Microstructural evolution during the heat treatment of nanocrystalline alloys

2007 ◽  
Vol 22 (11) ◽  
pp. 3233-3248 ◽  
Author(s):  
A.J. Detor ◽  
C.A. Schuh
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Microstructural Evolution ◽  
Nanocrystalline Materials ◽  
Boundary Segregation ◽  
Nanocrystalline Alloys ◽  
Analytical Models ◽  
Boundary Structure ◽  
Chemical Ordering ◽  
Wide Range

Nanocrystalline alloys often show exceptional thermal stability as a consequence of kinetic and thermodynamic impediments to grain growth. However, evaluating the various contributions to stability requires detailed investigation of the solute distribution, which is challenging within the fine structural-length-scales of nanocrystalline materials. In the present work, we use a variety of techniques to assess changes in the grain size, chemical ordering, grain-boundary segregation, and grain-boundary structure during the heat treatment of Ni–W specimens synthesized over a wide range of grain sizes from 3 to 70 nm. A schematic microstructural evolution map is also developed based on analytical models of the various processes activated during annealing, highlighting the effects of alloying in nanocrystalline materials.

Microstructures, Grain Boundaries and Superplasticity in Fine Grained Ceramics

1990 ◽  
Vol 196 ◽  
Author(s):  
C. Carry
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Boundary Structure ◽  
Fine Grained ◽  
Chemical Effects ◽  
Liquid Phases ◽  
Grain Boundary Structure ◽  
Wide Range ◽  
Points Of View

ABSTRACTDeformation studies in compression and in tension have clearly shown evidence for superplasticity for a wide range of fine grained ceramics from both macroscopic and microscopic points of view. The main purpose of this paper is to focus attention on chemical effects in ceramic grain boundaries which can lead to a great variety of behavior. Grain boundary segregation or precipitation, residual impurities or doping elements, and glassy or liquid phases at grain boundaries can strongly affect the macroscopic flow properties of superplastic fine grained ceramics. Some microstructural and grain boundary features, mainly in two oxide materials (alumina and yttria doped zirconia), are analyzed, compared, and discussed in connection with their observed superplastic behavior. Special attention is devoted to the relation between the overall chemistry of the materials (impurities and doping elements) and to the grain boundary structure and chemistry (segregation, precipitation, intergranular phases). Some consequences and implications on the tailoring of ceramic microstructures for superplasticity are discussed. In addition, some recent hot forming and hot bonding experiments are also reported.

Atomic Scale Characterisation of Electrodeposited Nanocrystalline Ni-P Alloys

1999 ◽  
Vol 581 ◽  
Author(s):  
Matthias Abraham ◽  
Mattias Thuvandert ◽  
Helen M. Lane ◽  
Alfred Cerezo ◽  
George D.W. Smith
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Three Dimensional ◽  
Boundary Segregation ◽  
Atom Probe ◽  
Atomic Scale ◽  
Grain Boundary Segregation ◽  
P Concentration

ABSTRACTNanocrystalline Ni-P alloys produced by electrodeposition have been characterised by three-dimensional atom probe (3DAP) analysis. In the as-deposited materials, there are indications of some variation in P concentration between grains and segregation to grain boundaries. After heat treatment however, strong grain boundary segregation and the formation of Ni3P precipitates have been observed.

Grain Boundary Precipitate Density as a Function of Time and Misorientation in an Al-5 WT% Cu Alloy

1993 ◽  
Vol 319 ◽  
Author(s):  
M. A. Cantrell ◽  
G. J. Shiflet
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Treatment Time ◽  
Boundary Plane ◽  
Heat Treatment Time ◽  
Boundary Structure ◽  
Plane Orientation ◽  
Cu Alloy ◽  
Grain Boundary Plane ◽  
Precipitate Density

AbstractThe variation of θ (CuAI2) precipitate density as a function of heat treatment time and grain boundary misorientation was investigated in an Al-5 wt % Cu alloy. In this study, precipitate densities have been quantitatively linked to grain boundary structure. It was found that, for a given heat treatment time, the precipitate density varied in a reproducible manner (108 to 1010 ppts/cm2) as a function of misorientation between the grains (20 to 60 degrees). Additionally, misorientation was found to be the most important factor governing the precipitate density at a given grain boundary. The grain boundary plane orientation played a secondary role in determining the precipitate density. Bollmann O-lattice modeling allows comparison of the relative effects of grain boundary plane orientation relative to the misorientation between grains.

Effect of Heat Treatment on Fracture during Bending in AA6016 Aluminium Alloy Sheets

2011 ◽  
Vol 488-489 ◽  
pp. 521-524
Author(s):  
Aleksandar Davidkov ◽  
Roumen H. Petrov ◽  
Peter De Smet ◽  
Leo Kestens
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Volume Fraction ◽  
Boundary Structure ◽  
Homogeneous Distribution ◽  
Fracture Mechanisms ◽  
Al Alloy ◽  
Technological Parameters ◽  
The Matrix ◽  
Strengthening Phases

The bending properties of high strength precipitation-hardening AA6016-type Al alloy thin sheets in pre-aged T4P temper state were studied in this work. Microstructural features like grain boundary particles distribution and volume fraction of the matrix strengthening phases were considered as factors controlling the mechanical properties and the fracture of this grade. Remarkable decrease in ductility, accompanied by severe deterioration of bendability occurred when coarse precipitates were found into the grain boundaries. The in-situ fracture sequence investigations as well as the post-failure surfaces observations indicated that grain boundary ductile fracture mechanisms were involved in the propagation of the cracks during bending. Heat treatment simulations were carried out and the results showed that the precise control of the technological parameters during production of these sheets is the key factor responsible for obtaining an appropriate combination of strength and bendability. Only by providing both, homogeneous distribution of the matrix strengthening phases and a favourable grain boundary structure, the severe and often contradictory requirements for the functional properties of these alloys can be successfully satisfied.

