The meanings of 'いよいよ' and 'ついに' are similar each other. When you say, however, 'tried, tried, tried and at last accomplished!', you can say ’ついに' but not 'いよいよ'. OK: ついに結婚できました！　 NG: いよいよ結婚できました！　 In other words, いよいよ indicates 'getting closer to...' while 'ついに' does ''got there' OK: 私もいよいよ結婚です。(I've got OK from the woman/man, and am getting closer to the wedding) OK: 私もついに結婚です。(I've got OK from the woman/man and say goodbye to the single days at last! ) Basically you shoud not uset 'いよいよ' when you talk about things done in the past, because it's already done and you won't get closer to.(already reached).

https://japanese.stackexchange.com/questions/12682/differences-between-いよいよ-やっと-ようやく-ついに-and-とうとう