Section A Question 1. A 10 mm diameter cylindrical tungsten rod is used for heating elements, op- erating at 2300 C. The melting temperature of tungsten is 3422 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. [8 marks] (b) If the load from (a) is increased 103 times, calculate the creep strain rate. [8 marks) c) How would you expect the creep behaviour to change if the grain size was reduced from 10 um to 1 um. What will be the consequences on the defor- mation mechanism map? Discuss your answer. [5 marks) (d) Explain the difference between dislocation creep and Coble creep. [4 marks] TUNGSTEN THEORETICAL STRENGTH DISLOCATION SLIDE SOCATION NORMALIZED TENSE STRESS TERRESTRESS 105 COGLE CREEP 3. 100 GROUP 12 . HOMOLOGOUS TEMPERATURE Page 4 of 9 TUNGSTEN Te In UI u THEORETICAL STRENGTH ? DISLOCATION GLIDE To DISLOCATION CREEP NORMALIZED TENSILE STRESS ON To TENSILE STRESS MN/? 10511 COGLE CREEP 10 10:45 10% NABARRO CREEP ,5 HOMOLOGOUS TEMPERATURE T/TM Section A Question 1. A 10 mm diameter cylindrical tungsten rod is used for heating elements, op- erating at 2300 C. The melting temperature of tungsten is 3422 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. [8 marks] (b) If the load from (a) is increased 103 times, calculate the creep strain rate. [8 marks) c) How would you expect the creep behaviour to change if the grain size was reduced from 10 um to 1 um. What will be the consequences on the defor- mation mechanism map? Discuss your answer. [5 marks) (d) Explain the difference between dislocation creep and Coble creep. [4 marks] TUNGSTEN THEORETICAL STRENGTH DISLOCATION SLIDE SOCATION NORMALIZED TENSE STRESS TERRESTRESS 105 COGLE CREEP 3. 100 GROUP 12 . HOMOLOGOUS TEMPERATURE Page 4 of 9 TUNGSTEN Te In UI u THEORETICAL STRENGTH ? DISLOCATION GLIDE To DISLOCATION CREEP NORMALIZED TENSILE STRESS ON To TENSILE STRESS MN/? 10511 COGLE CREEP 10 10:45 10% NABARRO CREEP ,5 HOMOLOGOUS TEMPERATURE T/TM