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Purpose The purpose of this study is to investigate the microstructural evolution of high-strength 2024 Al alloy prepared by the laser powder bed fusion (L-PBF) additive manufacturing (AM) route. The high-strength wrought Al alloy has typically been unsuitable for AM due to its particular solidification characteristics such as hot cracking, porosity and columnar grain growth. Design/methodology/approach In this research work, samples were fabricated using L-PBF under various laser energy densities by varying laser power and scan speed. The microstructural features that developed during the solidification are correlated with operating laser parameters. In addition, finite element modelling (FEM) was performed to understand the experimentally observed results. Findings Microstructure evolution and defect formation have been assessed, quantified and correlated with operating laser parameters. Thermal behaviour of samples was predicted using FEM to support experimental observations. An optimised combination of intermediate laser power and scan speed produced the least defects. Higher energy density increased hot tearing along the columnar grain boundaries, while lower energy density promoted void formation. From the quantitative results, it is evident that with increasing energy density, both the top surface and side wall roughness initially reduced till a minimum and then increased. Hardness and compressive strength were found to decrease with increasing power density due to stress relaxation from hot tearing. Originality/value This research work examined how L-PBF processing conditions influence the microstructure, defects, surface roughness and mechanical properties. The results indicates that complete elimination of solidification cracks can be only achieved by combining process optimisation and possible grain refining strategies.

In this study, the effect of minor (5 vol.%) addition of Al–10Si–0.2Mg (composition in wt.%) pre-alloyed powder on densification, microstructure and mechanical behaviour of spark plasma-sintered ZrB2-20 vol.% SiC composite has been investigated. The sintered composite records a relative density of 99.83% despite being processed at a relatively low temperature (1700 °C) in argon atmosphere. Interestingly, ZrB2–20SiC–5AlSiMg composite does not undergo any shape distortion though the liquidus temperature of this metallic alloy additive is quite low (~ 592 °C). Extensive phase and microstructure analyses by appropriate techniques indicate that no free or unreacted AlSiMg is detected in the sintered composite. Thermodynamic analysis suggests that AlSiMg serves as a reducing agent for ZrO2 oxide scale and forms respective high-melting oxide phases. Raman analysis confirms that incorporation of 5 vol.% AlSiMg enhances residual compressive stress of SiC grains. Furthermore, the addition of AlSiMg is found to enhance the thermal shock resistance of the composite. In brief, this new AlSiMg additive results in better densification (99.83%) and hence an attractive combination of useful mechanical properties like Vickers microhardness (17.63 ± 0.54 GPa), nano-hardness (18.62 ± 1.23 GPa), indentation fracture toughness (7.21 ± 1.13 MPa $$\sqrt {\text{m}}$$ ), elastic modulus (432.64 ± 32.90 GPa) and flexural strength (659.25 ± 32.40 MPa) in the AlSiMg-added ZrB2-20SiC composite.

Laser-assisted direct energy deposition (LDED) is an additive manufacturing technology which involves melting/fusion of materials in the form of powder or wire using laser as a focused heat source and its deposition in a layer-by-layer fashion on a dummy substrate to build the product in its final shape by one-step processing. LDED is a very important technology for obtaining component with extreme precision and with minimum loss of material and a flexible one to build component of any kind including metal/alloys, metal matrix composites, and intermetallics. LDED may be categorized in to laser engineered net shaping, laser metal deposition, direct metal deposition, and direct metal printing. In the present contribution, a detailed discussion on the principle of LDED, role of process parameters in influencing the properties, and the present status on the application of LDED for the fabrication of metallic, metal matrix composite, and intermetallics will be discussed in details. Finally, the future scope of research on LDED will be presented.

