Bonding and oxidation protection of Ti2AlC and Cr2AlC for a Ni-based superalloy

Alumina forming, oxidation and thermal shock resistant MAX phases are of a high interest for high temperature applications. Herein we report, on bonding and resulting interactions between a Ni-based superalloy, NSA, and two alumina forming MAX phases. The diffusion couples Cr₂AlC/Inconel-718/Ti₂AlC were assembled and heated to 1000 or 1100 °C in a vacuum hot press under loads corresponding to stresses of either 2 MPa or 20 MPa. The resulting interfaces were examined using X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Good bonding between Cr₂AlC and NSA was achieved after hot pressing at 1000 °C and a contact pressure of only 2 MPa; in the case of Ti₂AlC a higher temperature (1100 °C) and pressure (20 MPa) were needed. In both cases, a diffusion bond, in which mainly Ni and Cr out diffused from the NSA into the MAX phase and a concomittant out diffusion of Al from the latter, was realized with no evidence of interfacial damage or cracking after cooling to room temperature. The reactions paths were determined to be: Cr₂AlC/Cr₇C₃/Cr₇C₃,β-NiAl/α-Cr(Mo)/NSA and Ti₂AlC/Ti₂AlC,Ti₃NiAl₂C/β-NiAl/α-Cr(Mo)/NSA. Twenty thermal cycles from room temperature to 1000 °C showed that Ti₂AlC is a poor oxidation barrier for Inconel-718. However, in the case of Cr₂AlC no cracks, delamination nor surface degradation was observed, suggesting that this material could be used to protect Inconel-718 from oxidation.     

The possibility of lowering oil content of potato chips by combining atmospheric frying with postfrying vacuum application

Four protocols involving the application of low pressures, either toward the end of frying or after frying, were investigated with the aim of lowering the oil content of potato chips. Protocol 1 involving frying at atmospheric pressure followed by a 3 min draining time constituted the control. Protocol 2 involved lowering of pressure to 13.33 kPa, 40 s before the end of frying, followed by draining for 3 min at the same pressure. Protocol 3 was the same as protocol 2, except that the pressure was lowered 3 s before the end of frying. Protocol 4 involved lowering the pressure to 13.33 kPa after the product was lifted from the oil and holding it at this value over the draining time of 3 min. Protocol 4 gave a product having the lowest oil content (37.12 g oil/100 g defatted dry matter), while protocol 2 gave the product with highest oil content (71.10 g oil/100 g defatted dry matter), followed by those obtained using protocols 1 and 3 (68.48 g oil/100 g defatted dry matter and 52.50 g oil/100 g defatted dry matter, respectively). Protocol 4 was further evaluated to study the effects of draining times and vacuum applied, and compared with the control. It was noted that over the modest range of pressures investigated, there was no significant effect of the vacuum applied on the oil content of the product. This study demonstrates that the oil content of potato chips can be lowered significantly by combining atmospheric frying with draining under vacuum.     

Physico-chemical changes occurring in oil when atmospheric frying is combined with post-frying vacuum application

The aim of this study was to investigate the effect of atmospheric frying followed by drainage under vacuum on the stability of oil, compared to similar frying with drainage at atmospheric pressure. Changes in the oil were assessed by the free fatty acid (FFA) content, p-anisidine value (AnV), colour, viscosity, fatty acid profile and concentration of tocols. The rate of FFA formation in the case of vacuum drainage was found to be about half that of atmospheric drainage. Oil deterioration by oxidation and polymerisation was also reduced by the use of vacuum drainage. The AnV of the oil after vacuum drainage was lower by about 12%, the total colour difference was improved by 14% and viscosity was slightly reduced after 5 days of frying, compared to the values for oil that had been drained at atmospheric pressure. There was a reduction in the loss of polyunsaturated fatty acids in the case of vacuum drainage after 5 days of frying but differences in retention of tocols were only evident in the first two days of frying.     

