The bulk ultrafine grained (UFG) AA6063/4 wt.%SiC composite sheets with varying reinforcement size of SiC (12 μm (coarse), 1 μm (fine) and 45 nm (nano)) have been developed with a novel hybrid process of stir casting and cryo-severe plastic deformation process (cryorolling). The influence of SiC particle size during development of UFG composites and its effect on microstructural modification, strengthening mechanism and failure mechanism was studied in detail. The resultant effect of cryorolling and size of SiC particles has resulted in significant microstructural refinement (less than 350 nm in all UFG composites) and accumulation of high dislocation density; which resulted in improvement in tensile strength as 88%, 108% and 141% in UFG composites reinforced with coarse, fine and nano particles respectively as compared to the unreinforced base alloy. A good agreement in theoretical and experiment yield strength of UFG coarse and fine composites is observed with a variation in UFG nano composite. © 2018 Elsevier B.V.

Sushanta Kumar Panigrahi

Department of Mechanical Engineering

O. B. Bembalge

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Alloys and Compounds

This paper described the influence of varying sizes of SiC ceramic reinforcement (coarse (12 μm), fine (1 μm) and nano (45 nm)) in establishing the wear mechanisms and the wear mechanism maps of ultrafine grained (UFG) AA6063/4 wt%SiC composites. The UFG composites were developed by a hybrid manufacturing route of stir casting and cryorolling. The pin-on-disc machine under normal loads of 10–50 N and sliding speeds of 0.5–2 m/s was used to investigate wear behavior. The synergetic effect of cryorolling and varying ceramic reinforcement size has resulted in microstructural modification and has reducing effect on specific wear rate. Microstructural characterization revealed that, cryorolling has accumulated high dislocation density and arrested recovery and recrystallization at liquid nitrogen temperature. Frictional heat generated at wear surface with increase in sliding speed and load has activated the dynamic recovery, recrystallization and precipitation which further increased the hardness and reduced the specific wear rate. The wear mechanisms were established for UFG materials. The wear mechanism maps were constructed and correlated with the microstructures of worn surfaces of UFG materials to identify the dominant wear mechanism. © 2019 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Influence of SiC ceramic reinforcement size in establishing wear mechanisms and wear maps of ultrafine grained AA6063 composites

Bulk ultrafine-grained (UFG) AA6063/4wt pct SiC composites with varying reinforcement sizes [12 µm (coarse), 1 µm (fine), and 45 nm (nano)] have been developed by a hybrid route of stir-casting and cryorolling. In the current study, the influence of annealing temperatures (423 K to 573 K) on the precipitation evolution, particle-stimulated nucleation (PSN), recrystallization, grain growth kinetics, and thermal stability of developed bulk UFG composites have been studied, and the resultant effect of microstructural evolution is correlated with mechanical properties. UFG coarse and UFG fine composites have shown evidence of recrystallized grains via PSN and retained their UFG microstructure up to 473 K and 523 K, respectively. Superior microstructural stability with retained UFG microstructure up to 573 K was observed in the UFG nanocomposite due to the effective pinning of nano-SiC particles and precipitates along grain boundaries. This ultimately resulted in the increased grain growth activation energy and strength of the UFG nanocomposite. However, the overall increase in strength is maximum in the UFG nanocomposite due to the dominant effect of dislocation strengthening, grain boundary strengthening, and precipitation strengthening mechanisms. A thorough examination of the microstructural evolution of UFG composites at different annealing temperatures along with their mechanical behavior is presented in this paper. © 2019, The Minerals, Metals & Materials Society and ASM International.

Fulltext

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Thermal Stability, Grain Growth Kinetics, and Mechanical Properties of Bulk Ultrafine-Grained AA6063/SiC Composites with Varying Reinforcement Sizes

The present work investigated the synergetic effect of varying reinforcement sizes (12 μm (coarse), 1 μm (fine), 45 nm (nano)) and cryorolling on aging behavior and mechanical properties of bulk ultrafine grained (UFG) AA6063/4 wt%SiC composites produced via a hybrid route of stir casting and cryorolling. Aging of UFG composites was carried out at different temperatures in the range of 100 °C–175 °C. The results showed that decrease in SiC particle size accelerated the age hardening kinetics and the maximum age hardening effect was observed at 150 °C. The enhancement in age hardening kinetics is attributed to the presence of high dislocation density due to the (i) difference in coefficient of thermal expansion between SiC particles and matrix alloy and (ii) statistically stored dislocation during deformation. Also, the precipitation behavior in UFG composites is established and the microstructural characterization showed the accelerated precipitation kinetics in UFG nano composite. The enhanced age hardening kinetics ultimately improved the strength of the UFG composites compared to UFG base alloy. Among the UFG composites, UFG nano composite showed highest age hardening effect. The overall increase in strength in UFG nano composite is due to the dominant effect of precipitation, dislocation, and grain boundary strengthening mechanisms. © 2019

Materials Science and Engineering A

Aging behavior of ultrafine-grained AA6063/SiC composites with varying reinforcement sizes

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. © 2017 Elsevier B.V.

