Grain Boundaries, Trace Elements, and Fracture of Intermetallic Compounds

1994 ◽  
Vol 364 ◽  
Author(s):  
Hui Lin ◽  
Easo P. George ◽  
David P. Pope
Keyword(s):  
Trace Elements ◽  
Grain Boundaries ◽  
Intermetallic Compounds

Effects of Ca and RE Additions on the Precipitation and Microstructure of As-Cast AZ91 Alloy

2017 ◽  
Vol 865 ◽  
pp. 30-35 ◽  
Author(s):  
Li Fu ◽  
Qi Chi Le ◽  
Pei Li Gou ◽  
Xi Bo Wang ◽  
Xuan Liu
Keyword(s):  
Intermetallic Compound ◽  
Grain Boundaries ◽  
Intermetallic Compounds ◽  
Lamellar Structure ◽  
Az91 Alloy ◽  
Sem Images ◽  
Xrd Pattern ◽  
Microstructure Changes ◽  
Polygonal Structure ◽  
Cast Alloys

The effect of Ca and RE metal additions on the precipitation and microstructure of as-cast AZ91 alloy was systematically investigated. It was found that Ca and RE additions could result in phase and microstructure changes. The XRD pattern showed the crystallite phase of as-cast AZ91 alloys consists of α-Mg matrix and β-Mg17Al12, however, after adding 1.5wt. % Ca and 0.8wt. % RE (0.5wt. % Sm and 0.3wt. % La), peaks coincident with Al2Ca, Al2Sm and Al11La3 intermetallic compounds were found, suggesting the generation of relative precipitates. The SEM images indicated that in as-cast alloys, the Al2Ca intermetallic compound was located at grain boundaries with a lamellar structure, and the Al2Sm intermetallic compound was homogeneously distributed in the α-Mg matrix or near the grain boundaries with a polygonal structure, and the Al11La3 intermetallic compound was located at grain boundaries with a needlelike structure. These intermetallic compounds could reduce the amount of β-Mg17Al12 and refine the microstructure of as-cast AZ91 alloy.

Fracture Modes in Ll2 Compounds

1988 ◽  
Vol 133 ◽  
Author(s):  
C. L. Briant ◽  
A. I. Taub
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intermetallic Compounds ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Fracture Modes ◽  
Beneficial Effects ◽  
Boron Segregation ◽  
Total Composition ◽  
Carbon Additions

ABSTRACTThis paper reports a study of grain boundary segregation and fracture modes in Ll2 intermetallic compounds. Data obtained on Ni3A1, Ni3Si, Ni3Ga, Ni3Ge, and Pt3Ga will be presented. It will be shown that the amount of boron segregation and its ability to improve cohesion depends on the total composition of the compound. The beneficial effects of boron can be counteracted by the presence of borides on the grain boundaries. Carbon additions also produce some improvement in ductility in Ni3Si.

Mechanisms of ductility improvement in L12 compounds

1988 ◽  
Vol 3 (3) ◽  
pp. 426-440 ◽  
Author(s):  
Osamu Izumi ◽  
Takayuki Takasugi
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intermetallic Compounds ◽  
Present Article ◽  
Electronic Structures ◽  
Alloying Effect ◽  
Test Environment ◽  
Materials Development

The present article first describes some characteristics of structure, chemistry, and electronic (bond) nature for grain boundaries in the A3B Li2-type intermetallic compounds. Next, the phenomenological aspects for the grain boundary brittleness of the Li2-type intermetallic compounds are reviewed with respect to the combination of the constituent atoms, the alloying effect, the stoichiometry effect, and a role of impurity or gaseous atoms. It is emphasized that the brittleness of grain boundaries in the intermetallic compounds is directly controlled by the atomistic and electronic structures at grain boundary regions. Based on these systematic investigations, it is suggested that the brittleness of the Li2-type intermetallic compounds can be manipulated by appropriate control of composition and the corresponding electrochemical bond environment at grain boundary planes and by control of test environment. Furthermore, some examples of the materials development are described.

