The Effect of Solute Atoms on Aluminum Grain Boundary Sliding at Elevated Temperature

AbstractIt is necessary for grain boundary dislocations to slide and climb during the grain boundary sliding process that dominates fine-grained superplastic deformation. The process of climb requires either an influx of vacancies to the grain boundary plane or a local generation of vacancies. Transmission electron microscopy (TEM) observations of grain boundaries in superplastically deformed Al-Mg-Mn alloys quenched under load from the deformation temperature have revealed the presence of nano-scale cavities resulting from a localized supersaturation of vacancies at the grain boundary. Compositional measurements along interfaces have also shown an effect of solute atoms on the local structure. This is shown to result from a coupling of vacancy and solute atom flows during deformation and quenching. Calculations of the localized vacancy concentration indicate that the supersaturation along the grain boundary can be as much as a factor often. The effects of the local supersaturation and solute atom movement on deformation rates and cavity nucleation and growth will be discussed.

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Tribological Behavior of Mg-Mg2Si In Situ Composite

Materials Science Forum ◽

10.4028/www.scientific.net/msf.710.401 ◽

2012 ◽

Vol 710 ◽

pp. 401-406

Author(s):

Kumaraswamy Kaliamma Ajith Kumar ◽

Uma Thanu Subramonia Pillai ◽

Bellambettu Chandrasekhara Pai ◽

Madhusudan Chakraborty

Keyword(s):

Elevated Temperature ◽

Wear Rate ◽

Grain Boundary ◽

Tribological Behavior ◽

Grain Boundary Sliding ◽

Dry Sliding ◽

Boundary Sliding ◽

Si Content ◽

State Processing

Mg-Mg2Si in-situ composites by the addition of Si in Mg have become more attractive since the Mg2Si phase impedes the grain boundary sliding at elevated temperature because of its inherent properties which greatly improve the heat and wear resistances. In the present work, Mg-Mg2Si composites have been prepared by the liquid state processing with different amount of silicon additions. The microstructure and dry sliding tribological behavior of the composites have been studied. SEM studies reveal the wear mechanisms involved in these composites. The results indicate that wear rate of the composites is a function of Mg2Si content in the composite. The effect of Mg2Si morphology and distribution on the overall mechanism is also discussed.

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Effect of solute atoms on grain boundary sliding in magnesium alloys

The Philosophical Magazine A Journal of Theoretical Experimental and Applied Physics ◽

10.1080/14786435.2014.886021 ◽

2014 ◽

Vol 94 (12) ◽

pp. 1345-1360 ◽

Cited By ~ 28

Author(s):

Hidetoshi Somekawa ◽

Hiroyuki Watanabe ◽

Toshiji Mukai

Keyword(s):

Grain Boundary ◽

Magnesium Alloys ◽

Grain Boundary Sliding ◽

Boundary Sliding ◽

Solute Atoms

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Effects of Zn and Mg Segregations on the Grain Boundary Sliding and Cohesion in Al: Ab Initio Modeling

Metals ◽

10.3390/met11040631 ◽

2021 ◽

Vol 11 (4) ◽

pp. 631

Author(s):

Andrey Kuznetsov ◽

Lidia Karkina ◽

Yuri Gornostyrev ◽

Pavel Korzhavyi

Keyword(s):

Grain Boundary ◽

Ab Initio ◽

Strong Relationship ◽

Shear Resistance ◽

Grain Boundary Sliding ◽

Cohesive Properties ◽

Segregation Process ◽

Boundary Sliding ◽

Solute Atoms ◽

Experimental Findings

The formation of Zn and Mg segregations at a tilt Σ5{013} <100> grain boundary (GB) in Al and the effects of these solutes on deformation behavior of polycrystalline Al were investigated using ab initio total energy calculations. Using a step-by-step modeling of the segregation process, we found that the formation of a thick segregation layer of Zn at the GB is energetically preferable, while the formation of an atomically thin segregation layer is expected in the case of Mg. To reveal the effect of segregation on the cohesive properties of Al GBs, we calculated the energy of cleavage decohesion and the shear resistance for GB sliding. We show that the segregation of Zn results in a substantial decrease in barriers for GB sliding, while the segregation of Mg increases the barriers. The results obtained allow us to explain experimental findings and demonstrate a strong relationship between chemical bonding of solute atoms, their segregation ability, and GB strength.

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Examination of Fracture Interfaces in Silicon Nitride

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113925 ◽

1975 ◽

Vol 33 ◽

pp. 60-61

Author(s):

Nancy J. Tighe

Keyword(s):

Silicon Nitride ◽

Grain Boundary ◽

Crack Growth ◽

Subcritical Crack Growth ◽

Slow Crack Growth ◽

Ceramic Materials ◽

Grain Boundary Sliding ◽

Boundary Phase ◽

Turbine Engines ◽

Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

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