On the Mechanisms of Ductility Enhancement in β+γ′- Ni70Al30 and β+(γ+γ)-Ni50Fe30Al20In Situ Composites

1992 ◽  
Vol 273 ◽  
Author(s):  
A. Misra ◽  
R. D. Noebe ◽  
R. Gibala
Keyword(s):  
Room Temperature ◽  
Volume Fraction ◽  
Tensile Ductility ◽  
Nominal Composition ◽  
Substantial Portion ◽  
Directionally Solidified ◽  
Ductile Phase ◽  
Room Temperature Ductility ◽  
Slip Transfer ◽  
Slip Traces

ABSTRACTDuctile phase reinforcement is an attractive approach for improving room temperature ductility and toughness of intermetallics. Two alloys of nominal composition (at.%) Ni70Al30 and Ni50Fe30Al20 were directionally solidified to produce quasi-lamellar microstructures. Both alloys exhibit ∼10% tensile ductility at 300 K when the ductile phase is continuous, while the Ni70Al30 alloy has a tensile ductility of ∼4% when the γ′ phase is discontinuous. Observations of slip traces and dislocation substructures indicate that a substantial portion of the ductility enhancement is a result of slip transfer from the ductile phase to the brittle matrix. The details of slip transfer in the two model materials and the effect of the volume fraction and morphology of the ductile phase on the ductility enhancement in the composite are discussed.

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.

Slip Transfer Across Interphase Boundaries in Directionally Solidified β+(γ+γ') Ni-Fe-Al Alloys

1991 ◽  
Vol 238 ◽  
Author(s):  
A. Misra ◽  
R. Gibala
Keyword(s):  
Room Temperature ◽  
Tensile Elongation ◽  
Nominal Composition ◽  
Directionally Solidified ◽  
Β Phase ◽  
Slip Transfer ◽  
Temperature Observation ◽  
Interphase Boundaries ◽  
Slip Traces ◽  
Two Phases

ABSTRACTThe low ductility and toughness of β-NiAl alloys near room temperature pose major problems in their potential application as structural materials. The inability of the material to generate and move a sufficient density of dislocations at applied stresses below the fracture stress is the major cause for this inherent brittleness. A directionally solidified β+(γ+γ') composite of nominal composition Ni50Fe30Al20 (at.%) has been used to investigate the effect of interphase boundaries on the mechanical behavior of β phase. The composite exhibits 10% tensile elongation to fracture at room temperature. Observation of slip traces and dislocation substructures shows that the normally brittle β phase undergoes extensive plastic deformation afforded by slip transfer from the plastically soft (γ+γ') phase mixture across the semi-coherent β/(γ+γ') interface. The effect of the orientation relationship between the two phases and the interface strength on the transfer of slip across the interphase boundary is discussed.

Ductility and Fracture Behavior of Polycrystalline Ni3Al Alloys

1986 ◽  
Vol 81 ◽  
Author(s):  
C. T. Liu
Keyword(s):  
Fracture Behavior ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Grain Shape ◽  
Tensile Ductility ◽  
Dynamic Effect ◽  
Al Alloys ◽  
Gaseous Oxygen ◽  
Comprehensive Review ◽  
Room Temperature Ductility

AbstractThis paper provides a comprehensive review of the recent work on tensile ductility and fracture behavior of Ni3AI alloys tested at ambient and elevated temperatures. Polycrystalline Ni3Al is intrinsically brittle along grain boundaries, and the brittleness has been attributed to the large difference in valency, electronegativity, and atom size between nickel and aluminum atoms. Alloying with B, Mn, Fe, and Be significantly increases the ductility and reduces the propensity for intergranular fracture in Ni3 Al alloys. Boron is found to be most effective in improving room-temperature ductility of Ni3Al with <24.5 at. % Al.The tensile ductility of Ni3Al alloys depends strongly on test environments at elevated temperatures, with much lower ductilities observed in air than in vacuum. The loss in ductility is accompanied by a change in fracture mode from transgranular to intergranular. This embrittlement is due to a dynamic effect involving simultaneously high localized stress, elevated temperature, and gaseous oxygen. The embrittlement can be alleviated by control of grain shape or alloying with chromium additions. All the results are discussed in terms of localized stress concentration and grain-boundary cohesive strength.

