Precipitation hardening of ZnO.1 at. %Ti single crystals deformed on the (0001) {11-20} system

• Published in: Journal of alloys and compounds 2004-09, Vol.378 (1-2), p.135-139
• Main Authors: Boczkal, G, Mikulowski, B
• Format: Article
• Language: English
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2003.12.054

The size and dispersion of precipitates of the hardening phase considerably affect the yield point and the hardening characteristics of alloys. The mechanical properties (the critical resolved shear stress-CRSS, the work-hardening coefficient-BA) and a thermodynamic parameter (the activation volume-V*) have been studied in single crystals of ZnO.1 at.%Ti. The sample orientation allowed slip on the (0001)(11-20) system over a large range of strain. The investigations were conducted on samples which were both heat treated and not. The investigations were made using compression and stress relaxation tests in the range of easy glide at temperatures from 77 to 493 K. The single crystals appear to be hardened by precipitates while Ti solubility in Zn is negligible. Two types of the precipitates have been identified by TEM and microanalysis; very small precipitates were located uniformly in the matrix, and large needle-shaped obstacles with size of the order of 0.1 mm on the (0 0 0 1) orientation. The CRSS and the 9A showed a strong dependence on the temperature. The determined values of the CRSS were in the range of 4 MPa for 493 K to 12 MPa for 77 K. The obtained values of the activation volume V* were in the range of (10-110) x 10-16 cm3 and it was strongly dependent on the temperature and the stress at the beginning of relaxation. This value is attributed to small precipitates which are barriers for dislocation movement.