Artifact Relic is the only way to upgrade the Artifact Weapon level. Its original level is Lvl750. The Artifact Weapon has a total of 3 Relic slots on it. Two slots tie to the specific artifacts that players can socket into their weapon to increase the power with the original level, but the third slot is unlocked when you complete your Order Hall Campaign questline. Artifact ranks depend on the Artifact Relic ranks. 
Artifact Relic has 11 types that are similar to the Frost and Blood relic, and each class selects three of the Artifact specs to socket in. Artifact Relic drops from raid bosses, world drops and quest rewards from world quest. The initial Artifact Relic can be made out by crafting professions. 
Artifact Weapon ranks depend on the Artifact Relic ranks. Also, the different raid difficulty will drop different Artifact Relics, if you want to obtain an ultimate one, a strengthful team is very essential. Since Patch 7.0 equip set has a unique upgrades system, the Titan Artifact Relic Series will be your ultimate pursuit. Thinking of them as the crucial way for your Artifact upgrades, hope the luck will happen to you!
There is no doubt that Artifact Relic is crucial for the Artifact Weapon upgrades.