High-coercivity Nd-Fe-B Powders Obtained by High-Temperature Milling

2014 ◽  
Vol 59 (1) ◽  
pp. 47-50 ◽  
Author(s):  
W. Kaszuwara ◽  
B. Michalski ◽  
P. Orlowski
Keyword(s):  
High Temperature ◽  
Mechanical Alloying ◽  
Mechanical Milling ◽  
Room Temperature ◽  
The Other ◽  
Nanocrystalline Powders ◽  
High Coercivity ◽  
Milling Temperature ◽  
Constituent Elements ◽  
Hard Magnetic Properties

Abstract The possibility of employing high temperature milling (600°C) for the production of highly coercive Nd-Fe-B powders was examined. The materials were the Nd12Fe82B6, alloy which was subjected to mechanical milling and the powders of the constituent elements of this alloy which were processed by mechanical alloying. The processes were conducted in the two variants: the first variant consisted of mechanical milling performed at a high temperature which was maintained during the entire process, and the other variant included preliminary milling carried out at room temperature and then the milling temperature was increased. All the processes gave nanocrystalline powders with hard magnetic properties. The powders produced by mechanical milling had better properties than those produced by mechanical] alloying as they were more homogeneous and contained smaller amounts of the α-Fe phase.

Mechanical Alloying Behavior in the Nb-Si, Ta-Si, and Nb-Ta-Si Systems

1988 ◽  
Vol 133 ◽  
Author(s):  
K. S. Kumar ◽  
S. K. Mannan
Keyword(s):  
High Temperature ◽  
Mechanical Alloying ◽  
Mechanical Milling ◽  
Room Temperature ◽  
Crystalline Compound ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase

ABSTRACTThe mechanical alloying behavior of elemental powders in the Nb-Si, Ta-Si, and Nb-Ta-Si systems was examined via X-ray diffraction. The line compounds NbSi2 and TaSi2 form as crystalline compounds rather than amorphous products, but Nb5Si3 and Ta5Si3, although chemically analogous, respond very differently to mechanical milling. The Ta5Si3 composition goes directly from elemental powders to an amorphous product, whereas Nb5Si3 forms as a crystalline compound. The Nb5Si3 compound consists of both the tetragonal room-temperature α phase (c/a = 1.8) and the tetragonal high-temperature β phase (c/a = 0.5). Substituting increasing amounts of Ta for Nb in Nb5Si3 initially stabilizes the α-Nb5Si3 structure preferentially, and subsequently inhibits the formation of a crystalline compound.

scholarly journals Creep and Material Design

2012 ◽  
Vol 9 (1) ◽  
pp. 169-171
Author(s):  
Ram Oruganti
Keyword(s):  
High Temperature ◽  
Creep Resistance ◽  
Room Temperature ◽  
Shape Change ◽  
Creep Damage ◽  
Material Design ◽  
The Other ◽  
Permanent Shape ◽  
Total Life

When a material is subjected to temperature and stress, it deforms slowly resulting in permanent shape change. If the same amount of stress were applied at room temperature, the material would not budge. This deformation at high temperature under low stresses is called creep. This phenomenon is important for OEM’S like GE etc. since turbine components are exposed to low stress and high temperature and the resulting shape change is not a desirable consequence. Apart from the change in shape, the components can eventually rupture leading to catastrophic consequences. So it is imperative that the nature of this phenomenon is understood well. Some of the questions to be answered are 1) What makes one material more resistant to creep that the other 2) How can a material’s creep resistance be improved 3) How can the current creep damage in a component be measured 4) Is it possible to say what fraction of the total life of a component has been consumed by creep.

Preparation of Cu-Cr-Zr/AlN Nanocomposites and their Mechanical and Conductive Properties

2011 ◽  
Vol 239-242 ◽  
pp. 2756-2759
Author(s):  
Yong Qiang Qin ◽  
Yu Cheng Wu ◽  
Yan Wang ◽  
Yu Hong ◽  
Jing Quan Deng ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Wear Resistance ◽  
High Temperature ◽  
Powder Metallurgy ◽  
Mechanical Alloying ◽  
Room Temperature ◽  
Copper Alloys ◽  
Morphology Characterization ◽  
Conductive Properties ◽  
Conductivity Behavior

Copper and copper alloys had various applications in tremendous areas due to their unique properties, such as good conductivity, good thermal conductivity and so on. However, applications of copper and copper alloys were severely restricted as the result of the limited strength at room temperature and poor wear-resistance at high temperature. In this paper, we investigated the preparation of Cu-Cr-Zr/AlN nanocomposites by mechanical alloying process and then powder metallurgy technology. XRD and SEM were performed for the phase and morphology characterization. The conductivity properties were also tested and the results showed that Cu-Cr-Zr/AlN nanocomposites exhibited excellent conductivity behavior.

