Author: Hao ZhangPublisher:
ISBN:
Category : Alloys
Languages : en
Pages : 0
Book Description
Surface severe plastic deformation attracts more and more attentions because its capability to enhance material surface. However, for the hard-to-deform materials, higher peening intensity leads to surface or subsurface cracks, while lower peening intensity may not be sufficient to effectively induce beneficial microstructural changes. In this dissertation, energy assisted-surface severe plastic deformation is proposed to improve the effectiveness of surface severe plastic deformation on hard-to-deform alloys. Three different energy input methods, direct current, pulsed current, and laser were used to integrate with LSP and UNSM in processing metallic materials. Direct current can rapidly increase the bulk temperature of the 3D-printed Ti64 during UNSM process. Compared with the conventional UNSM process, better surface finish and lower subsurface porosities were obtained after DC-UNSM. DC-UNSM also led to a deeper plastically-affected depth compared with conventional UNSM. Numerical modelling showed that localized heating occurs near the pores in 3D-printed Ti64 subjected to electric current, which could potentially facilitate pore closure under ultrasonic striking. Electropulsing assisted-LSP (EP-LSP) produced higher surface hardness and deeper hardened layer on conventional Ti64, both of which indicate greater plastic deformation compared with LSP. Electropulsing assisted tensile test showed that pulsed current can more effectively decrease the flow stress even though the bulk heating effect is the same. In addition, the higher the peak current density, the more effective the flow stress reduction. It is believed that an athermal effect in addition to the thermal effect related to pulsed current exists in EP-LSP. Laser assisted UNSM (LA-UNSM) is proposed as an alternative to post-process 3D-printed Ti64. The localized thermal effect of continuous laser also decreases the flow stress of the alloy effectively. Smoother and harder surface was obtained after LA-UNSM due to the enhanced plasticity by pure thermal effect. In addition, LA-UNSM also led to a thicker plastically-affected layer and lower porosity compared with traditional UNSM process. In summary, an innovation concept and surface engineering technology, energy assisted surface severe plastic deformation was proposed to improve the effectivity and efficiency of severe plastic deformation on processing hard-to-deform alloys, which integrates the advantages of SSPD to introduce surface plastic deformation induced strengthening effect, with the ability of extra energies to improve plasticity through their thermal and athermal effects.
