A357 (Al–7Si–0.6Mg)-xTiB2 (x = 5, 10 wt.%) in-situ composites processed by the salt-melt reaction method were successfully foamed by melt processing with the addition of heat treated TiH2 as blowing agent. Holding time was varied in order to identify critical holding time beyond which cell wall collapse and drainage dominate. X-ray tomography was employed to characterize the geometric structure of cells. Cell structure with high degree of uniformity evolved in 5TiB2 composite foams compared with 10TiB2 composite foams for a given holding time. 5TiB2 composite foams showed better expansion compared to 10TiB2 composite foams. However, the number of cell wall remnants (defects) was more for highly expanded 5TiB2 composite foams. TiB2 particles present in the foam promoted foam stability. © 2016 Elsevier Ltd

Budaraju Srinivasa Murty

Department of Metallurgical and Materials Engineering

S. Sankaran

U. Athul Atturan

Aluminum

Aluminum alloys

Blowing agents

Casting

Cells

Cytology

Foams

In situ processing

Indium alloys

Metal foams

Metals

Alloy composites

cell structure

COMPOSITE FOAMS

Foam stability

GEOMETRIC STRUCTURE

IN-SITU COMPOSITE

Melt processing

X-ray tomography

Titanium alloys

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

Materials and Design

In-situ A357- xTiB2 (x=5, 10 wt%) composite foams were prepared through liquid melt route using TiH2 as blowing agent. The deformation and energy absorption characteristics of these foams with varying TiB2 content (5 and 10 wt%) were evaluated in terms of compression and high velocity impact tests. The compression test results showed that the plateau stress values of the composite foams are insensitive to weight fraction of TiB2 particles and for the given relative density, the energy absorption (area under the compressive stress-strain curve) of 5TiB2 composite foams is superior to 10TiB2 composite foam. X-ray computed tomography (XCT) study revealed the formation of TiB2 clusters on the gas-metal interface of 10TiB2 composite foams. The poor gas-metal interface and thick region of brittle interdendrites in 10TiB2 composite foam is responsible for its inferior energy absorption behaviour as compared to 5TiB2 foam. Fractographic analysis showed that the fracture takes place exactly at the inter-dendritic regions in both the foams. Energy absorption during compression and high velocity impact tests is almost same for either of the composite foams, which indicates the energy absorption is insensitive to a displacement rate of 1.6×10-5 m/s (compression) to a rate of 10 m/s (impact). © 2016 Elsevier B.V.

Materials Science and Engineering A

Deformation behaviour of in-situ TiB2 reinforced A357 aluminium alloy composite foams under compressive and impact loading

In this study, the foaming behavior of metal matrix composites (MMCs) containing micron- and nano-sized TiB2 particles was compared. Foaming was achieved by adding blowing agent into the MMC melt at 670&nbsp;°C. Macrostructural and microstructural characterization of the foams were performed by using X-ray tomography and scanning electron microscopy. Quasi-static compression tests were conducted to analyze the mechanical behavior of the foams. Foams stabilized by nanoparticles showed higher expansion than those stabilized by micron-sized particles indicating a better stabilization by nanoparticles. The foams containing nanoparticles also exhibited better mechanical properties. This is mainly due to the presence of nanoparticles in the microstructure. © 2017 Elsevier B.V.

Influence of nano and micro particles on the expansion and mechanical properties of aluminum foams

In this study, the effect of Sc addition on the grain refinement, modification of the eutectic Si, mechanical and wear properties of A356 and A356-10wt% TiB2 in situ composite has been investigated. The A356-10wt% TiB2 composites were prepared by an in situ reaction between K2TiF6 and KBF4 salts, which are added in proper stoichiometric ratio to form TiB2 in the A356 alloy melt at a temperature of 1073K (800°C). Al-2wt% Sc master alloy was added to A356 and A356-10wt% TiB2 melt to introduce 0.2 and 0.4wt% Sc in the alloy and the composite. Addition of Sc reduced the secondary dendrite arms spacing (SDAS) by 50% and changed the Si morphology from needle-like to fine spheroidal particles. Microstructure of Sc modified alloys which were cast for different holding times of 0, 30, 60 and 120min indicated that there was no fading or poisoning effect on the SDAS and eutectic Si morphology. Hardness was found to increase due to addition of Sc and TiB2. Pin-on-disk wear tests indicated that Sc addition increase the wear resistance of A356 alloy but reduced the wear resistance of A356-TiB2 composite. © 2015 Elsevier Ltd.

