工艺参数变化对冷喷涂铝沉积性能的影响

The Effect of Processing Variables on Deposition Characteristics of Aluminium by Cold Gas Dynamic Spraying

在环境温度下以氦气为驱动气,在低碳钢基体上冷喷涂铝粉,采用工业纯铝粉,颗粒尺寸范围为-75+15μm。测得涂层沉积效率达到40%,孔隙率低于1.0vol%,涂层的硬度由铝粉末的硬度31kgf.mm-2提高到了53kgf.mm-2,这主要是涂层内产生严重塑性变形的结果。研究了滞止压力、喷涂距离、送粉速率和喷枪与基板相对运动速度等工艺参数变化对沉积效率的影响。结果表明,以上每一个工艺参数的变化均对沉积效率产生显著影响。滞止压力、喷涂距离和送粉速率通过改变颗粒碰撞速度来影响沉积效率;当碰撞速率降低时沉积效率降低。然而,当颗粒速度降低时,由于参与冲击的颗粒(非沉积颗粒)比例增加,涂层的孔隙率并没有被影响。当增加喷枪与基体的相对运动速度时,沉积速率显著降低;这一结果表明沉积效率还存在某种喷射流量或剂量的影响因素,例如在沉积初期的"激活"期,喷射剂量就直接影响了沉积效率。

Cold gas-dynamic spray （cold spray） of commercial purity aluminium powder with a size range of -75＋15 μm onto mild steel substrates was carried out using helium gas at ambient temperature. Deposition efficiency of up to 40 % was achieved and coatings with porosity levels of less than 1.0 vol% were achieved. Heavy plastic deformation was observed in the coatings which resulted in an increase in hardness from 31 kgf·mm^-2 in the powder to 53 kgf·mm^-2 in the coatings. A number of process parameters were varied including stagnation pressure, standoff distance, powder feedrate and traverse velocity. Each parameter significantly affected the deposition efficiency. Stagnation pressure, standoff distance and powder feedrate affected the particle velocity on impact; lower impact velocities resulted in lower deposition efficiency. However, the porosity of the coatings was not adversely affected by the reduction in velocity as the proportion of peening （non-depositing） particles increased, thus leading to a reduction in porosity. Increasing traverse velocity of the jet with respect to the substrate resulted in a significant decrease in deposition efficiency; it is proposed that this results from some flux or dose dependent phenomena, such as an ＇activation＇ period during spraying in which little deposition is observed or deposition efficiency being directly related to flux.