An evaluation of the hexagonal close-packed to face-centered cubic phase transformation in a Ti-6Al-4V alloy during high-pressure torsion

The equiatomic face-centered cubic high-entropy alloy CrMnFeCoNi was severely deformed at room and liquid nitrogen temperature by high-pressure torsion up to shear strains of about 170. Its microstructure was analyzed by X-ray line profile analysis and transmission electron microscopy and its texture by X-ray microdiffraction. Microhardness measurements, after severe plastic deformation, were done at room temperature. It is shown that at a shear strain of about 20, a steady state grain size of 24 nm, and a dislocation density of the order of 1016 m−2 is reached. The dislocations are mainly screw-type with low dipole character. Mechanical twinning at room temperature is replaced by a martensitic phase transformation at 77 K. The texture developed at room temperature is typical for sheared face-centered cubic nanocrystalline metals, but it is extremely weak and becomes almost random after high-pressure torsion at 77 K. The strength of the nanocrystalline material produced by high-pressure torsion at 77 K is lower than that produced at room temperature. The results are discussed in terms of different mechanisms of deformation, including dislocation generation and propagation, twinning, grain boundary sliding, and phase transformation.

Download Full-text

Body-centered-cubic to face-centered-cubic phase transformation of iron under compressive loading along [100] direction

Materials Today Communications ◽

10.1016/j.mtcomm.2020.101961 ◽

2021 ◽

Vol 26 ◽

pp. 101961

Author(s):

Hongxian Xie ◽

Tong Ma ◽

Tao Yu ◽

Fuxing Yin

Keyword(s):

Phase Transformation ◽

Compressive Loading ◽

Cubic Phase ◽

Face Centered Cubic ◽

Body Centered Cubic ◽

Face Centered

Download Full-text

Preparation of Co3Ni Film Composed of Nanosheets and their Catalytic Activity in Hydrogen Generation from Sodium Borohydride Solution

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.860-863.822 ◽

2013 ◽

Vol 860-863 ◽

pp. 822-825

Author(s):

Jin Yun Liao ◽

Hao Li ◽

Xi Bin Zhang

Keyword(s):

Catalytic Activity ◽

High Performance ◽

Hydrogen Generation ◽

Deposition Process ◽

Cubic Phase ◽

Face Centered Cubic ◽

X Ray Diffraction ◽

Original Activity ◽

Hexagonal Close Packed ◽

Face Centered

In this study, aiming to obtain high performance nanocatalysts for NaBH4 hydrolysis, Co3Ni film composed of nanosheets with a mean thickness of 10 nm was fabricated by a magnetic field induced deposition process. X-ray diffraction analysis indicated that the as-prepared Co3Ni film is presented in both face-centered cubic phase and hexagonal close-packed phase. The nanostructured Co3Ni film catalyst showed good catalytic activity in the hydrolysis of NaBH4 and the rate constant was 5.77 mL·min-1. It was revealed that Co3Ni film catalysts didnt lose their catalytic original activity essentially after 10 cycles, which exhibited much improved reusability and stability compared with with recently reported nanocatalysts.

Download Full-text

In Situ HREM Observation of Phase Transformation Process in FePt and FePtCu Nanoparticles

MRS Proceedings ◽

10.1557/proc-0907-mm05-04 ◽

2005 ◽

Vol 907 ◽

Author(s):

Masatoshi Nakanishi ◽

Gen-ichi Furusawa ◽

Kokichi Waki ◽

Yasushi Hattori ◽

Takeo Kamino ◽

...

Keyword(s):

Phase Transformation ◽

Single Crystal ◽

Particle Formation ◽

Cubic Phase ◽

Fept Nanoparticles ◽

Crystal Formation ◽

Face Centered Cubic ◽

Shaped Particle ◽

Face Centered

AbstractThe processes of phase transformation in individual nanoparticles of FePt and FePtCu synthesized by the reverse micelle method, which are chemically homogeneous and monodisperse, have been investigated by an in-situ HREM observation in a FE-TEM. Polycrystalline FePt particles, initially of chemically disordered face-centered cubic phase (A1) were reconstructed into A1 single crystals between 25 °C and 650 °C, followed by phase transformation from A1 to chemically ordered face-centered tetragonal phase (L10) which began between 650 °C and 680 °C. The coalescence began concurrently with phase transformation, i. e., between 650 °C and 680 °C. They turned to be a round-shaped L10 particle between 680 °C and 720 °C. The single crystal formation, the phase transformation from A1 to L10, the coalescence and the round-shaped particle formation were also observed in the FePtCu nanoparticles. The temperatures of single crystal formation, phase transformation (and coalescence) and round-shaped particle formation of the FePtCu nanoparticles were between 25 °C and 500 °C, between 550 °C and 600 °C and between 600 °C and 650 °C, respectively. These temperatures were substantially lower than those for the FePt nanoparticles.

