Preparation and properties of (TiWTaMoV)C high entropy carbide by reactive spark plasma sintering

High entropy alloys have received a lot of attention in the last 2 decades. Recently, there have been lot of reports on high-entropy ceramics such as oxides, borides and carbides having a single-phase microstructure. There are several reports on transition metal high entropy carbides (HECs). HECs have been shown to have superior mechanical properties and good resistance to oxidation, corrosion and wear, making them promising candidate for aerospace applications as well as drill bits and cutting tools for machining. The objective of the thesis is to study the synthesis of single phase (TiWTaMoV)C high entropy carbide by powder metallurgy route, Further, the effect of C/M ratio and WC contamination on the HEC formation ability and its microstructure and properties will be evaluated. The effect of dry and wet milling on the alloying behaviour and HEC formation will also be studied. Finally, the oxidation behaviour and wear resistance of the HECs will be studied for potential applications. Preliminary studies have shown very promising results. Elemental powders of Ti, W, Ta, Mo, V (purity 99.5%, size 40–200 µm) and carbon black were used as the raw components for synthesizing (TiWTaMoV)Cx HEC.The metal powders are taken in equiatomic ratio and mixed with different amount of carbon black and subjected to ball milling. Mechanical alloying was carried out in a Fritsch Pulverisette 5planetary mill in toluene medium for 6–10 h using WC balls (10 mm dia.) used as milling media, with a ball-to-powder ratio of 10:1 by weight.Spark plasma sintering an efficient method for preparing fully dense compacts of high entropy carbides in one single heating cycle.So, reactive sintering was performed at 1400 °C, 1600 °C and 1800 °C with a heating rate of 50 °C/min and an applied uniaxial pressure of 50 MPa and holding time of 5 min at peak temperature. Dense HEC compacts were obtained using spark plasma sintering (SPS) above 1400°C. The higher synthesis temperatures of the five-component carbides are attributed to the sluggish diffusion effect induced by the large lattice distortions. XRD results showed the formation of single high entropy carbide phase having rocksalt structure above 1600 °C for C/M ratio of 0.6 but for C/M ratio of 0.75,single phase was formed only at 1800 °C. The second phase observed in the compact was found to be WC, which however dissolved at higher temperatures.The elemental mapping and point EDS of single phase HEC further showed uniform distribution of the elements in the microstructurewith no intermetallic phases or elemental segregation.The compact sintered at 1600 °C withC/M ratio of 0.6 exhibited a microhardness of ~1900 HV. The preliminary results show promise of RSPS as a low temperature sintering method for the synthesis of HECs.