تأثير ضخامت لايه پودر در فرايند ذوب بستر پودر با ليزر بر ريزساختار و خواص مكانيكي سوپرآلياژ هستلوي ايكس

In this study, the effect of powder layer thickness in the laser powder bed fusion (LPBF) additive manufacturing process (30, 60, an‎d 90 µm) on the microstructure, tensile properties, an‎d stress-rupture behavior of the nickel-based superalloy Hastelloy X was comprehensively investigated. Microstructural results revealed that samples fabricated with a 30 µm layer thickness exhibited smaller melt pools, finer dendritic cells, an‎d smaller grain sizes, attributable to higher energy input per layer an‎d faster cooling rates. At a layer thickness of 60 µm, the melt pool dimensions an‎d grain sizes were intermediate, whereas the 90 µm samples displayed coarser microstructures an‎d larger melt pools due to slower cooling rates. These findings indicate that variations in powder layer thickness directly influence solidification behavior, cellular microstructure evolution, an‎d melt pool geometry. Additionally, all samples were subjected to solution annealing heat treatment at 1177 °C for 75 minutes. Tensile test results showed that horizontally built specimens exhibited higher yield strength an‎d ultimate tensile strength than vertically built specimens, although their elongation to failure was lower. Among the investigated layer thicknesses, the 60 µm layer thickness demonstrated the best overall tensile performance, which is attributed to higher relative density an‎d a reduced number of lack-of-fusion defects. Stress-rupture test results indicated that although the creep rupture lives of all samples (181, 85, an‎d 94 hours for layer thicknesses of 30, 60, an‎d 90 µm, respectively) exceeded the stan‎dard requirement for the alloy (24 hours), the specimens fabricated with a 30 µm layer thickness exhibited significantly longer rupture life compared to those produced with 60 an‎d 90 µm layer thicknesses. Although increasing the layer thickness substantially enhances the build rate in the LPBF process, the results of this study demonstrate that such an increase in productivity may be accompanied by degradation in microstructural quality an‎d mechanical performance. Based on the findings, a layer thickness of 60 µm was identified as more suitable for improving tensile properties due to fewer structural defects, while a layer thickness of 30 µm was found to be more favorable for enhancing stress-rupture life under long-term loading conditions owing to a lower crack density.

احمد كرمانپور , محسن بدرسماي

بهزاد نيرومند , مسعود عطاپور