Showing papers by "Sushanta Kumar Panigrahi published in 2018"

Microstructural modification and its effect on strengthening mechanism and yield asymmetry of in-situ TiC-TiB2/ AZ91 magnesium matrix composite

Abstract: The application of AZ91 magnesium alloy is limited because of dendritic β-Mg17Al12 phase which degrades mechanical properties and causes high tension to compression yield asymmetry (R). To overcome this, a severe plastic deformation (SPD) based hybrid process has been implemented in this study, to develop in-situ AZ91 + TiC-TiB2 composite. This results in redistribution of β-Mg17Al12 phase on the grain boundaries along with notable grain refinement. The combined effect of in-situ reinforcement and grain refinement due to SPD process resulted in simultaneous enhancement of strength and ductility. Further, intense grain refinement and presence of TiC-TiB2 reinforcement in the grain boundary region is found to increase the stress concentration along the grain boundary which hinders twin nucleation and significantly reduces the R value from 1.42 (as-cast condition) to 1.04 (SPDed in-situ composite). The underlying mechanism of significant property enhancement in the developed material has been correlated with the tension and compression tests and microstructures.

Deformation behavior of ultrafine grained A356 material processed by cryorolling and development of Johnson–Cook model

Abstract: The present research work focuses on understanding the deformation behavior of cryorolled A356 material at various strain rates ranging from 0.001 s−1 to 10 s−1 in the temperature range of 25–400 °C. Microstructure of the material at each deformation temperature was characterized to completely analyze the material's behavior. Presence of ultrafine grained microstructure with highly unstable dislocation networks were found to play a major role in strengthening the material up to the deformation temperature of 200 °C. Recrystallization and thermal softening decreases the material's strength at deformation temperatures beyond 200 °C. With respect to the rate of deformation, a prominent change in the deformation mechanism is observed at strain rates higher than 1 s−1. The failure mechanism at various strain rate and temperature ranges is studied in detail. Finally a constitutive Johnson-Cook model is developed to predict the material's flow behavior for the range of strain-rates and temperatures under study.

Development of bulk ultrafine grained Al- SiC nano composite sheets by a SPD based hybrid process: experimental and theoretical studies

Abstract: In the present work, a hybrid manufacturing route, combining stir casting with cryorolling, is proposed for production of Ultrafine grained (UFG) nano composite sheets using an Al 1050 matrix in combination with β-SiC particles (0.5 wt%, 1 wt%, 2 wt%). The method provides the scope for generating UFG microstructures with homogeneous distributions of nano particles that are difficult to achieve with existing manufacturing routes. The influence of the nano SiC reinforcement on the mechanical properties of the UFG nano composites were studied with an emphasis on the characterization of the microstructure. The results show that with an increasing content of reinforcement, the degree of grain refinement and strength of the UFG nano composite increases while the ductility reduces. The microstructural information and the obtained yield strengths of the UFG nano composites were validated with a mathematical model. For this, an existing dislocation density based model was modified to account for the effect of nano reinforcement and processing parameters.

Microstructure and Texture of Cold Rolled and Recrystallized CrNoNi Medium-Entropy Alloy

Abstract: An equiatomic CrCoNi medium-entropy alloy plate was heavily deformed by conventional cold rolling and subsequently annealed at different temperatures. Microstructure and texture evolution of the deformed and annealed sheets were investigated by electron backscatter diffraction and X-ray diffraction. Heavy cold rolling induces an alloy type α-fibre texture with major brass component. This type of texture is indicative of low stacking fault energy of the CrCoNi alloy. Annealing at 700 °C leads to a homogeneously recrystallized microstructure with ultrafine grains of about 800 nm average size. The volume fraction of different texture components is almost similar after annealing at different temperatures. However, the overall texture intensity after annealing is very weak. Finally, in order to understand the microstructure and texture evolution of the CrCoNi alloy, it is critically compared with other low stacking fault energy FCC materials.

Synergetic Effect of Cryorolling and Postroll Aging on Simultaneous Increase in Wear Resistance and Mechanical Properties of an Al–Cu Alloy

Abstract: Aluminum–copper alloy system is extensively used in structural and aerospace applications for its high strength-to-weight ratio, good mechanical and tribological properties. Improving the properties of these alloys would likely widen their application area. In the present work, an attempt has been made to simultaneously enhance the wear resistance and mechanical properties of an Al–Cu alloy, AA2014 by imparting different levels of cryorolling strains and postroll aging treatment. The wear behavior of the material is studied under dry sliding condition by pin-on-disk experiments and mechanical properties are assessed by tensile test. Formation of high fraction of dislocation density and significant refinement of microstructure during cryorolling and nucleation of fine coherent Guinier–Preston (GP) zones of Al2Cu precipitates during postcryoroll aging has led to about 100% increment in the wear resistance of the material. Tensile test results proved that the synergetic effect of cryorolling and aging treatment led to 53% increment in strength (557 MPa) without compromising the material's ductility (22.5%). A detailed investigation on the various mechanisms responsible for the enhanced wear resistance and improved mechanical performance is presented based on the microstructural evidence.

Investigation into the micro deep drawing capabilities of a specially engineered refined aluminium alloy

Abstract: During miniaturisation, size of the part comes close to grain size of the material. There is an overall decrease in the total number grains undergoing deformation and most of these are surface grains. Therefore, microscale deformation is marked by abnormal stress-strain response which limits the manufacturing capabilities of microforming. Two distinct phenomena responsible for this are: (i) dominance of single crystal deformation behaviour, and (ii) increased strain localisation due to incompatibly between surface and core grains during deformation. The present work attempts to neutralise these effects by increasing the number of grains in the deformation zone. This has been achieved by engineering refined microstructure in the materials. To develop the refined microstructure, cryorolling followed by controlled annealing treatment has been employed. Microscale deformation behaviour and microforming capabilities of the refined material have been compared with its coarse-grained counterpart by analysing their tensile curves and by post-mortem study of micro deep drawn components over a wide range of sample thicknesses. Material with fully recrystallised, equiaxed, strain-free refined microstructure is found to have the best strain hardening response both in micro and macro deformation domains. This property is also reflected in the micro deep drawing capabilities of the same material.