I will not comment on the first half of the question about Athanasius (it is an excellent question that ctaylorgraphics well answered) but confine my comments to the second question about the interpretation of the text.
That the Bible itself is the most common understanding of the meaning of "logos" in Heb 4:12 is well-known. However there are several things that suggest that "logos" in this verse has the same referent as John 1:1-3, 14, 1 John 1;1, Rev 19:13.
- The respected BDAG suggests this interpretation under the heading "logos".
- In V13 (a continuation of the thought begun in V12), the author twice uses the pronoun "him" with antecedent the "word of God" in V12.
- In V13 there is another hint as well - the last phrase in V13 is (literally) "to the eyes of him, to whom is our [the] logos."
- The idiom of the "sharp two two-edged sword (machaira)" appears slightly different from the "sharp two edged sword (rhomphaia)" of Rev 1:12 from the mouth of Jesus but is nonetheless an allusion to it.
- In Heb 4:12, the logos is described as "living (Zoe) and active".
- In V12 we have the phrase, "and able to judge the thought and motives of the heart". This might be an allusion to John 5:22, 9:39, etc about Jesus judging.
Thus, Heb 4:12 & 13 gives the impression that the author is almost deliberately blurring the distinction between the written word of God and Jesus as the Word. If nothing else, one is a reflection of the other.