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The effect of phosphorus in the form of Fe3P (up to 3%) on the sintering behavior and mechanical properties of sintered ferritic stainless steel (434L) was investigated. The Fe3P and 434L powder mixtures were cold compacted using single action uniaxial pressing under 600 MPa pressure and sintered in the solid state and super solidus liquid state at 1100 and 1300 °C, respectively, under a (95% N2 and 5% H2) atmosphere. The density, hardness, yield strength, ultimate tensile strength and tensile rupture strength improved by 5%, 18%, 24%, 19% and 27%, respectively, and the rate of corrosion reduced by 1.64 times for 434L mixed with 3% Fe3P.

In the present investigation, the evolution of microstructure and microtexture of pure copper powder during solid state sintering was studied. The powder was compacted using 300 MPa uniaxial die pressure, and the green compact was sintered in an electric furnace at 610 °C, 880 °C, and 1020 °C in hydrogen atmosphere. The temperatures were selected to obtain different dominant densification processes comprised of grain boundary diffusion, surface diffusion, and volume diffusion, respectively. Electron backscatter diffraction (EBSD) studies indicated that there is a distinct evolution of microtexture and microstructure in terms of evolution of grain boundary character distribution (GBCD), size, shape, and morphology of grains and pores. The sample sintered at 610 °C showed poor densification and mechanical properties along with weak random microtexture. However, the sample sintered at 1020 °C showed relatively stronger 〈101〉 fiber texture, better strength, and better hardness. In addition, that sample exhibited a lower fraction of Σ3 twin and high-angle grain boundaries in comparison to samples sintered at lower sintering temperatures. This is attributed to high sintering temperature stimulated bulk diffusion that facilitated migration of grain boundaries and elimination of pores. A detailed analysis of microstructure and grain boundary character indicated the possibility of attempting grain boundary engineering during sintering for optimum processing and property enhancement.

The present study compares the mechanical properties and electrochemical behaviour of austenitic (AISI 316 L) stainless steel compacted at different pressures (200, 400 and 600 MPa), which are conventionally sintered at supersolidus temperature of 1,400°C. As expected, increase in compaction pressure (from 200 MPa) to 600 MPa has shown decreased shrinkage (from 7.3% to 4.2% radial and 5.5% to 3.4% axial, respectively) and increased densification (up to ~92%). Their electrochemical behaviour was investigated in 0.1 N H2SO4 solution by potentiodynamic polarization and electrochemical impedance spectroscopy. The mechanical properties (such as yield-, tensile- and transverse rupture strength) and electrochemical behaviour with pressure have been correlated with densification response and microstructure (pore type, volume and morphology). Highest densification (~92% theoretical) achieved at 600 MPa (compaction pressure) and 1,400°C (sintering temperature) resulted in excellent combination of tensile strength and ductility (456 ± 40 MPa and 25 ± 1.1% respectively), while showing lowest corrosion rate (0.1 mmpy or 4.7 mpy) due to the presence of isolated porosity in the sintered samples.

In the present work, 6061Al-TiB2 composites were synthesized using two types of base 6061Al powder (prealloyed and premixed) through powder metallurgy route. Dry sliding wear test was performed on the specimens using pin on disk apparatus to investigate the effect of TiB2 content on tribological characteristics. The microstructure, worn surface, and subsurface were also characterized using scanning electron microscope to examine the wear mechanism of prealloyed- and premixed-based composites. A mathematical model was developed using parameters (composition and applied load) to predict wear rate and correlated with experimental results. Adequacy of developed model has been validated using analysis of variance. Results indicated that premixed 6061Al-TiB2 composites have superior tribological properties as compared to the prealloyed 6061Al-TiB2 composite.

Tungsten–copper composites exhibit excellent resistance to erosion and good electrical as well as thermal conductivity. W–Cu composites are mainly used for heat sinks, electrical contacts and trans...

In the present study, Al6061-based alloy and composites were produced using powder metallurgy route. Two different kinds of base powders (prealloyed and premixed 6061Al alloy) were mixed with TiB2 particles in compositions ranging from 0 to 15 vol.%, respectively. The processed powders were compacted at 300 MPa and sintered at 620 °C under N2 atmosphere. The microstructural evolution of prealloyed and premixed 6061Al alloy, at different stages of sintering cycle, was studied using scanning electron microscope and EDS analysis. A comparative study was done between prealloyed- and premixed-based composites on the basis of densification, microstructure, hardness, transverse rupture strength and electrical conductivity as a function of TiB2 content. Results indicated that premixed-based composites have better mechanical properties than prealloyed-based composites.

