Microcantilever Fracture Tests on Eutectic NiAl–Cr(Mo) In Situ Composites

Abstract

Lamellar eutectic NiAl–Cr(Mo) alloys show an increased fracture toughness due to different toughening mechanisms. These mechanisms result from the fibrous or lamellar microstructure of the two constituting phases α‐Cr(Mo) and β‐NiAl. However, the fracture toughness of the individual phases and the evolution from early crack growth to the toughening mechanisms have not yet been systematically studied. Herein, bending tests on focused ion beam (FIB)‐notched microcantilever beams are used to characterize the small‐scale fracture properties. The micromechanical investigations reveal that the fracture toughness of the α‐Cr(Mo) phase (7.5−9.1 MPam) is much higher than the fracture toughness of β‐NiAl (2.2−2.9 MPam). Larger cantilevers in the crack arresting orientation show an enhanced fracture toughness with up to 14.4 MPam, which is still lower than the one of macroscopic experiments. This is attributed to the small interaction volume of the crack, which hinders the full exploitation of potential extrinsic toughening mechanisms.

Microcantilever Fracture Tests of α‐Cr Containing NiAl Bond Coats

“…[28,31] In comparison, studies on the eutectic NiAlÀCr(Mo) in situ composites, which were produced with vacuum melting, showed less embrittlement of α-Cr. [32] This is presumably a result of the absence of nitrogen and a lower content of soluted alloying elements.…”

A new method for microscale cyclic crack growth characterization from notched microcantilevers and application to single crystalline tungsten and a metallic glass

“…While tungsten shows a clear cleavage fracture during the experiment, the metallic glass shows more plasticity. The continuous crack growth resistance was calculated for both materials, as described in literature [23,24] in Fig. 2(b).…”

“…The displacement rate of the tip was set to 20 nm/s. The evaluation methodology for those fracture toughness measurements are described elsewhere [23][24][25]. To determine the fracture toughness of the materials, the 0.2 µm crack growth criteria was used, which was established by Ast et al [24,26].…”

Design and Characterization of a Novel NiAl–(Cr,Mo) Eutectic Alloy

“…Typically this material class is processed by vacuum arc remelting or in a conventional Bridgman process. [16][17][18][19] In the latter, the solidification rate can be adjusted by varying the withdrawal rate. Whittenberger et al investigated the impact of the withdrawal rate on the microstructure and thus on the mechanical properties of a Ni 33 Al 33 Cr 33 Mo 1 alloy (all following concentrations are given in at%).…”