マイクロインデンテーションによるβ-Sn単結晶の高温クリープ特性評価

抄録

This study is being conducted to determine whether the indentation creep test produces results equivalent to those of the conventional unidirectional creep tests in the dislocation creep regime. A hot-hardness tester is used to obtain information on the time dependent flow, or indentation creep, of the material beneath the indenter. When a conical indenter is pressed into the (110) plane of a β-Sn single crystal, the deformation in the (001) plane just under the indenter can be regarded approximately as an in-plane strain problem. Moiré analysis of strain reveals that the plastic region in the (001) plane beneath the indenter extends while maintaining geometrical self-similarity as indentation proceeds. Observation via the etch-hillock technique also gives the same result. These findings for self-similar indentation lead to a constitutive equation from which the power law creep exponent n and activation energy for creep Q can be derived. The values Q and n vary at a temperature of 0.81T_m(T_m: melting point of tin). At low temperatures ranging from 0.60T_m to 0.81T_m, the value of Q, 44 kJ/mol, so obtained is comparable to the activation energy for pipe diffusion and the n-value is 7.5. At high temperatures of 0.81T_m∼0.92T_m, the value of Q, 107 kJ/mol, corresponds to the activation energy for lattice diffusion and the n-value is 5.4. These values indicate that there are two parallel rate-controlling processes taking place simultaneously in the creep of β-Sn. The results obtained using creep indentation are in approximate agreement with the conventional creep test results, drawn from a number of sources.