Masami Fujiwara1 and Masahisa Otsuka2
1College of Engineering, Nihon University, Koriyama 963-8642
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. Moir´{e} 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 0.81Tm(Tm: melting point of tin). At low temperatures ranging from 0.60Tm to 0.81Tm, 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 {0.81}Tm~{0.92}Tm, 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.
(Received November 24, 1998; In Final Form January 28, 1999)
tin, indentation creep, self-similarity, constitutive equation, activation energy for creep, stress exponent, transition temperature, rate-controlling process, hot hardness
PDF (Free)
Table of ContentsPlease do not copy without permission.