The present study explores the feasibility of sputter deposition of two Sn-rich Sn(Zn) alloy coatings (Sn-8.8 wt.% Zn and Sn-30 wt.% Zn) using single or identical twin jet magnetron sputtering for improving surface mechanical and corrosion properties of interstitial free steel. The thickness, average grain size and hardness of the deposit varied with the target composition and deposition parameters. Detailed studies reveal that coating deposited from a single pre-alloyed (Sn-30Zn) target offered the most attractive combination of the highest hardness (HV0.01 175 ± 6) and improvement in wear and corrosion resistance. However, the highest corrosion resistance in terms of higher or more active corrosion potential was obtained when sputter deposition was made from twin targets of Sn-8.8Zn. The results indicate that Sn-rich Sn(Zn) alloy may reduce or even substitute total dependence on pure Zn coating (i.e., galvanizing) for corrosion and scratch protection of steel.

In the present study, laser periodic structuring of titanium-based alloy (Ti-6Al-4V) has been carried out using Ti:Sapphire laser with the wavelength of 800 nm and pulse duration of 3 ps and 100 fs with varying peak fluence and scan speed. After laser irradiation, the topography of the surface has been recorded using 3D surface profilometer. Laser surface processing leads to the formation of a periodically patterned surface with the average ablation depth of 37.25 µm-42.13 and average surface roughness of 0.991-1.862 µm as compared to 0.169 µm average roughness of as-received Ti-6Al-4V. In the microstructure, there is presence of fine periodic ripples with an average ripple width of 0.48 µm to 0.54 µm when processed with 3 ps laser and the average ripple width of 0.17 μm in addition to the presence of very fine pits, deposited particle, and oxide dispersed surface when processed with 100 fs laser. The microhardness of the surface is improved (395 VHN-373 VHN ) as compared to 282 VHN of as-received Ti-6Al-4V. There is a significant improvement in the corrosion resistance in terms of a decrease in corrosion rate (0.0037 to 0.0008 mm/year) in laser surface processed sample as compared to as-received Ti-6Al-4V (0.0932 mm/year) in Hank’s solution and also increase in pitting corrosion resistance in terms of increase in critical potential for pit formation (Epit) under a few employed parameters with both 3 ps laser (at a laser fluence of 0.063 J/cm2 and a scan speed of 20 mm/sec) and 100 fs laser (at a laser fluence of 0.63 J/cm2 and at a scan speed of 60 mm/sec).

Respiratory infections by RNA viruses are one of the major burdens on global health and economy. Viruses like influenza or coronaviruses can be transmitted through respiratory droplets or contamina...

In the present study, a detailed study of the effect of laser parameters on microstructure and phases of the laser surface-melted (using 2 kW continuous wave Yb-fibre laser) Inconel 718 has been carried out. Surface melting has been conducted with a power of 400 watts, scan speed of 500, 750, and 1000 mm/min and with a spot diameter of 3 mm. After laser surface melting, the microstructures, phase, surface roughness and crystallographic orientation (texture) of the melt zone has been carried out. There is refinement of microstructure and change in crystallographic texture which varied with process parameters. The effect of process parameters on the microhardness of the melt zone has been studied in detail.

This study concerns mechanism and kinetics of isothermal oxidation of four Fe-Cr-Al-Ti ferritic alloys in the range 700 °C to 900 °C for up to 50 hours in air. These four alloys with nominal compositions of 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C), and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) each with 1.0 wt pct nano-Y2O3 dispersion were synthesized by mechanical alloying and sintering at 1000 °C by hot isostatic pressing, high pressure sintering, hydrostatic extrusion and pulse plasma sintering techniques. A detailed characterization of the phase aggregate, microstructure and micro-composition of the oxide scale was carried out by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, respectively. Oxidation kinetics appear to follow a parabolic rate with an activation energy of 135 to 234 kJ/mol, which depend on alloy composition (i.e., Cr content). Oxidation mostly occurred by counter-ionic diffusion of oxygen from air to the interior and cations (Cr+3 or Fe+3) from the bulk toward the surface. Alloy D sintered by hot isostatic pressing offered the highest resistance to oxidation.

Leidenfrost (LF) and rewetting (RWT) phenomenon are both closely related and involved for the cooling of a very hot object utilizing a suitable cooling agent. The present study focusses on the infl...

