Effect of High Pressure Torsion on Crystal Orientation to Improve the Thermoelectric Property of a Bi2Te3-Based Thermoelectric Semiconductor

2010 ◽  
Vol 89-91 ◽  
pp. 41-46 ◽  
Author(s):  
Maki Ashida ◽  
Takashi Hamachiyo ◽  
Kazuhiro Hasezaki ◽  
Hirotaka Matsunoshita ◽  
Z. Horita
Keyword(s):  
High Pressure ◽  
Power Factor ◽  
Crystal Orientation ◽  
High Pressure Torsion ◽  
Preferred Orientation ◽  
Orientation Factor ◽  
X Ray Diffraction ◽  
Fine Grain ◽  
Maximum Value ◽  
P Type

A Bi2Te3-based thermoelectric semiconductor was subjected by high pressure torsion (HPT). Sample disks of p-type Bi0.5Sb1.5Te3.0 were cut from sintered compacts that were made by mechanically alloying (MA) followed by hot pressing. Disks were subjected by HPT with 1, 5 and 10 turns at 473 K under 6.0 GPa of pressure. Crystal orientation was investigated by X-ray diffraction. Microstructures were characterized using scanning electron microscopy. Results indicated that HPT disks after 5 turns had a preferred orientation and a fine grain compared with pre-HPT disks while the orientation factor was decreased after HPT using 10 turns. The power factor had a maximum value at 5 turns as determined by measuring its thermoelectric properties. A maximum power factor of 4.30×10-3 Wm-1K-2 was obtained for HPT disks after 5 turns. This value was larger than that for the pre-HPT disk. The over-HPT of 10 turns was found to have caused a decrease in the preferred orientation leading to a low power factor.

Control of Crystallographic Orientation and Grain Refinement in Bi2Te3-Based Thermoelectric Semiconductors by Applying High Pressure Torsion

2008 ◽  
Vol 584-586 ◽  
pp. 1006-1011 ◽  
Author(s):  
Maki Ashida ◽  
Takashi Hamachiyo ◽  
Kazuhiro Hasezaki ◽  
Hirotaka Matsunoshita ◽  
Masaaki Kai ◽  
...  
Keyword(s):  
High Pressure ◽  
Crystal Orientation ◽  
High Pressure Torsion ◽  
Crystallographic Structure ◽  
Nominal Composition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Refined Microstructure ◽  
Vertical Bridgman ◽  
P Type

Prepared were p-type Bi2Te3-based thermoelectric semiconductors, having a grain-refined microstructure and a preferred orientation of anisotropic crystallographic structure. Disks with a nominal composition Bi0.5Sb1.5Te3.0 were cut from an ingot grown by the vertical Bridgman method (VBM) and deformed at 473 K under a pressure of 6.0 GPa by high pressure torsion (HPT). The crystal orientation was characterized with X-ray diffraction. The microstructures were characterized by using optical microscopy and scanning electron microscopy. It was found that the HPT disks had a fine and preferentially oriented grain compared to that of the VBM disks. Further, the power factor of the HPT disks was about twice as large as that of the VBM disks. These results indicate that HPT is effective for improving the thermoelectric properties of Bi2Te3-based thermoelectric semiconductors.

Study on Phases and Thermoelectric Properties of Bulk Fe4Sb12 and Fe3CoSb12 Prepared by Milling and Sintering

2011 ◽  
Vol 121-126 ◽  
pp. 1526-1529
Author(s):  
Ke Gao Liu ◽  
Jing Li
Keyword(s):  
Thermoelectric Properties ◽  
Impurity Phase ◽  
Semiconductor Materials ◽  
Thermal Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
Seebeck Coefficients ◽  
Maximum Value ◽  
Type Semiconductor ◽  
P Type

Bulk Fe4Sb12 and Fe3CoSb12 were prepared by sintering at 600 °C. The phases of samples were analyzed by X-ray diffraction and their thermoelectric properties were tested by electric constant instrument and laser thermal constant instrument. Experimental results show that, the major phases of bulk samples are skutterudite with impurity phase FeSb2. The electric resistivities of the samples increase with temperature rising at 100~500 °C. The bulk samples are P-type semiconductor materials. The Seebeck coefficients of the bulk Fe4Sb12 are higher than those of bulk Fe3CoSb12 samples at 100~200 °C but lower at 300~500 °C. The power factor of the bulk Fe4Sb12 samples decreases with temperature rising while that of bulk Fe3CoSb12 samples increases with temperature rising at 100~500 °C. The thermal conductivities of the bulk Fe4Sb12 samples are relatively higher than those of and Fe3CoSb12, which maximum value is up to 0.0974 Wm-1K-1. The ZT value of bulk Fe3CoSb12 increases with temperature rising at 100~500 °C, the maximum value is up to 0.031.The ZT values of the bulk Fe4Sb12 samples are higher than those of bulk Fe3CoSb12 at 100~300 °C while lower at 400~500 °C.

