Residual stress distribution in different depths of TiNi/Ti_2Ni-based laser clad coating prepared at different environmental temperatures

This study aimed to effectively reduce the cracking susceptibility of the laser clad coating by enhancing the environmental temperature during laser cladding,and reveal the residual stress distribution in different depths of the coating.The TiNi/Ti2Ni-based coatings were prepared on Ti6Al4V by laser cladding at different environmental temperatures of25,400,600and800°C.The changes in residual stress along the depth of the coatings were investigated in detail by the nanoindentation method.Results showed that the average residual stress of2.90GPa in the coating prepared at25°C was largest.With the increase in environmental temperature,the average residual stress was reduced to1.34GPa(400°C),0.70GPa(600°C)and0GPa(800°C).For all the coatings,the residual stress was increased with increasing the distance from the coating surface.Enhancing the environmental temperature can effectively reduce the cracking susceptibility of the coatings.

Corrosion behavior of laser-clad coatings fabricated on Ti6Al4V with different contents of TaC addition

The coatings were produced on Ti6A14V by lasercladding the mixture of Ni-based alloy and different contents of TaC(0 wt%,5 wt%,10 wt%,20 wt%,30 wt%,40 wt%).The microstructure and corrosion behavior of the coatings were investigated in detail.The coating without TaC is composed of TiNi/Ti2Ni(matrix)and TiC/TiB/TiB2(reinforcement).Moreover,TaC is precipitated again and TiC/TiB/TiB2 solid solutions containing Ta are formed in the coatings.Corrosion potential of the coatings(-0.639,-0.636,-0.547,-0.534,-0.471 and-0.348 V)increases,and passive current density(1×10-5.4,1×10-5.6,1×10-6.4,1×10-6.8,1×10-6.7 and 1×10-6.9 A·cm-2)decreases.The passive films are more difficult to break down(breakdown potential of 0.003,0.080,0.204 and 0.605 V).When the content of TaC exceeds 20 wt%,no breakdown phenomenon is observed.The passive film on the surface of coating without TaC is mainly composed of TiO2,Al2O3,Cr2O3,CrO3,NiO,Ni2O3 and SiO2.After the addition of TaC,Ta2O5 is formed in the passive films.The content of Ta2O5 presents an increasing trend with the increase in the content of TaC.The addition of TaC has a positive effect on corrosion resistance of the coatings.