The present work aims to the study of developing porosity in hydroxyapatite (HAp) scaffold by using graphite porogen (with 0–30 vol%) followed by engineering the changes achieved by conventional- (CS) and microwave-sintering (MS) techniques. The generated porosity was controlled between ~6–27% as the porogen concentration increases in HAp scaffold. Voronoi tessellation was utilized in order to evaluate the distribution of pores. The enhanced mechanical properties including fracture toughness (0.83 MPa m 1/2 ), fracture strength (7.5 MPa), and hardness (183.7 VHN) were observed for microwave sintered HAp scaffold with 8% porosity. The fitting between porosity and fracture strength elicited that microwave sintered HAp with 8% porosity provides maximum crack-propagation resistance while restricting grain size (~0.23 µm) and eliciting high extent of sintering (~1.34) because of their rapid heating rates. The cell viability (MTT assay) and cell culture confirm the cytocompatibility of porous HAp for application as bone implant that need accelerated replacement of bone tissues.

In the present work, one batch of prealloyed 6061Al powder was mixed with different lead compositions (5, 10, 15 vol.%) and another set with same composition was ball-milled for 5 h at 300 rpm. Microstructural features such as lattice constant, crystallite size, particle size and morphology were studied using XRD, particle size analyzer and SEM. Both the as-mixed as well as ball-milled powders were compacted at 300 MPa and sintered under N2 atmosphere for 1 h in tube furnace at 590 °C. The ball milling of 6061Al alloy powder improved sinter density and densification while lead addition showed negligible influence on these parameters. The microstructure of as-mixed 6061Al–Pb alloys exhibited equiaxial morphology whereas ball-milling resulted in elongated grains with uniform lead distribution. Quasi-static compressive mechanical behavior was investigated for 6061Al–Pb alloys at 1 × 10−3 s−1 strain rate. Results indicated that ultimate compressive and yield strength were sensitive to milling and lead volume fraction.

The effect of intermetallic Ni3Al addition and heating mode on the electrochemical behavior of sintered austenitic (316L) and ferritic (434L) stainless steels is studied. The green compacts were sintered by conventional and microwave methods in solid state at 1350°C in H2 for a period of 60 min. The sintered samples were then subjected to several characterization techniques for evaluating their density and hardness, and finally their electrochemical response was evaluated through potentiodynamic polarization scan (1 mV/sec) in 0.1 N H2SO4. Upon addition of nickel aluminide, there was an increase in the densification of the composites, which was found more pronounced in case of 434L stainless steel with nickel-aluminide dispersoid composites. A positive response was also observed on the corrosion resistance of the composites as compared with the bare stainless steel compacts.

The present study examines the effect of sintering temperature and heating mode on densification, microstructure and mechanical properties of Fe-P alloys. The green compacts were heated conventionally and in microwave under 95%N2–5%H2 (forming gas) at 1120 °C and 1250 °C for 60 min. Both the compositions (Fe-1.5P and Fe-3P in wt%) were found to couple well in microwave field with rapid heating (~ 40 °C min− 1) and resulted in reduction of overall processing time by about 90% in comparison of conventional heating. Microwave sintering resulted in higher densification in case of Fe-P alloys. Moreover, an important feature of microwave and conventionally sintered samples was that their microstructures exhibited distinctly rounded pores. This resulted into improved corrosion and mechanical properties in general.

Powder metallurgical (P/M) processing has the main advantage of making near net shape products. Nowadays, in automobile industries, stainless steels have become the most promising material owing to their good corrosion resistance. In the current study, 316L and 434L stainless steel powders were sintered using microwave and conventional methods through powder metallurgy route. The effects of sintering modes on the microstructure, mechanical properties and corrosion responses of 316L and 434L stainless steel composites are investigated in detail. The results showed that the sample prepared through microwave sintering route exhibited significantly superior densification, higher hardness and better corrosion resistance as compared to the conventionally processed counterpart. On the whole, 316L composites showed better corrosion resistance than 434L stainless steels.

