Effect of process parameters on the formation of Ti-Al coatings fabricated by mechanical milling

A vibration technique was used to fabricate Ti-Al coatings. During mechanical milling, the sample surface was subjected to high-energy ball impacts. The powder particles trapped between the balls and substrate became cold-welded to the substrate surface. The repeated substrate-to-ball collisions flattened the particles and forged them onto the surface into a bulk material. The coating thickness and roughness can be optimized by the combinations of key factors such as the ball-to-powder weight ratio, milling duration, and ball size. The development of the coating structure is associated with the milling intensity. A Ti-Al coating formed rapidly as the milling intensity increased. Prolonged milling led to structural refinement of the top coating layer. The grain size may reach the nanometer scale under prolonged milling. The ball size was critical to coating formation.