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] based ceramics are a potential candidate for orthopedic implants, bone cements, and bioactive coating over metallic implants due to their compositional similarities [Ca/P = 1.67] with human bone. Cobalt doping in HA can greatly enhance angiogenesis and vascularization along with incorporating antimicrobial properties to HA. For the first time, this work reports the importance of Co doping sites on biological and magnetic properties of HA. In the current work, Co doing in HA has been carried out according to the chemical formula Ca10(PO4)6Cox(OH)2-α and Ca10-x Cox(PO4)6(OH)2, (x = 0, 0.2 and 0.3) to assess the correlation of individual Co incorporation sites on crystal chemistry, cytotoxicity, magnetic properties, ion leaching and antibacterial efficacy. Dependence of antibacterial efficacy on different doping sites revealed that cytocompatible Co doped HA is antibacterial against E. coli, and S. aureus mainly after substitution of Co in Ca site. Additionally, a minor antibacterial effect has been noticed after Co doping in OH channels. Interestingly, the Ca substituted Co doped HA shows Co leaching up to ∼758 ppb (obtained from inductively coupled plasma-mass spectrometry), which comes to only ∼27 ppb after incorporating Co in OH channel. This higher Co leaching (when doped at Ca site in comparison to that at OH channels) is the major cause of better antibacterial efficacy. Vibrating sample magnetometer measurements showed that the order of mr and ms values significantly changes after altering the doping sites, due to change in local Co environment. Thus, this work proves that different doping sites of Co doped HA can greatly enhance its antibacterial properties with significant changes in crystallographic and magnetic properties, which make Co doped HA an ideal choice as a bone replacement material or drug delivery agent with tailored properties depending on the doping sites.

We demonstrate unique evolutions of the shape of ferrofluid droplets during their motion over horizontal and inclined planes assisted by an applied field. We substantially extend the basic study regarding the motion of the ferrofluid droplets to address state-of-the-art parametric variation. While doing so, we describe some uncommon phenomena such as pearling, which has not been reported to date in connection with the motion of ferrofluid droplets. The contact angle varies dynamically with the motion of the droplet over horizontal and inclined planes. The shape of the ferrofluid droplet evolves continuously with the variation of different parameters. The spheroidal shape transforms into oblate, pear shape and tear drop with a symmetric corner and finally tears into daughter globules, famously known as pearling. The field strength, magnet velocity and concentration of nanoparticles control the motion, deformation and pearling. We emphasize that pearling is predominant during horizontal translation and depreciates during the ascent of an inclined plane (due to the resolved component of gravity). From a scale analysis, we demonstrate that the deformation and pearling can be predicted in terms of the magnetic Bond number, magnetic Laplace number and Bond number.

The effect of prior cold deformation and nitriding parameters on the kinetics and mechanism of plasma nitriding and the resultant hardness, wear and corrosion properties of automotive-grade interstitial-free (IF) steel has been investigated. Following controlled prior cold deformation (uniaxial rolling), plasma nitriding was carried out in pulsed direct current glow discharge mode with applied voltage, current, temperature and time varied in the range 540 to 710 V, 3 to 6 A, 350 to 480 °C and 1 to 4 hours, respectively. The phases formed after nitriding were found to be mostly γ-Fe4N with a small volume fraction of Fe3N embedded in a ferrite matrix. Prior cold deformation increases the kinetics of the nitride formation. The volume fraction of nitride phases increased with an increase in nitriding temperature and time. Detailed characterization suggested that 80 pct cold deformation followed by plasma nitriding led to significant improvement in hardness and wear resistance of IF steel, particularly when nitrided at 480 °C for 4 hours. Moreover, plasma nitriding also enhanced the corrosion resistance of IF steel, enhancement being directly related to the nitride volume fraction at the surface. Hence, it was concluded that prior cold deformation was effective in enhancing the kinetics of plasma nitriding and in turn surface hardness and resistance to wear and corrosion of IF steel, which otherwise possess a fairly poor bulk strength and does not respond to usual bulk/surface-hardening treatments.