Formation of a ternary silicide for Ni/Ti/Si (100) and Ni/TiSi2 structures

1989 ◽  
Vol 4 (5) ◽  
pp. 1218-1226 ◽  
Author(s):  
M. Setton ◽  
J. Van der Spiegel ◽  
B. Rothman
Keyword(s):  
Activation Energy ◽  
Phase Separation ◽  
High Temperature ◽  
Grain Boundaries ◽  
Intermetallic Compounds ◽  
Ternary Phase ◽  
Metal Silicide ◽  
Mobile Species ◽  
Metal Bilayers ◽  
Ternary Silicide

Phase formation was studied for Ni/Ti/Si and Ni/TiSi2 structures processed by vacuum RTP. Intermetallic compounds Ni3Ti and Ti2Ni form sequentially above 425 °C for metal bilayers Ni/Ti on Si, as Ni diffuses into Ti. When the temperature reaches 550 °C, Si becomes mobile and diffuses into the Ni–Ti compound, resulting in the growth of a ternary phase Ti4Ni4Si7, (V phase). If Ni is in excess with respect to this ternary silicide, a separate layer of Ni silicide grows between the substrate and the V phase, due to the fact that Ni is the main diffusing species. For the case of an excess Ti, the Si atoms are the most mobile species during Ti silicidation. Below 700 °C, TiSi2 grows with a C 49 structure whereas a mixture of TiSi2 C 54 and V phase forms at high temperature, without phase separation in distinct layers. Ni is also a fast diffuser in TiSi2. The activation energy for the diffusion along the grain boundaries of the Ti silicide is about 1.25 ± 0.2 eV. For these Ni/TiSi2 samples too, the same V phase starts to grow at the metal/silicide interface.

Thermal Stress and Texture Development in a Cu/Nb Composite between 4K and 1273 K

2005 ◽  
Vol 495-497 ◽  
pp. 1687-1692
Author(s):  
Wen-Hai Ye ◽  
Hans Georg Priesmeyer ◽  
Heinz Günter Brokmeier
Keyword(s):  
Thermal Expansion ◽  
Thermal Stress ◽  
Grain Boundaries ◽  
Intermetallic Compounds ◽  
Research Program ◽  
Linear Accelerator ◽  
Thermal Stresses ◽  
The Other ◽  
Texture Development ◽  
Long Time

Cu-Nb composites are characterized by some special properties, which were discussed since a long time by many different authors [1, 2, 3, and 4]. For manufacturing linear accelerator units it is a great advantage that Cu-Nb don’t form intermetallic compounds. One of the basic questions during application is the influence of the thermal expansion of copper and niobium. Thermal expansion of Cu-Nb was widely discussed by Nadeau and Ferrari [5]. Our research program consists of investigations on Cu50%-Nb50% composites and on Cu-Nb tubes, which on one hand have different textures and on the other hand the grain boundaries are much different in the composite with a curling microstructure and in co-extruded tubes. The present paper will concentrate on thermal stresses and the texture behavior in the temperature range 4K -1273K.

Rosenhain Centenary Conference - 3. Materials development present and future 3.10 Future developments in non-ferrous metallurgy Discussion

1976 ◽  
Vol 282 (1307) ◽  
pp. 437-450
Keyword(s):  
Trace Elements ◽  
Grain Boundaries ◽  
Trace Element ◽  
Boundary Migration ◽  
Copper Alloys ◽  
Precipitate Size ◽  
Zone Formation ◽  
Aluminium Copper ◽  
Wide Range ◽  
The Matrix

