Performance of ZrB2–Cu composite as an EDM electrode

The low wear resistance of electrodes like Cu, Cu alloys and graphite is a major problem for electrical discharge machining (EDM) operation. Here an attempt has been made to develop a metal matrix composite (ZrB2–Cu) to get an optimum combination of wear resistance, electrical and thermal conductivity. The ZrB2–Cu composite have been developed by adding different amounts of Cu and tested as a tool material at different process parameters of EDM during machining of mild steel. The ZrB2–40 wt.% Cu composite shows more metal removal rate (MRR) with less tool removal rate (TRR) than commonly used Cu tool. But the diameteral overcut and average surface roughness are found to be lesser in case of Cu tool than composite tool. The tools and workpiece surfaces are analyzed by scanning electron microscope (SEM)/EDS and XRD technique

Double SHS of ZrB2 powder

Production of ZrB2 powder through self-propagating high-temperature synthesis (SHS) from ZrO2, Mg and H3BO3 mixture often leads to incomplete conversion. A new technique, called DSHS (double SHS) has been developed, wherein the reaction product of the first SHS is mixed with calculated amounts of Mg and H3BO3 powder and subjected to a second SHS. The ZrB2 powder produced by DSHS technique yields increased conversion. The NaCl is used as a diluent during SHS to control the particle size of the product. The average particle size of SHS ZrB2 powder found to be 75–125 nm in range, which decrease to 25–40 nm after DSHS

Microanalysis of debris formed during electrical discharge machining (EDM)

The present investigation attempts to focus on the influence of EDM energy input on the structure and composition of the debris that forms during machining. An indigenously prepared ZrB2-Cu composite and mild steel plate were used as tool and workpiece (WP) material for the present study. The machining was carried out in a kerosene medium. The composition analysis of different debris particles was investigated by SEM/EDS. At low EDM energy input the SEM micrographs of WP debris showed formation of smaller size particles with few satellites. The SEM micrographs of high EDM energy input showed formation of hollow spheres, with dents, larger population of satellites, surface cracks and burnt core structures

Sintering behaviour of ultra-fine titanium diboride powder prepared by self-propagating high-temperature synthesis (SHS) technique

A systematic study on the sintering behaviour of titanium diboride (TiB2) powder of different particle sizes prepared by a SHS route is carried out in the temperature range of 1973–2173 K. The decrease of particle size increases the densification of the TiB2 powder compacts and a maximum densification of 93% of the theoretical density is achieved after sintering at 2173 K. The activation energies for sintering are observed to vary within 76 to 85 kJ/mol for the different particle sizes that indicate the boron diffusion in Ti as the possible rate-controlling process for sintering. The time dependent variation of densification under isothermal condition indicates the surface diffusion or vapour phase condensation mechanisms operative in the system. The microstructure and microhardness of different sintered samples reflect the densification behaviour of sintered pellets

Comparative studies on sintering behavior of self-propagating high-temperature synthesized ultra-fine titanium diboride powder

Sintering behavior of nano-sized titanium diboride (TiB2) powder prepared by a self-propagating high-temperature synthesis (SHS) technique was compared with that of the commercially available powder. The SHS-made powder showed excellent sinterability at low temperatures and a maximum of 97% densification was achieved at 2223 K, whereas the identically sintered commercial powder could only be densified to ∼86% at 2223 K. The estimated activation energies for sintering of 35±0.07 kJ/mole and 46±0.7 kJ/mole for the SHS and commercial powder, respectively, indicated the possibility of a different mechanism during sintering

Formation of sic whiskers from compacts of raw rice husks

The formation of SiC whiskers from compacts of raw rice husks without coking and catalyst has been studied. A pyrolysis temperature of 1600-degrees-C has yielded a considerable quantity of SiC whiskers. The formation of spherical particles of silica is observed. Whisker formation occurs by reaction between SiO(g) and CO(g)

Application of new tool material for electrical discharge machining (EDM)

In EDM, Cu and graphite are commonly used as tool materials. The poor wear resistance is the drawback of these tools. In the current study, an attempt has been made to develop a ZrB2-Cu composite as an EDM tool material to overcome this problem. Initially, the ZrB2 powder is prepared by self-propagating high-temperature synthesis (SHS) technique and synthesized powder is mixed with different amounts of Cu powder. Dense composite is developed by a pressureless sintering at 1250°C. The composites are tested as tool material at different EDM process parameters during machining of mild steel. The ZrB2-40 wt% Cu composite shows highest metal removal rate (MRR) with significant tool removal rate (TRR) than other composites. The performance of ZrB2-40 wt% Cu composite is compared to conventional Cu tool. The composite shows higher MRR with less TRR than Cu tool but it shows more average surface roughness and diameteral overcut than Cu tool

Carbothermal synthesis of zirconium diboride (ZrB2) whiskers

In the present investigation, carbothermal synthesis technique is used for the production of ZrB2 whiskers. The synthesis is carried out by heating the mixture of ZrB2, H3BO3 and carbon black over the temperature range of 1300 to 1700 degrees C in argon atmosphere. Different elements such as Ni, Co and Fe are tested for their role as catalysts. The synthesised powder contains ZrB2 as the major phase with minor phases of ZrC and B4C. Whisker yield is found to be low at lower temperatures (<1500 degrees C) and then increases with the pyrolysis temperature. The Ni addition seems more effective as a catalyst than Co or Fe. Shorter length whiskers are found in the case of Co catalyst, whereas use of Fe catalyst shows whisker with rod shape and a special bird's nest type whiskers. The electron microscope study of whisker reveals the presence of various defects

Sintering of ultrafine zirconium diboride powder prepared by modified SHS technique

Pressureless sintering of ultrafine zirconium diboride ZrB2 powder produced by a self-propagating high temperature synthesis (SHS) route was investigated at 1973-2223 K with continuous flow of pure argon gas (20 mL min(-1)). Ultrafine ZrB2 powder produced by the addition of an inert SHS diluent showed excellent sinterability, and a maximum densification of 97.5% was observed at 2223 K. In contrast, the identically sintered diboride powder produced without the addition of SHS diluent showed only 81.2% densification. The apparent activation energy for sintering was found to vary with particle size from around 37 to 43 kJ. Boron diffusion through ZrB2 is likely the rate controlling factor for the sintering reaction

Self-propagating-high-temperature synthesis (SHS) of ultrafine ZrB2 powder

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