scholarly journals Development of new Fe–Al–Nb(–B) alloys for structural applications at high temperatures

MRS Advances ◽  
2021 ◽  
Author(s):  
Angelika Gedsun ◽  
Frank Stein ◽  
Martin Palm
Keyword(s):  
Microstructural Evolution ◽  
Annealing Time ◽  
Composition Range ◽  
Boron Doping ◽  
Laves Phase ◽  
Time Dependent ◽  
Homogeneous Distribution ◽  
Heusler Phase ◽  
Structural Applications ◽  
The Matrix

Abstract It is known for Fe–Al–Ta alloys, that a homogeneous distribution of strengthening Laves phase precipitates in the matrix and aligned at the grain boundaries can be obtained when the formation of the stable Laves phase is preceded by the formation of the metastable Heusler phase. Several Fe–Al–Nb alloys with different Al and Nb contents and with or without boron doping are studied to elucidate whether comparable microstructures can be obtained in this system. It was found that the Heusler phase only occurs within a limited composition range. The time-dependent evolution of the microstructure shows that the transformation proceeds faster in Fe–Al–Nb alloys. Microhardness was measured in dependence on the microstructural evolution with increasing annealing time, and compressive yield stress was determined for alloys annealed 700 °C/1000 h to evaluate the influence of microstructure and composition. Graphic Abstract

scholarly journals Expression of VEGF-A Signaling Pathway in Cartilage of ACLT-induced Osteoarthritis Mouse Model

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Jia-jia Qian ◽  
Qi Xu ◽  
Wei-min Xu ◽  
Ren Cai ◽  
Gui-cheng Huang
Keyword(s):  
Signaling Pathway ◽  
Cruciate Ligament ◽  
Time Dependent ◽  
Pathological Changes ◽  
The Matrix ◽  
Vegfr2 Signaling ◽  
Cox 2 ◽  
Anterior Cruciate ◽  
A Disintegrin And Metalloproteinase ◽  
Safranin O

Abstract Background Anterior cruciate ligament transection surgery (ACLT)-induced OA model was often used to investigate the molecular mechanism of knee osteoarthritis (KOA). Researches have shown that vascular endothelial growth factor (VEGF) played an important role in OA. The present study aimed to investigate the pathological changes after ACLT surgery and reveal the expression characteristics of the VEGF-A/VEGFR2 signaling pathway in this model. Methods Moderate KOA model was established by ACLT, and 1, 2, 4, 8, and 12 weeks after surgery, hematoxylin-eosin (HE) and Safranin-O(S-O) staining were used to detect the pathological changes in mouse knee cartilage, and the matrix biomarkers A Disintegrin and Metalloproteinase with Thrombospondin Motifs 5(ADAMTS5), Collagen II (COL-II) were detected using immunohistochemistry (IHC), CD31 was detected by immunofluorescence (IF) to show the vascular invasion in cartilage, and proteins expression of VEGF-A pathway were detected by Western blot (WB). Meanwhile, the inflammatory biomarkers cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) in cartilage were detected by WB. Results ACLT surgery can lead to degeneration of cartilage in mice, and the characteristics of the lesion were time-dependent. The ADAMTS5-positive cells increased while COL-II decreased in OA cartilage with time, and new blood vessels labeled by CD31 can be seen from 1 week in OA cartilage, and increased in 8 and 12 weeks. The expression of VEGF-A, VEGFR2, COX-2, and iNOS were higher than control groups, which were basically consistent with the degree of osteoarthritis. Conclusions The degenerative degree of articular cartilage was time-dependent; angiogenesis and inflammation were important pathological changes of cartilage in KOA. The expression of the VEGF-A/VEGFR2 signaling pathway was basically correlated with the degree of KOA.

