Flow stress anisotropy and Bauschinger effect in ultrafine grained copper

• Published in: Acta materialia Vol. 54; no. 20; pp. 5477 - 5488
• Main Authors: Haouaoui, M., Karaman, I., Maier, H.J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.12.2006; Elsevier Science
• Subjects: ANISOTROPY; Applied sciences; Bauschinger effect; BILLETS; Boundary element method; Compressing; Copper; Equal channel angular extrusion; Exact sciences and technology; FLOW STRESS; GRAIN SIZE AND SHAPE; MATHEMATICAL ANALYSIS; Metals. Metallurgy; STRESS; Tension–compression asymmetry; Texture; TEXTURES; Ultrafine grained materials; YIELD STRENGTH; Ultrafine grained materials; Bauschinger effect; Equal channel angular extrusion; Anisotropy; Tension–compression asymmetry; Fine grain structure; Forming; Spinning; Tension-compression asymmetry; Flow stress
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2006.07.022

The effect of strain path and magnitude on the flow stress anisotropy and Bauschinger effect (BE) in ultrafine grained (UFG) copper was investigated. The material billets were deformed via multipass equal channel angular extrusion (ECAE) following several deformation routes. The monotonic stress–strain responses under tension and compression and forward compression/reverse tension response along three perpendicular directions were determined in each billet. It was observed that, in certain cases, the strong tension/compression asymmetry was in favor of tension as opposed to what has so far been reported for UFG materials, and an increase in the number of ECAE passes caused a decrease in yield strength along certain sample directions. Finally, the BE was found to be more pronounced for the lower number of passes. It was shown that crystallographic texture and grain size differences cannot be the only factors responsible for these unexpected observations. Grain morphology and grain boundary character are argued to be additional parameters that have to be taken into account. How these factors affect tension/compression asymmetry, flow anisotropy and BE in UFG copper and how they can help elucidating the observations are discussed.