scholarly journals Refinement of orientation relations occurring in phase transformation based on considering only the orientations of the variants

2011 ◽  
Vol 64 (2) ◽  
pp. 114-117 ◽  
Author(s):  
M. Humbert ◽  
P. Blaineau ◽  
L. Germain ◽  
N. Gey
Keyword(s):  
Phase Transformation ◽  
Orientation Relations

The calculation of a parent grain orientation from inherited variants for approximate (b.c.c.–h.c.p.) orientation relations

2002 ◽  
Vol 35 (4) ◽  
pp. 401-405 ◽  
Author(s):  
M. Humbert ◽  
N. Gey
Keyword(s):  
Phase Transformation ◽  
Grain Orientation ◽  
The Body ◽  
Orientation Relation ◽  
Hexagonal Close Packed ◽  
Orientation Relations ◽  
Parent Orientation

The orientations of parent β grains are evaluated from several α variants inherited from the same parent during the body-centred cubic (b.c.c.) to hexagonal close packed (h.c.p.) phase transformation. The proposed calculation, based on orientation correlating and orientation averaging, is particularly useful when the inherited variants are not strictly related to the parent orientation by a strict Burgers orientation relation or when the orientations of the inherited volumes vary slightly at different locations of the variant. This method of parent identification from variant orientations is an improvement of a previously published method.

scholarly journals Nucleation of {1012} Twins in Magnesium through Reversible Martensitic Phase Transformation

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1030
Author(s):  
Jamie Ombogo ◽  
Amir Hassan Zahiri ◽  
Tengfei Ma ◽  
Lei Cao
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Tetragonal Phase ◽  
Metastable Phase ◽  
Critical Role ◽  
Martensitic Phase ◽  
Growth Speed ◽  
Orientation Relations ◽  
Martensitic Phase Transformations ◽  
Dynamics Simulations

We report the discovery of a rigorous nucleation mechanism for {101¯2} twins in hexagonal close-packed (hcp) magnesium through reversible hcp-tetragonal-hcp martensitic phase transformations with a metastable tetragonal phase as the intermediate state. Specifically, the parent hcp phase first transforms to a metastable tetragonal phase, which subsequently transforms to a twinned hcp phase. The evanescent nature of the tetragonal phase severely hinders its direct observation, while our carefully designed molecular dynamics simulations rigorously reveal the critical role of this metastable phase in the nucleation of {101¯2} twins in magnesium. Moreover, we prove that the reversible hcp-tetragonal-hcp phase transformations involved in the twinning process follow strict orientation relations between the parent hcp, intermediate tetragonal, and twin hcp phases. This phase transformation-mediated twinning mechanism is naturally compatible with the ultrafast twin growth speed. This work will be important for a better understanding of the twinning mechanism and thus the development of novel strategies for enhancing the ductility of magnesium alloys.

Phase Transformation In Ti-6al-4v Alloys

1972 ◽  
Vol 30 ◽  
pp. 584-585
Author(s):  
Shiro Fujishiro
Keyword(s):  
Phase Transformation ◽  
Grain Boundary ◽  
Cryogenic Temperature ◽  
Β Phase ◽  
Heat Treated ◽  
Mixed Microstructure ◽  
Ductile Behavior

The Ti-6 wt.% Al-4 wt.% V commercial alloys have exhibited an improved formability at cryogenic temperature when the alloys were heat-treated prior to the tests. The author was interested in further investigating this unusual ductile behavior which may be associated with the strain-induced transformation or twinning of the a phase, enhanced at lower temperatures. The starting materials, supplied by RMI Co., Niles, Ohio were rolled mill products in the form of 40 mil sheets. The microstructure of the as-received materials contained mainly ellipsoidal α grains measuring between 1 and 5μ. The β phase formed an undefined grain boundary around the a grains. The specimens were homogenized at 1050°C for one hour, followed by aging at 500°C for two hours, and then quenched in water to produce the α/β mixed microstructure.

Microstructural and Microchemical Characterization of Nickel Sulfide Inclusions in Plate Glass

1991 ◽  
Vol 49 ◽  
pp. 962-963
Author(s):  
J. Cooper ◽  
O. Popoola ◽  
W. M. Kriven
Keyword(s):  
Thermal Expansion ◽  
Phase Transformation ◽  
Glass Matrix ◽  
Nickel Sulfide ◽  
Plate Glass ◽  
Thermal Expansion Mismatch ◽  
Volume Increase ◽  
Β Phase ◽  
Microchemical Characterization

Nickel sulfide inclusions have been implicated in the spontaneous fracture of large windows of tempered plate glass. Two alternative explanations for the fracture-initiating behaviour of these inclusions have been proposed: (1) the volume increase which accompanies the α to β phase transformation in stoichiometric NiS, and (2) the thermal expansion mismatch between the nickel sulfide phases and the glass matrix. The microstructure and microchemistry of the small inclusions (80 to 250 μm spheres), needed to determine the cause of fracture, have not been well characterized hitherto. The aim of this communication is to report a detailed TEM and EDS study of the inclusions.

