Core'splitter was forged nearly 300 years ago by Corgra Darkmine and her husband. At the time, it was made to fight against fire and earth Elementals that would sometimes enter Azeroth due to the Dwarves constant digging. It was a long, twin bladed Greataxe made out of elementium. Corgra runed the axe to be lighter and more effective, not to mention baleful to Elementals.
After the civil war, it was hidden away in a vault, where it sat undisturbed until the Cataclysm. There it was rediscovered by Crura Darkmine and wielded by her in the battle for Shadowforge city. Its enchantments proving a great boon in aiding Moira in removing the remaining Elementals and Twilight Cultists.
Since then, it has absorbed some of her Sister of Steel power and became an extension of herself. As well as turning a reddish/black color from the constant absorption of Fire elemental essences. But, after visiting Ulduar where her Steely exterior was removed, the axe was also shattered.
Crura reformed the axe, this time into a Battleaxe to be wielded with Molt'ar, the artifact she obtained from the same Ulduar visit.
Core'splitter reforged managed to retain its magical enchantments, remaining baleful to Elementals. Its blade ignites into fire when battle is joined and is nearly indestructible!
Molt'ar on the other hand is a disc of Titansteel the color of gold, on the outward facing center it also appears to be made out of flowing magma. However, the magma never drips or falls out of the shields center and when trying to touch the magma one is stopped by an invisible force but still feel the intense heat. The Shield has many powers granted to it by its titanic forging, but its most potent is the ability to unleash the magma within in a massive gout of fire that burns all in its way!
For a 5e D&D homebrew of these, consult the Master Homebrew link found under 5th Edition D&D. Its under the google docs called "Items".