The present study compares the effect of Y2O3 addition and heating mode on the electrochemical response on austenitic (316L) and ferritic (434L) stainless steel during solid state sintering. Up to 12 vol.-%Y2O3 was added to 316L and 434L stainless steel. The compacts were sintered at 1350°C for 60 min. The sintered samples were characterised for their density and hardness. The effect of heating mode and Y2O3 addition on the microstructural evolution and electrochemical (corrosion) response for the microwave sintered samples are compared with conventionally sintered samples. The density of stainless steel samples sintered through the microwave sintering was higher than that of conventional sintering.

In the present investigation, the evolution of microstructure and microtexture of commercially available copper powder during solid state sintering using microwave furnace has been studied. The powder was compacted using 300 MPa uniaxial die pressure and the green compacts were sintered at 610 °C, 880 °C and 1020 °C in argon atmosphere at 20 min and 45 min isothermal holding times using multi-mode microwave furnace which has output power of 3 kW and operated at 2.45 GHz frequency. The temperatures were selected to obtain different dominant densification processes. For sintered samples comparative analysis has been made based on densification behavior, microstructural and microtexture evolution and mechanical properties. Electron backscatter diffraction (EBSD) study indicated that there is a distinct evolution of microtexture and microstructure in terms of evolution of grain boundary character distribution, misorientation, size, shape and morphology of grains and pores. Attributed to high temperature driven volume diffusion process, 1020 °C sintered samples showed better sintering between copper particles, grain growth, grain coalescence, reduction in porosity area fraction and increased pore rounding. For all microwave sintered samples, the highest fraction of CSL boundary fraction found to be Σ3 boundary with a common (111) grain boundary plane which indicated coherent twin boundaries with low energy. More Σ3 twin population is found on intermediate sintering temperature range whereas significant reduction is observed higher temperature sintering which might be the result of grain coalescence and volume diffusion at higher sintering temperature that reduced high angle grain boundaries. Microwave sintered copper samples brought random microtexture evolution with variation of sintering temperature and holding time. This might indicate the presence of non-conventional sintering mechanisms during microwave sintering.

The powder characteristics of metallic powders play a key role during sintering. Densification and mechanical properties were also influenced by it. The current study examines the effect of heating mode on densification, microstructure, phase compositions and properties of Fe, Fe–2Cu and Fe–2Cu–0·8C systems. The compacts were heated in 2·45 GHz microwave sintering furnaces under forming gas (95%N2–5%H2) at 1120 °C for 60 min. Results of densification, mechanical properties and microstructural development of the microwave-sintered samples were reported and critically analysed in terms of various powder processing steps.

In recent years, microwave processing has gained wide acceptance as a novel method for sintering metal powders. As compared to conventional sintering, microwave sintering provides rapid and volumetric heating involving conversion of electromagnetic energy into thermal energy within the material. This results in finer microstructures, thereby providing improved mechanical properties and quality of the products. This study examines the dependence of densification, microstructure and mechanical properties on the heating mode of Fe–2%Cu and Fe–2%Cu–0·8%C. The powdered compacts were sintered in conventional (radiation mode) and microwave (2·45 GHz, multimode) furnaces at 1120°C in 90N2–10H2 atmosphere, and comparative analysis of the properties was investigated.

The redistribution of carbon during partitioning between retained austenite and bainitic ferrite decides the stability of the retained austenite. The martensitic start temperature (MS) based on the carbon enriched retained austenite is observed to be the deciding factor for the volume fraction of the constituent phases obtained on isothermal bainitic transformation. The volume fraction of the phases is also calculated on the basis of metastable equi-free energy (T0) curve. A good agreement is found between experimentally and theoretically calculated fractions of the phases. The isothermal holding temperature and time, the fraction of phases based on initial carbon content of the steel and MS temperatures have a close relation with the optimum mechanical properties of bainitic steels.

The present study compares the densification response and the mechanical and electrochemical behavior of austenitic (AISI 316L) stainless steel conventionally sintered in solid state (1200 and 1300 °C) and supersolidus (1400 °C) state. The densification increased with temperature and the overall performance of austenitic stainless steel (AISI 316L) was significantly improved with supersolidus (1400 °C) state sintering. A detailed correlation has been drawn between the processing parameters, the evolved microstructure and the resulting properties.

