Relaxation Processes at High Temperature in TiAl-Nb-Mo Intermetallics

2012 ◽  
Vol 1516 ◽  
pp. 41-46 ◽  
Author(s):  
Pablo Simas ◽  
Thomas Schmoelzer ◽  
Svea Mayer ◽  
Maria L. Nó ◽  
Helmut Clemens ◽  
...  
Keyword(s):  
High Temperature ◽  
Relaxation Process ◽  
Activation Parameters ◽  
Relaxation Processes ◽  
Thermal Treatments ◽  
Intermetallic Alloys ◽  
Mechanical Spectroscopy ◽  
Responsible Mechanism ◽  
Defect Mobility

ABSTRACTIn the last decades there was a growing interest in developing new light-weight intermetallic alloys, which are able to substitute the heavy superalloys at a certain temperature range. At present a new Ti-Al-Nb-Mo family, called TNM™ alloys, is being optimized to fulfill the challenging requirements. The aim of the present work was to study the microscopic mechanisms of defect mobility at high temperature in TNM alloys in order to contribute to the understanding of their influence on the mechanical properties and hence to promote the further optimization of these alloys. Mechanical spectroscopy has been used to study the internal friction and the dynamic modulus up to 1460 K of a TNM alloy under different thermal treatments. These measurements allow to follow the microstructural evolution during in-situ thermal treatments. A relaxation process has been observed at about 1050 K and was characterized as a function of temperature and frequency in order to obtain the activation parameters of the responsible mechanism. In particular, the activation enthalpy has been determined to be H= 3 eV. The results are discussed and an atomic mechanism is proposed to explain the observed relaxation process.

Mechanical Spectroscopy in Advanced TiAl-Nb-Mo Alloys at High Temperature

2011 ◽  
Vol 1295 ◽  
Author(s):  
Pablo Simas ◽  
Thomas Schmoelzer ◽  
Maria L. Nó ◽  
Helmut Clemens ◽  
Jose San Juan
Keyword(s):  
High Temperature ◽  
Activation Parameters ◽  
Relaxation Peak ◽  
Thermal Treatments ◽  
Torsion Pendulum ◽  
Hot Workability ◽  
Mechanical Spectroscopy ◽  
Final Microstructure ◽  
Multi Phase ◽  
Internal Friction Spectra

ABSTRACTNew advanced multi-phase γ-TiAl based alloys (TiAl-Nb-Mo), so called TNM alloys, have been developed to promote hot workability and to allow easier processing by conventional forging. However, to control and stabilize the final microstructure, specific processing and further thermal treatments are required. In the present work we used mechanical spectroscopy techniques to obtain a better understanding of the microstructural mechanisms taking place at high temperature applying two different heat treatments. Internal friction spectra and dynamic modulus evolution have been measured in an inverted torsion pendulum up to 1220 K. A stable relaxation peak was observed in both cases at about 1050 K for 1 Hz. Spectra acquired at several frequencies between 0.01 Hz and 3 Hz allow us to measure the activation parameters of this peak. In addition, a high temperature background (HTB) has been observed. This HTB, which has been found to be dependent on thermal treatments, has been analyzed to obtain the apparent activation enthalpy, which seems to be correlated to the creep behavior. Finally, we discuss the relaxation peak and the HTB in terms of the microstructural evolution during thermal treatments.

scholarly journals Additive Manufacturing of Ti-Based Intermetallic Alloys: A Review and Conceptualization of a Next-Generation Machine

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4317
Author(s):  
Thywill Cephas Dzogbewu ◽  
Willie Bouwer du Preez
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Additive Manufacturing ◽  
Complex Geometries ◽  
Intermetallic Alloys ◽  
Tial Alloys ◽  
Conventional Methods ◽  
Manufacturing Technologies ◽  
In Situ Heat Treatment

TiAl-based intermetallic alloys have come to the fore as the preferred alloys for high-temperature applications. Conventional methods (casting, forging, sheet forming, extrusion, etc.) have been applied to produce TiAl intermetallic alloys. However, the inherent limitations of conventional methods do not permit the production of the TiAl alloys with intricate geometries. Additive manufacturing technologies such as electron beam melting (EBM) and laser powder bed fusion (LPBF), were used to produce TiAl alloys with complex geometries. EBM technology can produce crack-free TiAl components but lacks geometrical accuracy. LPBF technology has great geometrical precision that could be used to produce TiAl alloys with tailored complex geometries, but cannot produce crack-free TiAl components. To satisfy the current industrial requirement of producing crack-free TiAl alloys with tailored geometries, the paper proposes a new heating model for the LPBF manufacturing process. The model could maintain even temperature between the solidified and subsequent layers, reducing temperature gradients (residual stress), which could eliminate crack formation. The new conceptualized model also opens a window for in situ heat treatment of the built samples to obtain the desired TiAl (γ-phase) and Ti3Al (α2-phase) intermetallic phases for high-temperature operations. In situ heat treatment would also improve the homogeneity of the microstructure of LPBF manufactured samples.

