Surface hardening of die steel by superplastic deformation of thermo-sprayed powder alloy

The superplastic forming is an advanced processing technique and has been used in manufacturing some dies, especially extrusion die and forging die. In heavy load condition, the superplastic formed dies often exhibit low service life owing to the low surface strength and poor wear resistance. A commercial cold working die steel GCr15 pre-treated into ultra-fine grain sizes was chosen as the substrate material, on which the surface was thermal-sprayed with the powders of a wear-resistant alloy. At some appropriate temperatures and strain rates, the accommodated superplastic deformation of the substrate and coating occurred and the good cohesion was well performed. The coated layer shows high microhardness values and fairly smooth transition in hardness from substrate to the surface. The wear resistance of superplastically formed specimen has also been improved, compared with the GCr15 steel coated with the same alloy powder and treated by flame remelting.