AEM of reaction-bonded SiC

1992 ◽  
Vol 50 (1) ◽  
pp. 344-345
Author(s):  
K Das Chowdhury ◽  
R. W. Carpenter ◽  
W. Braue
Keyword(s):  
Mechanical Properties ◽  
Phase Transformation ◽  
High Temperature ◽  
Epitaxial Growth ◽  
Liquid Silicon ◽  
Structural Ceramic ◽  
Few Data

Research on reaction-bonded SiC (RBSiC) is aimed at developing a reliable structural ceramic with improved mechanical properties. The starting materials for RBSiC were Si,C and α-SiC powder. The formation of the complex microstructure of RBSiC involves (i) solution of carbon in liquid silicon, (ii) nucleation and epitaxial growth of secondary β-SiC on the original α-SiC grains followed by (iii) β>α-SiC phase transformation of newly formed SiC. Due to their coherent nature, epitaxial SiC/SiC interfaces are considered to be segregation-free and “strong” with respect to their effect on the mechanical properties of RBSiC. But the “weak” Si/SiC interface limits its use in high temperature situations. However, few data exist on the structure and chemistry of these interfaces. Microanalytical results obtained by parallel EELS and HREM imaging are reported here.

Phase transformation and layer evolution in molybdenum disilicide-silicon carbide nanolayered coatings

1994 ◽  
Vol 52 ◽  
pp. 538-539
Author(s):  
H. Kung ◽  
T. R. Jervis ◽  
J.-P. Hirvonen ◽  
M. Nastasi ◽  
T. E. Mitchell ◽  
...  
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Oxidation Resistance ◽  
Elevated Temperatures ◽  
Matrix Material ◽  
Molybdenum Disilicide ◽  
High Temperature Strength ◽  
Cross Sectional ◽  
Good Oxidation Resistance ◽  
Structural Applications

MoSi2 is a potential matrix material for high temperature structural composites due to its high melting temperature and good oxidation resistance at elevated temperatures. The two major drawbacksfor structural applications are inadequate high temperature strength and poor low temperature ductility. The search for appropriate composite additions has been the focus of extensive investigations in recent years. The addition of SiC in a nanolayered configuration was shown to exhibit superior oxidation resistance and significant hardness increase through annealing at 500°C. One potential application of MoSi2- SiC multilayers is for high temperature coatings, where structural stability ofthe layering is of major concern. In this study, we have systematically investigated both the evolution of phases and the stability of layers by varying the heat treating conditions.Alternating layers of MoSi2 and SiC were synthesized by DC-magnetron and rf-diode sputtering respectively. Cross-sectional transmission electron microscopy (XTEM) was used to examine three distinct reactions in the specimens when exposed to different annealing conditions: crystallization and phase transformation of MoSi2, crystallization of SiC, and spheroidization of the layer structures.

Ferroelectric Domain Structure of Pb(Zr.52Ti.48)03

1980 ◽  
Vol 38 ◽  
pp. 214-215
Author(s):  
E.K. Goo ◽  
R.K. Mishra
Keyword(s):  
Phase Transformation ◽  
Domain Structure ◽  
Tetragonal Phase ◽  
Ferroelectric Domain ◽  
Cubic Phase ◽  
Ion Milling ◽  
Thin Foils ◽  
Ferroelectric Domain Structure ◽  
Ferroelectric Domains

Ferroelectric domains are twins that are formed when PZT undergoes a phase transformation from a non-ferroelectric cubic phase to a ferroelectric tetragonal phase upon cooling below ∼375°C.,1 The tetragonal phase is spontaneously polarized in the direction of c-axis, making each twin a ferroelectric domain. Thin foils of polycrystalline Pb (Zr.52Ti.48)03 were made by ion milling and observed in the Philips EM301 with a double tilt stage.

One-Step Synthesis and Magnetic Phase Transformation of Ln-TM-B Alloy by Chemical Reduction

2007 ◽  
Vol 0 (0) ◽  
pp. 0-0
Author(s):  
C.W. Kim ◽  
Y.H. Kim ◽  
H.G. Cha ◽  
D.K. Lee ◽  
Y.S. Kang
Keyword(s):  
Phase Transformation ◽  
Magnetic Phase ◽  
Chemical Reduction ◽  
One Step
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