New cast niobium alloy holds strength at 1400 C
Published
Researchers at the University of Utah, Oak Ridge National Laboratory and UC Davis report a new cast niobium alloy that stays strong at extreme temperatures. The alloy is Nb-20W-1Zr-0.13C by weight, made by plasma arc melting and casting, according to the Scientific Reports paper.
At room temperature the authors measured a yield strength of 582 MPa, a tensile strength of 687 MPa, 1.5% elongation and a fracture toughness of 13 MPa√m. The headline numbers are at heat: tensile strength of 414 MPa at 1200 C and 250 MPa at 1400 C. The paper says that is 57% stronger at 1400 C than additively manufactured C-103 and 36% stronger than Nb-521, and comparable to the molybdenum alloy TZM.
Creep, the slow stretching under load, was low in tests at 1200 C. The authors report very little strain up to 150 MPa over about 100 hours. They credit carbides along the grain boundaries and fine precipitates inside the grains.
The catch is ductility: 1.5% elongation at room temperature is low, and the data is for lab samples of a cast alloy, not a flown part. Niobium alloys such as C-103 are common in rocket nozzles and other hot hardware, so a stronger option is of interest, though the paper's funding acknowledgement points to ARPA-E, an energy programme, not a space one.
Which matters more for a hot rocket part, strength at 1400 C or ductility at room temperature?