10 NORMALIZED TENSILE STRESS ?/? THEORETICAL...

10 NORMALIZED TENSILE STRESS ?/? THEORETICAL STRENGTH DISLOCATION GLIDE TUNGSTEN d = 10 µm DISLOCATION CREEP 105 10 TENSILE STRESS MN/m² 10-5s-1 COBLE CREEP 10-7s-1 10-8 NABARRO CREEP 102 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 HOMOLOGOUS TEMPERATURE T/TM

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A 10 mm diameter cylindrical tungsten rod is used for heating elements, operating at 2300 Â°C. The melting temperature of tungsten is 3422 Â°C. The strain at failure after 6 months of operation was 4.7%. The deformation mechanism map is given in the figure below. (a) Calculate the maximum load that this element can withstand. (b) If the load from (a) is increased 103 times, calculate the creep strain rate. (c) How would you expect the creep behavior to change if the grain size was reduced from 10 Âµm to 1 Âµm? What will be the consequences on the deformation mechanism map? Discuss your answer. (d) Explain the difference between dislocation creep and Coble creep. TUNGSTEN 10 d-10m THEORETICAL STRENGTH THIO STRESS TENSILE NORMALIZED DISLOCATION GLIDE DISLOCATION CREEP TENSILE 10^5 s^-1 COBLE CREEP 10^-8 NABARRO CREEP 0 .1 2 .3 4 .5 .6 .7 .8 HOMOLOGOUS TEMPERATURE T/TM .9 1.0

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10 NORMALIZED TENSILE STRESS ?/? THEORETICAL STRENGTH DISLOCATION GLIDE TUNGSTEN d = 10 µm DISLOCATION CREEP 105 10 TENSILE STRESS MN/m² 10-5s-1 COBLE CREEP 10-7s-1 10-8 NABARRO CREEP 102 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 HOMOLOGOUS TEMPERATURE T/TM

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