Phase Stability and High Temperature Tensile Properties of W doped gamma-TiAl

2000 ◽  
Vol 646 ◽  
Author(s):  
Keizo Hashimoto ◽  
Hirohiko Hirata ◽  
Youji Mizuhara
Keyword(s):  
High Temperature ◽  
Phase Stability ◽  
Ternary Phase ◽  
Elevated Temperatures ◽  
Ternary Phase Diagram ◽  
Arc Melting ◽  
Structural Applications ◽  
High Temperature Tensile ◽  
Promising Alloys ◽  
High Temperature Tensile Properties

ABSTRACTTungsten (W) doped γ-TiAl is one of promising alloys among many other proposed TiAl base alloys, for the purpose of structural applications at elevated temperatures. Ingots of W doped γ-TiAl were produced by plasma arc melting, followed by homogenizing heat treatment and isothermal forging to control their microstructures. The phase stability of W doped γ-TiAl has been studied quantitatively, using the specimens quenched from 1273 K. Equilibrium compositions of consisting phases were analyzed by means of EDS analysis in a TEM. An isothermal cross section of the Ti-Al-W ternary phase diagram at 1273K has been proposed based on the experimental observations. Small amounts of W addition (< 1at%) to Ti-48at%Al cause a phase shift from α2+γ to α2+β+γ, which suggests that W is the strongest β stabilizer among transition metals, such as Cr and Mo. Mechanical property measurements of W doped γ-TiAl show that the high temperature tensile strength has been improved by the W addition. Relationships between the microstructures and the mechanical properties of W doped γ-TiAl have been discussed.

Role of Ti/Al Ratio of Ti-Al-X (X=Cr, Nb, Ta and W) Intermetallics on High Temperature Tensile Properties

2014 ◽  
Vol 783-786 ◽  
pp. 1136-1141
Author(s):  
Keizo Hashimoto
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Tensile Properties ◽  
First Generation ◽  
Elevated Temperatures ◽  
Atomic Ratio ◽  
High Temperature Strength ◽  
The Third ◽  
High Temperature Tensile ◽  
High Temperature Tensile Properties

The mechanical properties of g-TiAl at elevated temperatures have been investigated extensively over the last 30 years. Designed alloys have been proposed from the first generation alloy (Ti-48Al-2Cr-2Nb) to the second, the third and the fourth generations. However, a decisive chemical composition of g-TiAl has not been agreed among researchers yet. The main reasons for this situation are difficulties in compositional control of Ti-Al-X-Y. In this paper, the high temperature tensile properties of g-TiAl alloy with lots of different composition have been examined from the room temperature to 1200C and the tensile strength data of those specimens have been summarized. It is clear that Ti/Al atomic ratio plays an important role on the behaviors of the high temperature strength since the Ti/Al atomic ratio is strongly related to the phase stabilities between g and a2phases in the binary Ti-Al phase diagram. A very narrow confine of a/a2atomic ratio exists in the specimens having the comparatively high tensile strength at the elevated temperatures. Moreover, additions of the third elements such as Cr, Nb, Ta and W to g-TiAl contribute on the increase of the tensile strength and the shift of the phase stability among a2, b and g phases. In order to utilize g-TiAl alloys in the various machine components at high temperatures, the severe process controls of melting, casting, thermo-mechanical treatments and heat treatments are indispensable.

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.

scholarly journals Development of Creep-Resistant, Alumina-Forming Ferrous Alloys for High-Temperature Structural Use

2018 ◽  
Author(s):  
Y. Yamamoto ◽  
M. P. Brady ◽  
G. Muralidharan ◽  
B. A. Pint ◽  
P. J. Maziasz ◽  
...  
Keyword(s):  
High Temperature ◽  
Elevated Temperatures ◽  
Extreme Environments ◽  
Alloy Design ◽  
Austenitic Steels ◽  
Strength Development ◽  
Second Phase ◽  
Ferrous Alloys ◽  
Steel Alloys ◽  
Structural Applications

This paper overviews recent advances in developing novel alloy design concepts of creep-resistant, alumina-forming Fe-base alloys, including both ferritic and austenitic steels, for high-temperature structural applications in fossil-fired power generation systems. Protective, external alumina-scales offer improved oxidation resistance compared to chromia-scales in steam-containing environments at elevated temperatures. Alloy design utilizes computational thermodynamic tools with compositional guidelines based on experimental results accumulated in the last decade, along with design and control of the second-phase precipitates to maximize high-temperature strengths. The alloys developed to date, including ferritic (Fe-Cr-Al-Nb-W base) and austenitic (Fe-Cr-Ni-Al-Nb base) alloys, successfully incorporated the balanced properties of steam/water vapor-oxidation and/or ash-corrosion resistance and improved creep strength. Development of cast alumina-forming austenitic (AFA) stainless steel alloys is also in progress with successful improvement of higher temperature capability targeting up to ∼1100°C. Current alloy design approach and developmental efforts with guidance of computational tools were found to be beneficial for further development of the new heat resistant steel alloys for various extreme environments.

Further experiments and modeling for microscale compression molding of metals at elevated temperatures

2007 ◽  
Vol 22 (7) ◽  
pp. 1839-1848 ◽  
Author(s):  
J. Jiang ◽  
W.J. Meng ◽  
G.B. Sinclair ◽  
E. Lara-Curzio
Keyword(s):  
High Temperature ◽  
Aspect Ratio ◽  
Tensile Testing ◽  
Elevated Temperatures ◽  
Low Cost ◽  
Mold Insert ◽  
Compression Molding ◽  
Mechanics Model ◽  
Replication Technique ◽  
High Temperature Tensile

Replication of metallic high-aspect-ratio microscale structures (HARMS) by compression molding has been demonstrated recently. Molding replication of metallic HARMS can potentially lead to low-cost fabrication of a wide variety of metal-based microdevices. Understanding the mechanics of metal micromolding is critical for assessing the capabilities and limitations of this replication technique. This paper presents results of instrumented micromolding of Al. Measured molding response was rationalized with companion high-temperature tensile testing of Al using a simple mechanics model of the micromolding process. The present results suggest that resisting pressure on the mold insert during micromolding is governed primarily by the yield stress of the molded metal at the molding temperature and a frictional traction on the sides of the insert. The influence of strain rate is also considered.

Mechanical Behavior of 2D C/SiC Composites at Elevated Temperatures under Uniaxial Compression

2011 ◽  
Vol 462-463 ◽  
pp. 1-6 ◽  
Author(s):  
Tao Suo ◽  
Yu Long Li ◽  
Ming Shuang Liu
Keyword(s):  
Compressive Strength ◽  
High Temperature ◽  
Carbon Fiber ◽  
Mechanical Behavior ◽  
Uniaxial Compression ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Carbon Matrix ◽  
Structural Applications ◽  
Sic Composites

As Carbon-fiber-reinforced SiC-matrix (C/SiC) composites are widely used in high-temperature structural applications, its mechanical behavior at high temperature is important for the reliability of structures. In this paper, mechanical behavior of a kind of 2D C/SiC composite was investigated at temperatures ranging from room temperature (20C) to 600C under quasi-static and dynamic uniaxial compression. The results show the composite has excellent high temperature mechanical properties at the tested temperature range. Catastrophic brittle failure is not observed for the specimens tested at different strain rates. The compressive strength of the composite deceases only 10% at 600C if compared with that at room temperature. It is proposed that the decrease of compressive strength of the 2D C/SiC composite at high temperature is influenced mainly by release of thermal residual stresses in the reinforced carbon fiber and silicon carbon matrix and oxidation of the composite in high temperature atmosphere.

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