Numerical Alloy Development for Additive Manufacturing towards Reduced Cracking Susceptibility

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.

Tools for the Assessment of the Laser Printability of Nickel Superalloys

“…Besides indices indicating printability factors, mechanical properties, cost and weight were also considered. Additionally, Wahlmann et al defined 4 different cracking criteria, and designed an alloy composition trying to reduce each crack susceptibility individually; unfortunately cracking remained in all the new alloys [31] . Tang et al designed a "medium γ' fraction" alloy (ABD-900AM), i.e.…”

“…There are many forms of failure associated with metallic components, the ones selected below are particularly applicable to nickel superalloys. Some of these occur during solidification while others occur during heat treatment; solidification cracking is frequently thought of as being the biggest issue in AM of nickel superalloys [12,31,32] . Other cracking mechanisms in AM of nickel superalloys are explored in detail in the review by Markanday [3] .…”

Effects of Fe, Si, Cu, and TiB2 Grain Refiner Amounts on the Hot Tearing Susceptibility of 5083, 6061, and 7075 Aluminum Ingots

“…Because the cooling conditions did not meet the equilibrium solidification (i.e., the infinite diffusion coefficient of solutes in the primary αAl phase) while casting, the Scheil model was utilized for discussion. This approach can be referenced in the literature [24,25]. The comparison between equilibrium solidification and Schiel solidification for a multicomponent aluminum alloy is shown in [Supplementary Figure S2] (see Supplementary Materials).…”