I should like to enlarge on the part of our paper (3.10) in which we considered the effect of trace additions of specific elements on precipitation and on methods of controlling precipitate size. By the term ‘trace elements’ I differ from those working with steel and mean deliberate additions of specific elements in amounts from a few hundreths to about one tenth of an atomic percentage. The atoms of these elements tend to be different in size from those of the matrix and so it is natural that they should seek some site in the lattice at which they can reduce their energy. This they do by segregating preferentially to defects and interfaces and this is how their effects can be utilized. There are four typical sites: 1. Grain boundaries which have recieved most attention. Here trace elements can be used to control the rate at which boundaries can migrate. This can be at higher or lower rates than the normal migration rate of the boundaries in a pure alloy depending on the nature of the trace element. Thus they can cause grain refinement or at the other extreme, they can introduce a property akin to superplasticity for which only about 0.1 atomic percentage is needed. Unwanted trace additions can cause embrittlement but intentional additions can replace detrimental elements at boundaries and thus increase ductility. Embrittlement is often caused by discontinuous precipitation which is a consequence of grain boundary migration. The use of boron in steel to increase the depth of hardening is an example of a trace element effect at grain boundaries. By reducing boundary migration, the formation of pearlite is inhibited. 2. Dislocations which have been well treated especially in steels and aluminium alloys. 3. The matrix/precipitate interface which is now thought to be a special case of segregation to dislocations, in this case to growth dislocations at the m atrix/precipitate interface. Trace elements have been detected at this interface and as long as they remain there, growth of the precipitate is prevented. This avoids the coarsening to which Professor Honeycombe has referred. 4. Vacant lattice sites where they can control diffusion rates. This is extremely im portant as less than 0.1 % of one atomic species can control the whole diffusion process over a wide range of temperature. If the trace element forms part of the precipitate or structure which is produced by diffusion, then the trace element will accelerate precipitation; whereas if the trace element plays no part in the precipitate structure, it denies vacancies to the diffusing species. We have cases of elements added to aluminium -copper alloys delaying g.p. zone formation for more than three years, when in the absence of the trace element, g.p. zone formation would be complete in about 48 h. I would like to concentrate on the last two processes and illustrate them by an example which enabled us to develop a new engineering material from first principles using our knowledge of trace element effects.

Semi-Solid Processing and Properties of RE-Containing Mg Alloys

2016 ◽  
Vol 256 ◽  
pp. 75-80 ◽  
Author(s):  
Shu Sen Wu ◽  
Xiao Gang Fang ◽  
Shu Lin Lü ◽  
Li Zhao ◽  
Jing Wang
Keyword(s):  
Grain Boundaries ◽  
Intermetallic Compounds ◽  
Average Particle Size ◽  
Acoustic Streaming ◽  
Mg Alloys ◽  
Average Particle ◽  
Squeeze Pressure ◽  
Semi Solid ◽  
T Phase ◽  
Zr Alloy

The RE-containing Mg alloys usually have big RE-rich intermetallic compounds distributed along grain boundaries. In this paper, a 3 wt.% RE containing Mg alloy is processed by combination of semi-solid slurry-making with ultrasonic vibration (UV) and squeeze casting. Results show that good semi-solid slurry with fine and spherical primary α-Mg particles can be obtained due to the effects of the cavitation and acoustic streaming induced by UV, and the average particle size and average shape factor are about 30 μm and 0.70 respectively. The RE-rich intermetallic compounds are refined and uniformly distributed along grain boundaries. With the increase of squeeze pressure from 0 MPa to 200 MPa during the casting of semi-solid slurry, the tensile strength and the elongation of the as-cast samples are increased continuously, which reach 182 MPa and 8.4% respectively. The microstructure is also analyzed with SEM, TEM, XRD and EDS, and the phase constitutions of this Mg-RE-Zn-Y-Zr alloy are mainly α-Mg matrix, α-Zr, W phase (Mg3Zn2Y3), I phase (Mg3Zn6Y) and T phase ((La,Ce)(Mg1-xZnx)11). The mechanism of refinement of RE-rich intermetallic compounds is also discussed.

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