Densification behaviour, phase transformation, microstructural evolution and hardness values of microwave sintered Al–7Zn–2·5Mg–1Cu (7775) aluminum alloy were investigated and compared with conventionally sintered samples. Microwave sintering was performed in 2·45 GHz multimode microwave furnace at temperatures ranging from 570–630 °C. Microwave sintering at a heating rate of as high as 22°C/min resulted in ~55% reduction of processing time as compared to conventional sintering. A lower sintered density observed in the case of microwave processed samples was attributed to the inhomogeneity in microstructure and phase distribution. The X-ray diffraction results of conventionally sintered samples showed the presence of MgZn2, Mg2Zn11 and CuMgAl2, while only MgZn2 and CuMgAl2 phases were found in the case of microwave sintered samples and in lesser amount. Higher hardness and high standard deviation values were noticed for microwave sintered samples as compared to conventional counterparts.

Microwave sintering has been a well-established technique to consolidate metal powders due to its instantaneous volumetric and rapid heating as compared to conventional heating. Al-3.8Cu-1Mg-0.8Si-0.3Sn (2712) alloy powders were compacted (200 and 400 MPa) and microwave sintered at different temperatures (570 to 630 degrees C) under different atmospheres (vacuum, N2, Ar and H2). Increasing sintering temperature enhanced sintered density from 91% to 98%. Sintering under vacuum at 590 degrees C was more efficient with a densification parameter of 0.36 followed by N2, Ar and H2. Regardless of the sintering condition, phase analysis via XRD revealed the presence of only alpha-Al peak attributed to lesser time available for diffusion of alloying elements. In addition, microstructural inhomogeneity leading to more intergranular melt formation was observed for all sintered compacts. Contrasting to densification, sintering in N2 resulted in better corrosion resistance.

The present study investigates the effect of compaction pressure and sintering temperature on densification response and mechanical properties of the Al–3.8Cu–1Mg–0.8Si–0.3Sn (2712) alloy. The compacts were pressed at 200 and 400 MPa and sintered at temperatures ranging from 570–630°C in vacuum (10−6 Torr). The objective of the present work is to obtain an optimum sintering conditions for achieving higher sintered densities and mechanical properties. The effect of sintering temperature is evaluated by measuring the sintered density, densification parameter, microstructure, phase changes and mechanical properties. While a higher sintering temperature results in densification enhancement, it also leads to microstructural coarsening. Significant improvement in mechanical properties is obtained through age-hardening of sintered alloy under various ageing conditions (T4, T6 and T8).

Effect of heating mode and sintering temperature on sinterability and properties of the 6711 (Al–1Mg–0.8Si–0.25Cu) alloy was investigated. Alloy compacts were consolidated in conventional and microwave furnace at 570, 590, 610 and 630 °C under vacuum (10−6 torr). Microwaves coupled with the compacts and resulted in ∼58% reduction in processing time along with higher heating rates when compared to conventional sintering. However rapid heating rate resulted in inhomogeneous microstructure with larger melt fraction at grain boundaries. XRD analysis showed absence of intermetallics due to insufficient time for diffusion. With increasing sintering temperature, all compacts did undergo supersolidus liquid phase sintering (SLPS), accordingly higher densification and shrinkage was observed. The electrical conductivity and hardness followed similar trend as sintered density in both modes. Alloy compact sintered at 630 °C resulted in significant improvement of mechanical properties (TRS: 57%↑; UTS: 27%↑and ductility: 41%↑) in conventional mode. Age hardening treatment under T6 temper enhanced the tensile strength by 136% with drastic reduction in ductility as compared with sintered compacts.

The current study examines the effect of sintering atmosphere and heating mode on the densification, microstructure, phase analysis and properties of Al–1Mg–0?8Si–0?25Cu (6711) and Al–7Zn–2?5Mg–1Cu (7775) alloys. The compacts were heated in conventional and 2?45 GHz microwave sintering furnaces under vacuum, N2, Ar and H2 at 630uC. Both alloy compacts coupled well with microwaves and underwent rapid heating (y22uC min 21 ). The overall processing time was reduced to about 55–58% through microwave sintering. Microwave sintering resulted in greater densification for 6711 alloy under vacuum followed by N2. In contrast, 7775 alloy resulted in poor densification under all atmospheres as compared with conventional sintering. For all compositions and atmospheres, microwave sintering resulted in microstructural inhomogeneity with the absence/presence of a lower amount of intermetallic phases. This has been correlated with lesser time available for the diffusion of alloying elements into the Al matrix. The conductivity, hardness and corrosion properties of both compacts improved depending upon heating mode and atmosphere.

