First single-shot image of the alpha->beta Phase Transformation in Pure Nanocyrstalline Ti with Nanosecond Resolution.

AbstractWe demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes complete stress relaxation and a large decrease in the resistance of tantalum thin films. 100 nm beta tantalum thin films were deposited onto thermally oxidized <100> silicon wafers by dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured during temperature-ramped annealing in purified He. Upon heating, films that were initially compressively stressed showed increasing compressive stress due to thermo-elastic deformation from 25 to 550°C, slight stress relief due to plastic deformation from 550 to 700°C and complete stress relief due to the beta to alpha phase transformation at approximately 700–800°C. Incomplete compressive stress relaxation was observed at high temperatures if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800°C. This incomplete beta to alpha phase transition was most commonly observed on samples that had radio frequency substrate bias greater than -100 V. We conclude that the main stress relief mechanism for tantalum thin films is the beta to alpha phase transformation that occurs at 700 to 800°C.

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Evolution of Grain Boundary Texture in Zirconium Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.702-703.710 ◽

2011 ◽

Vol 702-703 ◽

pp. 710-713

Author(s):

Karri V. Mani Krishna ◽

Sudipto Mandal ◽

Ankur Agrawal ◽

Vijay Hiwarkar ◽

Dinesh Srivastava ◽

...

Keyword(s):

Phase Transformation ◽

Grain Boundary ◽

Annealing Time ◽

Considerable Increase ◽

Direct Evidence ◽

Texture Evolution ◽

Zirconium Alloys ◽

Alpha Phase ◽

Variant Selection ◽

Alpha Beta

Grain boundary texture evolution in case of two of the Zr based alloys (Zircaloy-4 and Zr-2.5\%Nb) was studied. In case of Zircaloy-4, grain boundary texture evolution during $\beta$ $\to$ $\alpha$ phase transformation was monitored. Direct evidence of variant selection during this transformation is presented. In case of Zr-2.5\%Nb alloy, considerable increase in $\alpha/\beta$ interfaces following Burger's orientation relationship was noticed with increasing annealing time at 700 \textdegree{}C.

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Study of Alpha-Beta Transformation in Ti-6Al-4V-ELI. Mechanical and Microstructural Characteristics

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.712 ◽

2010 ◽

Vol 638-642 ◽

pp. 712-717 ◽

Cited By ~ 2

Author(s):

Pascual Tarín ◽

Aurelio Gualo ◽

Atonio Garcia Simón ◽

Nuria M. Piris ◽

Jose Maria Badía

Keyword(s):

Beta Phase ◽

Alpha Phase ◽

Thermal Treatments ◽

Conductivity Measurements ◽

Transformation Kinetics ◽

Microstructural Characteristics ◽

Annealed Condition ◽

Heat Treated ◽

Metallographic Observation ◽

Alpha Beta

In the Ti-6Al-4V-ELI alloy, the alpha phase is gradually transformed into the beta phase until beta-transus temperature ( 980°C) is reached, and the transformation is completed. It is important to identify the transformation kinetics to accomplish the solution heat treatments in which a phase alpha percentage remains unchanged. Kinetics and other transformation characteristics are evaluated, as well as their influence on subsequent cooling transformations, by differential and dilatometric thermal analysis, electric conductivity measurements, hardness measurements and metallographic observation, after performing controlled thermal treatments. Starting from the mill annealed condition, samples were heated at temperatures between 650-1000 °C for 1 hour, then water quenched and subsequently heated for aging, air cooled. Finally, the mechanical properties of samples heat treated were obtained.

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Mechanical Behaviour and Microstructure Evolution of Severely Deformed Two-Phase Titanium Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.584-586.771 ◽

2008 ◽

Vol 584-586 ◽

pp. 771-776 ◽

Cited By ~ 5

Author(s):

Sergey V. Zherebtsov ◽

Sergey Mironov ◽

Maria A. Murzinova ◽

S. Salishchev ◽

S. Lee Semiatin

Keyword(s):

Titanium Alloys ◽

Microstructure Evolution ◽

High Strain ◽

Beta Phase ◽

Alpha Phase ◽

Steady State Flow ◽

Two Phase ◽

Globular Microstructure ◽

Flow Response ◽

Alpha Beta

Microstructure evolution and mechanical behavior of alpha/beta Ti-6Al-4V (VT6) and near-beta Ti-5Al-5Mo-5V-1Cr-1Fe (VT22) titanium alloys during uniaxial compression at 600°C to a high strain of 70% was studied. The plastic-flow response for both alloys is characterized by successive stages of strain hardening, flow softening, and steady-state flow. During compression the lamellae spheroidized to produce a partially globular microstructure. Globularization in VT6 is associated with the loss of the initial Burgers-type coherency between the alpha and beta phases and the subsequent individual deformation of each phase. The misorientations of boundaries increase to the high-angle range by means of the accumulation of lattice dislocations. In VT22 alloy the alpha phase evolves similar to that in VT6 alloy, while in the beta phase mainly low-angle boundaries are observed even after 70 pct. reduction.

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