I won't pretend to understand a whole lot about tachyons and their properties, but how would surrounding a blade with faster-than-light particles make it able to cut through any substance short of adamantium? Did the writers decide to call it a tachyonic energy field just because they knew it sounds kinda 'science-y' but that most people wouldn't know what tachyon's actually are?

LMAO.

" I won't pretend to understand a whole lot about tachyons and their properties, but how would surrounding a blade with faster-than-light particles make it able to cut through any substance short of adamantium? Did the writers decide to call it a tachyonic energy field just because they knew it sounds kinda 'science-y' but that most people wouldn't know what tachyon's actually are? "

His powers state that he can generate a tachyonic field from in his body. the sword is his preferred focus to charge the energy with, but his power set indicates he can charge anything with should be able to generate an "atomic energy buzzsaw".
 
Theoretically if he were to focus the energy on karate chops or kicks he would be a deadlier version of Iron Fist. And also faster than light charged weapon would be constantly cutting so the sword should never be stuck in somebody, it should cut like a laser chainsaw  
Writers need to get more creative with this guy. Could be a great street leveler in my opinion.