Hall-Petch Basis for Assessing Alloy Strengthening

1994 ◽  
Vol 362 ◽  
Author(s):  
Ronald W. Armstrong ◽  
R. Michael Douthwaite
Keyword(s):  
Grain Boundary ◽  
Alloy Composition ◽  
Friction Stress ◽  
Face Centered Cubic ◽  
Square Root ◽  
Petch Relation ◽  
Face Centered ◽  
Al Mg Alloys ◽  
Zn Alloys ◽  
Grain Boundary Strengthening

AbstractThe Hall-Petch relation σ = σo + kl−½, provides for the separate consideration of friction stress strengthening within the polycrystal grain volumes through σo and grain boundary strengthening through the product of the microstructural stress intensity k and the reciprocal square root of the grain diameter l Smaller grain diameters are normally obtained at higher alloy contents as illustrated for yield strength results reported for different face-centered-cubic Al-Mg alloys. Results on Al-Li alloy give an interesting example of substantial grain boundary strengthening that is associated with reduced ductility of the material. More complete results reported for the Cu-Al system, allow an evaluation of the strengthening component dependencies on alloy composition, in particular, connecting with a predicted square root of grain boundary obstacle stress in k. The much studied Cu-Zn alloys bring out subtle changes in σo and k

Nearly Dislocation-Free APB Termination at Pure Grain Boundary Step Defects in L10 Alloys

1993 ◽  
Vol 319 ◽  
Author(s):  
Abha Singh ◽  
A.H. King
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Tetragonal Phase ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Antiphase Boundaries ◽  
New Type ◽  
Face Centered ◽  
Fcc Phase ◽  
Step Defect

AbstractL10 alloys typically derive from a high-temperature, disordered fcc phase. For example, CuAu has a face centered tetragonal structure below 380°C and is derived from its high temperature, disordered face centered cubic phase. As the material transforms from the disordered fcc phase to the ordered tetragonal phase, the four distinct Σ3 fcc twin misorientations generate twelve distinct tetragonal twin misorientations, four being characterized as Σ3 and eight as Σ6. Of particular interest is the Σ6 structure because it is possible to terminate lattice antiphase boundaries without dislocations at this interface. A pure step defect at the interface can accommodate the APB termination due to anti-site coincidence (coincidence between copper and gold sites). We term these defects “antiphase steps”. The antiphase step is a new type of interfacial defect that has not been described by other workers. The possibility of forming antiphase steps in ordered L10 alloys is related to even-Σ interfaces. Since the Σ6 boundary is common in the ordered phase, the formation of dislocation-free APB terminations may be important in L10 alloys.

Nanoindentation study of slip transfer phenomenon at grain boundaries

2009 ◽  
Vol 24 (3) ◽  
pp. 607-615 ◽  
Author(s):  
T.B. Britton ◽  
D. Randman ◽  
A.J. Wilkinson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Cold Work ◽  
Pure Copper ◽  
Displacement Curve ◽  
Interstitial Free ◽  
Face Centered Cubic ◽  
Slip Transfer ◽  
Individual Contributions ◽  
Face Centered

Nanoindentation was undertaken near grain boundaries to increase understanding of their individual contributions to the material’s macroscopic mechanical properties. Prior work with nanoindentation in body-centered cubic (bcc) materials has shown that some grain boundaries produce a “pop-in” event, an excursion in the load–displacement curve. In the current work, grain boundary associated pop-in events were observed in a Fe–0.01 wt% C polycrystal (bcc), and this is characteristic of high resistance to intergranular slip transfer. Grain boundaries with greater misalignment of slip systems tended to exhibit greater resistance to slip transfer. Grain boundary associated pop-ins were not observed in pure copper (face-centered cubic) or interstitial free steel ~0.002 wt% C (bcc). Additionally, it was found that cold work of the Fe–0.01 wt% C polycrystal immediately prior to indentation completely suppressed grain boundary associated pop-in events. It is concluded that the grain boundary associated pop-in events are directly linked to interstitials pinning dislocations on or near the boundary. This links well with macroscopic Hall–Petch effect observations.

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