It may be due to the property of basic ceramic, may i know which material you are using?

they are all first generation cracks, due to influence of processing, if the material is known then reason can be predicted

K V Arun Its a TiC-CNT composite

Looks like the cracks are exposed to surface (of particles) and about tens of nm wide.

Can there be any electrical field-assisted phase transformation at surface that have generated volume strain at surface?

Can there be electrostriction (similar to magnetostriction) of TiC and CNT, and Can surface crack be generated if their electrostrictive response or nano-thermal response (one region of surface getting faster cooled than others) are widely different?

Was there any trace/micro-alloying element in the chemical reagents that generates brittle/more expandable carbides/ Titanides in GB/inside lattice of TiC and especially sensitive to heat and electric filed of spark (i.e. vaporizable during spark striking particles).

Ti metal is known to absorb significant amount of H and O in their lattice, and CNT, like rGO, may hold some residual O/N/H/S etc. containing radicals, depending on purity and preparation route. If any adhesive (especially organic) is used to make the composite, especially those are surface active w.r.t TiC, can be culprit as well. I know Si Nitrides and Carbides can coexist in solid solution, while nitride-oxide co-existnce (i.e. no precipitation or segregation) is seen in SiAlON glasses. Is it same for Ti?

Consider these issue. Good luck!

Thanks Sumit Bhowmick

Generally post heat treatment (sintering in your case) cracks may appear in the system because of non-optimized cooling rate. System may try to bring down it's energy (stain) by way of cracking, i.e. towards relaxing. However, from the image attached with your question, you may also try to see these from the view point of grains and grain boundaries.

May be you need to share some more details for better discussion and conclusion.

Aman Arora After SPS the system was shut off and left for normal cooling. Please elaborate more on your view point of grains and grain boundaries.

It is usually tough to consolidate defect-free ceramics. Microcracks occur during the cooling stage because of thermal expansion mismatch among grains of different phases or even between anisotropic grains having the same phase. Phase transformations during the heating/cooling cycle may also form microcracks. Microcracks, to some extent, may be favorable as they increase fracture toughness (K1C) by microcrack toughening mechanism, but a significant amount is not desirable because it decreases the effective elastic modulus of the material system.