Effect of Sc addition on the microstructure and wear properties of A356 alloy and A356-TiB2 in situ composite

In situ composites are multiphase materials where the reinforcing phase is synthesized within the matrix during composite fabrication. The present paper deals with the processing, microstructural and mechanical characterization of Al-7Si-0.3Mg-10TiB2 and Al-4Cu-10TiB2 foams. Composite foams with very low relative density (ρr = 0.17-0.37) and foams containing uniform cell sizes were successfully processed. Since the TiB 2 particle sizes are less than 2 μm and have a good wetting behaviour, TiB2 can be very good foam stabilizers. Microstructural characterization of the cell walls showed significant grain refinement since TiB2 is a grain refiner. Elemental mapping clearly showed TiB2 particles at inter dendritic boundaries. Compression testing of the processed foams showed some interesting features. Stress-strain curve showed a lot of serrations which indicated brittle fracture of the cell walls and edges. Hence, it is observed that a balance should be attained between the grain refinement of α-Al grains and the amount of TiB2 particles to obtain desirable mechanical properties. Energy absorbed by the processed foams was calculated and they were observed to be close to that of the commercially available ALPORAS foams.

Transactions of the Indian Institute of Metals

Microstructural and mechanical characterization of two aluminium based in situ composite foams

Al-7Si-0.3Mg-TiB2 in-situ composites were made by the salt-metal reaction i.e., the reaction of K2TiF6 and KBF4 salts with the molten alloy. The kinetics of the formation of intermediate metastable precipitates in the process of Mg2Si formation in Al-7Si-0.3Mg-TiB2 in-situ composites with three different amounts of TiB2 particles (2.5, 5 and 10 wt.%) were studied using differential scanning calorimeter (DSC) and also compared with the Al-7Si-0.3Mg base alloy. Kissinger analysis of non-isothermal DSC scans at various heating rates was carried out to evaluate the activation energies associated with the precipitation processes. The metastable precipitates were characterized by taking the solutionized samples to their respective DSC peak temperatures at a particular heating rate and the samples were then observed under a transmission electron microscopy. It was found that there is a decrease in the activation energies of the GP zones with increase in TiB2 content. © 2011 Indian Institute of Metals.

Precipitation kinetics in Al-Si-Mg/TiB2 in-situ composites

In the present paper the authors studied isolated metallic films made from the same material used for making metallic foams, and then characterised their properties. Metal films were made from a liquid aluminium alloy reinforced with ceramic particles of known concentration. Melts without such particles were also investigated. It is shown that stable films could not be made from Al-Si alloy having no particles, and just extremely thin and fragile films could be made from commercially-pure Al. In contrast, aluminium alloys containing particles such as SiC and TiB2 allowed pulling thin, stable films, which did not rupture. Significant thinning of films was observed when the particle concentration in the melt decreased. By in situ X-ray monitoring of liquid films during pulling, film thickness and drainage effects within the liquid film could be studied. The morphology and microstructure of films was characterised after solidification. Our work shows that the question of how foams are stabilised can be studied using a simplified system such as a film, instead of having to deal with the multitude of different structural elements present in a foam. © the Owner Societies.

Physical Chemistry Chemical Physics

Study on aluminium-based single films

Plant Genetic Researches

Assessment of Genetic Diversity in Groundnut (Arachis hypogea L.) Germplasm Using Morphological Traits

Processing and characterization of in-situ TiB2 stabilized closed cell aluminium alloy composite foams

Journal	Data powered by TypesetMaterials and Design
Publisher	Data powered by TypesetElsevier Ltd
ISSN	02641275
Open Access	No