Interfacial Structure of Grain Boundary Precipitate in a Ni-45 mass%Cr Alloy

It is known that a lamellar discontinuous precipitate forms in aged Cu-1.8wt.% Be alloys. The purpose of this study was to investigate factors which influence the formation of the precipitate and to characterize its growth.To determine the effect of solution treatment on the discontinuous precipitate, specimens were solution treated at 800°C, 850°C, and 900°C for 1 hour followed by an ice water quench. Some of the solution treated specimens were examined in the as-quenched condition. The remaining specimens were aged at 340°C for 24 hours. The specimens were thinned with a twin-jet electropolishing unit using 30% HNO3 in methanol at -60°C. The specimens were then examined using either an RCA-EMU3G or a Philips EM-300 electron microscope.Each solution treated specimen was not single phase, but showed some residual grain boundary precipitate which implies that the solution anneal was not sufficient, or else precipitation had occurred during quenching. The higher solution treatment temperatures slightly reduced the amount of this grain boundary precipitate, but none completely removed it, even after five hours at temperature,indicating quench decomposition as the mechanism responsible.

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The interfacial structure of orthogonally oriented twins in YBa2Cu3O7

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100150526 ◽

1993 ◽

Vol 51 ◽

pp. 938-939

Author(s):

Yimei Zhu ◽

M. Suenaga ◽

J. Tafto

Keyword(s):

Grain Boundary ◽

Critical Current Density ◽

Critical Current ◽

Twin Boundary ◽

Current Density ◽

Interfacial Structure ◽

Hrem Image ◽

Twin Boundaries ◽

Wedge Shape

Interfaces such as the twin boundary and grain boundary in YBa2Cu3O7-δ are thought to be important in reconciling the large discrepancy between the low critical-current density observed in bulk polycrystalline. Recently, we studied another type of frequently encountered interface, i.e., the interface between the orthogonally orientated (110) and (-110) twins. In the vicinity of the interface, the crystal has a characteristic geometry because of additional constrains due to the impediment and the local orientational difference. The impinging twins usually have a wedge shape (Fig. la), and when the wedge slope is large, the tip of the twin splits (Fig. lb). A HREM image of a tapered twin is shown in Fig.2. Four twin variants give rise to five boundaries. Boundaries between IV-III, III-IV, IV-II, and II-IV are twin boundaries, while II-III, which has no apparent structure, is the interface of the orthogonal twins. If there is no constrain, the orientation of II and III should be equivalent (Fig.3a and 3b); however, we observed that the lattice in II does not align with that in III.

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Grain Boundary Precipitate Modification for Improved Intergranular Corrosion Resistance

Materials Science Forum - Aluminium Alloys 2006 ◽

10.4028/0-87849-408-1.327 ◽

2006 ◽

pp. 327-332

Author(s):

Kinga A. Unocic ◽

Paul Kobe ◽

Michael J. Mills ◽

Glenn S. Daehn

Keyword(s):

Corrosion Resistance ◽

Grain Boundary ◽

Intergranular Corrosion ◽

Boundary Precipitate ◽

Intergranular Corrosion Resistance

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Grain boundary-precipitate interactions in γ′ Ni3(Al,Ti)

Scripta Metallurgica et Materialia ◽

10.1016/0956-716x(95)00158-r ◽

1995 ◽

Vol 33 (1) ◽

pp. 1-6 ◽

Cited By ~ 3

Author(s):

V. Gehanno ◽

M.-L. Turi ◽

G.C. Weatherly ◽

G.R. Purdyn

Keyword(s):

Grain Boundary ◽

Boundary Precipitate

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On the Effect of Local Grain-Boundary Chemistry on the Macroscopic Mechanical Properties of a High Purity Y2O3-Al2O3-Containing Silicon Nitride Ceramic

MRS Proceedings ◽

10.1557/proc-839-p3.14 ◽

2004 ◽

Vol 839 ◽

Author(s):

A. Ziegler ◽

J.M. McNaney ◽

M. J. Hoffmann ◽

R. O. Ritchie

Keyword(s):

Mechanical Properties ◽

Silicon Nitride ◽

Grain Boundary ◽

Oxygen Content ◽

High Purity ◽

Interfacial Structure ◽

Crack Advance ◽

Transgranular Fracture ◽

Boundary Films ◽

Boundary Chemistry

ABSTRACTThe effects of grain-boundary chemistry on the mechanical properties of a high-purity silicon nitride ceramics were investigated, with specific emphasis on the role of oxygen. Variations in the grain-boundary oxygen content, through control of oxidizing heat treatments and sintering additives, was found to result in a transition in fracture mechanism from transgranular to intergranular fracture, with an associated increase in fracture toughness. This phenomenon is correlated to an oxygen-induced change in grain-boundary chemistry that appears to affect fracture by “weakening” the interface, facilitating debonding and crack advance along the boundaries, thereby enhancing the toughness by grain bridging. It is concluded that if the oxygen content in the thin grain-boundary films exceeds a lower limit, which is ∼0.87 equiv% oxygen content, then the interfacial structure and bonding characteristics favor intergranular debonding during crack propagation; otherwise, transgranular fracture ensues, with consequent low toughness.

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