ARSENIDES OF THE TRANSITION METALS: II. THE NICKEL ARSENIDES

1957 ◽  
Vol 35 (10) ◽  
pp. 1205-1215 ◽  
Author(s):  
R. D. Heyding ◽  
L. D. Calvert
Keyword(s):  
High Temperature ◽  
Melting Point ◽  
Transition Metals ◽  
Stability Region ◽  
Room Temperature ◽  
Metastable Phase ◽  
The Other ◽  
Incongruent Melting ◽  
Diffraction Patterns ◽  
The Stability

Alloys of nickel and arsenic containing up to 60% As by weight have been studied by means of room temperature and high temperature Debye-Scherrer diagrams. Three compounds have been identified: Ni5As2, Ni12−xAs8 (maucherite), and NiAs (niccolite). The first of these is homogeneous from Ni5As2 to Ni4.8A2 at room temperature, and to Ni4.6As2 above 250 °C., while the latter is homogeneous from NiAs to Ni0.95As. Contrary to expectations the stability region of the compound Ni12−xAs8 is very narrow, and occurs at Ni11As8 rather than at Ni3As2. Evidence is presented in support of Hansen's contention that this compound has an incongruent melting point. Alloys in the region corresponding to Ni4.6As2 undergo two transitions below 200 °C, one of which is martensitic and produces a metastable phase, while the other is believed to result in the formation of a new compound, as yet unidentified. The diffraction patterns are discussed in some detail.

Holmium induced enhanced functionality at room temperature and structural phase transition at high temperature in bismuth ferrite nanoparticles

2016 ◽  
Vol 4 (4) ◽  
pp. 780-792 ◽  
Author(s):  
Smita Chaturvedi ◽  
Rabindranath Bag ◽  
Vasant Sathe ◽  
Sulabha Kulkarni ◽  
Surjeet Singh
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
High Temperatures ◽  
Structural Phase Transition ◽  
Room Temperature ◽  
Bismuth Ferrite ◽  
Structural Phase ◽  
Ferrite Nanoparticles ◽  
High Coercivity ◽  
Remnant Magnetization

Ho-doped sample simultaneously exhibits high-coercivity and enhanced remnant magnetization with a polar R3c symmetry at room temperature. The onset of R3c to Pnma phase transition is observed at high temperatures in the Ho-doped samples.

High Temperature Implantation in Graphite

1983 ◽  
Vol 27 ◽  
Author(s):  
G. Braunstein ◽  
B.S. Elman ◽  
M.S. Dresselhaus ◽  
G. Dresselhaus ◽  
T. Venkatesan
Keyword(s):  
High Temperature ◽  
Radiation Damage ◽  
High Temperatures ◽  
Room Temperature ◽  
Pyrolytic Graphite ◽  
Rutherford Backscattering ◽  
The Other ◽  
Highly Oriented Pyrolytic Graphite ◽  
Graphite Lattice ◽  
Partial Annealing

ABSTRACTIn previous studies it was found that when highly oriented pyrolytic graphite (HOPG) is implanted at room temperature, the damage caused by the implantation could be completely annealed by heating the sample to temperatures higher than ∼ 2500°C. However at these high temperatures, the implanted species was found to diffuse out of the sample, as evidenced by the disappearance of the impurity peak in the Rutherford backscattering (RBS) spectrum. If, on the other hand, the HOPG crystal was held at a high temperature (≥ 600°C) during the implantation, partial annealing could be observed. The present work further shows that it is possible to anneal the radiation damage and simultaneously to retain the implants in the graphite lattice by means of high temperature implantation (Ti ≥ 450°C) followed by annealing at 2300°C.

Increased High Temperature Oxidation Resistance of Ni20Cr20Fe5Nb1Y2O3 Alloy with Nano-Sized Grains

2005 ◽  
Vol 486-487 ◽  
pp. 109-112 ◽  
Author(s):  
Il Ho Kim ◽  
S.I. Kwun
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Mechanical Alloying ◽  
Tensile Properties ◽  
Oxidation Resistance ◽  
Tensile Property ◽  
High Temperature Oxidation ◽  
Room Temperature ◽  
Dispersion Strengthening ◽  
Temperature Oxidation

The oxidation and tensile properties of a Ni20Cr20Fe5Nb alloy and a Ni20Cr20Fe 5Nb1Y2O3 alloy with nano-sized grains were compared with those of the comercial IN718 alloy. The oxidation resistance of the Ni20Cr20Fe5Nb1Y2O3 alloy was superior to that of the Ni20Cr20Fe5Nb and IN 718 alloys. This superior oxidation resistance was the result of both the formation of dense oxides on the surface of the alloy and the interruption of Cr migration in the alloy by the addition of Y2O3. Moreover, the tensile property of the Ni20Cr20Fe5Nb1Y2O3 alloy at room temperature and 400oC was higher than that of the Ni20Cr20Fe5Nb and IN718 alloys by more than 300MPa (30%). This result can be attributed to the dispersion strengthening of Y2O3. The relatively low tensile strength at 600°C and 800°C of the alloys fabricated by mechanical alloying was attributed to grain refinement showing intergranular fracture at high temperatures.

