Influence of strain-hardening on the wear resistance of metallic materials
Creators: Kumar, Aakash
Publisher: name: University of Alberta Library
Year: 2022

<p>Although it is known that strain-hardening helps improve the wear resistance of metallic materials, puzzles or inconsistent phenomena still exist regarding the effect of strain-hardening on the wear resistance of metallic materials. It was reported that strain-hardening showed little or limited benefits to the wear resistance of some carbon steels. Besides, if the strain-hardening works, its benefit to the wear resistance may not be as large as expected. In this thesis, a study on the influence of strain hardening on the wear resistance of cold worked metallic materials is reported in three parts. </p>

<p>In part 1, the effects of strain-hardening (cold work) on dry sliding wear of Cu and Mg were investigated. The dry sliding wear tests were performed under different contact loads of 2N, 5N, 8N, and 12N, respectively, at room temperature. It was demonstrated that the strain-hardening decreased Young’s moduli of Cu and Mg samples due to deteriorated crystalline integrity, which reduced the benefit of strain-hardening to their wear resistance. The strain-hardening benefited the FCC Cu more than the HCP Mg, and the effectiveness of strain-hardening decreased with increasing the contact load. Relevant mechanisms were elucidated from the viewpoint of wearing energy consumption.  </p>

<p>In part 2, we investigated the wear behaviors of strain-hardened Cu and Mg and demonstrated that the H/E (H=Hardness, E=Young’s modulus) ratio markedly overestimated the wear resistance of these pure metals. The H/E ratio is often used as an index to represent the wear resistance of materials and coatings. The larger the H/E ratio, the higher the wear resistance. However, though this ratio is shown to be a measure of the wear resistance for reported cases, whether it can be generalized as an index of wear resistance is questionable. Although the cold work increases hardness, it deteriorates the material integrity with introduced lattice imperfections, which negatively influence the atomic bonding, thus decreasing the benefit of strain-hardening to the wear resistance.  As a result, the H/E ratio should not be generalized as a measure of wear resistance.  </p>

<p>In part 3, we investigated the influence of the Bauschinger effect on the wear behavior of cold worked Cu and Mg under unidirectional and bidirectional sliding wear conditions. The Bauschinger effect has been studied for a long time, which influences the wear of materials under the unidirectional sliding wear and reciprocating wear conditions. The Bauschinger effect could be altered during the wear of cold worked metals with different crystal structures such as Cu (FCC) and Mg (HCP).  The strain-hardened Cu had dislocation pileups while strain-hardened Mg had vacancies, pores, or micro-cracks with fewer dislocations. Volume losses of the cold worked metals are higher caused by unidirectional sliding than those caused by bidirectional sliding, attributed to the fact that during bidirectional sliding, reversible movement dislocations may occur, and dislocations with opposite signs may cancel each other due to the reversal of the wearing stress, leading to lowered wear damage. </p>