The role of rapid solidification processing in the fabrication of fiber reinforced metal matrix composites

Advanced composite processing techniques for fiber reinforced metal matrix composites require the flexibility to meet several widespread objectives. The development of uniquely desired matrix microstructures and uniformly arrayed fiber spacing with sufficient bonding between fiber and matrix to transmit load between them without degradation to the fiber or matrix are the minimum requirements necessary of any fabrication process. For most applications these criteria can be met by fabricating composite monotapes which are then consolidated into composite panels or more complicated components such as fiber reinforced turbine blades. Regardless of the end component, composite monotapes are the building blocks from which near net shape composite structures can be formed. The most common methods for forming composite monotapes are the powder cloth, foil/fiber, plasma spray, and arc spray processes. These practices, however, employ rapid solidification techniques in processing of the composite matrix phase. Consequently, rapid solidification processes play a vital and yet generally overlooked role in composite fabrication. The future potential of rapid solidification processing is discussed

A Compendium of Brazed Microstructures For Fission Power Systems Applications

NASA has been supporting design studies and technology development for fission-based power systems that could provide power to an outpost on the Moon, Mars, or an asteroid. Technology development efforts have included fabrication and evaluation of components used in a Stirling engine power conversion system. This investigation is part of the development of several braze joints crucial for the heat exchanger transfer path from a hot-side heat exchanger to a Stirling engine heat acceptor. Dissimilar metal joints are required to impart both mechanical strength and thermal path integrity for a heater head of interest. Preliminary design work for the heat exchanger involved joints between low carbon stainless steel to Inconel 718, where the 316L stainless steel would contain flowing liquid metal NaK while Inconel 718, a stronger alloy, would be used as structural reinforcement. This paper addressed the long-term microstructural stability of various braze alloys used to join 316L stainless steel heater head to the high conductivity oxygen-free copper acceptor to ensure the endurance of the critical metallic components of this sophisticated heat exchanger. The bonding of the 316L stainless steel heater head material to a copper heat acceptor is required to increase the heat-transfer surface area in contact with flowing He, which is the Stirling engine working fluid

Intrahepatic persistent fetal right umbilical vein: a retrospective study

Introduction: To appraise the incidence and value of intrahepatic persistent right umbilical vein (PRUV). Methods: This was a single-center study. Records of all women with a prenatal diagnosis of intrahepatic PRUV were reviewed. The inclusion criteria were women with gestational age greater than 13 weeks of gestation. Exclusion criteria were fetuses with situs abnormalities, due to the hepatic venous ambiguity, and extrahepatic PRUV. The primary outcome was the incidence of intrahepatic PRUV in our cohort. The secondary outcomes were associated malformations. Results: 219/57,079 cases (0.38%) of intrahepatic PRUV were recorded. The mean gestational age at diagnosis was 21.8 ± 2.9 weeks of gestations. PRUV was isolated in the 76.7%, while in 23.3% was associated with other major or minor abnormalities. The most common associated abnormalities were cardiovascular abnormalities (8.7%), followed by genitourinary abnormalities (6.4%), skeletal abnormalities (4.6%), and central nervous system abnormalities (4.1%). Within the cardiovascular abnormalities, the most common one was ventricular septal defect (six cases). Conclusion: In most cases PRUV is an isolated finding. Associated minor or major malformations are presented in the 23.3% of the cases, so this finding should prompt detailed prenatal assessment of the fetus, with particular regard to cardiovascular system

Effects of Microalloying on the Microstructures and Mechanical Properties of Directionally Solidified Ni-33(at.%)Al-31Cr-3Mo Eutectic Alloys Investigated

Despite nickel aluminide (NiAl) alloys' attractive combination of oxidation and thermophysical properties, their development as replacements for superalloy airfoils in gas turbine engines has been largely limited by difficulties in developing alloys with an optimum combination of elevated-temperature creep resistance and room-temperature fracture toughness. Alternatively, research has focused on developing directionally solidified NiAl-based in situ eutectic composites composed of NiAl and (Cr,Mo) phases in order to obtain a desirable combination of properties a systematic investigation was undertaken at the NASA Glenn Research Center to examine the effects of small additions of 11 alloying elements (Co, Cu, Fe, Hf, Mn, Nb, Re, Si, Ta, Ti, and Zr) in amounts varying from 0.25 to 1.0 at.% on the elevated-temperature strength and room-temperature fracture toughness of directionally solidified Ni-33Al-31Cr-3Mo eutectic alloy. The alloys were grown at 12.7 mm/hr, where the unalloyed eutectic base alloy exhibited a planar eutectic microstructure. The different microstructures that formed because of these fifth-element additions are included in the table. The additions of these elements even in small amounts resulted in the formation of cellular microstructures, and in some cases, dendrites and third phases were observed. Most of these elemental additions did not improve either the elevated-temperature strength or the room-temperature fracture toughness over that of the base alloy. However, small improvements in the compression strength were observed between 1200 and 1400 K when 0.5 at.% Hf and 0.25 at.% Ti were added to the base alloy. The results of this study suggest that the microalloying of Ni-33Al-31Cr-3Mo will not significantly improve either its elevatedtemperature strength or its room-temperature fracture toughness. Thus, any improvements in these properties must be acquired by changing the processing conditions

