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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...

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 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.

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 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.

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.

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.

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.

Microwave processing is emerging as an innovative and highly effective material processing method offering many advantages over conventional methods, especially for sintering applications. It 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 which lead to better product performance. Major constraints in conventional sintering of refractory material such as tungsten and its alloys are high sintering temperatures and long soaking times which cause abnormal grain growth and lead to poor mechanical properties. They get further aggravated at smaller (submicron and nano) tungsten powder sizes. This study describes recent research findings; W-18Cu and W-7Ni-3Cu alloys have been successfully consolidated using microwave heating which resulted in an overall reduction of sintering time of up to 80%. The microwave sintered samples exhibited finer microstructure and superior mechanical properties when compared with the conventional samples.

This study describes the alloy design approaches for processing high-performance hardmetals for metal cutting and mining applications. In fine-grained hardmetals for metal cutting applications combined addition of VC and Cr3C2 in optimal proportion, as grain-growth inhibitors, enhances the hardness as well as indentation fracture toughness. In addition, the synergistic action of these grain-growth inhibitors also results in a more homogeneous microstructure. Consequently, the variation in the mechanical properties of these fine-grained hardmetals is reduced. This research also highlights the influence of carbon on the transverse rupture strength and toughness of the mining and fine-grained hardmetals. A lower carbon in the two-phase WC + Co region of the hardmetal microstructure results in higher fracture toughness and transverse rupture strength without compromising the hardness.

The flow induced shear stress on the wall of the blast furnace hearth has been computed by solving the Navier–Stokes equations along with a momentum source to represent numerically the pressure dro...

The electrochemical behaviour of 434L ferritic stainless steels produced by the powder metallurgy (PM) route has been studied. The effects of sintering temperature (1250°C and 1400°C) and dispersoid addition (10%Y2O3) have been investigated by potentiodynamic polarisation and electrochemical impedance studies in 0·05M H2SO4 solution. All the alloys exhibited active-passive behaviour in the electrolyte. The critical current density for passivation was lower in the case of the PM samples when compared with 430, which has been attributed to the presence of Mo in the samples. The passive current density of the PM samples correlated with the sintered porosities. All the other passivation parameters were similar for all the materials. The nature of passive film was investigated using electrochemical impedance spectroscopy. A lower capacitance (i.e. more corrosion resistant) surface film was obtained after sintering at the higher temperature. Yttria dispersoids in ferritic stainless steel decreased the c...