The results for joints obtained by dynamic diffusion bonding of a 90MnCrV8 high strength steel coated with WC-Co are shown in the present work. This high strength steel substrate was coated with WC-Co, sprayed by HVOF technique (Diamond Jet Hybrid DJH-2700) using propylene as fuel gas at different conditions.
The dynamic diffusion bonding was carried out in a high frequency furnace, all joints were made in air.
Before doing the joints, the steel was coated with Ni and Cu by electrochemical processes in order to obtain a soft 20 μm interlayer of Ni30Cu alloy.
Microstructure and reacted zones in the joints were investigated by means of Scanning Electron Microscopy (SEM) and Dispersive X Ray Spectrometry (EDX).
In all joints can be distinguished four reacted zones:
Zone A: Reacted zone from the steel to the Ni30Cu interlayer. In this zone, close to the steel, appears a narrow zone constituted by austenite phase due to the diffusion of Ni and Cu into the Fe.
Zone B: Reacted zone mainly formed by Ni30Cu interlayer and Fe, W, Co in solid solution.
Zone C: Reacted zone of Ni30Cu/WC-Co, where the reaction between Ni/Cu and WC-Co origin the decomposition of WC crystal, the W element diffuses to the interlayer and Co diffuses to the steel through the NiCu interlayer.
Zone D : WC-Co/steel coating interface, that is formed during the joint. There is Fe in the coated WC-Co (HVOF), and W and Co in the ferrite phase of the steel.

The mechanical properties of the joints were carried out after joints in an universal tensile machine, using a constant load of  0.1MPa/s. All joints broke by the WC-Co coating zone by delamination processes. The fracture was studied by SEM-EDX in order to know the fracture mechanism of the joints. The maximum tensile strength obtained confirm a very promising technology for industrial applications.