Tapas Laha

Nanomechanical behaviour of plasma sprayed PZT coatings

Abstract Nanomechanical properties of the plasma sprayed lead zirconate titanate (PZT) coating have been investigated using nanoindentation technique. PZT coating processed at higher plasma power of 32 kW exhibited lower elastic modulus E of 98 GPa compared with the modulus (113 GPa) of the coating processed at plasma power of 20 kW. The variation in the elastic modulus is attributed to the fine porosity of the PZT coating, which is formed during plasma spraying. Porosity increases by evaporation of PbO phase during plasma spraying. Overall effective elastic modulus of both coatings is computed using micromechanics models and compared with the experimentally obtained values. Hashin–Shtrikman and rule of mixtures models predict values that closely match with nanoindentation values.

Al Alloy Nanocomposite Reinforced with Physically Functionalized Carbon Nanotubes Synthesized via Spark Plasma Sintering

Nanocrystalline Al–11.5Si (in wt%) powders were prepared by high-energy ball milling of microcrystalline Al–Si powders, which were subsequently mixed with pristine and physically functionalized multiwalled carbon nanotubes (MWCNTs) separately and were consolidated by spark plasma sintering. Improvement in MWCNT dispersion was observed as a result of functionalization, which resulted in improved densification of the nanocomposites (NCs). Scanning electron microscopy was performed to understand the agglomeration and dispersion of CNTs. Distribution of MWCNTs, the dislocation activity, and the effect of primary Si particles in NC matrix were studied by carrying out transmission electron microscopy. Nanoindentation was performed to measure the elastic modulus and microhardness of the NCs which showed appreciable improvement for functionalized MWCNT reinforced NC.

Role of Sn on the adhesion in Cu–Sn alloy-coated steel–rubber interface

Cu–Sn coatings with varying Sn content were deposited on steel substrate by immersion route and the effect of variation of Sn content and the substrate roughness on the interfacial adhesion strength of Cu–Sn-coated steel substrates vulcanized with styrene butadiene rubber were investigated. The surface roughness of the coatings did not vary compared to pristine steel substrate with change in Sn weight% in the coatings. The coated surfaces exhibited bare spots or deep trough as micro-discontinuities in the coatings, where formation of Fe2O3 was evident from SEM-EDS, AES, and XPS analysis. Microstructural study of the coating cross-section and coating-substrate interface by transmission electron microscopy of cross-sectioned samples revealed inadequate penetration of coating inside these troughs. Peel test carried out on the Cu–Sn-coated steel–rubber joints showed mixed mode i.e. adhesive and cohesive mode of interfacial fracture irrespective of the coating composition. The peel test further indicated higher interfacial adhesion strength for Cu–Sn-coated samples than pure Cu-coated samples, with an optimum adhesion strength for the coatings containing 3–4 wt.% Sn.

Carbon nanotube-reinforced Al alloy-based nanocomposites via spark plasma sintering

Carbon nanotubes have emerged as potential reinforcements that can be used to engineer composites with tailored combinations of physical and mechanical properties. In the present study, an Al alloy-based nanostructured composite containing multiwalled carbon nanotubes (MWCNT) as a reinforcement phase has been synthesized by a combination of two novel processing techniques, which are cryomilling and spark plasma sintering. Scanning electron microscopy and quantitative image analysis have been performed to provide insight into the microstructural evolution and to verify the retention of the carbon nanotubes in the consolidated samples. Nanoindentation, microhardness, and tribological studies have been carried out to understand the effect of variation in MWCNT content and processing on the mechanical response of the consolidated nanocomposites. The characterization results affirm the retention of carbon nanotubes and varied improvement in mechanical properties in the nanocomposites. Raman spectroscopy analysis revealed that the MWCNTs were partially damaged during cryomilling.

Effect of Cu strike coating on adhesion between Cu–Sn coated steel and rubber

In order to improve the adhesion between steel and rubber, a novel coating deposition technique has been developed, where steel substrate with orchestrated surface roughness was coated with double-layer coatings consisting of a thin Cu strike layer followed by a Cu–Sn layer with varying Sn compositions by immersion route. Coating surface characteristics studied using scanning electron microscope coupled with energy dispersion spectroscopy analyzer, electron probe micro analyzer, and inductively coupled plasma optical emission spectroscopy showed improvement in surface coverage with coating after employing the strike layer coating attributed to the better coating penetration in the deep roughness troughs. Peel test of the coated samples vulcanized with styrene butadiene rubber (SBR) was carried out which showed improvement in adhesion strength of the double-layer-coated samples inferring more uniform Cu-sulfide layer formation at interface due to more uniform coating coverage in these samples. Highest peel strength with uniform cohesive fracture within rubber was observed for optimum 2–3 wt% Sn content in the coatings. This result was further supported by pull-out test conducted on coated wire samples vulcanized with SBR.

