Sunkulp Goel

Biocompatibility of ultrafine grained zircaloy-2 produced by cryorolling for medical applications

The present work deals with development of ultrafine grained zircaloy-2 and studying its potential for orthopedic application. The multimodal structure, i.e. the combination of coarse, ultrafine grained (UFG) and nanograined structures of zircaloy-2 is obtained by cryorolling the bulk alloy followed by annealing at 400 °C, and 450 °C for 30 min. An estimation of surface wettability of the alloy was obtained through contact angle measurement. The bioactivity of the alloy samples was investigated by incubating bone marrow derived stem cells. The cellular attachment, adhesion and proliferation at different intervals of incubation were characterized by scanning fluorescent microscopy and MTT assay. Cell culture results indicated that liquid nitrogen rolled alloy samples exhibited excellent in-vitro biocompatibility together with satisfactory bioactivity. Excellent genomic expressions were observed for zircaloy 2 processed by cryorolling.

Mechanical properties and microstructural evolution of ultrafine grained zircaloy-4 processed through multiaxial forging at cryogenic temperature

Abstract The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48, 2.96, 4.44 and 5.91 through multiaxial forging (MAF) at cryogenic temperature (77 K) were investigated. The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment. The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238, respectively, as compared with the as-received alloy. However, there was a noticeable decrement in ductility (from 18% to 3.5%) due to the low strain hardening ability of deformed zircaloy-4. The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging. The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy (TEM). The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150–250 nm.

Evaluating Fracture Toughness of Rolled Zircaloy-2 at Different Temperatures Using XFEM

Fracture toughness and mechanical properties of the zircaloy-2 processed by rolling at different temperatures have been investigated, and simulations have been performed using extended finite element method (XFEM). The solutionized alloy was rolled at different temperatures for different thickness reductions (25–85%). Fracture toughness has been investigated by compact tension test. The improved fracture toughness of the rolled zircaloy-2 samples is due to high dislocation density. SEM image of the fractured surface shows the reduction in dimple sizes with the increase in dislocation density due to the formation of microvoids as a result of severe strain induced during rolling. Compact tension test, edge crack, center crack and three-point bend specimen simulations have been performed by XFEM. In XFEM, the cracks are not a part of finite element mesh and are modeled by adding enrichment function in the standard finite element displacement approximation. The XFEM results obtained for compact tension test have been found to be in good agreement with the experiment.

Experimental and XFEM Simulation of Tensile and Fracture Behavior of Al 6061 Alloy Processed by Severe Plastic Deformation

The tensile and fracture behavior of ultrafine-grained Al 6061 alloy has been studied by experimental testing and extended finite element method simulation. The ultrafine-grained alloy processed by cryorolling has been produced from its bulk alloy with different thickness reductions. Microstructural features have been evaluated by electron backscattered diffraction. The EBSD results show the formation of subgrains and large number of high-angle grain boundaries in the rolled Al alloy. Mechanical behavior has been investigated using microhardness, tensile test, fracture toughness, and fractography of all samples. The extended finite element method has been used to investigate elastic–plastic deformation behavior of ultrafine-grained Al 6061 alloy. The extended finite element method has been used to simulate tensile and fracture behavior of ultrafine-grained alloy with material constants evaluated from experimentally measured tensile properties. Simulated tensile and fracture properties are in tandem with the experimental results. Ultrafine-grained Al 6061 alloy has shown better tensile strength and fracture toughness as evident from experimental and simulation results.

Experimental evaluation of mechanical properties and fracture-fatigue simulation of cryo– and room–temperature–rolled zircaloy–2

In this study, the mechanical properties of mercury–quenched, cryorolled (CR) and room–temperature–rolled (RTR) zircaloy–2 have been examined by performing the tensile and hardness tests. The effect of cryorolling and room temperature rolling on the fracture properties has been evaluated by performing two–dimensional (2D) quasi–static crack growth simulations using finite element approach under plane stress condition. J–integral and internal energy of the mercury–quenched, CR and RTR zircalloy–2 are evaluated and compared with each other. The S–N curves for mercury–quenched, CR and RTR zircaloy–2 are obtained through finite element simulations. After performing the fracture and fatigue simulations, it is found that 85% cryorolled zircaloy–2 possesses better fracture and fatigue behaviour when compared with mercury–quenched and 85% RTR zircaloy–2.