Brazing is a widely used process to improve the performance of steels used in automotive applications. The substrate material is often exposed to harsh conditions in these applications and may affect the service life of the component. Reactive boride brazing aims to improve the mechanical properties of the substrate material by forming a ceramic-metal composite coating in a single-step process in situ. In this study, sintered Ancor 4300 low-alloy steel is used as the substrate with chromium-rich braze and chromium-lean braze materials. The mechanical properties of the brazed samples were studied in detail using microindentation hardness measurements and the transverse rupture test. The results indicate that the brazed superlayer has a 10 times higher hardness. There was a significant improvement in the transverse rupture strength of the steel brazed with the chromium-rich boride as compared to the pure substrate material. In an effort to reduce processing time, green compacts of the substrate were also directly brazed and yielded favorable results.

Reaction sinter bonding is a process that aims to bond two materials for improvement in properties through reactive sintering technique. The process has been effectively used to sinter hard materials like borides in situ which not only possess excellent oxidation resistance, good corrosion resistance but also resistant to abrasive wear. Sinter bonding is a unique surface modification process achieved through powder metallurgy and is competent with other techniques like boronizing sintering and sinter-brazing since it eliminates the additional operations of heat treatment and assembly and removes the inherent setbacks with these processes. This study focuses on identifying the phase evolution mechanism using characterization tools like x-ray diffractometry and energy dispersive spectroscopy and study of sinter bonding of the boron containing precursors (Mo-Cr-Fe-Ni-FeB-MoB) onto plain carbon steel. A microstructure containing Fe-based matrix dispersed with complex borides develops with temperature in the tape cast sheets. A fivefold increase in hardness between plain carbon steel in wrought condition and sinter bonded steel was observed. The multilayer consisted of a reaction zone adjacent to the interface and was investigated with the composition profile and hardness measurements. A model of sinter bonding between the cermet and the steel has also been proposed.

In ferrous powder metallurgy, copper and graphite are used as common alloying elements. Copper melts at low temperature compared to iron and forms liquid which promote interparticle bond formation. However, it also results in compact swelling. To negate this, graphite is used as an additive. This study examines the influence of copper and graphite addition on the densification, dimensional changes, and mechanical properties of iron compacts sintered at 1120°C. These properties have been correlated with the microstructure.

The present study compares the sintering response of 90W–7Ni–3Fe alloys consolidated in a 2.45 GHz microwave furnace and a conventional furnace. The W–Ni–Fe compacts were sintered in a temperature range of 1200–1500 °C corresponding to solid-state as well as liquid phase sintering. The compacts were successfully sintered in a microwave furnace with about 80% reduction in the overall processing time. For both the heating modes, the W–Ni–Fe alloys exhibited significant densification prior to melt formation through solid-state sintering. The in situ dilatometric studies revealed that the contribution to densification from solid-state sintering is higher at lower heating rates. In comparison to conventional sintering, microwave sintered compacts showed relatively refined microstructure and higher hardness and flexural strength.

Tungsten based composites such as W–Cu have been widely used as electrical contacts, especially in heavy duty applications and as spark erosion electrodes. The lack of solubility between tungsten and copper makes it very difficult to achieve full densification through liquid phase sintering. Higher sintering temperatures or longer holding times always help to improve the densification but Cu may leach out from the skeleton which leads to Cu segregation and results in non-homogeneous microstructure and poor product performance. Microwave heating has been increasingly gaining popularity in the field of sintering of particulate materials. As compared to conventional heating, microwave heating is more rapid resulting in substantial reduction in the overall sintering time. In addition to the energy efficiency, the faster heating rate achieved in microwave furnaces minimises microstructural coarsening and improves homogeneity. This study examines the effect of heating mode (conventional and microwave) and temperature on the consolidation of specially prepared commercial W–Cu powder. Near theoretical density has been achieved under optimum conditions in microwave sintering. The bulk hardness and electrical conductivity of the samples sintered by two methods have been determined and the data compared.