MICROSTRUCTURAL EVOLUTION OF Al-Cu-Mg-Ag ALLOY WITH TRACE Zr ADDITION DURING TWO-STEP HOMOGENIZATION

2009 ◽  
Vol 23 (06n07) ◽  
pp. 855-862 ◽  
Author(s):  
FEIYUE MA ◽  
ZHIYI LIU
Keyword(s):  
Melting Point ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Cast Alloy ◽  
Scanning Calorimetry ◽  
Zr Addition ◽  
Homogenization Time ◽  
The Matrix ◽  
Higher Temperature ◽  
Lower Temperature

The microstructural evolution in an Al - Cu - Mg - Ag alloy with trace Zr addition during homogenization treatment was characterized by Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDS). It was shown that the low-melting-point phase segregating toward grain boundaries is Al 2 Cu , with a melting point of 523.52°C. A two-step homogenization process was employed to optimize the microstructure of the as-cast alloy, during which the alloy was first homogenized at a lower temperature, then at a higher temperature. After homogenized at 420°C for 6 h, Al 3 Zr particles were finely formed in the matrix. After that, when the alloy was homogenized at an elevated temperature for a longer time, i.e., 515°C for 24 h, most of the precipates at the grain boundaries were removed. Furthermore, the dispersive Al 3 Zr precipitates were retained, without coarsening greatly in the final homogenization step. A kinetics model is employed to predict the optimal homogenization time at a given temperature theoretically, and it confirms the result in present study, which is 420°C/6h+515°C/24h.

scholarly journals A Numerical Approach for Evaluating the Time-Dependent Distribution of a Quasi Birth-Death Process

2021 ◽  
Author(s):  
Michel Mandjes ◽  
Birgit Sollie
Keyword(s):  
Continuous Time ◽  
Real Life ◽  
Numerical Approach ◽  
Time Dependent ◽  
Death Process ◽  
Continuous Time Markov Chain ◽  
Likelihood Estimator ◽  
Real Life Data ◽  
The Matrix ◽  
Birth Death

AbstractThis paper considers a continuous-time quasi birth-death (qbd) process, which informally can be seen as a birth-death process of which the parameters are modulated by an external continuous-time Markov chain. The aim is to numerically approximate the time-dependent distribution of the resulting bivariate Markov process in an accurate and efficient way. An approach based on the Erlangization principle is proposed and formally justified. Its performance is investigated and compared with two existing approaches: one based on numerical evaluation of the matrix exponential underlying the qbd process, and one based on the uniformization technique. It is shown that in many settings the approach based on Erlangization is faster than the other approaches, while still being highly accurate. In the last part of the paper, we demonstrate the use of the developed technique in the context of the evaluation of the likelihood pertaining to a time series, which can then be optimized over its parameters to obtain the maximum likelihood estimator. More specifically, through a series of examples with simulated and real-life data, we show how it can be deployed in model selection problems that involve the choice between a qbd and its non-modulated counterpart.

scholarly journals Thermal degradation of hemicellulose and cellulose in ball-milled cedar and beech wood

2021 ◽  
Vol 67 (1) ◽  
Author(s):  
Jiawei Wang ◽  
Eiji Minami ◽  
Mohd Asmadi ◽  
Haruo Kawamoto
Keyword(s):  
Thermal Degradation ◽  
Ball Milling ◽  
Cell Walls ◽  
Uronic Acid ◽  
Beech Wood ◽  
Cellulose Microfibrils ◽  
Homogeneous Distribution ◽  
Japanese Beech ◽  
Temperature Range ◽  
The Matrix

AbstractThe thermal degradation reactivities of hemicellulose and cellulose in wood cell walls are significantly different from the thermal degradation behavior of the respective isolated components. Furthermore, the degradation of Japanese cedar (Cryptomeria japonica, a softwood) is distinct from that of Japanese beech (Fagus crenata, a hardwood). Lignin and uronic acid are believed to play crucial roles in governing this behavior. In this study, the effects of ball milling for various durations of time on the degradation reactivities of cedar and beech woods were evaluated based on the recovery rates of hydrolyzable sugars from pyrolyzed wood samples. The applied ball-milling treatment cleaved the lignin β-ether bonds and reduced the crystallinity of cellulose, as determined by X-ray diffraction. Both xylan and glucomannan degraded in a similar temperature range, although the isolated components exhibited different reactivities because of the catalytic effect of uronic acid bound to the xylose chains. These observations can be explained by the more homogeneous distribution of uronic acid in the matrix of cell walls as a result of ball milling. As observed for holocelluloses, cellulose in the ball-milled woods degraded in two temperature ranges (below 320 °C and above); a significant amount of cellulose degraded in the lower temperature range, which significantly changed the shapes of the thermogravimetric curves. This report compares the results obtained for cedar and beech woods, and discusses them in terms of the thermal degradation of the matrix and cellulose microfibrils in wood cell walls and role of lignin. Such information is crucial for understanding the pyrolysis and heat treatment of wood.

