https://hal.archives-ouvertes.fr/hal-02551361/document

Hot cracking mechanism affecting a non-weldable Ni-based superalloy produced by selective electron Beam Melting

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

Laser powder bed fusion (LPBF) is a proven additive manufacturing (AM) technology for producing metallic components with complex shapes using layer-by-layer manufacture principle. However, the fabrication of crack-free high-performance Ni-based superalloys such as Hastelloy X (HX) using LPBF technology remains a challenge because of these materials’ susceptibility to hot cracking. This paper addresses the above problem by proposing a novel method of introducing 1 wt.% titanium carbide (TiC) nanoparticles. The findings reveal that the addition of TiC nanoparticles results in the elimination of microcracks in the LPBF-fabricated enhanced HX samples; i.e. the 0.65% microcracks that were formed in the as-fabricated original HX were eliminated in the as-fabricated enhanced HX, despite the 0.14% residual pores formed. It also contributes to a 21.8% increase in low-angle grain boundaries (LAGBs) and a 98 MPa increase in yield strength. The study revealed that segregated carbides were unable to trigger hot cracking without sufficient thermal residual stresses; the significantly increased subgrains and low-angle grain boundaries played a key role in the hot cracking elimination. These findings offer a new perspective on the elimination of hot cracking of nickel-based superalloys and other industrially relevant crack-susceptible alloys. The findings also have significant implications for the design of new alloys, particularly for high-temperature industrial applications.

Additive manufacturing of high-strength crack-free Ni-based Hastelloy X superalloy

The influence of Re and Ru on phase diagram, as-cast microstructure, and segregation behavior has been investigated using a series of 12 experimental nickel-base superalloys derived from the parent alloy CSMX-4. Up to 2 at. pct Re and 4 at. pct Ru were added at the expense of nickel, while all other alloying elements were kept constant. The Re is found to increase the liquidus temperature and to decrease the γ′-solvus. The Re additions also strongly increase the amount of eutectic and the tendency for microsegregation. The Ru, on the other hand, displays much weaker effects or even no effect at all. The effects of Re on the eutectic formation and on segregation are shown to be related. Calculations based on ThermoCalc software were carried out and compared with the experimental results. ThermoCalc is found to be able to predict the changes in the phase diagram rather well. However, the calculation of the eutectic fraction with the Scheil–Gulliver model is not satisfying, which is due to the one-dimensionality of the model.

Y.Z. Zhou

Papers

Effect of dendrite arm spacing on castability of a directionally solidified nickel alloy

Effect of grain boundary fraction on castability of a directionally solidified nickel alloy