The present study investigates the possibility of consolidating premixed 90W–7Ni–3Cu alloy – designated as 90W–PM (Ni–Cu) – through microwave sintering. An attempt has been made to compare the results between microwave and conventionally sintered samples. This study also compares the sintering behavior of 90W–7Ni–3Cu with prealloyed 90W–PA (Ni–Cu) in both conventional as well as microwave furnace at various temperatures. The comparative analysis is based on the sintered density, densification parameter, hardness and microstructures of the samples. The present investigation also includes the variation of matrix composition as a function of temperature by EPMA analysis. The results show that microwave sintering requires about 75% less processing time than required by conventional method and still provides better physical and mechanical properties.

Microwave heating is recognized for its various advantages, such as time and energy saving, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved properties. The present paper investigates the feasibility of consolidating tungsten powders through microwave sintering. A comparative analysis has also been attempted between the sintering response of pure tungsten powder compact in a microwave and conventional furnace.

Powders with a composition of 85W–15Cu (wt-%) were prepared by mixing, milling and mechanical alloying of W and Cu powders and electroless Cu coating onto W powder. Sinterability was improved by mechanical alloying and coating. The improvement due to mechanical alloying comes from a reduced particle size, assisted by activated sintering from transition element contamination in milling. Coating improved the copper dispersion, packing densities and led to a microstructure having reduced number of W–W particle contacts after compaction. Accordingly, rearrangement on liquid formation resulted in improved densification. Since copper wetting on tungsten is sensitive to oxygen contamination, coated powders ensure liquid copper dispersion throughout the compact without concern over wetting and liquid flow during liquid phase sintering.

The present study compares the corrosion behavior of Al-Sn, Al-Si and Al-Sn-Si alloys processed by spray forming with that of the conventional chill cast ones in aqueous 0.1 N NaCl solution. Spray forming resulted in finer microstructural features with uniform distribution of second-phase particles. The spray formed Al-Si samples showed improved corrosion resistance as compared to the chill cast ones. The Sn containing alloys showed inferior corrosion resistance in the neutral electrolyte. The addition of 12.5 wt.% Si to Al-Sn alloys improves the corrosion resistance.

The present study investigates the effect of varying particle size and porosity on the heating behavior of a metallic particulate compact in a 2.45GHz multimode microwave furnace. Experiments on copper suggest that unlike monolithic (bulk) materials, metallic materials do couple with microwaves when they are in particulate form. The powder compacts having higher porosity and smaller particle sizes interact more effectively with microwaves and are heated more rapidly. A dynamic electromagnetic-thermal model was developed to simulate the temporal temperature distribution using a 2-D finite difference time domain (FDTD) approach. The model predicts the variation in temperature with time during heating of copper powder compacts. The simulated heating profiles correlate well with those observed from experiments.

The present study compares the effect of SiC reinforcement on densification and properties of supersolidus liquid phase sintered 6711Al-SiC composites. The prealloyed 6711 powders were mixed with SiC ranging from 5 to 20 vol.%, compacted at 400 MPa and sintered at 630?C under vacuum. It was shown that better densification, yield strength, wear and corrosion resistance were achieved up to 10 vol.% due to uniform distribution of SiC particles throughout matrix. Beyond 10 vol.%, SiC resulted in clustering and had detrimental effect on densification and mechanical properties. Age hardening of 6711-10SiC composites led to improvement in mechanical properties.

The present study compares the temperature distribution within cylindrical samples heated in microwave furnace with those achieved in radiatively-heated (conventional) furnace. Using a two-dimensional finite difference approach the thermal profiles were simulated for cylinders of varying radii (0.65, 6.5, and 65 cm) and physical properties. The influence of susceptor-assisted microwave heating was also modeled for the same. The simulation results reveal differences in the heating behavior of samples in microwaves. The efficacy of microwave heating depends on the sample size and its thermal conductivity.

Materials requiring improved resistance to wear have been researched in coatings as well as in bulk form. A new process that aims to produce a wear resistant surface through powder metallurgy exists. The process brazes a green tape containing a reactive mixture of Mo, Fe, Cr, MoB and FeB and which produces a microstructure of hard complex borides dispersed in a soft metallic matrix, onto a compatible metallic substrate. Hence the process is called as “Braze-bonding”. In the process the phenomena of coating densification, microstructure development and interface development occur simultaneously. The resultant hard layer is evaluated for performance under sliding wear, erosive wear and abrasive wear conditions. It has been found that the coating is competitive to other hard materials. The process has inherent advantages like applying the coating in situ and easily allows for varying the thickness of the coated layer. A diffusion driven interface between coating and substrate improves bond strength. Complex borides of more than 50 vol.% dispersed in a Fe based ductile matrix help in abating wear through different mechanisms, which have been discussed here. The braze coatings can be used for applications involving wear resistance like pump impeller parts, machining tools, and injection molding screws.