Thermal Spray Forming Using the HVOF Technique

1997 ◽  
Author(s):  
J.M. Guilemany ◽  
J.R. Miguel ◽  
M.J. Dougan ◽  
J.M. de Paco ◽  
Z. Dong ◽  
...  
Keyword(s):  
Thermal Spray ◽  
Spray Forming ◽  
Homogeneous Distribution ◽  
Material Decomposition ◽  
Hvof Spraying ◽  
Free Standing ◽  
Hvof Spray ◽  
The Matrix ◽  
Low Levels ◽  
Microstructural Examination

Abstract The feasibility of using the HVOF process for the thermal spray-forming of free-standing components has been investigated. HVOF spray forming offers a number of potential advantages compared to the established procedure of plasma forming, including increases in component density, and reduction in material decomposition during spraying. Using blends of carbide and superalloy powders in various proportions, HVOF spraying has been successfully used to form free-standing cylinders and cones of various lengths and thicknesses. Microstructural examination of the spray-formed material has shown a homogeneous distribution of carbides in the superalloy matrix, with very low levels of porosity. Refinement of the procedure has allowed reduction of the matrix content, and the forming of fragile materials.

A UNIFIED FORMALISM OF THERMAL QUANTUM FIELD THEORY

1994 ◽  
Vol 09 (14) ◽  
pp. 2363-2409 ◽  
Author(s):  
H. CHU ◽  
H. UMEZAWA
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Vacuum Polarization ◽  
Time Dependent ◽  
Quantum Field ◽  
Bogoliubov Transformation ◽  
Transformation Matrices ◽  
Thermo Field Dynamics ◽  
The Matrix ◽  
Recent Developments

We present a comprehensive review of the most fundamental and practical aspects of thermo-field dynamics (TFD), including some of the most recent developments in the field. To make TFD fully consistent, some suitable changes in the structure of the thermal doublets and the Bogoliubov transformation matrices have been made. A close comparison between TFD and the Schwinger-Keldysh closed time path formalism (SKF) is presented. We find that TFD and SKF are in many ways the same in form; in particular, the two approaches are identical in stationary situations. However, TFD and SKF are quite different in time-dependent nonequilibrium situations. The main source of this difference is that the time evolution of the density matrix itself is ignored in SKF while in TFD it is replaced by a time-dependent Bogoliubov transformation. In this sense TFD is a better candidate for time-dependent quantum field theory. Even in equilibrium situations, TFD has some remarkable advantages over the Matsubara approach and SKF, the most notable being the Feynman diagram recipes, which we will present. We will show that the calculations of two-point functions are simplified, instead of being complicated, by the matrix nature of the formalism. We will present some explicit calculations using TFD, including space-time inhomogeneous situations and the vacuum polarization in equilibrium relativistic QED.

Retrogression and Re-aging Heat Treatment: AA7XXX Aluminum Alloys

2019 ◽  
Author(s):  
V. Anil Kumar ◽  
S. Arjun ◽  
R.K. Gupta ◽  
P.V. Venkitakrishnan
Keyword(s):  
Heat Treatment ◽  
Aluminum Alloys ◽  
Industrial Applications ◽  
Age Hardening ◽  
Large Cross Section ◽  
Structural Applications ◽  
The Matrix ◽  
Peak Aged ◽  
Aged Temper ◽  
Short Time

Retrogression and re-aging (RRA) treatment was introduced to increase the stress corrosion cracking (SCC) resistance while retaining the strength attainable in T6 (peak aged) temper. Retrogression is a short-term heat treatment at an elevated temperature wherein a partial dissolution of metastable precipitates occurs, which are responsible for the hardening. During the next step, the material is re-aged in the regime of typical age hardening parameters to restore the strength with improved ductility. Response of RRA treatment has been reported on AA7XXX series Aluminum alloys such as AA7075, AA7050, AA7150, AA7049, and AA7010. Studies have been done on the effect of RRA on microstructure, mechanical properties such as tensile and hardness, corrosion, exfoliation corrosion, and SCC resistance by various researchers. The key characteristic of RRA is retrogression, which makes the re-precipitation in the matrix and coarsening of grain boundary precipitates such as MgZn2, η′. The retrogression treatment however requires high temperature and a short time, which limits the industrial application of RRA, especially in the heat treatment of the components with large cross section, due to the inherent thermal conductivity limitations. Hence, further work needs to be done in this area to apply this specialized heat treatment for industrial applications. This article brings out a comprehension of the changes in microstructure, tensile properties, and corrosion resistance of the various commonly used AA7XXX Aluminum alloys in structural applications with RRA heat treatment. The future scope of the work in RRA heat treatment is also discussed in this article.

