PSI - Issue 60

B.P. Kashyap et al. / Procedia Structural Integrity 60 (2024) 494–509 B.P. Kashyap et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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Table 3. Summary of experimental key points employed for different materials.

Material

Composition (wt.%)

Processing

Experimental characterization

References

Microscopy

Tensile test

Al-Si Alloy

Al-12Si, Al-30Si

Melting and Casting, Hot Extrusion (810 K) Alcan superplastic forming (SPF) grade AA8090, Rolling Melting and casting-rolling explosive working Melting and casting-hot rolling (793 K) Room temperature rolling and subsequent annealing for 1 hr. at 1173 K.

Leica DM750 P optical microscope

NA

(Kashyap et al., Unpublished)

Al-Li Alloy

Al-2.5Li-1.4C 1.2Mg-0.11Zr

TSL orientation image microscope attached to JEOL 840 scanning electron microscope

Computer interfaced Instron universal testing machine

(Kashyap and Chaturvedi, 2000)

Pb-Sn Alloy

Pb-62Sn

Optical microscope

-

(Kashyap and Telang, 1991)

Al-Cu Alloy

Al-33Cu

Optical microscopy,Scanning electron microscopy

Instron universal testing machine Instron universal testing machine

(Kashyap and Tangri, 1987, 1989)

SS316L

0.03 C, 16 Cr, 10 Ni, 2 Mo, 2 Mn, 1 Si, 0045 P, 0.03 S and the balance Fe

Optical microscopy, JEOL 2000 FX scanning electron microscope, Philips 300 transmission electron microscope

(Kashyap et al., 1988; Kashyap and Tangri, 1995)

3.2. Experimental results and analyses True steadystate behavior, where stress does not change with strain, was reported in Pb-Sn eutectic earlier (Kashyap and Murty, 1981) by collecting the stress-strain rate data after pre-deforming all the samples to 30% strain and then performing differential strain rate tests at different temperatures and for different grain sizes. Under superplastic conditions, the parameters of the constitutive relationship were found to be m = 0.6, Q = 44.7 kJ/mol( T < 408 K) and 81.1 kJ/mol ( T > 408 K); p = 3.34, which suggests that the existing models are not fully applicable except that some of the predictions (Table 1)of m, p, Q for superplastic deformation mechanisms seem to be obeyed. High temperature deformation behavior reported in many cases exhibits deviation from steady state deformation, where stress varies with strain. In such cases, only the apparent values of m, p, and Q are reported in the literature. Presently, the constitutive relationship used is modified for the different regions of stress-strain rate plot, and the equations followed for strain rate are divided into (i) power law, as in Eq. 6, (ii) exponential law and (iii) hyperbolic sine law(Mishra et al., 2017). However, the variations in parameters of constitutive relationships with strain appear not to follow similar trends for different materials (Ammouri et al., 2015; Ghosh et al., 2021; Mohamadizadeh et al., 2015; Zhang et al., 2016) which makes it difficult to rationalize deformation behavior but adds to further complication in understanding the deformation mechanisms. This necessitates to following the microstructural evolution as a function of strain in order to relate the effects of same with this new approach of constitutive relationship and develop appropriate mechanisms for deformation. Initial microstructures of materials used for high temperature deformation study widely range from as cast to mechanically processed microstructures in ingot metallurgy route. Examples of some typical microstructures given in Fig. 2(a-d) below are (a) as-cast dendritic structure shown for Al-12Si (eutectic), (b) equiaxed microstructure as obtained from hot extrusion of Al-30Si (hypereutectic), and (c,d) elongated and banded structure as shown for thermo-mechanically processed AA8090 Al-Li alloy and Pb-62Sn subjected to