close follow‐up.