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

The high-temperature tensile deformation behavior of ultrafine-grained (UFG) QE22 alloy developed by friction stir processing was investigated at various strain rates (5 × 10−4 – 1 × 10−2 s−1) and temperatures (300–450 °C). The UFG QE22 alloy exhibited excellent high strain rate superplasticity with the maximum elongation of 1630% at a temperature of 450 °C and strain rate of 1 × 10−2 s−1, which is the highest elongation reported till date in QE22 alloy. The UFG QE22 alloy also shows superior low-temperature superplasticity with a maximum elongation of 850% at a temperature of 350 °C and strain rate of 3 × 10−3 s−1. Thus, the developed UFG microstructure is found to demonstrate dual-mode superplasticity; both at high strain rate and low-temperature. The primary UFG microstructure and basal texture developed via multi-pass FSP, along with pinning action of Mg12Nd eutectic and fine nano precipitates of Mg12Nd2Ag at grain boundaries played a major role in contributing to the dual-mode superplasticity. The cavitation behavior of the UFG QE22 alloy during superplastic deformation in a dual-mode regime has been studied. The kinetics of superplastic deformation of UFG QE22 alloy was estimated and found to be significantly faster as compared to conventional magnesium alloys processed by various severe plastic deformation routes. © 2018 Elsevier B.V.

Achieving excellent superplasticity in an ultrafine-grained QE22 alloy at both high strain rate and low-temperature regimes

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. © 2018 Elsevier B.V.

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

The present work aims to study the individual as well as the combined effect of in-situ particles and precipitates on the tension-compression asymmetricity of AZ91 magnesium (Mg) alloy and AZ91 + TiC-TiB2 Mg matrix composites. Investigations have been done on four different material conditions: (a) alloy without particles or precipitates, (b) alloy with precipitates, (c) composite with particles, (d) composites with both particles and precipitates. Both the particle and precipitate significantly contribute towards lowering of tension to compression yield asymmetry. These particles/precipitates increase the critical stress for twinning by exerting a back stress which hinders the twin propagation. Due to decrease in the twinning propensity, the tension to compression asymmetry reduces from 1.30 (at base condition) to 1.04 (peak aged condition of the composite). This phenomenon has been experimentally validated by means of tension and compression tests and the results have been correlated with the pre and post-deformation microstructures. © 2017 Elsevier B.V.

A study on the combined effect of in-situ (TiC-TiB2) reinforcement and aging treatment on the yield asymmetry of magnesium matrix composite

In the present work, influence of in-situ TiC-TiB2 reinforcement on age hardening behavior and mechanical properties of TiC-TiB2/AZ91 composite was investigated. The base and in-situ composite materials were solution treated at 400 °C for 24 h and then aged at different temperatures up to 100 h. The kinetics of age hardening results revealed that the addition of in-situ TiC-TiB2 reinforcement increase the age hardening kinetics of the composite as compared to AZ91 magnesium alloy. The improvement in age hardening kinetics is attributed to the presence of high dislocation density resulted from the mismatch of coefficients of thermal expansion between in-situ TiC-TiB2 reinforcement and magnesium matrix. The precipitation behavior of Mg17Al12 phase in both AZ91 alloy and TiC-TiB2/AZ91 composites were established. After age hardening, base and in-situ composite materials show significant improvement in ultimate tensile strength by 47.72% and 66.49% respectively as compared with the base monolithic alloy. The enhancement of mechanical properties in the base and in-situ composites is explained in detail by analyzing their fractographs and microstructures. © 2018

Materials Characterization

Effect of in-situ (TiC-TiB2) reinforcement on aging and mechanical behavior of AZ91 magnesium matrix composite

Development and strengthening mechanisms of bulk ultrafine grained AA6063/SiC composite sheets with varying reinforcement size ranging from nano to micro domain

Journal	Data powered by TypesetJournal of Alloys and Compounds
Publisher	Data powered by TypesetElsevier Ltd
ISSN	09258388
Open Access	No