The present work investigates the effect of supersolidus sintering and intermetallics (Ni3Al, Fe3Al) additions on the densification, mechanical, tribological, and electrochemical behavior of sintered austenitic (316L) stainless steels. The performances of the supersolidus liquid phase sintered (SLPS) compacts are compared with the conventional solid-state sintered (SSS) compacts of similar compositions. Correspondingly, the sintering was carried out at two different temperatures 1200 °C (SSS) and 1400 °C (SLPS). Supersolidus sintering results in significant improvement in densification, wear resistance, corrosion resistance, strength, and ductility in both straight as well as aluminide added composites.

This study investigates the effect of gas flow rates of air, nitrogen and argon on the synthesis of silica nano-powders in a diffusion flame reactor. The silica powders were prepared by high temperature oxidation of tetraethyl-ortho silicate (TEOS) in a three-port diffusion flame burner. The present configuration resulted in synthesis of silica powders in the range of 45 to 69 nm. The characteristics of the burner design in terms of flame height and temperature have been extensively investigated over a wide range of flow conditions of the fuel (H2), oxidizer (air), and the carrier gas (N2) and correlated to the resultant silica powder size. The flame height decreases with increase in air and nitrogen flow rate. It is found out that the fuel–air mixing plays an important role in controlling the particle size as it affects the flame temperature. Increasing the flow rate of nitrogen or air increases the silica size while an increase in fuel flow rate results in slight reduction in the particle size.

The present study examines the effect of aluminide (Ni3Al, Fe3Al) additions on the sintering behavior of ferritic 434L stainless steels during solid-state sintering (SSS) and supersolidus liquid-phase sintering (SLPS). 434L stainless steel matrix composites containing 5 and 10 wt pct of each aluminide were consolidated at 1200 °C (SSS) and 1400 °C (SLPS). The effects of sintering and aluminide additions on the densification, microstructural evolution, mechanical, tribological, and corrosion behavior of sintered ferritic (434L) stainless steels were investigated. The performances of the 434L-aluminide composites were compared with the straight 434L stainless steels processed at similar conditions. Supersolidus sintering resulted in significant improvement in densification, mechanical, wear, and corrosion resistance in both straight 434L and 434L-aluminide composites. Fe3Al additions to 434L stainless steels result in improved wear resistance without significant degradation of corrosion resistance in 3.56 wt pct NaCl solution.

The present study investigates the effect of yttrium aluminium garnet (YAG) addition on the densification, mechanical, tribological and corrosion behaviour of ferritic (434L) stainless steels. The composites were sintered at both solid-state (1200 °C) and supersolidus (1400 °C) sintering conditions. Supersolidus sintering results in superior densification, hardness and corrosion resistance of both straight 434L stainless steel as well as YAG reinforced 434L stainless steels. The addition of YAG to 434L stainless steels at supersolidus sintered conditions improves the strength and wear resistance of 434L stainless steels without significantly degrading the corrosion performance.

An innovative powder metallurgy based technique has been investigated to fabricate multilayer tapes having configurations Ni/Ni–5 at.% W and Ni/Ni–5 at.% W/Ni for use as mechanically strong and textured substrates for coated superconductor applications. Development of cube texture ({0 0 1}〈1 0 0〉) following heavy cold rolling (∼95%) and annealing has been studied in the Ni side(s) of these multilayer tapes and this has been compared to a monolithic Ni tape. The deformation textures in the Ni side(s) of the tapes are found to be quite similar to that of monolithic Ni strained to similar level of deformation. However, the cube texture upon annealing has been found to be significantly stronger in the Ni side(s) of the multilayer tapes as compared to the monolithic Ni tape after different annealing treatments. Cross-sectional EDS analyses in form of X-ray area mapping of the multilayer tapes reveal significant diffusion of W from the alloy side to the Ni side(s). All these facts amply demonstrate the beneficial role of the alloying element W on the development of cube texture in Ni. Finally, the mechanical properties of the multilayer tapes have been evaluated to ascertain their suitability in the actual application scenario.

