Effect of ball milling of feedstock powder on microstructure and properties of TiN particle-reinforced Al alloy-based composites fabricated by cold spraying

Dense Al5356/TiN composites with TiN particles uniformly dispersed in the matrix were produced by cold spraying (CS) using both the mechanically mixed (MM) and ball-milled (BM) powder blends with 50 wt.% TiN compared to that of CS pure Al5356 deposit. The microhardness of the composite deposited with the BM blend was three times higher than that of pure Al5356 coating. Compared to the coating deposited with the MM powder (MM composite), the hardness of the coating deposited with the BM powder (BM composite) was significantly increased owing to the increase of TiN volume fraction, which is comparable to that of the MM composite deposited with the 75 wt.% TiN feedstock. The adhesive strength of the composites was remarkably improved in comparison with the pure Al5356 coating because of the pinning effect of TiN particles. The coefficient of frication (COF) and wear rate (WR) were measured using a ball-on-disc tribometer. It was found that the COFs and WRs of the composites were much lower than those of pure Al5356 coating. Especially, the WRs of the MM and BM composites were, respectively, decreased by about 14 and 50 times than that of pure Al5356 deposit. This phenomenon could be ascribed that TiN particles contribute to a third-body abrasion in the following sliding process, which benefits the decrease of COF by rolling action partially instead of sliding action. For the BM composite, more and finer TiN particles present in the worn surface compared to the MM composite, which will be helpful to the further decrease of the COF and WR.