The Development of Inhomogeneous Microstructures during 3-Axis Forging

• Other Authors: Carnrike, Talya Rachel (author)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Mechanical engineering; Materials science
• Online Access: http://purl.flvc.org/fsu/fd/2019_Fall_Carnrike_fsu_0071E_15479

Severe plastic deformation, especially 3-Axis Forging (3AF), has been used in several industries as a production method for various tools and equipment. Components or items produced by this method are characterized by inhomogeneous microstructures. A prior study done in this laboratory using 3AF on Cu and Nb materials revealed the presence of microstructural inhomogeneities upon the first cycle of processing. In this study, finite element method (Deform) was used to investigate the nature of the development of microstructural inhomogeneity when materials are subjected to 3AF. Analysis of the strain distribution patterns was carried out for uniaxial compression, 1 cycle and 2 cycles of 3AF subjected to three different primary displacement rates (2.54, 25.4, and 254 mm/s) and various friction factors (0, 0.08, 0.12, 0.25, 0.3, 0.4, 0.7, and 0.8). The study was confined to the first two cycles because the majority of grain refinement occurred in this region. Particular attention was paid to the friction factor, m, which is a function of the type of lubricant used during deformation. The results show that using lubricants with higher friction factor increased the strain range (difference between maximum and minimum effective strain), thus the degree of inhomogeneity during deformation. A critical friction factor, mc, was found to exist above which an inhomogeneous microstructure emerges. Analysis of the strain parameters revealed that there is a logarithmic relationship, y = a ln(x) + b, between the strain range, maximum effective strain and/or minimum effective strain, y, and the displacement rate, x. It is important to note that a and b are material constants. Niobium, Nb, was characterized by a higher strain range in all forms of deformation when compared to Cu. Flownet maps constructed for the deformation processes for friction factor m > mc revealed the existence of four major zones. Zone A (core), which corresponds to the maximum strain was found in the regions not affected by friction between the sample and compression plates. Zone C had the lowest strain due to its contact with the compression plates thereby restricted by friction. However, zones (B and D) exhibited medium to low strain as they are affected by friction but not to the degree of zone C. The flownet maps were found to correlate well with the experimental hardness data of the materials. The study clearly shows that the microstructural inhomogeneity developed during 3AF depends very much on the lubricant type used. === A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === 2019 === November 6, 2019. === Includes bibliographical references. === Peter N. Kalu, Professor Directing Dissertation; Kamal S. Tawfiq, University Representative; Simone P. Hruda, Committee Member; Carl A. Moore, Committee Member.