4.8 Article

Enhanced Hardness in Transition-Metal Monocarbides via Optimal Occupancy of Bonding Orbitals

Journal

ACS APPLIED MATERIALS & INTERFACES
Volume 13, Issue 12, Pages 14378-14389

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsami.0c23049

Keywords

electronic origin; hardness enhancement; spark plasma sintering; transition-metal monocarbides

Funding

  1. Fundamental Research Funds for the Central Universities [2232019A3-13, 2232018D3-32]
  2. National Natural Science Foundation of China [52032001, 51671126, 51872045]
  3. Science and Technology Commission of Shanghai Municipality [20ZR1400900, 18ZR1401400]
  4. Guangdong Innovative & Entrepreneurial Research Team Program [2016ZT06C279]
  5. Shenzhen Peacock Plan [KQTD2016053019134356]
  6. Shenzhen Development and Reform Commission Foundation for Shenzhen Engineering Research Center for Frontier Materials Synthesis at High Pressure
  7. Shenzhen Science and Technology Innovation Committee [JCYJ20190809173213150]

Ask authors/readers for more resources

An efficient strategy for enhancing the hardness of transition-metal monocarbides (TMCs) by optimally filling the bonding orbitals of valence electrons has been reported. Newly developed W1-xRexC samples show significantly enhanced hardness compared to their parent phase (WC), making them the hardest TMCs for practical applications. The hardness enhancement can be rationalized by the balanced occupancy of bonding and antibonding states, offering a guide for the design of other hard and superhard compounds.
An efficient strategy that can guide the synthesis of materials with superior mechanical properties is important for advanced material/device design. Here, we report a feasible way to enhance hardness in transition-metal monocarbides (TMCs) by optimally filling the bonding orbitals of valence electrons. We demonstrate that the intrinsic hardness of the NaCl- and WC-type TMCs maximizes at valence electron concentrations of about 9 and 10.25 electrons per cell, respectively; any deviation from such optimal values will reduce the hardness. Using the spark plasma sintering technique, a number of W1-xRexC (x = 0-0.5) have been successfully synthesized, and powder X-ray diffractions show that they adopt the hexagonal WC-type structure. Subsequent nano-indentation and Vickers hardness measurements corroborate that the newly developed W1-xRexC samples (x = 0.1-0.3) are much harder than their parent phase (i.e., WC), marking them as the hardest TMCs for practical applications. Furthermore, the hardness enhancement can be well rationalized by the balanced occupancy of bonding and antibonding states. Our findings not only elucidate the unique hardening mechanism in a large class of TMCs but also offer a guide for the design of other hard and superhard compounds such as borides and nitrides.

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