A high-strength silicide phase in a stainless steel alloy designed for wear-resistant applications
Journal: Nature Communications
Publication Date: 10 April, 2018
Department of: Materials
A new method of wear-protection in challenging environments.
Researchers at the University of Manchester have identified a new silicide phase within a chemically complex stainless steel alloy. Such alloys, known as hardfacings, are used as wear-resistant coatings in light-water nuclear reactors. Typically, hardfacing alloys are formed from cobalt, which provides a high degree of wear resistance and corrosion resistance. However, in an irradiating environment, cobalt becomes activated and poses a hazard, even after the plant has been decommissioned. The nuclear industry is keen to develop cobalt-free alternative hardfacings such as iron-based stainless steel alloys, which do not become neutron-activated during service. Unfortunately, many alternative iron-based hardfacing alloys suffer from poor wear-resistance whilst under the high-temperature conditions of a light-water nuclear reactor. This study shows that a new class of silicide-strengthened iron-based hardfacings are stronger than their conventional carbide-strengthened counterparts. The great strength of these alloys and high degree of coherence between the silicide phase and surrounding matrix will lead to a higher degree of wear resistance in these materials. This research, the result of collaboration between academia and industry, has led to new work aimed at developing the alloys, which could revolutionise future methods of wear-protection.
- Under compressive loading, the silicide phase is incredibly strong. It is so strong that the yield point (where a material becomes irreversibly deformed) couldn’t be reached in our experiments. The test rig reached its 10-tonne limit when compressing a silicide-strengthened sample piece, which was not much wider than the diameter of a pencil!
- The silicide phase decomposes above 920 °C meaning that these alloys can be engineered to be worked using processes such as forging, where the presence of the hard silicide phase would otherwise limit the workability of such an alloy. When the alloy is cooled below 920 °C, the silicide phase will form within the alloy again.
- Electron diffraction tomography was used to establish the crystal structure of the silicide phase. By tilting the sample within the transmission electron microscope, a three-dimensional representation of the silicide crystal could be reproduced.
- Small adjustments to the silicon and nickel contents of these alloys means that tailor-made silicide-strengthened hardfacing alloys with various mechanical properties could be produced in the future.