Date post: | 24-Jan-2018 |
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Principles of Equal-channel Angular Pressing as a processing tool for grain
refinement
Sharath C M
BENGALURU
INTRODUCTION
SEVERE PLASTIC DEFORMATION
EQUAL-CHANNEL ANGULAR PRESSING (ECAP)
CASE STUDY
CONCLUSION
Overview of this presentation involves:
Mechanical and physical properties of all crystalline materials are determined by
several factors;AVERAGE GRAIN SIZE of a material plays a
dominant role.
ULTRAFINE-GRAINED MATERIALS (UGM)
Mechanical Performance
PropertiesFabricate the
microstructureProcessing techniques
Roughly speaking, there are two major directions:
consolidation of powder materials,
refining of coarse-grained materials.
we will be concerned with the second direction
How does one obtain UFG materials ?
Thus, the strength of all polycrystalline materials is related to the grain size(d), through the hall–petch
equation which states that the yield stress, 𝜎𝑦, is given by
𝜎𝑦=𝜎0+KYD-1/2
Where, 𝜎0 is termed the friction stress andky is a constant of yielding
Two basic approaches have been developed for the synthesis of UFG
materials and these are known as the ‘‘bottom-up’’ and the ‘‘top-down’’
approaches;
BOTTOM-UP approach, UFG materials arefabricated by assembling individual atoms or byconsolidating Nano particulate solids.Examples of these techniques include inert gas
condensation, electrodeposition, ball millingwith subsequent consolidation and cryomillingwith hot isostatic pressing.
TOP-DOWN approach is different because
it is dependent upon taking a bulk solid
with a relatively coarse grain size and
processing the solid to produce a UFG
microstructure through heavy straining or
shock loading.
SPD is a generic term describing a group of metal working techniques involving,
very large strains typically involving a complex stress state or high shear, resulting in a high defect density and equiaxed "ultrafine" grain.
SEVERE PLASTIC DEFORMATION (SPD)
SPD
REFINING OF MATERIALS VIA SPD
SPD
REFINING OF MATERIALS VIA SPD
EQUAL-CHANNEL ANGULAR PRESSING (ECAP)
Equal channel angular
extrusion (ECAE,
sometimes called Equal
channel angular pressing,
ECAP) was developed in the
1970s.
It can be applied to fairly large billets wide range of structural applications.
Reasonable homogeneity is attained through most of the as pressed billet
Development of near uniform, intensive and oriented simple shear in bulk billets
Potential for developing ECAP for use in commercial metal-processing
ECAP is an especially attractive processing technique because;
Equipment parameters cross-section of die channel and intersect at an angle additional angle ψ defining the arc of curvature at the outer point of intersection of the two channels
PROCESSING USING EQUAL-CHANNEL ANGULAR
PRESSING
Processing routes in ECAP
slip systems for the different processing routes
FUNDAMENTAL PARAMETERS IN ECAP
The colors red, mauve, green and blue correspond to the first, second, third and fourth pass,
Shearing patterns associated with ECAP
Angles within the die between the two parts of the channel and at the outer arc of curvature where the channels intersect.
Speed of pressing, the temperature of the pressing operation and the presence or absence of any back-pressure.
Nature of the crystallographic texture and the distribution of grain misorientations in the unpressed material
Experimental factors influencing ECAP
Influence of the channel angle
Influence of the pressing speed
From the practical point of view, it is important to acknowledge that recent studies have demonstrated very clearly a great potential for the use of SPD processing and the incorporation of ECAP in industrial applications.
There are very good reasons for believing that, in the relatively near future, SPD processing will become established as the basis for the commercial production of semi-products and products with UFG structuresusing a wide range of metals and alloys.
CONCLUSION