• K Chandra

      Articles written in Bulletin of Materials Science

    • Characteristics of porous zirconia coated with hydroxyapatite as human bones

      V V Narulkar S Prakash K Chandra

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      Since hydroxyapatite has excellent biocompatibility and bone bonding ability, porous hydroxyapatite ceramics have been intensively studied. However, porous hydroxyapatite bodies are mechanically weak and brittle, which makes shaping and implantation difficult. One way to solve this problem is to introduce a strong porous network onto which hydroxyapatite coating is applied. In this study, porous zirconia and alumina-added zirconia ceramics were prepared by ceramic slurry infiltration of expanded polystyrene bead compacts, followed by firing at 1500°C. Then slurry of hydroxyapatite–borosilicate glass mixed powder was used to coat the porous ceramics, followed by firing at 1200°C. The porous structures without the coating had high porosities of 51–69%, high pore interconnectivity, and sufficiently large pore window sizes (300–500 𝜇m). The porous ceramics had compressive strengths of 5.3∼36.8 MPa, favourably comparable to the mechanical properties of cancellous bones. In addition, porous hydroxyapatite surface was formed on the top of the composite coating, whereas a borosilicate glass layer was found on the interface. Thus, porous zirconia-based ceramics were modified with a bioactive composite coating for biomedical applications.

    • Ceramic coated Y1 magnesium alloy surfaces by microarc oxidation process for marine applications

      V V Narulkar S Prakash K Chandra

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      The magnesium alloys occupy an important place in marine applications, but their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To meet these defects, some techniques are developed. Microarc oxidation is a one such recently developed surface treatment technology under anodic oxidation in which ceramic coating is directly formed on the surface of magnesium alloy, by which its surface property is greatly improved. In this paper, a dense ceramic oxide coating, ∼ 20 𝜇m thick, was prepared on an Y1 magnesium alloy through microarc oxidation in a Na3SiO3–Na2WO4–KOH–Na2EDTA electrolytic solution. The property of corrosion resistance of ceramic coating was studied by CS300P electrochemistry–corrosion workstation, and the main impact factor of the corrosion resistance was also analysed. Microstructure and phase composition were analysed by SEM and XRD. The microhardness of the coating was also measured. The basic mechanism of microarc coating formation is explained in brief.

      The results show that the corrosion resistance property of microarc oxidation coating on the Y1 magnesium surface is superior to the original samples in the 3.5 wt% NaCl solutions. The microarc oxidation coating is relatively dense and uniform, mainly composed of MgO, MgAl2O4 and MgSiO3. The microhardness of the Y1 magnesium alloy surface attained 410 HV, which was much larger than that of the original Y1 magnesium alloy without microarc oxidation.

    • Effect of carbon on corrosion resistance of powder-processed Fe–0.35%P alloys

      Yashwant Mehta Shefali Trivedi K Chandra P S Mishra

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      The corrosion behaviour of phosphoric irons containing 0.35 wt % P, 2% copper, 2% nickel, 1% silicon, 0.5% molybdenum, with/without 0.15% carbon prepared by powder forging route were studied in different environments. The various environments chosen were acidic (0.25 M H2SO4 solution of pH 0.6), neutral/marine (3.5% NaCl solution of pH 6.8) and alkaline (0.5 M Na2CO3 + 1.0 M NaHCO3 solution of pH 9.4). The corrosion studies were conducted using Tafel extrapolation and linear polarization methods. The studies also compare Armco iron with phosphoric irons. It was observed that the addition of carbon improved the corrosion resistance of a Fe–0.35%P–2%Ni–2%Cu–1%Si–0.5%Mo alloy in all the environments. Corrosion rates were highest in acid medium, minimal in alkaline medium and low in neutral solution. SEM/EDAX was used to characterize the compositions.

    • Effect of carbon on mechanical properties of powder-processed Fe–0.35%P alloys

      Shefali Trivedi Yashwant Mehta K Chandra P S Mishra

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      The present paper records the results of mechanical tests on iron-phosphorus powder alloys which were made using a hot powder forging technique. In this process mild steel encapsulated powders were hot forged into slabs, hot rolled and annealed to relieve the residual stresses. These alloys were characterized in terms of microstructure, porosity content/densification, hardness and tensile properties. Densification as high as 98.9% of theoretical density, has been realized. Microstructures of these alloys consist of single-phase ferrite only. Alloys containing 0.35 wt% P, such as Fe–0.35P–2Cu–2Ni–1Si–0.5Mo and Fe–0.35P–2Cu–2Ni–1Si–0.5Mo–0.15C show very high strength. It was observed in this present investigation that, the alloying additions, such as Si, Mo, Ni, and C to Fe–P based alloys caused increase in strength along with reduction in ductility. Cu reduces porosity of Fe–P alloys. Alloys developed in the present investigation were capable of hot working to very thin gauge of sheets and wires.

    • Development of P/M Fe–P soft magnetic materials

      S K Chaurasia Ujjwal Prakash P S Misra K Chandra

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      Phosphorous is treated as an impurity in conventional steels owing to segregation of phosphorous and formation of brittle phosphides along the grain boundaries. It is responsible for cold and hot shortness in wrought steels. In conventional powder metallurgy, involving compaction and sintering, high phosphorous content (up to 0.7%) in Fe-based alloys exhibit attractive set ofmechanical andmagnetic properties. These powder-processed alloys suffer from increasing volumetric shrinkage during sintering as phosphorous is increased beyond 0.6%. Thus both cast as well as conventional powder metallurgy routes have their own limitations in dealing with iron–phosphorous alloys. Hot-powder forging was used in the present investigation for the development of high-density soft magnetic materials containing 0.3–0.8% phosphorous to overcome these difficulties. It was observed that phosphorous addition improves the final density of the resulting product. It was further observed that hot-forged iron–phosphorous alloys have excellent hot/cold workability and could be easily shaped to thin strips (0.5–1.0 mm thick) and wires (0.5–1.0 mm diameter). The powder hot-forged alloys were characterized in terms of microstructure, porosity content/densification, hardness, softmagnetic properties and electrical resistivity.Magnetic properties such as coercivity 0.35–1.24 Oe, saturation magnetization 14145–17490 G and retentivity 6402–10836 G were observed. The obtained results were discussed based on the microstructures evolved.

    • Processing, structure and flexural strength of CNT and carbon fibre reinforced, epoxy-matrix hybrid composite

      K Chandra Shekar M Sai Priya P K Subramanian Anil Kumar B Anjaneya Prasad N Eswara Prasad

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      Advanced materials such as continuous fibre-reinforced polymer matrix composites offer significant enhancements in variety of properties, as compared to their bulk, monolithic counterparts. These properties include primarily the tensile stress, flexural stress and fracture parameters. However, till date, there are hardly any scientific studies reported on carbon fibre (Cf) and carbon nanotube (CNT) reinforced hybrid epoxy matrix composites (unidirectional). The present work is an attempt to bring out the flexural strength properties along with a detailed investigation in the synthesis of reinforced hybrid composite. In this present study, the importance of alignment of fibre is comprehensively evaluated and reported. The results obtained are discussed in terms of material characteristics, microstructure and mode of failure under flexural (3-point bend) loading. The study reveals the material exhibiting exceptionally high strength values and declaring itself as a material with high strength to weight ratio when compared to other competing polymer matrix composites (PMCs); as a novel structural material for aeronautical and aerospace applications.

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      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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