The present study concerns a detailed investigation of the microstructure, phase identity, composition, residual stress, wear and corrosion behavior of Ti, Zn and Zn + Ti coatings developed on IF steel by sputter deposition technique. A significant improvement in average microhardness (350-700 VHN) is noticed following sputter deposition compared to that of as-received IF steel (190 VHN). The highest microhardness recorded is 500 VHN for Ti, 350 VHN for Zn and 700 VHN for Ti + Zn bilayer, respectively. Improvement in surface hardness is accompanied by a marked improvement in wear resistance of the sputter-deposited surface against hardened steel ball. The corrosion rate of coated sample in 3.56 wt.% NaCl solution is marginally decreased (2.95 × 10−2 to 3.25 × 10−2 mm/year) as compared to that of as-received IF steel (3.55 × 10−2 mm/year). Ti-deposited IF steel registers the minimum corrosion rate (2.95 × 10−2 mm/year) among all the coated samples.

This investigation aims to enhance both wear and corrosion resistance of interstitial-free (IF) steel through deposition of pre-determined thickness of pure Sn or Zn or alternate elemental Sn–Zn layers by twin-target magnetron sputtering at desired deposition rate. The thickness, average grain size, hardness and resistance to wear and corrosion of the deposit depend on the deposition parameters. Deposition of either Sn or Zn from single target seems more effective than that from twin target in improving these tribo-corrosion properties of IF steel. The results indicate that sputter deposition of Sn or Zn offers a superior wear and corrosion resistance to galvanized steel and can be a potential route to replace the conventional practice of hot dip galvanizing for the said objective.

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] is among the most sought after bioceramics having chemical structure similar (with Ca/P ratio of 1.67) to that of human bone and other hard tissues. Zn doping in HA based implants not only enhances bone mineralization, biological calcification but also introduces antibacterial efficacy that reduces the chances of implant failure due to periprosthetic infection. This is for the first time, dopant site specific biological properties of Zn doped HA has been investigated. In this work, Zn doping in HA is performed as per the stoichiometric formula Ca10(PO4)6Znx(OH)2-δ and Ca10-x Znx(PO4)6(OH)2, (x = 0, 0.1 and 0.25) to investigate the effect of different doping sites on the lattice parameter, cytocompatibility, hemocompatibility and antibacterial efficacy. Phase analysis has confirmed Zn substitution in Ca site and incorporation in OH channels of HA. Zn doping in Ca site of HA up to the level 2.5% shows cytocompatibility and no cytotoxic effects have been found after altering the doping site and incorporating Zn in the OH channel. Zn substitution either in Ca site or incorporation in OH channel in improving the antibacterial efficacy of HA has been confirmed against E. coli, and S. aureus. The antibacterial test reveals that Zn doped HA shows antibacterial efficiency only when Zn is substituted in Ca site of HA, which can be attributed to restricted Zn+2 leaching (∼5.28 ppb) when Zn is incorporated in OH channels of HA. But, when Zn is substituted in Ca site of HA, Zn+2 leaching increases to ∼413 ppb (confirmed by inductively coupled plasma-mass spectrometry). Thus, site specific doping of Zn in hydroxyapatites can serve as potential bioceramic for bone implant applications with tailored biological properties and controlled antibacterial efficiency depending on the doping site.

Respiratory infections by RNA viruses are one of the major burdens upon global health and economy. Viruses like influenza or coronaviruses can be transmitted through respiratory droplets or contaminated surfaces. An effective antiviral coating can decrease the viability of the virus particles in the outside environment significantly, hence reducing their transmission rate. In this work, we have screened a series of nanoparticles and their composites for antiviral activity using Nano Luciferase based highly sensitive influenza A reporter virus. Using this screening system, we have identified copper-graphene (Cu-Gr) nanocomposite shows strong antiviral activity. Extensive material and biological characterization of the nanocomposite suggested a unique metal oxide embedded graphene sheet architecture that can inactivate the virion particles only within 30 minutes of pre-incubation and subsequently interferes with the entry of these virion particles into the host cell. This ultimately results in reduced viral gene expression, replication and production of progeny virus particles, slowing down the overall pace of progression of infection. Using PVA as a capping agent, we have been able to generate a Cu-Gr nanocomposite based highly transparent coating that retains its original antiviral activity in the solid form.