Molecular characterization of a phytoplasma causing phyllody in clover and other herbaceous hosts in northern Italy

Red clover (Trifolium pratense) and Ladino clover (Trifolium repens) plants showing phytoplasma-associated symptoms (yellowing/reddening, virescence and phyllody) have been recovered in Friuli-Venezia Giulia, Italy. Using AluI RFLP analysis of PCR amplified 16S rDNA we showed that the disease can be caused independently by two phylogenetically distinct phytoplasmas. One of them showed the very typical 16S rDNA RFLP pattern of the agent of Clover Phyllody in Canada (CCPh). The 16S rDNA of the other phytoplasma (Italian Clover Phyllody phytoplasma, ICPhp) has been PCR amplified, cloned and sequenced. The sequence revealed high similarity (>98%) with phytoplasmas belonging to the X disease cluster, which includes organisms not reported to cause phyllody on their hosts. The analysis by AluI RFLP of the PCR amplified pathogen 16S rDNA from other herbaceous plants (Crepis biennis, Taraxacum officinale, Leucanthemum vulgare) collected nearby with phytoplasma-associated symptoms showed similar patterns. Southern blot hybridization of their EcoRI digested total DNA revealed identical RFLP patterns, suggesting that the causative agent may be the same organism

LCF Life of NiCr-Y Coated Disk Alloys After Shot Peening, Oxidation and Hot Corrosion

In a prior companion study (Ref. 1), three different Ni-Cr coating compositions (29, 35.5, 45 wt% Cr) were applied at two thicknesses by Plasma Enhanced Magnetron Sputtering (PEMS) to two similar Ni-based disk alloys. One coating also received a thin ZrO2 overcoat. The low cycle fatigue (LCF) life of each coating was determined at 760 C and was less than that of the uncoated specimens. In this followon effort, shot peening was examined as a means to improve the as-deposited coating morphology as well as impart a residual compressive stress in the near-surface region. After evaluating the effect of the shot peening on the LCF life, the effectiveness of the shot-peened coating in protecting the disk alloy from oxidation and hot corrosion attack was evaluated. This evaluation was accomplished by exposing coated and shot-peened specimens to 500 h of oxidation followed by 50 h of hot corrosion, both at 760 C in air. These exposed specimens were then tested in fatigue and compared to similarly treated and exposed uncoated specimens. For all cases, shot peening improved the LCF life of the coated specimens. More specifically, the highest Cr coating showed the best LCF life of the coated specimens after shot peening, as well as after the environmental exposures. Characterization of the coatings after shot peening, oxidation, hot corrosion and LCF testing is presented and discussed

High Resolution X-Ray Micro-CT of Ultra-Thin Wall Space Components

A high resolution micro-CT system has been assembled and is being used to provide optimal characterization for ultra-thin wall space components. The Glenn Research Center NDE Sciences Team, using this CT system, has assumed the role of inspection vendor for the Advanced Stirling Convertor (ASC) project at NASA. This article will discuss many aspects of the development of the CT scanning for this type of component, including CT system overview; inspection requirements; process development, software utilized and developed to visualize, process, and analyze results; calibration sample development; results on actual samples; correlation with optical/SEM characterization; CT modeling; and development of automatic flaw recognition software. Keywords: Nondestructive Evaluation, NDE, Computed Tomography, Imaging, X-ray, Metallic Components, Thin Wall Inspectio

Development of High Temperature Dissimilar Joint Technology for Fission Surface Power Systems

NASA is developing fission surface power (FSP) system technology as a potential option for use on the surface of the moon or Mars. The goal is to design a robust system that takes full advantage of existing materials data bases. One of the key components of the power conversion system is the hot-side Heat Exchanger (HX). One possible design for this heat exchanger requires a joint of the dissimilar metals 316L stainless steel and Inconel 718, which must sustain extended operation at high temperatures. This study compares two joining techniques, brazing and diffusion bonding, in the context of forming the requisite stainless steel to superalloy joint. The microstructures produced by brazing and diffusion bonding, the effect of brazing cycle on the mechanical tensile properties of the alloys, and the strength of several brazed joints will be discussed

Physics Behind Precision

This document provides a writeup of contributions to the FCC-ee mini-workshop on "Physics behind precision" held at CERN, on 2-3 February 2016.Comment: https://indico.cern.ch/event/469561