Influence of Ingot and Powder Metallurgy Production Route on the Tensile Creep Behavior of Mo–9Si–8B Alloys with Additions of Al and Ge

Abstract

Refractory metals and their alloys show potential for high temperature applications, due to the elevated melting points often paired with very good creep resistance. Spark plasma sintering (SPS) as well as arc-melting is used here to prepare quaternary and quinternary Mo-9Si-8B-xAl-yGe (x is 0 or 2; y is 0 or 2, all numbers in at%) samples. All samples consist of a Mo solid solution (Mo ss ) and two intermetallic phases: Mo 3 Si (A15) and Mo 5 SiB 2 (T2). Aluminum and germanium reduce the melting point and slightly decrease the density of the material. The specimens are homogenized and coarsened by a subsequent heat-treatment in vacuum at 1850C for 24 h. The resulting microstructure is investigated using scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma optical emission spectrometry (ICP-OES) analysis. A vacuum creep testing device for small tensile creep specimens is presented. It is heated by graphite radiation heaters usable up to 1500 C in vacuum of 2 Á 10 -4 Pa with an oil diffusion pump. Tensile creep tests are performed at 1250 C and stresses from 50 MPa up to 250 MPa. Specimens produced by ingot metallurgy feature superior creep properties compared to powder metallurgy samples.

Tensile creep behavior of HfNbTaTiZr refractory high entropy alloy at elevated temperatures

“…The flat sides of gage were grinded by 1200 grit SiC sandpaper. The vacuum tensile creep test device was hand-built by Metals and Alloys, University of Bayreuth, details of the setup was described by earlier reports [40,56]. The device contains a graphite-heating element inside the vacuum chamber and a type-S thermocouple close to the specimen.…”

“…It showed a transition from solute drag creep (stress exponent, n=3) to dislocation climb creep (n>3) at high-stress regions. Kellner et al [40] investigated the creep of Mo-9Si-8B based alloys under vacuum at 1250°C with stresses from 50 to 250 MPa; the stress exponent was found to be 3.8, indicating dislocation climb controlled creep.…”