Microstructure Control in Iron Aluminides by Phase Decomposition or by Mechanical Alloying for Improved Strength and Ductility

1996 ◽  
Vol 460 ◽  
Author(s):  
D. G. Morris ◽  
S. Gunther
Keyword(s):  
High Temperature ◽  
Mechanical Alloying ◽  
Creep Strength ◽  
Room Temperature ◽  
Iron Aluminides ◽  
Chemical Compositions ◽  
Two Phase ◽  
High Temperature Tensile ◽  
Room Temperature Strength ◽  
Strength And Ductility

ABSTRACTThe iron aluminides based on Fe3Al or FeAl being developed for intermediate temperature applications suffer from mediocre room temperature strength and ductility and poor high temperature tensile and creep strength. Attempts to overcome these problems have been restricted by the limited possibilities of structure modification by, for example, precipitation of stable strengthening particles. The present study examines two approaches to obtaining two-phase mixtures for improved strength and ductility: by adjusting chemical compositions such that two-phase order-disorder (α-α″) mixtures are obtained, and by mechanical alloying. Two-phase α-α″ mixtures are obtained by heat treatment of Fe-Al alloys with Al content near 20–24% and in ternary Fe-Al-Si alloys with suitably adjusted Al and Si contents. Microstructures of such alloys can be modified during heat treatments by ordering, precipitation or decomposition, and two-phase mixtures similar to those in the γ-γ superalloys obtained. Such two-phase alloys show good high temperature tensile and creep strength with some indication of reasonable ductility and reduced environmental sensitivity. Mechanical alloying can easily produce FeAl alloys of fine grain size reinforced with stable oxide particles. These structures lead to high room temperature strength with some ductility: controlled recrystallization can significantly modify both strength and ductility.

4H-SiC PIN Diode as High Temperature Multifunction Sensor

2017 ◽  
Vol 897 ◽  
pp. 630-633 ◽  
Author(s):  
Shuo Ben Hou ◽  
Per Erik Hellström ◽  
Carl Mikael Zetterling ◽  
Mikael Östling
Keyword(s):  
High Temperature ◽  
Bias Voltage ◽  
Temperature Sensitivity ◽  
Room Temperature ◽  
Optical Sensing ◽  
Temperature Sensing ◽  
The Other ◽  
Pin Diode ◽  
Forward Current

An in-house fabricated 4H-SiC PIN diode that has both optical sensing and temperature sensing functions from room temperature (RT) to 550 °C is presented. The two sensing functions can be simply converted from one to the other by switching the bias voltage on the diode. The optical responsivity of the diode at 365 nm is 31.8 mA/W at 550 °C. The temperature sensitivity of the diode is 2.7 mV/°C at the forward current of 1 μA.

Enhanced Thermoelectric Figure-of-merit at Room Temperature in Bulk Bi(Sb)Te(Se) With Grain Size of ∼100nm

2013 ◽  
Vol 1543 ◽  
pp. 93-98 ◽  
Author(s):  
Tsung-ta E. Chan ◽  
Rama Venkatasubramanian ◽  
James M. LeBeau ◽  
Peter Thomas ◽  
Judy Stuart ◽  
...  
Keyword(s):  
Grain Size ◽  
Mechanical Alloying ◽  
Grain Boundaries ◽  
Figure Of Merit ◽  
Room Temperature ◽  
High Energy ◽  
High Density ◽  
Nanocrystalline Powders ◽  
Bulk Materials ◽  
P Type

ABSTRACTGrain boundaries are known to be able to impede phonon transport in the material. In the thermoelectric application, this phenomenon could help improve the figure-of-merit (ZT) and enhance the thermal to electrical conversion. Bi2Te3 based alloys are renowned for their high ZT around room temperature but still need improvements, in both n- and p-type materials, for the resulting power generation devices to be more competitive. To implement high density of grain boundaries into the bulk materials, a bottom-up approach is employed in this work: consolidations of nanocrystalline powders into bulk disks. Nanocrystalline powders are developed by high energy cryogenic mechanical alloying that produces Bi(Sb)Te(Se) alloy powders with grain size in the range of 7 to 14 nm, which is about 25% finer compared to room temperature mechanical alloying. High density of grain boundaries are preserved from the powders to the bulk materials through optimized high pressure hot pressing. The consolidated bulk materials have been characterized by X-ray diffraction and transmission electron microscope for their composition and microstructure. They mainly consist of grains in the scale of 100 nm with some distributions of finer grains in both types of materials. Preliminary transport property measurements show that the thermal conductivity is significantly reduced at and around room temperature: about 0.65 W/m-K for the n-type BiTe(Se) and 0.85 W/m-K for the p-type Bi(Sb)Te, which are attributed to increased phonon scattering provided by the nanostructure and therefore enhanced ZT about 1.35 for the n-type and 1.21 for the p-type are observed. Detailed transport properties, such as the electrical resistivity, Seebeck coefficient and power factor as well as the resulting ZT as a function of temperature will be described.

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