Influence of the Channel Angle, Φ:

The channel angle, Φ, is the most significant experimental factor since it dictates the total strain imposed in each pass and thus it has a direct influence on the nature of the as-pressed micro structure. Generally the channel angle varies from 90° – 157.5°. It is proved that an array of ultrafine equiaxed grains is achieved most easily when the sample is subjected to a very intense plastic strain using a die with a channel angle of 90°1.
The shear strain imposed can be found using a general solution
γ = 2 cot(Φ/2+Ψ/2) +Ψ cosec(Φ/2+Ψ/2)1
The equivalent strain after n passes, εn, may be expressed by the relationship εn = n/√3 {2 cot(Φ/2+Ψ/2) +Ψ cosec(Φ/2+Ψ/2)} 1