Surface Nanostructuring of a CuAlBe Shape Memory Alloy Produces a 10.3 ± 0.6 GPa Nanohardness Martensite Microstructure.

Carlos Gabriel Figueroa,Rafael Schouwenaars,Jacinto Cortés-Pérez,Víctor Hugo Jacobo

doi:10.3390/ma13245702

Carlos Gabriel Figueroa, Rafael Schouwenaars + Show 2 more

Open Access

https://doi.org/10.3390/ma13245702

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Journal: Materials	Publication Date: Dec 14, 2020
Citations: 5	License type: CC BY 4.0

Affiliation: Universidad Nacional Autónoma de México

Abstract

Severe plastic deformation (SPD) has led to the discovery of ever stronger materials, either by bulk modification or by surface deformation under sliding contact. These processes increase the strength of an alloy through the transformation of the deformation substructure into submicrometric grains or twins. Here, surface SPD was induced by plastic deformation under frictional contact with a spherical tool in a hot rolled CuAlBe-shape memory alloy. This created a microstructure consisting of a few course martensite variants and ultrafine intersecting bands of secondary martensite and/or austenite, increasing the nanohardness of hot-rolled material from 2.6 to 10.3 GPa. In as-cast material the increase was from 2.4 to 5 GPa. The friction coefficient and surface damage were significantly higher in the hot rolled condition. Metallographic evidence showed that hot rolling was not followed by recrystallisation. This means that a remaining dislocation substructure can lock the martensite and impedes back-transformation to austenite. In the as-cast material, a very fine but softer austenite microstructure was found. The observed difference in properties provides an opportunity to fine-tune the process either for optimal wear resistance or for maximum surface hardness. The modified hot-rolled material possesses the highest hardness obtained to date in nanostructured non-ferrous alloys.

Highlights

Severe plastic deformation (SPD) is a method for extreme microstructural refinement in bulk materials [1,2,3], producing a nanoscale microstructure which allows to increase the yield strength by a factor up to 3 as compared to conventional processing methods
As a reference to evaluate the results of this work, it can be noted that an increase in hardness from 600 to to 1400
As cast and hot rolled CuAlBe-SMA samples were subject to sliding contact surface modification

Summary

Introduction

Severe plastic deformation (SPD) is a method for extreme microstructural refinement in bulk materials [1,2,3], producing a nanoscale microstructure which allows to increase the yield strength by a factor up to 3 as compared to conventional processing methods. In analogy with the well-known shot peening treatment, the goal is to increase surface hardness and induce compressive residual stresses to inhibit fatigue crack initiation while maintaining a tough microstructure in the core of the treated part. This is achieved in processes such as Surface mechanical attrition [4,5,6], large strain machining [7], ultrasonic surface modification [8], high-speed pounding [9,10] or sliding contact modification [11,12]. Rainforth presented an in-depth analysis of the physical phenomena involved in tribolayer formation and found that strain hardening was the dominating factor, as it determines the achievable subgrain size near the surface [20]

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