Study of the erosive wear behaviour of cryogenically and tempered WC-CoCr coating deposited by HVOF

In this work the influence of deep cryogenic treatment followed by a double tempering at 150 °C on the erosive wear resistance of high velocity oxy-fuel (HVOF) WC-10Co-4Cr coating was evaluated. Cryogenically treated coatings exhibited a microstructural densification effect; more compact splats, lower porosity, and a clear redistribution of Co, enhancing its hardness with respect to that observed in the as-sprayed conditions. On the other hand, a reduction in fracture toughness was noticed. A dependence of the erosive wear mechanism was observed in regard to: 1) the erosive test parameters and; 2) the metallurgical conditions of the material. Cryogenically treated coatings displayed better erosive resistance at low impact angles such as 30° and both particle impact testing velocities i.e.100 m/s and 130 m/s. In contrast, at higher angles between 60° and 90° and 130 m/s, more material removal trough brittle mechanism was observed to occur in cryogenically treated coatings, reducing its erosive wear performance. At lower impact velocities (lower normalized load) this type of erosion was less evident suggesting the presence of a threshold velocity at which low fracture toughness coatings erode preferentially trough brittle mechanisms.