Reduction of micro-cracking in nickel superalloys processed by Selective Laser Melting: A fundamental alloy design approach

The Selective Laser Melting (SLM) process generates large thermal gradients during rapid melting of metallic powdered feedstock. During solidification certain alloys suffer from thermally induced micro-cracking which cannot be eliminated by process optimisation. An alloy’s crack susceptibility may reduce by increasing its Thermal Shock Resistance (TSR), potentially achieved through an increase in tensile strength. This hypothesis is investigated with Hastelloy X, a common nickel-base superalloy of known high crack susceptibility when processing SLM. It is demonstrated that through consideration of the imposed rapid solidification conditions, Hastelloy X can be made to form a supersaturated solid solution in the as deposited state. The fundamental solid solution strengthening (SSS) effect is exploited to generate an increase in lattice stress, by increasing the most potent SSS elements present within the alloy, whilst maintaining specification composition. The modified alloy displayed a 65% reduction in cracking and an increase in elevated temperature tensile strength, lending support to the initial hypothesis and identifying a possible approach for developing further SLM crack resistant versions of well-known alloy compositions.