A Comparative Study of the Characteristics of French Fries Produced by Deep Fat Frying and Air Frying

Air frying is being projected as an alternative to deep fat frying for producing snacks such as French fries. In air frying, the raw potato sections are essentially heated in hot air containing fine oil droplets, which dehydrates the potato and attempts to impart the characteristics of traditionally produced French fries, but with a substantially lower level of fat absorbed in the product. The aim of this research is to compare: (1) the process dynamics of air frying with conventional deep fat frying under otherwise similar operating conditions, and (2) the products formed by the 2 processes in terms of color, texture, microstructure, calorimetric properties, and sensory characteristics. Although, air frying produced products with a substantially lower fat content but with similar moisture contents and color characteristics, it required much longer processing times, typically 21 min in relation to 9 min in the case of deep fat frying. The slower evolution of temperature also resulted in lower rates of moisture loss and color development reactions. Differential scanning calorimetry (DSC) studies revealed that the extent of starch gelatinization was also lower in the case of air fried product. In addition, the 2 types of frying also resulted in products having significantly different texture and sensory characteristics.     

Potato glycoalkaloids: formation and strategies for mitigation

With the increasing production and consumption of potato and its products, glycoalkaloid (GA) formation and toxicity are likely to become an important focus for food safety researchers and public health agencies. Not only the presence of GA, particularly in the form of α‐solanine and α‐chaconine, but also the changes occurring as a result of various post‐harvest handling practices and storage, are critical issues influencing the quality of stored potatoes. Studies on various factors (pre‐harvest, during harvest and post‐harvest) affecting GA have been carried out from time to time, but it is difficult to compare the results of one study with another due to wide variation in the parameters chosen. This review aims to develop a clear understanding of these issues. Published information on the types of GA, their effects on health, their typical concentrations in potatoes, their formation mechanisms, and how their levels can be controlled by following appropriate post harvest practices and storage regimes are critically analysed. The levels of GA in potato can be controlled effectively by adopting appropriate post‐harvest practices. Further studies are necessary, however, to investigate best practices, which either check completely or retard substantially their formation. Copyright © 2008 Society of Chemical Industry     

Processing of grain-size functionally gradient bioceramics for implant applications

This paper reports work on the processing of functionally gradient alumina bioceramics with a continuously decreasing grain size across the thickness, with the view of ultimately utilizing high-quality nano/ultrafine powders only at the surface of an implant to provide superior wear and mechanical properties. A model of disc geometry is used to examine the feasibility of producing this brand of materials. Wet processing/ball milling and sequential slip casting procedures were used to de-agglomerate alumina powders and deposit green layers of varying particle sizes from 50 to 250 nm. Both pressure-less sintering and hot pressing were evaluated as high temperature sintering/consolidation processes. The results indicate that pressure-less sintering may not be suitable. Hot pressing, however, achieved very promising results producing near fully dense product with a grain size that gradually changes across its thickness.     

Discussion of “relationship between deformation twinning and the stress-strain behavior of polycrystalline titanium and zirconium at 77 K”

Metallurgical and Materials Transactions A -     

Hertzian fracture of Pyrex glass under quasi-static loading conditions

Hertzian fracture tests were conducted using an Instron on Pyrex glass specimens with various surface conditions, including lubricants, employing steel, Al₂O₃, WC and Pyrex glass indentors of 0.79 to 12.7 mm radius under ambient air and high vacuum environments at cross-head speeds of 8.5×10^–6 to 2.1×10^–4m sec^–1. The results were not in strict accord with Auerbach's law, nor any of the existing energy-balance Hertzian fracture theories. Rather, they indicated that surface roughness and friction modified the Hertz stress field so that the maximum tensile stress at the surface occurred outside the contact circle. Further, they indicated that Hertzian fracture occurred by the direct, unstable growth into a cone crack of a pre-existing flaw at the displaced site of the maximum tensile stress, the flaw size responsible for the fracture decreasing with decrease in ball size (contact radius). Once a cone crack occurred, its length and growth were described reasonably well by Roesler's theory; however, his constant appears to be too high by a factor of about 5. A surface energy of @ 4 J m^–2 was derived from bend tests on specimens similar to those used in the Hertzian fracture tests. Using this value, the crack sizes which lead to fracture were estimated to range between 0.6 and 3.5 m for the conditions investigated here. The increase in the critical load for Hertzian fracture with indentation velocity was concluded to be due to kinetic effects of water vapour acting at the tip of the crack.     

Thermally Activated Slip in Rare Earth Containing Mg-Mn-Ce Alloy,ME10, Compared with Traditional Mg-Al-Zn Alloy,AZ31

JOM - It is of interest to assess the thermally activated nature of the deformation mechanisms responsible for the anisotropic response of textured Mg alloys, especially in those alloys that do and...