Relationship between Microstructure and Tensile Strength in the Directionally Solidified (23-27) at. % Al-Ni Alloys

2006 ◽  
Vol 510-511 ◽  
pp. 458-461 ◽  
Author(s):  
Y. Lu ◽  
H.C. Kim ◽  
Je Hyun Lee ◽  
Myung Hoon Oh ◽  
Dang Moon Wee ◽  
...  
Keyword(s):  
Room Temperature ◽  
Eutectic Composition ◽  
Volume Fraction ◽  
Solidification Rate ◽  
Transgranular Fracture ◽  
Hypoeutectic Alloy ◽  
Directionally Solidified ◽  
Dendritic Microstructure ◽  
Ni Alloys ◽  
Two Phases

Directional or single crystal technique was applied to enhance the ductility, and two phases of γ (Ni) phase or β (NiAl) phase in γ‘(Ni3Al) matrix were also considered to increase the strength and ductility. In this study, directionally solidified rods were prepared at the solidification rate of 50µm/s in 23-27 at.% Al-Ni alloys, and tensile strengths of these rods were analyzed at room temperature. Directionally solidified samples showed the γ dendrite fibers formed in the Ni3Al matrix in the hypo eutectic composition of 23 at.% Al, the γ‘ single phase in the eutectic composition of 24.5 at. % Al, and the β dendrite fibers in the γ‘ matrix in the hyper eutectic compositions of 25, 26, 27 at.% Al. The hypoeutectic alloy including γ dendrites with γ‘ matrix exhibited a large elongation of over 70% with ductile transgranular fracture at room temperature. With increasing Al contents, the γ dendritic microstructure changed to the β dendrite in the γ‘ matrix, which resulted in decreasing the elongation by increasing the volume fraction of the brittle β dendrites in the ductile γ’ matrix.

Plasma Deposited Ni-Al-Mo Metal-Metal Composites

1987 ◽  
Vol 98 ◽  
Author(s):  
M. R. Jackson ◽  
P. A. Siemers
Keyword(s):  
Room Temperature ◽  
Volume Fraction ◽  
Tensile Ductility ◽  
Plasma Deposition ◽  
Laminate Structure ◽  
Metal Composites ◽  
Expansion Behavior ◽  
Metal Metal ◽  
Low Pressure Plasma ◽  
Unreinforced Matrix

ABSTRACTSix different composite microstructures were produced by low pressure plasma deposition of γ/γ'-α Ni-Al-Mo materials. Interlaminate spacing, volume fraction of α Mo, and continuity of the laminate structure were varied. Thermal expansion behavior (25–1250°C), density, and room temperature elastic modulus were correlated with volume fraction of α Mo. Tensile ductility (25–960°C) was correlated with both volume fraction and distribution of the α Mo phase, while yield strength was nearly insensitive to composite structure. Composite strengths were greater than were the unreinforced matrix strengths.

Solidification Processing and Fracture Behavior of RuAl-Based Alloys

2004 ◽  
Vol 842 ◽  
Author(s):  
Todd Reynolds ◽  
David Johnson
Keyword(s):  
Solid Solution ◽  
Fracture Toughness ◽  
Fracture Behavior ◽  
Room Temperature ◽  
Volume Fraction ◽  
Solidification Processing ◽  
Ductile Phase

ABSTRACTAlloys of RuAl-Ru were processed using various solidification methods, and the fracture behavior was examined. The fracture toughness values for RuAl-hcp(Ru, Mo) and RuAl-hcp(Ru, Cr) alloys ranged from 23 to 38 MPa√m, while the volume fraction of RuAl ranged from 22 to 56 percent. Increasing the volume fraction of RuAl resulted in a decrease in fracture toughness. The hcp solid solution was shown to be the more ductile phase with a fracture toughness approaching 68 MPa?m, while the B2 solid solution (RuAl) was found to have a fracture toughness less than 13 MPa√m. An alloy of Ru-7Al-38Cr (at.%) that consisted of a hcp matrix with RuAl precipitates had the highest room temperature toughness and the greatest hardness.

Effect of titanium addition on a Ni-Al-Co alloy

1990 ◽  
Vol 48 (4) ◽  
pp. 938-939
Author(s):  
L. S. Lin ◽  
G. W. Levan ◽  
S. M. Russell ◽  
C. C. Law
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Room Temperature ◽  
Volume Fraction ◽  
X Ray Diffraction ◽  
Titanium Addition ◽  
X Ray ◽  
Gamma Prime ◽  
Room Temperature Ductility ◽  
Ti Addition

AEM examinations of a NiAlCo alloy of composition Ni-29 at.% Al-21 at.% Co after room temperature compression show that the microstructure consists of a twinned tetragonal matrix (L10, marked A in Figure 1a) and ordered fcc gamma prime precipitates (L12, marked B in Figure 1a) along grain boundaries. The compressive yield strengths of this alloy at room temperature and 760°C are 754 MPa and 163 MPa respectively. It also has superior room temperature ductility as compared to binary NiAl. An addition of 5 at.% Ti at the expense of Ni was made to this alloy in order to increase the yield strengths. The quarternary alloy shows compressive yield strengths of 976 MPa and 403 MPa at room temperature and 760°C, respectively, indicating that the Ti addition is having the desired effect.Comparison of the microstructures of the two alloys after room temperature compression (Figures la and lb) shows that the Ti containing alloy has a smaller grain size. X-ray diffraction data indicate that the gamma prime volume fraction increases from 10% to 20% as the result of the Ti addition. Titanium was also found to stabilize the B2 matrix (marked A in Figure lb) as no tetragonal L10 phase was found. All precipitates along grain boundaries were identified by micro-diffraction to be gamma prime.

