Is it permissible to limit interaction with university colleagues to merely exchanging greetings, and to avoid conversing with them during the study period, due to their negative impact on academic achievement?

If your relationship with friends you meet is limited to exchanging greetings (saying "peace be upon you" and responding to it), then you are not considered to be abandoning them in a forbidden way. As for anything beyond that in the relationship, it is viewed in terms of benefit. If there is a religious or worldly benefit in further communication, then do so; otherwise, leave it. If you are harmed by associating with those mentioned, and there is a benefit for you in limiting it to exchanging greetings, then there is no blame upon you.