Accelerated sintering of high-performance oxide dispersion strengthened alloy at low temperature

Powder metallurgy generally is a preferred method to consolidate and prepare some refractory metals considering their high melting temperatures. However, sintering such materials to high density while maintaining fine grain structure is challenging, and generally require ultrahigh temperature or need to be assisted by external pressure. Especially, the preparation of nanostructured oxide dispersion strengthened (ODS) refractory metals at low temperature is more difficult because grain coarsening and densification are simultaneously hindered by the common oxide addition. Thus, it is of great sense to explore a kind of oxide that can be used as both strengthening phase and sintering accelerator. In this work, after extensive theoretical calculation and experimental observation, it is found that the accelerated sintering at low temperature can be achieved in W-HfO2 system. In the absence of external pressure or activator, this system can be rapidly densified without undesirable grain coarsening at a relative low temperature of only 1480 degrees C. Through kinetic analysis and density functional theory (DFT) calculation, it was confirmed that the intergranular HfO2 particles provide a rapid diffusion transport pathway for W atoms in support of densification at temperature of interest. As a result, this alloy exhibits a homogeneous microstructure with similar to 97% relative density and similar to 200 nm grain size, which renders our alloy with an ultrahigh compres-sive strength of similar to 3 GPa, much higher than the reported values. We believe that the accelerated sintering mechanism found in our W-HfO2 system can be applicable to other refractory metals to prepare high-density nanocrystalline alloys with excellent properties. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Powder metallurgy is a preferred method for consolidating refractory metals with high melting temperatures, but achieving high density sintering while maintaining fine grain structure is challenging, usually requiring ultrahigh temperature or external pressure assistance. In the W-HfO2 system, an accelerated sintering mechanism was found at low temperature, enabling the preparation of high-density nanocrystalline alloys with excellent properties.