The adamantium covering Wolverine's bone claws is one of the strongest metals in the entire Marvel universe, but as tough and unbreakable as it may be, the comics themselves prove they're no match for Thor's hammer Mjolnir.
Wolverine is the best there is at what he does: ripping enemies to shreds with his adamantium bone claws. Originally bone claws that were already deadly weapons, Wolverine's adamantium claws can tear through almost anything--and in the Old Man Logan storyline, they actually managed to tear through Hulk. But when it comes to Mjolnir, a hammer forged from Uru metal as old as the universe itself, things are in another league entirely., a metal that has existed as long as the universe itself.
In Wolverine Vs. Thor#2 readers got to see what would happen when the mystical Mjolnir met Wolverine's lethal adamantium claws. During this storyline, Wolverine was tricked by Thor's evil adopted brother, The God of Mischief Loki to force him to see Thor as his long-time nemesis Sabertooth. Wolverine purposely leaves a trail behind to distract Thor and positions himself for a killing blow from higher ground. Unfortunately, the claw swing meant to rip Thor to shreds meets his hammer instead.
Every time Wolverine slashes at Thor with his adamantium claws and makes contact with Mjolnir, his attack is parried, his deadly claws completely useless against the Uru Mjolnir is crafted from. Though Wolverine has the speed advantage against Thor, he is clearly outmatched, as Thor fights defensively until shocking Wolverine back to his senses. Wolverine's claws were able to give Thor a flesh wound, but had no effect on Mjolnir. Thor Odinson may not be The God of Thunder without Mjolnir, but he is a capable Asgardian warrior. What is Wolverine without his adamantium skeleton and claws? He has an amazing healing factor and animal-like instincts, but could he really stand against a hero or villain of Thor's caliber without his adamantium?
Wolverine is one of Marvel's fiercest characters because of his personality and beast-like nature. He can sheath and unsheath his claws but for most if not all major battles, he relies heavily on his trusty adamantium. Mjolnir renders that adamantium, one of the strongest of the Marvel universe's metals utterly useless. To add insult to injury, Thor bested Wolverine even though he was actively avoiding injuring him for most of their battle. Mjolnir also has the advantage of being enhanced by magic and holds the power of a cosmic storm within it. In the case of Thor's Mjolnir versus Wolverine's adamantium claws, Thor's hammer has a clear edge.