Effect of direct laser deposition process parameters on the microstructure and mechanical properties of new nickel-base superalloys based on ZhS6K

<jats:p>Introduction. Nickel-base superalloys are indispensable materials for hot-section components of gas turbine engines (GTE); however, traditional manufacturing of geometrically complex parts is highly time- and resource-consuming. The adoption of additive manufacturing (AM), in particular direct laser deposition (DLD), enables high-precision fabrication of free-form components. Nevertheless, most nickel-base superalloys with a high volume fraction of the γ′ phase (Ni3Al) are prone to cracking. A promising approach is the development of new alloy compositions specially adapted for AM. The purpose of this study is to investigate Investigation of the influence of DLD parameters on cracking behavior, microstructure, and mechanical properties of the previously designed Ni68 and Ni75 alloys based on the ZhS6K superalloy. Materials and methods. Thin-walled specimens were produced by DLD with varying laser power, scanning speed, laser spot diameter, and deposition strategy. Cracking susceptibility was evaluated by the specific crack length. Porosity, microstructure, and phase composition were analyzed by optical and scanning electron microscopy. Mechanical properties were assessed by microhardness measurements. Results and discussion. A non-linear dependence of the specific crack length on laser power was revealed, with a maximum at 700 W for small spot diameters. The bidirectional deposition strategy was shown to reduce cracking compared with the unidirectional strategy. For the Ni75 alloy, optimum parameters (power 300 W, speed 3 mm/s, spot diameter 1.0–1.5 mm) under the bidirectional strategy were identified, yielding defect-free specimens with a porosity below 0.2%. It was established that the lower carbon content in Ni75 suppresses carbide precipitation, thus reducing the cracking probability. Increasing the laser power from 300 to 1500 W only weakly affects the transverse grain size, but induces a transition from a near-equiaxed morphology to a columnar one with a pronounced &lt;100&gt; texture; the volume fraction of the strengthening γ′ phase remains constant at ~60% for Ni68 and ~41% for Ni75. Microhardness exhibits a weak dependence on the deposition parameters: 390–410 HV for Ni75 and 430–450 HV for Ni68, indicating the predominant contribution of the γ′ phase characteristics. The obtained results demonstrate the applicability of the developed alloys for the additive manufacturing of thin-walled high-temperature components.</jats:p>