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Debrecen vs Szombathelyi Haladas : Hungarian NB I:- Get LIve Here & Video Highlights

2008-09-12T01:30:00.000-07:00

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19:00 - 21:00	Hungarian NB I							Live!
			Debrecen	vs.	Szombathelyi Haladas

CONCLUSIONS:Cryo-Rolling

2008-09-04T10:49:00.000-07:00

1. In ECAP, the deformation is non uniform along the transverse axis. This is because the skin experiences more shear resistance than the center portion during deformation. Hence, the center portion of the structure is almost completely unaffected to the applied load in the initial stages.
2. The grain refinement is more predominant in Chilled Cast samples as compared to the other cast samples. This is due to higher grain boundary areas causing more refinement in the microstructure during deformation process.
3. The microstructures are prepared at different conditions (chilled, metallic mold and sand castings) showing three to four times increase in grain size from chilled cast to sand cast structure.
4. After two deformations through ECAP, chilled casting and metal mold castings crushed to such an extent that it is very difficult to identify individual grains at 100X magnification. And after four deformations the average grain size reduced to micron levels.

EFFECT OF INTITIAL GRAIN SIZE ON EQUAL CHANNEL ANGULAR PRESSING

2008-09-04T10:46:00.000-07:00

During last decade, Equal Channel Angular Pressing [ECAP] has emerged as a widely known procedure for the fabrication of ultra fine-grained metals and alloys. ECAP imposes large plastic strains on billets via a pure shear strain state. Intense plastic strain is introduced into materials without changing the cross sectional area of deformed billets in this technique. The interaction of shear plane with texture and crystal structure plays a primary role in grain refinement. The present work involves in study of initial microstructure on ECAP. Three different samples were prepared through sand casting, chilled casting and normal casting (using metallic mould). These samples were subjected to repeated pressings with a rotation of 1800 in each pass. Representative samples are taken after every two passes from the deformed samples to examine the grain size & shape effects on deformation and the corresponding hardness values are also reported for successive samples.

Influence Of The Pressing Temperature:

2008-09-04T10:45:00.000-07:00

The pressing temperature is a key factor in use of ECAP because it can be controlled relatively easily. There will be an increase in equilibrium grain size with increasing temperature. Also the fraction of low angle grain boundaries increase with increasing temperature due to the faster rates of recovery at the higher temperature which led to an increasing annihilation of dislocation within the grain and a consequent decrease in the number of dislocations absorbed into the sub grained walls. Although it is easier to press specimens at high temperature, optimum ultra fined grain micro structures will be attained when the pressing is performed at the lowest possible temperature where the pressing operation can be conducted without the introduction of any significant cracking in the billets. By maintaining a low pressing temperature ensures the potential for achieving both the smallest possible equilibrium grain size and the highest fraction of high angle grain boundaries.

Influence of the Channel Angle, Φ:

2008-09-04T10:44:00.000-07:00

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

EXPERIMENTAL FACTORS INFLUENCING ECAP:

2008-09-04T10:43:00.000-07:00

When materials are processed using ECAP, several different factors influence the workability and the micro structural characteristics of the as-pressed billets. These factors fall into three different categories. First, there are factors associated directly with the experimental ECAP facility, such as the values of the angles within the die between the two parts of the channel and at the outer arc of curvature where the channels intersect. Second, there are experimental factors related to the processing regimes where some control may be exercised by the experimentalist including, for example, the speed of pressing, the temperature of the pressing operation and the presence or absence of any back pressure. Third, there are also other factors which may play a role influencing the extent of grain refinement. These include the processing routes and the total number of passes imposed on the sample.