Nanoindentation studies of single-crystal (001)-, (011)-, and (111)-oriented TiN layers on MgO

Abstract

The mechanical properties of (001)-, (011)-, and (111)-oriented MgO wafers and 1-μm-thick TiN overlayers, grown simultaneously by dc magnetron sputter deposition at 700 °C in a mixed N2 and Ar discharge, were investigated using nanoindentation. A combination of x-ray-diffraction (XRD) pole figures, high-resolution XRD analyses, and Auger electron spectroscopy was used to show that all TiN films were single crystals with N/Ti ratios of 1.0±0.05. The nanoindentation measurements were carried out using a three-sided pyramidal Berkovich diamond indentor tip operated at loads ranging from 0.4 to 40 mN. All three orientations of MgO substrates, as-received, exhibited identical hardness values as determined using the Oliver and Pharr method. After a 1 h anneal at 800 °C, corresponding to the thermal treatment received prior to film growth, the measured hardness of MgO(001) was 9.0±0.3 GPa. All TiN films displayed a completely elastic response at low loads. Measured hardness values, which decreased with increasing loads, increased in the order (011)<(001)<(111). After a 30 s postdeposition anneal at 1000 °C, however, hardness was found to be independent of load except at displacements >100 nm where substrate effects were apparent. TiN(001) and (111) films had hardnesses of 20±0.8 and 21±1 GPa, respectively, while data obtained from (011) layers exhibited large scatter due to surface roughness effects. Young’s moduli for annealed samples, calculated from the elastic unloading curves, were found to be 307±15 GPa for MgO (001) and 445±38 and 449±28 GPa for TiN (001) and TiN (111), respectively.

Temperature dependence of TiN elastic constants fromab initiomolecular dynamics simulations

“…Young's modulus of TiN was measured in several experiments, 23,[26][27][28][29][30] but the data are rather scattered, ranging from 430 GPa (Ref. 29) to 590 GPa.…”

“…For example, TiN films display a completely elastic response at low loads. 23 Furthermore, the elastic anisotropy is essential for understanding and modeling the spinodal decomposition, 24 which occurs in some alloys of transition-metal nitrides and it is believed to be the main reason for the age hardening effect. 7,8,25 At the same time, experimental information on elastic properties of transition-metal nitrides is mostly limited to their Young's moduli.…”

“…7,8,25 At the same time, experimental information on elastic properties of transition-metal nitrides is mostly limited to their Young's moduli. 23,[26][27][28][29] With rare exceptions it does not include data on the single-crystal elastic constants. 30 Therefore, first-principles calculations are employed to obtain the missing information on elastic constants for these materials.…”

Nanocrystalline structure and hardness of thin films

“…Contrarily to the others, this film shows a very strong orientation, [1 1 1] instead of [2 0 0]. Recently, Ljungcrantz et al [19] deposited TiN coatings epitaxially on MgO substrates differently oriented. By calculating the Schmid factors for the particular case of fcc NaCl type structure of TiN, they obtained higher critical shear stresses for plastic deformation in the case of (1 1 1) oriented films.…”

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

“…Titanium nitride, one of the first hard-coating materials [15,40,41], serves as a model to probe diffusion dynamics and kinetics on NaCl-structure TM nitride surfaces in general.…”