Ultrafine Fully-Lamellar Structures in Two-Phase γ-TiAl Alloys

1996 ◽  
Vol 460 ◽  
Author(s):  
P. J. Maziasz ◽  
C. T. Liu
Keyword(s):  
Room Temperature ◽  
Interlamellar Spacing ◽  
Hot Extrusion ◽  
Processing Parameters ◽  
High Temperature Strength ◽  
Two Phase ◽  
Tial Alloys ◽  
Room Temperature Ductility ◽  
Heat Treated ◽  
Fully Lamellar

ABSTRACTSpecial ultrafine fully-lamellar microstructures have been found recently in γ-TiAl alloys with 46–48 at.% Al, when they are processed or heat-treated above the α-transus temperature (Tα). Hot-extrusion above Tα also produces a refined colony or grain size. Refined-colony/ultrafine-lamellar (RC/UL) microstructures produce an excellent combination of room-temperature ductility and high-temperature strength in Ti-47Al-2Cr-2Nb (at.%) alloys. UL structures generally have an average interlamellar spacing of 100–200 nm, and have regularly alternating γ and α2 lamellea, such that they are dominated by γ/α2 interfaces with relatively few γ/γ twin boundaries. The focus of this study is how variations in processing parameters or alloy composition affect formation of the UL structure, particularly the α2 component.

scholarly journals Key Microstructures Controlling the Mechanical Properties of Two-Phase TiAl Alloys with Lamellar Structures

1996 ◽  
Vol 460 ◽  
Author(s):  
C. T. Liu ◽  
P. J. Maziasz ◽  
J. L. Wright
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Tensile Elongation ◽  
Interlamellar Spacing ◽  
Hot Extrusion ◽  
Two Phase ◽  
Tial Alloys ◽  
Lamellar Structures

ABSTRACTThe objective of this study is to identify key microstructural parameters which control the mechanical properties of two-phase γ-TiAl alloys with lamellar structures. TiAl alloys with the base composition of Ti-47Al-2Cr-2Nb (at. %) were prepared by arc melting and drop casting, followed by hot extrusion at temperatures above the oc-transus temperature, Tα. The hot extruded materials were then heat treated at various temperatures above and below Tα in order to control microstructural features in these lamellar structures. The mechanical properties of these alloys were determined by tensile testing at temperatures to 1000° C. The tensile elongation at room temperature is strongly dependent on grain size, showing an increase in ductility with decreasing grain size. The strength at room and elevated temperatures is sensitive to interlamellar spacing, showing an increase in strength with decreasing lamellar spacing. Hall-Petch relationships hold well for the yield strength at room and elevated temperatures and for the tensile elongation at room temperature. Tensile elongations of about 5% and yield strengths around 900 MPa are achieved by controlling both colony size and interlamellar spacing. The mechanical properties of the TiAl alloys with controlled lamellar structures produced directly by hot extrusion are much superior to those produced by conventional thermomechanical treatments.

Factors affecting the lamellar spacing in two-phase TiAl alloys with fully lamellar microstructures

2001 ◽  
Vol 36 (9) ◽  
pp. 1737-1742 ◽  
Author(s):  
Jiancheng Tang ◽  
Baiyun Huang ◽  
Kechao Zhou ◽  
Wensheng Liu ◽  
Yuehui He ◽  
...  
Keyword(s):  
Lamellar Spacing ◽  
Two Phase ◽  
Tial Alloys ◽  
Factors Affecting ◽  
Fully Lamellar

scholarly journals The Microstructural Evolution, Tensile Properties, and Phase Hardness of a TiAl Alloy with a High Content of the β Phase

Materials ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 2757 ◽  
Author(s):  
Ning Cui ◽  
Qianqian Wu ◽  
Zhiyuan Yan ◽  
Haitao Zhou ◽  
Xiaopeng Wang
Keyword(s):  
Tensile Properties ◽  
Room Temperature ◽  
Tial Alloy ◽  
Microstructural Analysis ◽  
Phase Content ◽  
Tial Alloys ◽  
Β Phase ◽  
Room Temperature Ductility ◽  
One Step ◽  
Equiaxed Grains

In this paper, the microstructure, deformability, tensile properties, and phase hardness of the Ti–43Al–2Cr–0.7Mo–0.1Y alloy with a high β phase content were investigated. Microstructural analysis showed that the β phase precipitated not only at the colony boundaries but also inside the lamellae due to its high content. A high-quality forging stock was prepared through one-step noncanned forging. The total deformation reached above 80%, suggesting that the alloy has good hot deformability compared to other TiAl alloys. The deformed microstructure was composed of fine and equiaxed grains due to dynamic recrystallization. The high β phase content was shown to contribute to the decomposition of the initial coarse lamellae. Tensile testing showed that the alloy has good room-temperature ductility, even if the β phase content reaches above 20%. This is inconsistent with a previous study that showed that a large amount of the hard β phase is detrimental to the room-temperature ductility of TiAl alloys. Nanoindentation testing showed that the hardness of the β phase in the current alloy is about 6.3 GPa, which is much lower than that in the Nb-containing TiAl alloys. Low hardness benefits the compatible deformation among various phases, which could be the main reason for the alloy’s good room-temperature ductility. Additionally, the influence of various β stabilizers on the hardness of the β phase was also studied. The β phase containing Nb had the highest hardness, whereas the β phase containing Cr had the lowest hardness.

