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

The following are the references taken for discursion

-REFERENCES: