Severe Plastic Deformation under High Pressure: Upsizing Sample Dimensions

Abstract

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.

High-Pressure Torsion for Synthesis of High-Entropy Alloys

“…Although research on the HPT method as a synthesis route for HEAs is in its early stages, the method has high potential for the exploration of new materials for future applications. The next stage in this research field is the application of HPT to a wider range of high-entropy materials with new functional applications, although scaling up the sample size remains a major challenge for the commercialization of this method [39][40][41][42].…”

“…Compared to ball milling as a popular mechanical alloying technique [38], in the HPT method, the synthesis time is shorter, the rotation speed is lower, the contamination is minor, and the final product is in the bulk form, which does not require further consolidation processes [2,4]. However, the main disadvantage of HPT is the low quantity of the synthesized product; thus, scaling up the sample [39,40] and making the process continuous [41,42] are currently major challenges for the commercialization of HPT.…”

Microstructure, Texture and Mechanical Properties in Aluminum Produced by Friction-Assisted Lateral Extrusion

“…To date, only HPT processing is capable of producing such microstructures with an extremely large imposed strain in a single operation, but the sample size is limited in HPT. Although some upscaling efforts have been made to increase the sample size to 30 mm in diameter, it is typically limited to 10 mm [ 15 ], which is a barrier for industrial use. ECAP and its variants, including ECAP-conform [ 16 ] for producing continuous sheet samples, are able to produce larger size samples, but the shear strain imposed on the sample in each pass is relatively small; it is typically around 2 [ 17 ], while a shear of at least 10 is needed to reach the steady state grain size regime.…”

<i>In Situ</i> Synchrotron X-ray Analysis: Application of High-Pressure Sliding Process to Ti Allotropic Transformation

“…66,67) Such developments were intended for practical applications of the SPD process as described in a recent overview paper. 68) In this study, the HPS process is rather downsized for in situ X-ray analysis in a synchrotron facility during operation under high pressures and elevated temperatures.…”