Is there a rule to writing verbs in hiragana or kanji when used as a suffix?


A common pattern I've noticed is for verbs like 行く and 来る after the て form of
another verb. I know this is grammatically simply verb listing, but in terms
of meaning the verbs often times sort of merge.

For example:

> やってくる  
>  入っていく  
>  登っていく  
>  出てくる

I find that in these cases the second verb (くる / いく) is often times written in
hiragana instead of kanji. Is this a rule?