Effect of carrier gas on mechanical properties and fracture behaviour of cold sprayed aluminium coatings

Abstract Two different coatings of 1100 aluminium were cold sprayed onto similar substrates, using He and He–20N2 (vol.-%) mixture as carrier gases. Three point bend testing was carried out. The elastic moduli of the coatings were found to be close to each other and the substrate. The He processed coating showed higher fracture strength which was attributed to the higher degree of strain hardening. The He–20N2 processed coating failed at lower stress owing to its strain relaxed structure. The mode 1 fracture of the coating substrate system was found to be higher for the helium processed coating. The toughness was correlated to the microstructure. The delaminated coating showed a higher degree of brittle failure of the interface for the He processed coating.

Role of Sn on the Adhesion between Cu-Sn Alloy Coated Steel and SBR Based Rubber

The effect of Cu-Sn coating on steel towards improving the adhesion between steel and typical styrene butadiene rubber (SBR) based tyre bead composition has been investigated in this work. Steel coupons were coated with varying compositions of Cu-Sn via immersion coating, where the electrolyte bath composition was varied. Chemical analysis of the coatings using ICP-OES confirmed increase in Sn content with increasing SnSO4 concentration in the coating baths, keeping other parameters constant. No change in the coating weight was observed with change in Sn concentration in the coatings. Bare spots on the coating surface was observed under SEM XPS analysis confirmed formation of Fe oxide at the bare locations. The coated steel plates were vulcanized with SBR based rubber and peel strength was measured. The results confirmed an optimum Sn concentration of 3 - 4 wt% in the coatings up to which an increase (~ 25%) in adhesion strength was exhibited compared to only Cu coatings. Stereo-microscopic analysis of the peel tested samples validated mixed mode i.e. both adhesive and cohesive modes of failure.

Synthesis and Characterization of Oxide Dispersion Strengthened W-based Nanocomposite

The chapter involves fabrication and characterization of novel oxide dispersion strengthened (ODS) tungsten (W)-based nanocomposites used for kinetic energy penetrator (KEP) for defense and plasma facing materials (PCM) for nuclear reactor application. The chapter will discuss the benefits and challenges for using W-based alloys for high-temperature structural application. Synthesis of oxide-dispersed W-based nanocomposite (79W–10Mo–10Ni–1Y2O3) by mechanical alloying followed by consolidation through conventional pressureless sintering and advanced spark plasma sintering is carried out. The phase evolution, microstructure for milled powder, and sintered product have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The densification, hardness, and strengthening behavior of the alloy in two sintering mode are illustrated. The microstructure–mechanical properties are correlated to understand the operative densification and strengthening mechanism. Heterogeneous composition and bimodal grain size distribution of the alloy offers appreciable strength–ductility for structural applications. The chapter will provide a roadmap for design of novel alloys for similar applications.

Effect of Cu2O thin film on Cu–Sn alloy coated steel surface in promoting interfacial adhesion with rubber

Abstract In the present study, effect of Cu2O film deposited via successive ionic layer adsorption and corresponding chemical reaction (SILAR method) on Cu–Sn coated steel substrate was explored for the purpose of improving the adhesion of steel with rubber. The effect of the relative alkali concentration in the oxide film deposition bath and the number of immersion cycles on the interfacial adhesion affecting the nature of oxide film deposited, its thickness and surface coverage were investigated. In the current study, Cu–Sn coated steel bead wire with coated surface roughness (Ra) around 2 μm showed an improvement of 33% in adhesion (in terms of pull out force) with an optimum alkali/Cu ion concentration of 25:1 with single dipping cycle attributed to an optimum oxide coating thickness of ~70 nm. Surface morphology study exhibited formation of thicker coating with increase in number of dipping cycles. Satisfactory thermal stability of the Cu2O film was confirmed as no re-oxidation of the Cu2O film to CuO was observed in the 200 °C heat treated samples.

Microstructure and phase evolution in spark-plasma-sintered Al86Ni6Y4.5Co2La1.5 glassy alloy

Abstract Al86Ni6Y4.5Co2La1.5 amorphous powders synthesized after 200 h of mechanical alloying were spark plasma sintered at 25 and 400 MPa at 400 °C for 15 min. The sample sintered at 25 MPa showed precipitation of FCC-Al grains of sub-micron size attributed to a higher amount of localized high-temperature regions which favoured faster long-range atomic diffusion. On the contrary, the 400-MPa sintered sample showed the presence of nanocrystals (5–20 nm) distributed in an amorphous matrix. This is attributed to higher pressure sintering favouring local and short-range atomic redistributions. The higher amount of retained amorphous phase in the 400-MPa sintered sample could be accounted for by a smaller amount of localized high-temperature regions in comparison to those in 25-MPa sintered sample. High-pressure sintering induces shear fracturing and fragmentation of the brittle amorphous particles and provided better surface contact and packing density. The retention of a larger amount of amorphous phase and a higher relative density (96%) contributes to high microhardness (278 Hv) and nanoindentation hardness (3.7 GPa) of the 400-MPa sintered sample.