It is well known that severe plastic deformation (SPD) produces ultrafine-grained structures in bulk metallic materials. The SPD process becomes more versatile when it is performed under high pressure as high-pressure torsion (HPT) and high-pressure sliding (HPS). Not only the grain size is more refined but also the process is applicable to hard-to-deform materials such as intermetallics, semiconductors and ceramics, leading to enhancement of functional properties as well as structural properties. The major drawback is that the sample size is small so that the applicability is limited to a laboratory scale and it is an important subject to increase the sample dimensions. This paper presents an overview describing efforts devoted thus far to deal with this upscaling issue.

Mater. Trans. 61 (2020) 1177-1190に掲載

This paper focuses on the effect of tungsten addition on the steam oxidation behavior of the Fe-20Cr-35Ni (at％) alloy at 1073 K. Steam oxidation tests of the W added Fe-20Cr-35Ni (at％) alloy were carried out at 1073 K in an Ar-15％H₂O gas mixture for up to 604.8 ks. The oxidation resistance of the alloys was improved by adding W into the alloy. There are two effects of W on the steam oxidation behavior: the effect of solid solution and the effect of precipitation. Tungsten in the alloy is enriched as a Ni-W alloy in the matrix of the internal oxidation zone (IOZ) during oxidation. The Ni-W alloy in the IOZ may act as a diffusion barrier for oxygen and promote a continuous Cr₂O₃ layer. On the other hand, Fe₂W precipitated in the alloy decomposes during oxidation and provides alloying elements for forming FeCr₂O₄ and CrWO₄ in the IOZ, resulting in a continuous Cr₂O₃ layer formation.