Download Full-text

Effect of Different Post-Sintering Temperatures on the Microstructures and Mechanical Properties of a Pre-Sintered Co–Cr Alloy

Metals ◽

10.3390/met8121036 ◽

2018 ◽

Vol 8 (12) ◽

pp. 1036 ◽

Cited By ~ 3

Author(s):

Seong-Ho Jang ◽

Bong Min ◽

Min-Ho Hong ◽

Tae-Yub Kwon

Keyword(s):

Mechanical Properties ◽

Cubic Phase ◽

Carbide Formation ◽

Face Centered Cubic ◽

Cobalt Chromium ◽

Hexagonal Close Packed ◽

Soft Metal ◽

Face Centered ◽

Few Data ◽

Sintered State

Although a cobalt–chromium (Co–Cr) blank in a pre-sintered state has been developed, there are few data on the optimal temperature for the alloy in terms of the desired mechanical properties. A metal block (Soft Metal, LHK, Chilgok, Korea) was milled to produce either disc-shaped or dumbbell-shaped specimens. All the milled specimens were post-sintered in a furnace at 1250, 1350 or 1450 °C. The microstructures, shrinkage and density of the three different alloys were investigated using the disc-shaped specimens. The mechanical properties were investigated with a tensile test according to ISO 22674 (n = 6). The number and size of the pores in the alloys decreased with increased temperature. The shrinkage and density of the alloys increased with temperature. In the 1250 °C alloy, the formation of the ε (hexagonal close-packed) phase was more predominant than that of the γ (face-centered cubic) phase. The 1350 °C and 1450 °C alloys showed γ phase formation more predominantly. Carbide formation was increased along with temperature. The 1450 °C group showed the largest grain size among the three groups. In general, the 1350 °C group exhibited mechanical properties superior to the 1250 °C and 1450 °C groups. These findings suggest that 1350 °C was the most optimal post-sintering temperature for the pre-sintered blank.

Download Full-text

Plasticity and Size Effects in High Purity Cobalt: An Experimental Study

Materials Science Forum ◽

10.4028/www.scientific.net/msf.879.560 ◽

2016 ◽

Vol 879 ◽

pp. 560-565

Author(s):

Gwendoline Fleurier ◽

Mayerling Martinez ◽

Pierre Antoine Dubos ◽

Eric Hug

Keyword(s):

Size Effects ◽

Threshold Value ◽

Cubic Phase ◽

Face Centered Cubic ◽

Tem Analysis ◽

Cubic Metals ◽

Hexagonal Close Packed ◽

A Value ◽

Face Centered ◽

Two Phases

The occurrence of size effects in cobalt was examined by the analysis of mechanical properties of samples with thickness t, in a large range of grain size d giving a number of grains across the thickness t/d. On Hall-Petch plots, from the very beginning of plastic strain, two linear behaviors are notable: the polycrystalline one for higher t/d and the multicrystalline one for lower t/d in which the flow stress is strongly reduced. (t/d)c is the threshold value between the two behaviors taking a value of around 14. This high value is directly linked to the low stacking fault energy of cobalt. The microstructure of the polycrystalline samples exhibits a strong basal texture and a small proportion of a secondary face-centered cubic phase in a hexagonal close-packed main phase was evidenced. TEM analysis enables to characterize the dislocations and the stacking faults present in the two phases. To complete the analysis, two plasticity stages can be distinguished: stage A corresponding to dislocations gliding and stage B driven by twinning. Size effects in cobalt are found to occur during gliding process and could be related to surface effects as previously shown in face-centered cubic metals.

Download Full-text

Is there a hexagonal-close-packed (hcp) → face-centered-cubic (fcc) allotropic transformation in mechanically milled Group IVB elements?

Journal of Materials Research ◽

10.1557/jmr.2009.0423 ◽

2009 ◽

Vol 24 (11) ◽

pp. 3454-3461 ◽

Cited By ~ 18

Author(s):

Uma M.R. Seelam ◽

Gagik Barkhordarian ◽

Challapalli Suryanarayana

Keyword(s):

Phase Transformation ◽

Critical Analysis ◽

High Energy ◽

Argon Atmosphere ◽

Face Centered Cubic ◽

Allotropic Transformation ◽

Nanocrystalline State ◽

Hexagonal Close Packed ◽

Face Centered ◽

Fcc Phase

Allotropic hexagonal-close-packed (hcp) → face-centered-cubic (fcc) transformations were reported in Group IVB elements titanium (Ti), zirconium (Zr), and hafnium (Hf) subjected to mechanical milling in a high-energy SPEX shaker mill. Although the transformation was observed in powders milled under regular conditions, no such phase transformation was observed when the powders were milled in an ultrahigh purity environment by placing the powder in a milling container under a high-purity argon atmosphere, which was in turn placed in an argon-filled glove box for milling. From a critical analysis of the results, it was concluded that the hcp → fcc phase transformation was, at least partially, due to pick-up of interstitial impurities by the powder during milling of these powders to the nanocrystalline state.

Download Full-text