Toughness enhancement in hard ceramic thin films by alloy design

Abstract

Hardness is an essential property for a wide range of applications. However, hardness alone, typically accompanied by brittleness, is not sufficient to prevent failure in ceramic films exposed to high stresses. Using VN as a model system, we demonstrate with experiment and density functional theory (DFT) that refractory VMoN alloys exhibit not only enhanced hardness, but dramatically increased ductility. V0.5Mo0.5N hardness is 25% higher than that of VN. In addition, while nanoindented VN, as well as TiN reference samples, suffer from severe cracking typical of brittle ceramics, V0.5Mo0.5N films do not crack. Instead, they exhibit material pile-up around nanoindents, characteristic of plastic flow in ductile materials. Moreover, the wear resistance of V0.5Mo0.5N is considerably higher than that of VN. DFT results show that tuning the occupancy of d–t2g metallic bonding states in VMoN facilitates dislocation glide, and hence enhances toughness, via the formation of stronger metal/metal bonds along the slip direction and weaker metal/N bonds across the slip plane

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

“…NaCl-structure (B1) TiN is a model system for transition-metal (TM) nitrides, a class of technologically important ceramic materials characterized by outstanding combinations of mechanical [23][24][25][26][27], physical [28,29], optical [30,31], electrical [32], and catalytic properties [33,34]. In addition, the properties can be tuned by varying TM compositions in alloys [32,[35][36][37][38] and/or the N/TM ratio [39][40][41][42][43] over wide ranges while preserving the cubic phase.…”

Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN

“…Transition-metal (TM) nitride refractory ceramics possess outstanding physical and mechanical properties, including extreme hardness [1][2][3], high toughness [4][5][6], thermal stability [7,8], chemical inertness [9,10], and good electrical conductivity [2,11], which renders them important for a large variety of applications ranging from wear-resistant protective coatings on tools employed in industrial machining [12,13] to diffusion barrier in electronic devices [14,15].…”

Ti adatom diffusion on TiN(001): Ab initio and classical molecular dynamics simulations

“…Transition-metal (TM) nitrides exhibit excellent physical and mechanical properties, including high hardness [1,2] and toughness [3], chemical inertness, and good thermal stability and electrical conductivity [4]. Thus, they are employed in a wide variety of applications ranging from wear-resistant protective coatings on cutting tools and engine components [5,6] to diffusion barriers in electronic devices [7][8][9][10][11].…”