Correlation between microstructural evolution during high-pressure torsion and isothermal heat treatment of amorphous Al85Gd8Ni5Co2 alloy

2010 ◽  
Vol 25 (7) ◽  
pp. 1388-1397 ◽  
Author(s):  
Péter Henits ◽  
Ádám Révész ◽  
Erhard Schafler ◽  
Péter J. Szabó ◽  
János L. Lábár ◽  
...  
Keyword(s):  
Heat Treatment ◽  
High Pressure ◽  
High Pressure Torsion ◽  
Thermal Sensitivity ◽  
Heat Treatments ◽  
Isothermal Heat Treatment ◽  
X Ray Diffraction ◽  
Continuous Heat Treatment ◽  
Isothermal Heat Treatments ◽  
Continuous Heat

Al85Gd8Ni5Co2 metallic glass was subjected to partial devitrification by high-pressure torsion, continuous heat treatment, and isothermal annealing. The fully amorphous alloy exhibits a well-defined transition in its first devitrification product during isothermal heat treatments from τm + α-Al phase mixture to primary α-Al by increasing the annealing temperature above 555 K. This thermal sensitivity predestinates the composition to identify the controversial thermal contribution of the plastic deformation in metallic glasses. Thermal stability and structure of the partially devitrified samples were systematically analyzed and compared by calorimetry, x-ray diffraction, and electron microscopy. It seems that the effect of severe deformation cannot be singled out by a simple isothermal heat treatment; i.e., high-pressure torsion acts as a spectrum of heat treatments performed at different annealing temperatures.

scholarly journals Effects of Low Rotational Speed on Crystal Orientation of Bi2Te3-Based Thermoelectric Semiconductors Deformed by High-Pressure Torsion

2012 ◽  
Vol 53 (4) ◽  
pp. 588-591 ◽  
Author(s):  
Maki Ashida ◽  
Natsuki Sumida ◽  
Kazuhiro Hasezaki ◽  
Hirotaka Matsunoshita ◽  
Zenji Horita
Keyword(s):  
High Pressure ◽  
Rotational Speed ◽  
Crystal Orientation ◽  
High Pressure Torsion

scholarly journals Effect of the High-Pressure Torsion (HPT) and Subsequent Isothermal Annealing on the Phase Transformation in Biomedical Ti15Mo Alloy

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1194 ◽  
Author(s):  
Kristína Bartha ◽  
Josef Stráský ◽  
Anna Veverková ◽  
Pere Barriobero-Vila ◽  
František Lukáč ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressure Torsion ◽  
Phase Evolution ◽  
High Energy ◽  
Phase Precipitation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Solution Treated ◽  
Α Phase ◽  
Element Partitioning

Ti15Mo metastable beta Ti alloy was solution treated and subsequently deformed by high-pressure torsion (HPT). HPT-deformed and benchmark non-deformed solution-treated materials were annealed at 400 °C and 500 °C in order to investigate the effect of UFG microstructure on the α-phase precipitation. Phase evolution was examined using laboratory X-ray diffraction (XRD) and by high-energy synchrotron X-ray diffraction (HEXRD), which provided more accurate measurements. Microstructure was observed by scanning electron microscopy (SEM) and microhardness was measured for all conditions. HPT deformation was found to significantly enhance the α phase precipitation due the introduction of lattice defects such as dislocations or grain boundaries, which act as preferential nucleation sites. Moreover, in HPT-deformed material, α precipitates are small and equiaxed, contrary to the α lamellae in the non-deformed material. ω phase formation is suppressed due to massive α precipitation and consequent element partitioning. Despite that, HPT-deformed material after ageing exhibits the high microhardness exceeding 450 HV.

