Uniaxial creep behavior of nanostructured, solution and dispersion hardened V–1.4Y–7W–9Mo–0.7TiC with different grain sizes

Abstract

Abstract Nanostructured vanadium (V) alloys are expected to exhibit high performance under neutron irradiation environments. However, their ultra-fine or refined grains cause significant decrease in flow stress at high temperatures due to grain boundary sliding (GBS), which is the major concern for their high-temperature structural applications such as future fusion reactors. The contribution of GBS to plastic deformation is known to depend strongly on grain size (GS) and may give more significant influence on long-time creep test results than on short-time tensile test results. In order to improve the creep resistance through elucidation of the effect of GS on the uniaxial creep behavior of nanostructured V alloys, a solution and dispersion hardened V alloy, V–1.4Y–7W–9Mo–0.7TiC (in wt%), with GSs from 0.58 to 2.16 μm was developed by mechanical alloying and HIP processes, followed by annealing at 1473–1773 K, and creep tested at 1073 K and 250 MPa in vacuum. It is shown that the creep resistance of V–1.4Y–7W–9Mo–0.7TiC increases monotonically with GS: The creep life for the alloy with 2.16 μm in GS is as long as 114 h, which is longer by factors of 2–30 than those for the other finer grained alloys and by two orders than that for coarse-grained V–4Cr–4Ti (Nifs heat2, GS: 17.8 μm) that is a primary candidate material for fusion reactor structural applications. The minimum (steady state) creep rate decreases with increasing GS as έ s ∝ (1/ l ) 3 , where έ s is the steady state creep rate and l is the grain diameter. The observed superior creep resistance of V–1.4Y–7W–9Mo–0.7TiC is discussed in terms of GS effects on dislocation glide/climb, GBS, and strain hardening capability enhanced by solution and dispersion hardening.