Abstract
In this work, we investigated the viability of established hot cracking models for numerically based development of crack-resistant nickel-base superalloys with a high γ′ volume fraction for additive manufacturing. Four cracking models were implemented, and one alloy designed for reduced cracking susceptibility was deduced based on each cracking criterion. The criteria were modeled using CALPHAD-based Scheil calculations. The alloys were designed using a previously developed multi-criteria optimization tool. The commercial superalloy Mar-M247 was chosen as the reference material. The alloys were fabricated by arc melting, then remelted with laser and electron beam, and the cracking was assessed. After electron beam melting, solidification cracks were more prevalent than cold cracks, and vice versa. The alloys exhibited vastly different crack densities ranging from 0 to nearly 12 mm−1. DSC measurements showed good qualitative agreement with the calculated transition temperatures. It was found that the cracking mechanisms differed strongly depending on the process temperature. A correlation analysis of the measured crack densities and the modeled cracking susceptibilities showed no clear positive correlation for any crack model, indicating that none of these models alone is sufficient to describe the cracking behavior of the alloys. One experimental alloy showed an improved cracking resistance during electron beam melting, suggesting that further development of the optimization-based alloy design approach could lead to the discovery of new crack-resistant superalloys.
Highlights
Nickel-base superalloys are high-performance materials that are employed in the hottest sections of jet engines and stationary gas turbines
All alloys were chosen so that their cracking criteria were lower than those calculated for Mar-M247
The Solidification interval (SI) alloy was selected as the one with the lowest mean deviation in the middle section
Summary
Nickel-base superalloys are high-performance materials that are employed in the hottest sections of jet engines and stationary gas turbines. There is no consensus on the exact formation process of these cracks [9] and the types of cracks vary depending on the material and process conditions, two factors seem to play important roles: the alloy’s solidification range and the presence of large amounts of γ phase. This intermetallic phase, with the ordered L12 structure, has the stoichiometric composition Ni3(Al, Ti). Typically 60–70% of γ phase is present
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