Graphite/UPE Nanocomposite: Transport, Thermal, Mechanical and Viscoelastic Properties

2019 ◽  
Vol 23 ◽  
pp. 201-212
Author(s):  
Shivkumari Panda ◽  
Dibakar Behera ◽  
Tapan Kumar Bastia
Keyword(s):  
Transport Properties ◽  
Unsaturated Polyester ◽  
Homogeneous Distribution ◽  
Thermo Gravimetric ◽  
New Class ◽  
The Matrix ◽  
Novel Method ◽  
Water Transport Properties ◽  
First Time

This chapter presents the preparation and characterization of some unique properties of nanocomposites by dispersing graphite flakes in commercial unsaturated polyester (UPE) matrix. The composite was prepared by a novel method with the use of solvent swelling technique. Three different specimens of UPE/graphite nanocomposites were fabricated with addition of 1, 2 and 3 wt% of graphite flakes. Except mechanical, viscoelastic and thermo gravimetric properties, transport properties like electrical conductivity, thermal conductivity and water transport properties were studied for the first time. Graphite flakes propose enhanced properties to the composites suggesting homogeneous distribution of the nanofiller in the matrix and strong interaction with the matrix. 2wt% nanofiller loading showed superior essential characteristics and after that the properties reduced may be due to the nucleating tendency of the nanofiller particles. The XRD pattern showed the compatibility of the graphite flakes by introducing a peak around 26.550 in the nanocomposites. SEM Properties are also in agreement with the compatibility. Nanocomposite with 2wt% graphite also showed remarkable enhancement in transport, mechanical, viscoelastic and thermo gravimetric properties. So by introduction of a small quantity of graphite endow the new class of multiphase nanocomposites with inimitable structure and tremendous application.

scholarly journals Development in mechanical and fatigue properties of AA6061/AL2O3 nanocomposites under stirring temperature (ST)

2021 ◽  
Vol 4 (12(112)) ◽  
pp. 47-52
Author(s):  
Raad Mohammed Abed ◽  
Ali Yousuf Khenyab ◽  
Hussain Jasim M. Alalkawi
Keyword(s):  
Mechanical Properties ◽  
Cost Effective ◽  
Fatigue Tests ◽  
Core Material ◽  
Fatigue Properties ◽  
Uniform Distributions ◽  
Al2o3 Composite ◽  
Structural Applications ◽  
The Matrix ◽  
High Fatigue

Aluminum is expected to remain the core material for many critical applications such as aircraft and automobiles. This is due to the high resistance to different environmental conditions, desired and manageable mechanical properties, as well as high fatigue resistance. Aluminum nanocomposites such as AA6061/Al2O3 can be made in many ways using a liquid metallurgy method. The main challenges for this method in the production of nanocomposites are the difficulties of achieving a uniform distribution of reinforcing materials and possible chemical reactions between the reinforcing material and the matrix. For structural applications exclusive to aerospace sectors. The growing cost-effective nanocomposites mass production technology with essential operational and geometric flexibility is a big challenge all the time. Each method of preparing AA6061/Al2O3 nanocomposites can provide different mechanical properties. In the present study, nine nanocomposites were prepared at three stirring temperatures (800, 850, and 900 °C) with the level of Al2O3 addition of 0, 5, 7, and 9 wt %. The results of tensile, hardness and fatigue tests revealed that the composite including 9 wt % Al2O3 with 850 °C stirring temperatures has the best properties. It was also revealed that the 850 °C stirring temperature (ST) with 9 wt % Al2O3 composite provide an increase in tensile strength, VHN and reduction in ductility by 20 %, 16 % and 36.8 % respectively, compared to zero-nano. Also, the fatigue life at the 90 MPa stress level increased by 17.4 % in comparison with 9 wt % nanocomposite at 800 °C (ST). Uniform distributions were observed for all nine microstructure compositions.

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