Effect of single-crystal orientation on the molybdenum structure and hardness upon high pressure torsion

2021 ◽  
pp. 105754
Author(s):  
L.M. Voronova ◽  
T.I. Chashchukhina ◽  
T.M. Gapontseva ◽  
A.M. Patselov ◽  
V.P. Pilyugin ◽  
...  
Keyword(s):  
High Pressure ◽  
Single Crystal ◽  
Crystal Orientation ◽  
High Pressure Torsion

scholarly journals Studies on Amorphous Alloy Dispersed Aluminium Matrix Composite Prepared by High Pressure Torsion

2015 ◽  
Vol 5 (1) ◽  
pp. 89
Author(s):  
S. Hembrom ◽  
B. N. Roy ◽  
N. Khobragade ◽  
D. Roy
Keyword(s):  
High Pressure ◽  
Amorphous Alloy ◽  
High Pressure Torsion ◽  
Base Alloy ◽  
Hardness Measurement ◽  
Aluminium Matrix ◽  
Wear Property ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Aluminium Matrix Composite

<p class="1Body">Aluminium-based composite reinforced with Cu base amorphous alloy dispersed composite was prepared by means of high pressure torsion between a powder mix of aluminium and amorphous Cu base alloy. The X-ray diffraction pattern of powdered and consolidated composites shows the aluminium phase while the thermal stability of the amorphous alloy was studied with the aid of differential scanning calorimetry (DSC). The microstructural feature of the composite through scanning electron microscope reveals the well-distributed reinforcements in the host aluminium matrix. The hardness measurement on the as prepared composites shows significant increase in hardness with increase in reinforced amorphous alloy. Wear property of the synthesized composites were measured by using ball on plate wear tester which shows increase in wear resistance with increase in reinforced amorphous alloys.</p>

Microstructural Evolution in an Al-6061 Alloy Processed by High-Pressure Torsion and Rapid Annealing

2010 ◽  
Vol 667-669 ◽  
pp. 223-228 ◽  
Author(s):  
Aicha Loucif ◽  
Roberto B. Figueiredo ◽  
Thierry Baudin ◽  
François Brisset ◽  
Terence G. Langdon
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
Grain Refinement ◽  
High Pressure Torsion ◽  
Applied Pressure ◽  
Al 6061 ◽  
Fine Grain ◽  
Grain Structures ◽  
Average Grain Size ◽  
Continuous Recrystallization

The processing of bulk metals through the application of severe plastic deformation provides the opportunity for introducing significant grain refinement into bulk solids. In the present investigation, an aluminum alloy (Al-6061) was processed by high-pressure torsion (HPT) at room temperature under an applied pressure of 6.0 GPa up to a total of 5 turns. Detailed measurements after processing revealed the occurrence of continuous grain refinement and material strengthening with increasing imposed strain. The average grain size of the alloy was reduced from ~150 m to a grain size in the range of ~500 nm through processing by HPT. Although there was a difference in the average grain size of samples processed to different levels of imposed strain, careful inspection showed that the structures became similar after annealing at 250°C for 5 min. This suggests that the additional grain refinement introduced at large amounts of deformations is less stable at high temperatures. The results of this investigation, including the distributions of the grain sizes after annealing, are consistent with the predictions of a model based on the occurrence of continuous recrystallization in aluminum alloys having fine grain structures, large fractions of high-angle grain boundaries and where there is a large amount of deformation.

scholarly journals Influence of HPT and Accumulative High-Pressure Torsion on the Structure and Hv of a Zirconium Alloy

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 573
Author(s):  
Dmitry Gunderov ◽  
Andrey Stotskiy ◽  
Yuri Lebedev ◽  
Veta Mukaeva
Keyword(s):  
High Pressure ◽  
Zirconium Alloy ◽  
High Pressure Torsion ◽  
Ti Alloy ◽  
Micro Hardness ◽  
X Ray Diffraction ◽  
X Ray ◽  
Ω Phase ◽  
First Time ◽  
Torsion Deformation

The authors previously used the accumulative high-pressure torsion (ACC HPT) method for the first time on steel 316, β-Ti alloy, and bulk metallic glass vit105. On low-alloyed alloys, in particular, the zirconium alloy Zr-1%Nb, the new method was not used. This alloy has a tendency to α → ω phase transformations at using simple HPT. When using ACC HPT, the α → ω transformation can be influenced to a greater extent. This article studies the sliding effect and accumulation of shear strain in Zr-1%Nb alloy at various stages of high-pressure torsion (HPT). The degree of shear deformation at different stages of HPT was estimated. The influence of various high-pressure torsion conditions on the micro-hardness and phase composition by X-ray diffraction (XRD) of Zr-1%Nb was analyzed. It is shown that at high-pressure torsion revolutions of n = 2, anvils and the specimen significantly slip, which is a result of material strengthening. It was found that despite sliding, regular high-pressure torsion resulted in the high strengthening of Zr-1%Nb alloy (micro-hardness more than doubled), and after high-pressure torsion n = 10, up to 97% of the high-pressure ω-phase was formed in it (as in papers of other researchers). Accumulative high-pressure torsion deformation leads to the strongest transformation of the Zr-1%Nb structure and Hv and, therefore, to a higher real strain of the material due to composition by upsetting and torsion in strain cycles.

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