Cu-Zr-Al Bulk Metallic Glasses Coatings Deposited Using Cold Gas Dynamics Spraying and Pulsed Gas Dynamics Spraying

Bulk metallic glasses were produced using atomized amorphous powder of Cu-Zr-Al, using Cold Gas Dynamic Spray at different parameters. The detailed microstructure of the powder was analyzed in order to confirm the amorphous state of the alloy. X-ray diffractometry (XRD), electron microscopy (TEM, SEM), differential scanning calorimetry (DSC) and nanohardess were used to characterized the powder. Cold gas dynamics spraying (CGDS) and pulsed gas dynamics spraying (PGDS) were used to produce dense coatings and consolidate the particles in a BMG. Helium was used in both system, and special attention was taken in the powder preheating step during PGDS process to avoid crystallization in the particles.

In order to determinate if there was a modification in the microstructure of the coating compared to the powders, the coatings were tested using XRD, DSC, SEM and microhardenss. Using XRD it was determined that the coatings were completely amorphous, which shows that during the cold sprays process it was possible deform, and consolidate, a coating while avoiding crystallization of the particles. SEM images showed a dense, porosity free, coating. DSC showed a decrease of 10% of the energy released during the recrystallization, which indicates a relaxed structure compared with the powder before deposition. Hardness tests indicate a reduction in hardness, which is possible due the creation of shear bands during the deposition process. Previous studies describe the effort of spraying partially amorphous powder, and it was shown that the deformation process during the spraying was conducted by the crystalline part. In this study a completely amorphous powder was sprayed and due the lack of crystalline phase, the deformation must be conducted by shear bands.