The tensile behaviour of austenitic stainless steel after cryorolling and subsequent annealing has been reported. The defect structures generated during cryorolling, lead to the formation of alpha' and epsilon-martensite. Subsequent annealing leads to the formation of refined austenitic grains surrounded by martensitic islands. These martensitic islands consist of alpha' phase only. The dislocation-martensite interaction leads to discontinuous yielding for high Ultimate Tensile Strength (UTS)/Yield Strength (YS) ratio. In case of annealing at 923 K (650 degrees C) for 10 min after 30% cryorolling leads to nearly 30% untransformed martensite whereas only 7% martensite remains after annealing for 1 h. The effect of remnant martensite on tensile behaviour leading to yield plateau has been discussed in this work. It can be noticed that sample with 20% cryo rolling and annealed at 650 degrees C for 1 h shows higher YS (721 MPa) with YS/UTS ratio of 0.79 and similar to 18% uniform elongation. Sample with 30% cryo rolling and annealed at 650 degrees C for 1 h shows YS of 305 MPa with YS/UTS ratio of 0.27 and uniform elongation of similar to 24%. Therefore, 20% cryo rolled and annealed at 650 degrees C for 1 h has the best combination of mechanical properties.

In this study, dispersion of tungsten carbide on AISI 304 stainless steel substrate has been carried out by laser melting of the sand blasted substrate using a 5 kW continuous wave (CW) Nd:YAG laser (with the beam diameter of 3 mm) with an output power ranging from 1.5–2 kW, and scan speed varying from 12 to 16 mm s−1 and simultaneous feeding of premixed WC + Co powders in the ratio (wt) of 1:4 (with a flow rate of 10 mg s−1). The microstructure of the composite zone is dendritic or cellular in morphology and consists of nano-tungsten carbide (both WC and W2C) and M23C6 precipitates. There is an enhancement in hardness due to carbide dispersion from 220 VHN of the as-received substrate to 290–400 VHN. The wear resistance is improved significantly with a maximum enhancement observed in the sample processed with an applied power of 2 kW and a scan speed of 12 mm s−1. The corrosion rate in a 3.56 wt% NaCl solution is significantly reduced due to laser processing in most samples except when processed with 2.5 kW applied power and 12 mm s−1 scan speed. However, pitting corrosion resistance is found to be improved (shifting of Epit towards noble direction) for the sample processed with an applied power of 2 kW and a scan speed of 12 mm s−1.

The effective thermal conductivity of a composite coating depends on intrinsic thermal conductivity of the constituent phases, its characteristics (size, shape) and volume fraction of porosities. The present study concerns studying the effect of CoNiCrAlY and Al 2 O 3 content on the coefficient of thermal expansion and thermal conductivity of the YSZ (YSZ-CoNiCrAlY and YSZ-Al 2 O 3 ) based composite coatings developed by thermal spray deposition technique. The coefficient of thermal expansion and thermal conductivity of the composite coatings were measured by push rod dilatometer and laser flash techniques, respectively, from room temperature to 1000 °C. Variation in density, porosity, coefficient of thermal expansion, and thermal conductivity was observed in the composite coatings with the addition of different volume fraction of CoNiCrAlY and Al 2 O 3 powders in YSZ-CoNiCrAlY and YSZ-Al 2 O 3 composites, respectively. Comparison between the theoretical and experimental thermal conductivities showed a mismatch varying from 4% to 58% for YSZ-CoNiCrAlY composite coatings and from 58% to 80% for YSZ-Al 2 O 3 composite coatings. Model based analyses were used to understand the mechanism of thermal conductivity reduction in the composite coatings. It was concluded that the morphology of porosities varied with composition.