Materials with high thermal conductivity and thermal expansion coefficient matching with that of GaAs are being used for packaging high-density microwave integrated circuits (MICs) due to their ability of faster heat dissipation. Powder metallurgy (P/M) has emerged as a promising technique for the processing of metal matrix composites (MMCs) in satellite applications such as thermal management materials. Individual components in these composites must retain their metallurgical identity. The present study investigates the processing of silvar (Fe-Ni-Co-Ag) alloys for thermal management materials. For these silvar alloys, composition was varied by varying the silver content from 15 to 35 wt.%. The compacts were pressed at 400 and 600 MPa and sintered/infiltrated at 1100degC, 1150degC,and 1225degC. Quantitative metallographic measurements were performed on all sample and the results were discussed. It was observed that all samples were sintered without any shape distortion. Microstructural evaluation reveals that higher compaction pressure resulted in highly contiguous structure. In spite of density differences between constituents, none of the alloys showed segregation. Coefficient of thermal expansion (CTE) values of the liquid phase sintered composites is near to the values obtained by rule of mixtures.

In recent years, sintered stainless steel with carbon addition has been proposed for potential use as exhaust flanges in automotive applications. The net-shaping requirements for such applications necessitate the use of powder metallurgical (P/M) processing route. However, due to the presence of porosity, most sintered steels have poor corrosion resistance. The present study compares the effect of sintering temperature, heating mode and graphite addition (up to 1.5%) on the densification and electrochemical response of both ferritic (434L) and austenitic (316L) stainless steels. The compacts were sintered in both conventional (radiatively heated) as well as microwave furnace. As compared to conventional sintering, samples consolidated in microwaves have higher densification (particularly at 1200°C) and exhibit better corrosion properties.

The present study investigates the effect of sintering temperature on the electrochemical response of ferritic (434L) stainless steels determined through potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) studies. To understand the corrosion mechanism, the EIS was done at open circuit potential (OCP), passive region (500mV) and near breakdown potential region of polarization curve of 434L stainless steel. The compacts sintered at higher temperature (1400°C) exhibit better corrosion resistance. To explain the EIS results, an electrical circuit has been conceptualized at open circuit potential (OCP) that indicates the presence of two time constants. This can be attributed to the presence of Electrical Double Layer (EDL) and formation of a protective passive during corrosion. EIS results on compacts done at 500mV shows only one time constant which suggests nearly complete passivation of the surface due to the formation of passive film.

Problems in the synthesis of phase-pure BiFeO 3 , a multiferroic material, are well known and presence of other phases often leads to inferior properties. Work reported here was carried out to obtain pure phase BiFeO 3 via a solid-state-reaction method in both pure and Sm-doped form. X-ray diffraction (XRD) of the calcined undoped samples showed that maximum amount of pure BiFeO 3 phase was obtained at a calcination temperature of 825 °C while a deviation in calcination temperature led to the increased amount of secondary phases such as Bi 25 FeO 40 . On the other hand, XRD patterns of Sm doped calcined samples of composition Bi 0.9 Sm 0.1 FeO 3 revealed that secondary phases do not appear on calcination at and above 800 °C for 1 h in air. Vibrating sample magnetometry (VSM) measurements showed that Bi 0.9 Sm 0.1 FeO 3 samples possess higher room temperature remnant magnetization than undoped samples. Temperature dependent measurements suggested antiferromagnetic behavior of Sm doped samples with Neel temperature of ∼ 370 °C. Ferroelectric measurements showed that Sm doping improves the polarization but enhances the leakage current.

In recent years, microwave processing of metal/alloy powders have gained considerable potential in the field of material synthesis. Microwave heating is recognized for its various advantages such as: time and energy saving, rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved mechanical properties, better product performance, etc. Microwave material interaction for materials having bound charge are well established, but for highly conductive materials like metals, there is not much information available to interpret the mechanism of microwave heating and subsequent sintering of metallic materials. The present study describes how the thermal profile of electrically conductive powder metal like copper changes with particle size and also with porosity content; in other words, initial green density when the material is exposed to 2.45 GHz microwave radiation in a multimode microwave furnace.