Structure And Composition Of Grain Boundaries In SrTiO3

1999 ◽  
Vol 5 (S2) ◽  
pp. 94-95
Author(s):  
O. Kienzle ◽  
F. Ernst ◽  
Manfred Rühle
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Point Defects ◽  
Coincidence Site Lattice ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Boundary Structure ◽  
Dopant Atoms ◽  
Charged Point ◽  
Atomistic Structure

The electrical properties of SrTiO3 (strontium titanate) ceramics are strongly influenced or even dictated by grain boundary segregation of charged point defects, such as dopant atoms, impurities, vacancies, or self-interstitials. The atomistic structure of the grain boundaries, their energy, and the segregation of point defects mutually depend on each other. Grain boundary segregation of charged point defects induces the formation of space charge layers in the adjoining crystals. In order to investigate the relation between grain boundary structure and composition, grain boundaries in Fedoped SrTiO3 bicrystals and in SrTiO3 ceramics were studied by HRTEM and by AEM with subnanometer resolution.Quantitative HRTEM served to investigate the atomistic structure of Σ=3, (111) grain boundaries in Fe-doped SrTiO3 bicrystals with a doping level of Fe/Ti= 0.04at% (Fig. 1). Analysis of the translation state revealed that the Σ=3, (111) grain boundary has an excess volume: normal to the boundary plane, the spacing between the two crystals exceeds what one would expect from a coincidence site lattice model by (0.06 ±0.01 )nm.

Monte Carlo Simulation of Solute-Atom Segregation at Grain Boundaries In Single-Phase Binary Face-Centered Cubic Alloys

1998 ◽  
Vol 4 (S2) ◽  
pp. 764-765
Author(s):  
David N. Seidman ◽  
John D. Rittner ◽  
Dmitry Udler
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Solute Atom ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Diffusional Creep ◽  
Boundary Structure ◽  
Temper Brittleness ◽  
Face Centered Cubic ◽  
Boundary Properties

Solute-atom segregation to grain boundaries has been of interest since the 1930's when it was realized that some steels were susceptible to failure by intergranular fracture when certain impurities were present. Segregation of impurities or intentionally added alloying elements at grain boundaries can greatly affect various grain boundary properties, which in turn affect numerous macroscopic properties. Materials phenomena that have been linked to grain boundary segregation include temper brittleness, fatigue strength, adhesion, precipitation, diffusional creep, intergranular corrosion, and grain boundary diffusivity. Although grain boundary segregation has been extensively studied for many years, the effects of different grain boundary structures on segregation was generally not considered. It has been established both experimentally and theoretically that the level of segregation varies from grain boundary to grain boundary in the same alloy, but there is little direct information on how grain boundary structure influences segregation.

New Grain-Boundary Phases for Nitrogen Ceramics

1992 ◽  
Vol 287 ◽  
Author(s):  
Derek P. Thompson
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Crystal Chemistry ◽  
Residual Glass ◽  
Double Chain ◽  
Wide Range ◽  
Typical Composition ◽  
Approximate Composition ◽  
The Many ◽  
Mineral Silicates

ABSTRACTThe drive for improved refractoriness in nitrogen ceramics, which has motivated the removal of residual glass from grain-boundaries by heat-treatment at sub-solidus temperatures, has resulted in the discovery of a wide range of crystalline oxynitride phases. Generally, these phases are oxygen-rich, and can be classified in the same way as the mineral silicates, in which oxygen atoms are coordinated to a maximum of two silicon atoms, with SiO4 tetrahedra joined at either 0,1,2,3 or 4 corners to other tetrahedra. However, the field of oxynitride crystal chemistry is wider than this, because nitrogen in SiN4 tetrahedra commonly occurs coordinated to three silicon atoms, and an additional range of structures exist with nitrogen in this coordination.Oxynitride analogues of mineral silicates are well known in neso-, soro- and cyclostructure types; new structures have recently been reported which belong to the pyroxene family (ino-silicates), and information on their preparation and crystal chemistry is reported here. The sialon U-phase (typical composition Ln3Si3Al3O12N2, Ln = La,Ce,Nd,Sm), is an example of an oxynitride with a structure intermediate between layer (phyllo-) and framework (tecto-) types. Sialon W-phase (approximate composition Ln4Si9Al5O30N, Ln = La,Ce,Nd) has not been completely characterized, but appears to have a structure related to the amphibole group of double-chain silicates.Comments are made on the many oxynitride structures which are still uncharacterized. The suitability of all these oxynitrides as grain-boundary phases in silicon nitride and sialon ceramics is discussed.

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