Copper-doped hydroxyapatite (HA) of nominal composition Ca10(PO4)6[Cux(OH)2-2xOx] (0.0 &le, x &le, 0.8) was prepared by solid-state and wet chemical processing to explore the impact of the synthesis route and mode of crystal chemical incorporation of copper on the antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) strains. Apatites prepared by solid-state reaction showed unit cell volume dilation from 527.17 &Aring, 3 for copper-free HA to 533.31 &Aring, 3 for material of the putative composition Ca10(PO4)6[Cu0.8(OH)0.4O0.8] consistent with Cu+ insertion into the [001] hydroxyapatite channel. This was less pronounced (528.30 &Aring, 3 to 529.3 &Aring, 3) in the corresponding wet chemical synthesised products, suggesting less complete Cu tunnel incorporation and partial tenancy of Cu in place of calcium. X-ray absorption spectroscopy suggests fast quenching is necessary to prevent oxidation of Cu+ to Cu2+. Raman spectroscopy revealed an absorption band at 630 cm&minus, 1 characteristic of symmetric O-Cu+-O units tenanted in the apatite channel while solid-state 31P magic-angle-spinning nuclear magnetic resonance (MAS NMR) supported a vacancy-Cu+ substitution model within the apatite channel. The copper doping strategy increases antibacterial efficiency by 25% to 55% compared to undoped HA, with the finer particle sizes and greater specific surface areas of the wet chemical material demonstrating superior efficacy.

This study aims at the development of composite surface on austenitic stainless (AISI 304 stainless steel) by laser surface alloying with WC and Co in the weight ratio of 4:1. Laser processing has been carried out by laser melting of sandblasted AISI 304SS using a 5 kW continuous-wave Nd: YAG laser having a beam diameter of 3 mm and simultaneous addition of powder (WC and Co in the ratio of 4:1) at a rate of 10 mg/sec using He as shroud (at a flow rate of 6 l/min) in the melted surface. The process parameters are applied power (1.75–2 kW) and scan speed (12–30 mm/sec) with a powder feed rate of 10 mg/s. The laser-treated surface has been subjected to microstructural investigation and wear resistance (fretting wear behaviour) testing. There is formation of different carbides (WC, W2C, Fe7C3, Cr23C6, Fe6W6C, and Co6W6C) in the gamma matrix of the treated zone. The microhardness of composite surface is significantly higher (980 VHN) than that of AISI 304SS (242 VHN). The fretting wear kinetics and coefficient of friction (COF) of the composite surface are reduced as compared to the substrate. The mechanism of wear has been established.

In this study, the role of 5 and 10 vol% TiC addition on densification, microstructure, phase evolution and mechanical properties of ZrB2–20 vol% SiC composite has been investigated maintaining the volume fraction of SiC constant. It is found that TiC addition reduces the spark plasma sintering (SPS) temperature from 1900 °C to 1700 °C producing in a nearly fully dense (∼99.6% theoretical density) material and forming (Zr,Ti)B2, a mixed compound of Zr and Ti. The lattice parameters (c and a) of (Zr,Ti)B2 are found to lie between that of pure ZrB2 and TiB2 with its c/a ratio varying inversely with the extent of TiC addition. Phase and microstructure analyses reveal that, while the entire amount of TiC dissolves in ZrB2 in the ZrB2–20SiC–5TiC (vol%), undissolved TiC exist in the ZrB2–20SiC–10TiC (vol%) composite after sintering indicating that the solubility limit of TiC in sintered ZrB2 lies in between 5 and 10 vol%. The elastic modulus values of the TiC added composites predicted by model based calculation agree well with the values experimentally determined by nano-indentation suggesting that these sintered composites are highly dense and nearly defect-free. The calculated residual stress of the matrix phase (using appropriate analytical models) was found to be tensile in nature but decreasing with increase in TiC addition. The residual stress of the reinforcement phase manifests similar trend but is compressive in nature. Compared to the conventional ZrB2–20SiC (vol%) composite, TiC added composites record better bulk and nano-mechanical properties (e.g., hardness, indentation fracture toughness, flexural strength, stiffness and elastic modulus) at ambient temperature indicating that the ZrB2–SiC–TiC system is a more promising ultrahigh temperature ceramics than the base composite.

