Assalamualykum. 
Yes it is permissible to make duaa in sajdah , however certain scholars regard it as reprehensible as people might mistake it to be an act of sunnah,  hence ones intention should be clear. It is permissible and not a virtuous or sunnah act.
جزاكم الله خيرا احسن الجزاء 
Request duaas