Electrochemical Passivation Properties of Valve Transition Metal Carbides

Transition metal carbides have the potential to be employed as corrosion protective coating for a variety of applications such as e.g. steel based bipolar plates, porous transport layers or as catalyst support in polymer electrolyte membrane fuel cells and water electrolyzers. Yet, little is known of their fundamental, intrinsic corrosion and passivation properties. Herein, we conducted a detailed electrochemical passivation study of various valve transition metal carbides such as titanium carbide, tantalum carbide or tungsten carbide. Via flow cell measurements coupled to an inductively coupled plasma mass spectrometer, the in-situ transition metal dissolution was monitored, and the faradaic dissolution efficiency was calculated. Together with the determination of the grown oxide layer via X-ray photoelectron spectroscopy, a thorough evaluation of the passivation efficiency was conducted. Moreover, it was shown that a beneficial stabilization effect can be achieved through alloying of different carbides, which paves the way towards tailor-made coatings or catalyst support materials.

Study on Mechanical and Wear Behaviour of AA7075/TaC/Si3N4/Ti Hybrid Metal Matrix Composites

This research article focuses on the development of AA7075 alloy reinforced with different wt% of Tantalum Carbide (TaC), Silicon Nitride (Si3N4) and Titanium (Ti) particulates using stir casting. Mechanical characteristics like tensile, compression and microhardness of the developed composites were analysed. High temperature tribological properties of the hybrid MMCs were studied for various input control factors like sliding speed, load and temperature. Design analysis has been executed by Taguchi orthogonal array and ANOVA (Analysis of Variance). The incorporated reinforcements exhibited improved wear resistance at ambient temperature along with elevated temperatures. Monolithic dissemination of reinforcement’s in the prepared composites magnifies the mechanical and tribological characteristics for composites compared to matrix material. From the optimization technique, it was witnessed that Wear Rate and Frictional Coefficient are afflicted by temperature go after load & sliding speed. The optimal amalgamation of control parameters of distinct tribo-responses has been detected.

The Effect of the Crucible on the Temperature Distribution for the Growth of a Large Size AlN Single Crystal

The appropriate distribution of temperature in the growth system is critical for obtaining a large size high quality aluminum nitride (AlN) single crystal by the physical vapor transport (PVT) method. As the crystal size increases, the influence of the crucible on the temperature distribution inside the growth chamber becomes greater. In order to optimize the field of temperature and study the specific effects of various parts of the crucible on the large size AlN single crystal growth system, this study carried out a series of numerical simulations of the temperature field of two crucibles of different materials and put forward the concept of a composite crucible, which combines different materials in the crucible parts. Four composite crucible models were established with different proportions and positions of tantalum carbide (TaC) parts and graphite parts in the crucible. Calculations reveal that different parts of the crucible have different effects on the internal temperature distribution. The axial temperature gradient at the crystal was mainly governed by the crucible wall, whereas the temperature gradient was determined by the integrated effect of the crucible lid and the crucible wall in the radial direction. One type of composite crucible was chosen to minimize the thermal stress in grown AlN crystal, which is applicable to the growth of large sized AlN crystals in the future; it can also be used to grow AlN single crystals at present as well.

The Effect of Incorporating Ceramic Particles with Different Morphologies on the Microstructure, Mechanical and Tribological Behavior of Hybrid TaC_ BN/AA2024 Nanocomposites

Improving the mechanical durability and wear resistance of aluminum alloys is a research challenge that can be solved by their reinforcement with ceramics. This article is concerned with the improvement of the mechanical properties and wear resistance of the AA2024 aluminum alloy surface. Surface composites were prepared by incorporating a hybrid of heavy particles (tantalum carbide (TaC), light nanoparticles, and boron nitride (BN)) into the AA2024 alloy using the friction stir process (FSP) approach. Three pattern holes were milled in the base metal to produce the composites with different volume fractions of the reinforcements. The effects of the FSP and the reinforcements on the microstructure, mechanical properties, and wear resistance are investigated. In addition to the FSP, the reinforced particles contributed to greater grain refinement. The rolled elongated grains became equiaxed ultrafine grains reaching 6 ± 1 µm. The refinement and acceptable distribution in the reinforcements significantly improved the hardness and wear resistance of the produced composites. Overall, the hardness was increased by 60% and the wear resistance increased by 40 times compared to the base alloy.