Microstructures and High-temperature Strength of Silicide-reinforced Nb Alloys

2000 ◽  
Vol 646 ◽  
Author(s):  
C.L. Ma ◽  
Y. Tan ◽  
H. Tanaka ◽  
A. Kasama ◽  
R. Tanaka ◽  
...  
Keyword(s):  
High Temperature ◽  
Quaternary System ◽  
Eutectic Reaction ◽  
High Temperature Strength ◽  
Quaternary Alloys ◽  
Two Phase ◽  
Practical Applications ◽  
Arc Melting ◽  
Heat Treated ◽  
Very High

ABSTRACTThis article describes the phase stability, microstructures and mechanical properties of silicide-reinforced Nb alloys in Nb-Mo-W-Si quaternary system prepared by arc melting and heat treatment. There exists an equilibrium two-phase field of Nb solid solution (Nbss) and α(Nb,Mo,W)5Si3 in a Nb-rich region of this quaternary system. Alloys in this region have a eutectic reaction of L → Nbss+β(Nb,Mo,W)5Si3 during solidification. The β(Nb,Mo,W)5Si3 transforms to the stable α(Nb,Mo,W)5Si3 at very high temperature. The cast and heat treated hypoeutectic alloys consist of dendritic Nbss, network-shaped Nbss matrix and α(Nb,Mo,W)5Si3. These quaternary alloys exhibit excellent high-temperature strength, although the fracture toughness is still unacceptable for practical applications.

Microstructure Transformation of a Refined High Nb Containing TiAl Alloy

2013 ◽  
Vol 747-748 ◽  
pp. 38-43 ◽  
Author(s):  
Li Hua Chai ◽  
Liang Yang ◽  
Jian Peng Zhang ◽  
Zhi Yong Zhang ◽  
Lai Qi Zhang ◽  
...  
Keyword(s):  
Room Temperature ◽  
Tial Alloy ◽  
High Strength ◽  
Temperature Limit ◽  
Tial Alloys ◽  
Β Phase ◽  
Α Phase ◽  
Refined Microstructure ◽  
Fully Lamellar ◽  
Sem Microstructure

High Nb containing TiAl alloys have been investigated traditionally as potential high temperature structural materials because of their high strength, good oxidation and creep resistance. However, the poor ductility and fracture toughness at room temperature limit their application, which could be improved by controlling microstructure to get refine and homogeneous fully lamellar structure. In this study, a high Nb containing TiAl alloy alloying Mn, B and Y with refined microstructure was produced. The solidification path was analyzed by DSC and SEM microstructure of the alloy was observed, after heating at a certain temperature for 1-24hrs and then quenching in water. The dissolution of β phase was also investigated. The results showed that the β phase could decompose only by heating in single β or near α phase field.

Hall–Petch relationship in two-phase TiAl alloys with fully lamellar microstructures

2002 ◽  
Vol 37 (7) ◽  
pp. 1315-1321 ◽  
Author(s):  
Jiancheng Tang ◽  
Baiyun Huang ◽  
Yuehui He ◽  
Wensheng Liu ◽  
Kechao Zhou ◽  
...  
Keyword(s):  
Two Phase ◽  
Tial Alloys ◽  
Petch Relationship ◽  
Fully Lamellar

Microscopic study of the room temperature deformation mechanisms in β+γ' – (70 at.% Ni −30 at.% Al) in situ composite

1992 ◽  
Vol 50 (1) ◽  
pp. 912-913
Author(s):  
A. Misra ◽  
R. Gibala
Keyword(s):  
Microscopic Study ◽  
Room Temperature ◽  
Temperature Deformation ◽  
Nominal Composition ◽  
Second Phase ◽  
Directionally Solidified ◽  
Ductile Phase ◽  
Two Phase ◽  
Room Temperature Ductility

Ductile phase reinforcement is an attractive approach for enhancing the room temperature ductility and toughness of brittle intermetallics such as β−NiAl. For example, a directionally solidified alloy of nominal composition 70 at.% Ni −30 at.% Al, having a two-phase β (brittle matrix) and γ (ductile second phase) microstructure, exhibits up to 9% tensile ductility at room temperature [1]. In the present investigation, a microscopic study has been made to understand the mechanisms involved in the ductility enhancement of the β + γ composite.

Microstructures and Creep Properties of Powder Metallurgy Ti-48Al-2Cr-2Nb + W

2007 ◽  
Author(s):  
H. Saari ◽  
S. Bulmer ◽  
D. Y. Seo ◽  
P. Au
Keyword(s):  
Heat Treatment ◽  
Powder Metallurgy ◽  
Lamellar Microstructure ◽  
Controlled Cooling ◽  
Tial Alloys ◽  
Creep Properties ◽  
Rupture Ductility ◽  
Heat Treated ◽  
Fully Lamellar ◽  
Lamellar Interfaces

The microstructures and creep properties at 760 °C and 276 MPa of three powder metallurgy TiAl alloys (Ti-48Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb+0.5W, and Ti-48Al-2Cr-2Nb+1W (atomic percent)) are presented. The results indicate that the addition of W to the base composition, the use of a solution heat treatment combined with controlled cooling (to generate a fully lamellar microstructure), and the use of an aging heat treatment (to generate precipitate particles at the lamellar interfaces) improve creep properties dramatically. The solution heat treated and aged Ti-48Al-2Cr-2Nb+1W alloy has a time to 0.5% strain of 8.3 hours, a time to 1% strain of 46.4 hours, and a creep life of 412 hours with a rupture ductility of 16.9%.

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