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In the present work, strain rate sensitivity, using tensile and compression test data at different strain rates, fracture toughness using three-point bend test on multi axially forged (MAF) 6063 Al alloys at liquid nitrogen temperature have been investigated. The hardness, tensile strength and strain rate sensitivity (SRS) of the deformed alloy have increased to 116 HV, 337 MPa, and 0.02, from 60 HV, 220 MPa and 0.004 respectively, due to accumulation of high dislocation density in the alloy processed multi axial forging at cryo temperature. Large plastic strain induced during cryo forging of 6063 Al alloy led to effective fragmentation of grains, facilitating grain refinement in the alloy. The cryoforged alloy exhibits multimodal microstructure composed of nanocrystalline, ultrafine and coarse grains. The fracture toughness of deformed (MAF and CR) 6063 Al alloy has been increased from 8.32 MPa m1/2 to 13.78 MPa m1/2 due to grain refinement and high fraction of grain boundaries. The reduction in dimple size with increasing strain showed the presence of fine grains in multiaxial forged 6063 Al as evident from fractography studies.

The dielectric behavior of spark plasma sintered SiC(O)/HfCxN1-x nanocomposites synthesized through polymer derived ceramic route was investigated in the frequency range of 1 kHz to 1 MHz at room temperature. The nanostructural features revealed HfCxN1-x nanocrystals encapsulated in a nanometric thin layer of carbon dispersed uniformly in a SiC(O) matrix with segregated free carbon. The nanocomposites exhibited colossal permittivity values in the order of 103 at 1 kHz which reduced to 646 at 1 MHz. The interfacial polarization mechanism existing between complex nanostructural interfaces and the percolation of HfCxN1-x nanocrystals are believed to be responsible for the high permittivity values observed in the measured frequency range. The AC conductivity exemplified a frequency independent behavior at lower frequencies while at higher frequencies, the conductivity exhibited frequency dependence, indicating the existence of hopping type mechanism.