Microstructure and Tensile Ductility of a Ti-43Al-4Nb-1Mo-0.1B Alloy

2008 ◽  
Vol 1128 ◽  
Author(s):  
Laura M. Droessler ◽  
Thomas Schmoelzer ◽  
Wilfried Wallgram ◽  
Limei Cha ◽  
Gopal Das ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Thermodynamic Equilibrium ◽  
Room Temperature ◽  
Volume Fraction ◽  
Tensile Ductility ◽  
Heat Treatments ◽  
Air Cooling ◽  
B2 Phase ◽  
Treatment Step ◽  
Heat Treatment Step

AbstractThe microstructural development of a forged Ti-43Al-4Nb-1Mo-0.1B (in at%) alloy during two-step heat-treatments was investigated and its impact on the tensile ductility at room temperature was analyzed. The investigated material, a so-called TNM™ gamma alloy, solidifies via the β-route, exhibits an adjustable β/B2-phase volume fraction and can be forged under near conventional conditions. Post-forging heat-treatments can be applied to achieve moderate to near zero volume fractions of β/B2-phase allowing for a controlled adjustment of the mechanical properties. The first step of the heat-treatment minimizes the β/B2-phase and adjusts the size of the α-grains, which are a precursor to the lamellar γ/α2-colonies. However, due to air cooling after the first annealing step, the resulting microstructure is far from thermodynamic equilibrium. Therefore, a second heat-treatment step is conducted below the eutectoid temperature which brings the microstructural constituents closer to thermodynamic equilibrium. It was found that temperature and duration of the second heat-treatment step critically affect the solid-state phase transformations and, thus, control the plastic fracture strain at room temperature. Scanning and transmission electron microscopy studies as well as hardness tests have been conducted to characterize the multi-phase microstructure and to study its correlation to the observed room temperature ductility.

Processing and Mechanical Properties of RuAl-Based Alloys

2007 ◽  
Vol 539-543 ◽  
pp. 1469-1474 ◽  
Author(s):  
T.D. Reynolds ◽  
M. Acosta ◽  
David R. Johnson
Keyword(s):  
Fracture Toughness ◽  
Cyclic Oxidation ◽  
Room Temperature ◽  
Single Phase ◽  
Tensile Ductility ◽  
Tensile Behavior ◽  
Directionally Solidified ◽  
Two Phase ◽  
Heat Treated ◽  
Temperature Fracture

Alloys of Ru-Al-Cr with compositions between Ru-10Al-35Cr and Ru-3Al-39Cr (at.%) were directionally solidified and heat treated to produce single phase hcp-Ru(Cr,Al) and two phase B2-hcp microstructures. The room temperature fracture toughness, tensile behavior, and cyclic oxidation behavior at 1100°C were investigated and compared to previous results measured from RuAl and Ru-Al-Mo alloys. For microstructures consisting of a Ru(Cr,Al) matrix with fine RuAl precipitate, a good room temperature fracture toughness, tensile ductility, and oxidation resistance at 1100°C were measured.

Compendium of alloy phases observed after low temperature aging of Ni-rich NiAl

1990 ◽  
Vol 48 (4) ◽  
pp. 944-945
Author(s):  
Ivan E. Locci ◽  
P. S. Khadkikar ◽  
R. D. Noebe ◽  
K. Vedula
Keyword(s):  
Low Temperature ◽  
Room Temperature ◽  
Single Phase ◽  
Tensile Ductility ◽  
Intermetallic Alloys ◽  
Directionally Solidified ◽  
Two Phase ◽  
Low Temperature Aging ◽  
Temperature Aging ◽  
Stable And Metastable Phases

An overwhelming amount of research has been performed on Ni3Al (γ’) and NiAl (β) intermetallic alloys over the last decade. Yet, very little is known about the two phase field between these ordered compounds, including the occurrence and stability of phases other than γ’ or β Identifying and understanding these other phases are important since one approach to improving the ductility and toughness of NiAl is to design an alloy with a dual phase microstructure (i.e. NiAl + Ni3Al). Preliminary alloying attempts have encountered varying degrees of success. They range from powder metallurgy alloys with significantly increased fracture strengths over single phase (β-alloys to directionally solidified γ’ + β crystals which exhibit up to 9% tensile ductility at room temperature. Unfortunately, aging of these alloys at low temperature (<973 K) results in the formation of several complex, stable and metastable phases which may negate any original improvements in mechanical behavior.

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