Experimental Considerations and Limitations in the Application of Ultra High Temperature (2100°C) X-Ray Diffraction

1991 ◽  
Vol 35 (A) ◽  
pp. 425-429
Author(s):  
Sampath S. Iyengar
Keyword(s):  
High Temperature ◽  
Crystalline Material ◽  
Thermal Treatments ◽  
Ceramic Fibers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Controlled Atmospheres ◽  
Heat Treated ◽  
Multiple Samples

In-situ, high temperature X-ray diffraction (XRD) is an extremely useful tool for studying, monitoring or investigating crystal structure modifications as well as phase transformations in crystalline material during thermal treatments in controlled atmospheres. This technique has been used to investigate the thermal behavior of materials such as carbonate minerals, ceramic fibers, coating pigments, etc. The advantages of such a technique over the conventional practice, where samples are heat treated in a separate oven and then analyzed by XRD include: consistency of sample placement; preservation of high temperature structures to facilitate observation of metastable phases that are unstable upon exposure to outside atmosphere or during cooling; real time monitoring of reactions that occur, and products that are formed at a desired temperature or environment; and need for multiple samples or analysis.

Investigations of Tungsten Based Intermetallic Alloys by Self Propagating High Temperature Synthesis from Metal Oxide Precursors

2012 ◽  
Vol 488-489 ◽  
pp. 300-304
Author(s):  
Tawat Chanadee ◽  
Jessada Wannasin ◽  
Sutham Niyomwas
Keyword(s):  
High Temperature ◽  
Phase Distribution ◽  
Equilibrium Composition ◽  
Intermetallic Alloys ◽  
Reaction Products ◽  
Temperature Synthesis ◽  
Minimization Method ◽  
High Temperature Synthesis ◽  
Mixture System

The in-situself propagating high temperature synthesis technique were used to synthesis tungsten based intermetallic alloys from WO3/SiO2/Al and WO3/B2O3/Al reactant mixture system. The reaction was carries out in a SHS reactor under static argon gas at the pressure of 0.5 MPa. The standard Gibbs energy minimization method was used to calculate the equilibrium composition of the reacting species. The microstructure and phase distribution of the SHS reaction products were characterized by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX), respectively. The results indicate that complete reaction of precursors to yield Al2O3-WSi2 and Al2O3-WB as product composites with clearly separation between Al2O3 and WB.

Solution and Precipitation Hardening in Carbon-Doped Two-Phase γ-Titanium Aluminides

1996 ◽  
Vol 460 ◽  
Author(s):  
F. Appel ◽  
U. Christoph ◽  
R. Wagner
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Precipitation Hardening ◽  
Titanium Aluminides ◽  
Activation Parameters ◽  
High Temperature Strength ◽  
Thermal Treatments ◽  
Two Phase ◽  
Carbon Doped ◽  
Titanium Aluminide Alloy

ABSTRACTA two-phase titanium aluminide alloy was systematically doped with carbon to improve its high temperature strength. Solid solutions and precipitates of carbon were formed by different thermal treatments. A fine dispersion of perovskite precipitates was found to be very effective for improving the high temperature strength and creep resistance of the material. The strengthening mechanisms were characterized by flow stresses and activation parameters. The investigations were accompanied by electron microscope observation of the defect structure which was generated during deformation. Special attention was paid on the interaction mechanisms of perfect and twinning dislocations with the carbide precipitates.

In-situ Measurement of Viscous Flow of Thermal Silicon Dioxide Thin Films at High Temperature

1996 ◽  
Vol 446 ◽  
Author(s):  
Chia-Liang Yu ◽  
Paul A. Flinn ◽  
John C. Bravman
Keyword(s):  
Thin Films ◽  
High Temperature ◽  
Stress Relaxation ◽  
Silicon Dioxide ◽  
Viscous Flow ◽  
Relaxation Process ◽  
Structural Relaxation ◽  
Wafer Curvature ◽  
Thermal Oxide

AbstractWith a newly constructed high temperature wafer curvature system, we measured significant viscous flow of thermal oxides at temperatures as low as 800°C. In-situ measurements were performed at temperatures between 800°C and 1100°C for wet and dry thermal oxide films of various thicknesses. We found that dry oxides have higher stresses and slower stress relaxation compared to wet oxides grown at higher temperatures. The viscosity of thermal oxide thin films was found to increase with time during relaxation and a structural relaxation process is suggested to explain this phenomenon.

UHV-STM studies of silicon nano-pyramid growth on silicon surface at high temperature

1992 ◽  
Vol 50 (2) ◽  
pp. 1144-1145
Author(s):  
T. Sato ◽  
S. Kitamura ◽  
T. Sueyoshl ◽  
M. Iwatukl ◽  
C. Nielsen
Keyword(s):  
High Temperature ◽  
Relaxation Process ◽  
Thermal Effect ◽  
Bias Voltage ◽  
Silicon Surface ◽  
Growth Process ◽  
Tunneling Current ◽  
Fabrication Technique ◽  
Nano Fabrication ◽  
Electromigration Effect

Recently, the growth process and relaxation process of crystalline structures were studied by observing a SI nano-pyramid which was built on a Si surface with a UHV-STM. A UHV-STM (JEOL JSTM-4000×V) was used for studying a heated specimen, and the specimen was kept at high temperature during observation. In this study, the nano-fabrication technique utilizing the electromigration effect between the STM tip and the specimen was applied. We observed Si atoms migrated towords the tip on a high temperature Si surface.Clean surfaces of Si(lll)7×7 and Si(001)2×l were prepared In the UHV-STM at a temperature of approximately 600 °C. A Si nano-pyramid was built on the Si surface at a tunneling current of l0nA and a specimen bias voltage of approximately 0V in both polarities. During the formation of the pyramid, Images could not be observed because the tip was stopped on the sample. After the formation was completed, the pyramid Image was observed with the same tip. After Imaging was started again, the relaxation process of the pyramid started due to thermal effect.

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