Figure 4 Powder Morphology of AlTiCrFeCoNi HEA
Preheating Temperature on the Optimization Process for Crack Elimination
There are various methods used in optimizing parameters such as; solidification or thermos-mechanical control and heat treatment [47]. The laser additive technique aside from its numerous advantages is also known to cause defects due to internal stresses depending on the phase transformations, cooling and solidification rate, thermal expansion coefficients etc. To minimize the defects observed on all samples after the first phase of experiments, preheating the base plates at 400 °C was done before deposition. Preheating drives moisture and contaminants reducing the rate at which the part cools down thus preventing locked-in stresses which can inhibit crack formation [48]. In view of this, samples without preheat temperature showed extensive cracks compared to those with preheat temperature also reported by Zhang, Shi [49] and 9 samples which were completely crack free were obtained from those specimens with 400 °C preheat temperature. The optimal range of scanning speed and laser power for excellent dilution rates which were obtained from the crack free samples, are 8-12 mm/s and 1200-1600 W, shown in Figure 5 and 6.