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Is the RIB stored in TCAM ?
Usually, yes.
And does the Layer 3 engine (Arp table and RIB ) software based or hardware based
Usually both.
Ideally, special ASICs work to forward "normal" traffic. However, "unusual" packets get "punted" to the main CPU and are software processed. Also, if TCAM is overfilled, forwarding is done in software too. (NB: sometimes system documentation will note what can trigger software processing. Items such as IP/TCP options might, as might certain configuration options [e.g. some PBR options].)
Generally, software forwarding on a L3 switch is much, much, much slower than it's dedicated hardware support. (NB: in fact, such software forwarding might be slower than many small software based routers because the L3 switch is designed to forward using its dedicated hardware.)
