Mechanical properties of NiAl-Mo composites produced by specially controlled directional solidification

Abstract

Mo fiber reinforced NiAl in-situ composites with a nominal composition Ni-43.8Al-9.5Mo (at.%) were produced by specially controlled directional solidification (DS) using a laboratory-scale Bridgman furnace equipped with a liquid metal cooling (LMC) device. In these composites, single crystalline Mo fibers were precipitated out through eutectic reaction and aligned parallel to the growth direction of the ingot. Mechanical properties, i.e. the creep resistance at high temperatures (HT, between 900 °C and 1200 °C) and the fracture toughness at room temperature (RT) of in-situ NiAl-Mo composites, were characterized by tensile creep (along the growth direction) and flexure (four-point bending, vertical to the growth direction) tests, respectively. In the current study, a steady creep rate of 10 -6 s -1 at 1100 °C under an initial applied tensile stress of 150MPa was measured. The flexure tests sustained a fracture toughness of 14.5 MPa·m 1/2 at room temperature. Compared to binary NiAl and other NiAl alloys, these properties showed a remarkably improvement in creep resistance at HT and fracture toughness at RT that makes this composite a potential candidate material for structural application at the temperatures above 1000 °C. The mechanisms responsible for the improvement of the mechanical properties in NiAl-Mo in-situ composites were discussed based on the investigation results.

Influence of Strengthening Elements and Heat Treatment on Microstructure and Fracture Toughness of NiAl-Cr(Mo)-Based Eutectic Alloy

“…To improve the fracture toughness and strength of NiAl-based materials, many techniques have been tried and many NiAl-based alloys or composites have been designed and fabricated [16][17][18][19]. Among these NiAl-based materials, the ceramic-particle-strengthened NiAl-based composites exhibit high strength, while the fiber-or lamella-phase-strengthened alloys demonstrate better fracture toughness [20][21][22]. Hu et al [23] fabricated Ni 3 (Al,Ti)and TiC-strengthened NiAl-based composite and demonstrated that the composite had ultra-high hardness and increased fracture toughness when the temperature was below 800 • C. The cleavage in the binder NiAl compound and de-cohesion of TiC from the Ni 3 (Al,Ti) interface were determined as the dominating fracture mechanism.…”