Did Miles Davis make any free/avant-garde jazz work? If so, what albums?
I think what you're looking for is Miles Davis's Second Great Quintet, which, aside from Davis, featured four young, untried musicians:
About the Second Great Quintet, the Wikipedia article reads:
The performance style of the Second Great Quintet was often referred to by Davis as "time, no changes", incorporating elements of free jazz without completely surrendering to the approach, allowing the five men to contribute to the group as equals rather than as a leader and sidemen peeling off unrelated solos.
So while not fully in the "free jazz" camp, it was essentially Davis's foray into that area. Davis recorded 6 studios albums and 1 live box set with the Second Great Quintet.
- E.S.P. (1965)
- Miles Smiles (1967)
- Sorcerer (1967)
- Nefertiti (1968)
- Miles In The Sky (1968)
- Filles de Kilimanjaro (1968)
- The Complete Live at the Plugged Nickel 1965 (recorded 1965, released 1995)
After these albums, Davis started trending towards jazz fusion, and the Second Quartet split up.