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Title: The influence of temperature on the mechanical behaviour of ceramics in Ti1-xAlxN system
Author: Ciurea, Constantin
ISNI:       0000 0005 0732 0573
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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High temperature nanoindentation has been employed to study the influence of temperature on mechanical properties of ceramics in Ti1-xAlxN system. The temperature had a strong effect on the hardness of the bulk single crystal TiN (TiNbulk), leading to a drop from 21.4 ± 0.4 GPa at 22 °C to 13.7 ± 0.4 GPa at 350 °C. Plastic deformation of TiNbulk mainly occurred along the (110) crystallographic planes, over the temperature range 22 °C - 350 °C, suggesting that the drop in hardness with the temperature was attributed to a change of ease of plastic slip. Hardness of magnetron sputtered Ti0.66Al0.34N coatings dropped with temperature in a similar manner to TiNbulk, although from a higher starting value. Approaching the compositional atomic ratio Al : Ti = 1:1, maximum hardness was reached and the thermal stability of hardness improved. It was proposed that the high hardness stability with the temperature of magnetron sputtered coatings is linked to the presence of the two crystallographic domains, fcc TiN and stabilized fcc AlN. The small difference between the lattice parameters of these phases seems to be accommodated by distortion of lattices, in order to form coherent boundaries between domains. It has been shown that stabilised fcc AlN formed during deposition and remained in the structure after annealing at 600 °C. Aluminium addition increased the activation energy for slip from 0.75 eV for TiNbulk to 1.26 eV for Ti0.48Al0.52N coatings. These values indicate the deformation took place by lattice controlled dislocation glide mechanism. The hardness of industrial cathodic arc Ti0.4Al0.6N films decreased with temperature in a similar way to TiNbulk, although at higher values. High deposition energies promoted fcc AlN alongside fcc TiN, and a change of growing direction from (200) to (111). The differences in structure and mechanical properties attributed to different physical vapour depositions are presented.
Supervisor: Giuliani, Finn; Alford, Neil Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral