D.P. Mondal

Titanium cenosphere syntactic foam with coarser cenosphere fabricated by powder metallurgy at lower compaction load

Abstract Titanium cenosphere syntactic foam of varying relative densities with coarse cenospheres was developed through powder metallurgy route at lower compaction loads. The cold compaction load was varied in the range of 60 to 75 MPa to obtain the foams of different relative densities. A function of cold compaction load between crushing tendency of cenosphere and relative density was investigated. The compressive deformation behavior of these foams was studied, and empirical relationships among plateau stress, elastic modulus, densification strains and energy absorption are formulated considering their practical significance. The performance indices of the developed foam in comparison with dense titanium were studied and it was found that the foam is superior alternative to titanium for engineering applications.

Effect of Al–TiB master alloy addition on microstructure, wear and compressive deformation behaviour of aluminum alloys

Abstract Aluminum-10% TiB master alloy was added in various proportions in 7178 Al alloy in order to examine the effect of TiB on grain refinement, wear and compressive deformation of the later one. Microstructural characterization reveals that TiB particles act as grain refiners for primary base alloy and result in globular dendrites. It was observed that the wear resistance and strength of the alloy decreased when the master alloy addition increased beyond 20%, even though the dendrites become much finer and almost spherical in nature.

Compressive Deformation Behavior of Highly Porous AA2014-Cenosphere Closed Cell Hybrid Foam Prepared Using CaH2 as Foaming Agent: Comparison with Aluminum Foam and Syntactic Foam

Closed Cell AA2014-cenosphere hybrid foams have been prepared through stir-casting technique using varying amount of CaH2 powder as foaming agent. The cenospheres in hybrid foams created micro-pores in the cell wall and in the plateau region. It reduced the requirement of CaH2 for foaming by 30–40% by attaining equivalent level of relative density. These foams have been characterized for of microarchitechtural characteristics and mechanical properties like strength, densification strain and energy absorption. The properties of hybrid foams have been compared with those of conventional AA2014-SiC foam and Al-cenosphere syntactic foam. The closed cell AA2014-cenosphere hybrid foam exhibited comparable plateau stress, densification strain and energy absorption characteristics to those of AA2014-SiC foams with same relative density. Empirical relations to correlate plateau stress, densification strain and energy absorption for entire range of porosities have been established.

Characteristics and wear behavior of cenosphere dispersed titanium matrix composite developed by powder metallurgy route

Abstract The cenosphere dispersed Ti matrix composite was fabricated by powder metallurgy route, and its wear and corrosion behaviors were investigated. The results show that the microstructure of the fabricated composite consists of dispersion of hollow cenosphere particles in α -Ti matrix. The average pore diameter varies from 50 to 150 μm. The presence of porosities is attributed to the damage of cenosphere particles due to the application of load during compaction as well as to the hollow nature of cenospheres. A detailed X-ray diffraction profile of the composites shows the presence of Al 2 O 3 , SiO 2 , TiO 2 and α -Ti. The average microhardness of the composite (matrix) varies from HV 1100 to HV 1800 as compared with HV 240 of the as-received substrate. Wear studies show a significant enhancement in wear resistance against hardened steel ball and WC ball compared with that of commercially available Ti–6Al–4V alloy. The wear mechanism was established and presented in detail. The corrosion behavior of the composites in 3.56% NaCl (mass fraction) solution shows that corrosion potential ( φ corr ) shifts towards nobler direction with improvement in pitting corrosion resistance. However, corrosion rate of the cenosphere dispersed Ti matrix composite increases compared with that of the commercially available Ti–6Al–4V alloy.

Compressive Deformation Behavior of Open-Cell Cu-Zn-Al Alloy Foam Made Through P/M Route Using Mechanically Alloyed Powder

Cu-Zn-Al foams of varying porosity fractions using mechanical alloyed powder have been made through powder metallurgy route. Here, NH4 (HCO3) was used as a space holder. Mechanically alloyed Cu-Zn-Al is made using a planetary ball mill taking the ratio of Cu/Zn/Alxa0=xa070:25:5 (by weight ratio). The ball/powder ratios were varied in the four ranges 10:1, 15:1, 20:1, and 25:1. Green compacts of milled powder and space holder samples were sintered at three stages at three different temperatures 350, 550, and 850xa0°C for 1xa0h at each stage. The crystalline size and particle size as a function of ball/powder ratios were examined. The compressive deformation responses of foams are varied with relative density and the ball/powder ratio. The plateau stress and energy absorption of these foams increase with an increase in relative density but decreases with increase in ball/powder ratio, even though crystalline size decreases. This has further been explained on the basis of particle morphology as a function of ball/powder ratio.