The present study aims at a detailed evaluation of mechanical, tribological, and high temperature oxidation resistance (at 1000 °C under isothermal condition) properties of YSZ, and Al 2 O 3 based thin films developed by pulsed laser deposition technique. The mechanical and tribological properties of YSZ and Al 2 O 3 thin films showed significant improvement with increasing the deposition temperature during pulsed laser deposition process. The kinetics of oxidation was reduced due to pulsed laser deposition and Al 2 O 3 coating offered a superior oxidation resistance property as compared to YSZ coating. However, the deposition temperature has no significant effect in reducing the TGO growth rate of the pulsed laser deposited thin films.

In this work, laser engineered net shaping (LENS™) technique was used to create SiC reinforced titanium matrix composite (TMC) on titanium surface. These composite coatings developed by injecting SiC powder into titanium melt pool, created using a high-power laser. The laser parameters strongly influenced the dissolution of SiC particles leading to formation of TiSi2, Ti5Si3, and TiC phases along with residual SiC in the composite layers. A graded microstructure, with high concentration of secondary phases on top compared to the bottom region was formed. The reinforcing ceramic phases in the TMC coatings enhanced the wear resistance of titanium by about 100 times. The wear resistance of the composite coatings in physiological environment found to increase with increase in the laser power and concentration of SiC particles injected into the melt pool. These composite coatings also showed better corrosion resistance than Ti. In vitro biocompatibility studies performed using osteoblast (MG63) and fibroblast cells (NIH3T3) demonstrated non-toxic nature of these composite coatings. It is envisioned that such coatings may find applications in articulating surfaces of load-bearing implants to enhance their in vivo lifetime with reduced metal ion release. Keywords: Laser processing, Composite coatings, Wear resistance, Biocompatibility

Magnetic nanofluids, commonly known as ferrofluids, containing surfactant coated magnetite nanoparticles (having mean size ∼11 nm) uniformly dispersed in water are synthesized by chemical co-precipitation method. The rheological properties of magnetic nanofluid at different concentrations of nanoparticle loading have been investigated by varying different parameters including the magnetic field strength. Shear thinning is observed in the non-Newtonian magnetic nanofluids under the application of magnetic field. The observed increase in yield stress (calculated by fitting the Herschel and Bulkley model) with the applied magnetic field and concentration of dispersed nanoparticles confirm the formation of large aggregates that restrict or prohibit the flow characteristics of the otherwise Newtonian magnetic nanofluid. The hysteresis observed during the application and withdrawal of magnetic field suggests that the chain or column like structures fail to relax within the allowed measurement time interval.

The present investigation focusses on the rewetting of a vertical tube bottom flooded by alumina dispersed water nanofluids. Emphasis is on the estimation of the apparent rewetting temperature and most importantly the construction of boiling curve from the temperature–time responses recorded during the rewetting phenomenon. The boiling curves provide an insight into the different regimes of boiling under flow conditions. Rewetting in nanofluids takes place faster than water. Rewetting in general, depends on coolant inlet velocity, initial wall temperature and axial location of the tube from the inlet. For nanofluids, it also depends on the concentration of nanoparticles. An earlier rewetting and an enhanced maximum heat flux exhibited by nanofluids can be attributed to the deposition of nanoparticles which results in the formation of several micro-cavities. This in turn alters the surface wettability and roughness, thereby inducing an enhanced rate of heat transfer and an earlier collapse of vapor film. The deposition of nanoparticles and its morphology, confirmed from microscopic and spectroscopic analysis, supports this conjecture.