Effect of silver addition on the creep parameters of Sn-7 wt. percent Bi alloy during transformation

摘要

The strain-time relations of Sn-7 wt. percent Bi and Sn-7 wt. percent Bi-1 wt. percent Ag alloys have been obtained under different constant stresses (8.7-19.1 MPa) in the temperature range (313-373 K). The results showed that the transient and the steady state creep parameters n, beta and epsilon_(st) depend on both the deformation temperature and the applied stress. The temperature dependence of these parameters indicates a transition temperature at 343 K. The Ag-free samples are more hard than those with Ag addition. This is explained by precipitation of Bi atoms which segregate to form a non-coherent cubic alpha-phase Sn-7 wt. percent Bi samples. While, Ag addition prevents precipitation segregate on the grain boundaries. The analysis of the X-ray diffraction patterns shows that, Ag addition increases the Sn crystallite size but decreases Bi crystallite size. The energy activating the steady state creep in the two alloys in the low and high temperature ranges (before and after transformation temperature) were found to be 51.2 + -1.6 and 88.1 9+ -1.4 kJ/mol for Sn-7 wt. percent Bi alloy and 34.3 +- 1.9 and 57 + -1.8 kj/ mol for Sn-7 wt. percent Bi-1 wt. percent Ag alloy, respectively.