Enhanced microwave absorption property of aluminum composites using fly ash derived cenosphere

In the present investigation, influence of micronsize cenosphere particles derived from fly ash on the properties of aluminum composites was investigated. Aluminum-cenosphere (AC) composite was fabricated by modified stir casting technique. The mechanical and electromagnetic interference (EMI) shielding properties of AC composites were investigated. The obtained composites with cenosphere (+100 μm) loading demonstrate the excellent compressive strength of 251.3 MPa. This enhancement is due to the smaller size of cenosphere size provides the finer surface of the cenosphere. The addition of cenosphere in aluminum matrix improved dielectric and microwave absorption properties of composites in X band frequency region (8.2-12.4 GHz). The AC composites possess good EMI shielding effectiveness of -32.7 to -44.3 dB with 30% loading of cenosphere with various sizes (+212, +150 and +100 μm). The incorporation of lower size cenosphere (+100μm) in aluminum matrix significantly increases the interfacial polarization which leads to a higher absorption EMI shielding effectiveness (SE) of -31.1 dB at 2.0 mm thickness. This technique is very simple, economical and highly reproducible, which may facilitate the commercialization of such composite and it can be used as microwave absorbing materials in defense and aerospace applications. Copyright

Effect of Cenosphere Size and Volume Fraction on the Microstructure and Deformation Behavior of Ti-Cenosphere Syntactic Foam Made Through Powder Metallurgy Route

An attempt was made for making Titanium–cenosphere metal syntactic foams with varying relative densities, using different cenosphere sizes and volume fractions. Cold compaction of Ti and cenosphere powder mix was carried out at a pressure of 75u2009MPa, followed by sintering at 1100°C for 2u2009h. The sintered foam samples were characterized in terms of microstructure, primarily to observe the extent of cenosphere crushing, distribution of cenosphere, and extent of sintering. Uniform distribution of cenosphere with some extent of cenosphere crushing has been observed within the Ti matrix. XRD and EDX analysis confirms the oxidation of Ti particles to a small extent and also the entrapment of crushed cenosphere shells within the matrix, which makes the foam stronger but brittle in nature. The plateau stress, energy absorption, and modulus of these foams vary with the cenosphere size and volume fraction. Foams made with finer size cenosphere exhibits higher plateau stress and higher energy absorption for a fixed cenosphere volume fraction and at a constant foam density. Crushing of cenosphere, while compaction causes an increased density of the foam as compared to the theoretical value. As a consequence, the foam with higher cenosphere volume fraction or with coarser cenosphere size exhibited marginally higher strength and energy absorption. The variation in deformation mechanism as a function of cenosphere size and volume fraction was examined. These foams exhibited considerably higher strength and stiffness than the conventional foam and demonstrate the possibility of using them for biomedical and engineering applications.

Effect of Relative Density and Strain Rate on the Deformation Behaviour Ni-Ti Foam Made through Powder Metallurgy Route Using NH4(HCO3) as Space Holder

Ni-Ti foams of varying relative densities have been made by varying the size and volume fraction of NH4(HCO3), which was used as space holder. The green compacted pellets, after evaporation of NH4(HCO3), were sintered at 1100°C for 2 hrs. The XRD and EDX analysis confirms that there is no residual space holder. The extent of openness of cell walls increases with increase in porosity. The compressive stress-strain behavior of these foams varies with the relative density. The peak stress and energy absorption of these foam increases with relative density following power law and linear relationships respectively, and the densification strain decreases with relative density following a linear relationship. The pseudo elastic recovery strain and shape recovery strain decrease with increase in porosity. The overall recovery increases with decrease in degree of deformation. This phenomenological behavior indicates that these foams can be used for their shape memory effect.

Use of Cenosphere for Making Metal-Microspheres Syntactic Foam through Powder Metallurgy Route

Cenospheres are very cheap, and are reasonably strong and thermally stable upto 1200°C. In view of this attempt has been made to use these cenosphere for making Titanium syntactic foams with varying relative densities. Precautions were taken for selecting cold compaction pressure to minimize cenosphere crushing. The sintered samples were then characterized in terms of microstructures primarily to see the extent of cenosphere crushing, distribution of cenosphere, and extent of sintering. The foams made using optimized pressure and sintering parameters, exhibits uniform distribution of cenosphere without any significant crushing. The plateau stress, energy absorption and modulus of these foams are varying with the cenosphere content or the relative density, and these parameters can be engineered by varying cenosphere content in the foam. These foams exhibit considerably higher strength and stiffness than the conventional foam and show the possibility of using them for biomedical and engineering applications.

The Effect of Magnesium Addition on the Microstructure & Compressive Deformation Behavior of Al-Ca Alloy.

The Al-Ca-Mg alloys containing varying amount of Mg are used to study the effect of Mg addition on their microstructure and deformation behavior at varying strain rate (0.01/s, 0.1/s, 1/s). The material is prepared using stir casting technique. The yield stress, flow stress and elastic limit are measured from the true stress-strain graph. The strain rate sensitivity and strain-hardening exponent were also determined for each material at different strain rates. The elastic limit decreases with increases in strain rate. The strain rate sensitivity m is found to be negative at a flow strain and invariant to the strain rate. Its microstructure reveals that the microstructural characteristics changes with Mg addition. The variation of microstructural features primarily leading to the variation of deformation behavior.