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13.13 Tungsten is being used at half its melting point (Tm ≈ 3,400 °C) and a stress level of 160 MPa. An engineer suggests increasing the grain size by a factor of 4 as an effective means of reducing the creep rate. (a) Do you agree with the engineer? Why? What if the stress level were equal to 1.6 MPa? (b) What is the predicted increase in length of the specimen after 10,000 hours if the initial length is 10 cm? (Hint: Use a Weertman--Ashby map.) 1) Where in the book/slides is this covered? = page # or slide session/number 2) What equations and concepts apply here? Normalized tensile stress, o/G 10-² 10-4 10-6 10-8 0 Tungsten d=10um, p = 4x 1010/cm² Theoretical strength Dislocation glide Coble creep 0.2 0.4 10-10 Dislocation creep /s 10-6 0.6 0.8 Homologous temperature, T/TM -10-2 10-4 10-6 Nabarro creep 1.0 SS ADGb b KBT d Gw~ 160 GPa Dislocation creep mechanism Dislocation glide climb, climb controlled Dislocation glide climb, glide controlled Dissolution of dislocation loops Dislocation climb without glide Dislocation climb by pipe diffusion Diffusional creep mechanisms Vacancy flow through grains Vacancy flow along grain boundaries Interface reaction control TABLE 17.6 Creep Equation Exponents and Diffusion Paths for Various Creep Mechanisms Creep mechanism Р Diffusion path Grain boundary sliding mechanisms Sliding with liquid Sliding without liquid (diffusion control) 0 3 2-3 n 4-5 3 4 σ 3 5 n Lattice Lattice Lattice Lattice Dislocation core Lattice Grain boundary Lattice/grain boundary Liquid Lattice/grain boundary

13.13 Tungsten is being used at half its melting point (Tm ≈ 3,400 °C) and a stress level of 160 MPa. An engineer suggests increasing the grain size by a factor of 4 as an effective means of reducing the creep rate. (a) Do you agree with the engineer? Why? What if the stress level were equal to 1.6 MPa? (b) What is the predicted increase in length of the specimen after 10,000 hours if the initial length is 10 cm? (Hint: Use a Weertman--Ashby map.) 1) Where in the book/slides is this covered? = page # or slide session/number 2) What equations and concepts apply here? Normalized tensile stress, o/G 10-² 10-4 10-6 10-8 0 Tungsten d=10um, p = 4x 1010/cm² Theoretical strength Dislocation glide Coble creep 0.2 0.4 10-10 Dislocation creep /s 10-6 0.6 0.8 Homologous temperature, T/TM -10-2 10-4 10-6 Nabarro creep 1.0 SS ADGb b KBT d Gw~ 160 GPa Dislocation creep mechanism Dislocation glide climb, climb controlled Dislocation glide climb, glide controlled Dissolution of dislocation loops Dislocation climb without glide Dislocation climb by pipe diffusion Diffusional creep mechanisms Vacancy flow through grains Vacancy flow along grain boundaries Interface reaction control TABLE 17.6 Creep Equation Exponents and Diffusion Paths for Various Creep Mechanisms Creep mechanism Р Diffusion path Grain boundary sliding mechanisms Sliding with liquid Sliding without liquid (diffusion control) 0 3 2-3 n 4-5 3 4 σ 3 5 n Lattice Lattice Lattice Lattice Dislocation core Lattice Grain boundary Lattice/grain boundary Liquid Lattice/grain boundary

Elements Of Electromagnetics
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
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13.13 Tungsten is being used at half its melting point (Tm 3,400 °C) and a stress level of 160 MPa. An engineer suggests increasing the grain size by a factor of 4 as an effective means of reducing the creep rate. (a) Do you agree with the engineer? Why? What if the stress level were equal to 1.6 MPa? (b) What is the predicted increase in length of the specimen after 10,000 hours if the initial length is 10 cm? (Hint: Use a Weertman--Ashby map.) 1) Where in the book/slides is this covered? = page # or slide session/number 2) What equations and concepts apply here? Normalized tensile stress, o/G 10-² 10-4 10-6 10-8 0 Tungsten d = 10um, p = 4x 1010/cm² Theoretical strength Dislocation glide Coble creep 0.2 10-10 0.4 Dislocation creep /s 10-6 0.6 0.8 Homologous temperature, T/TM 10-2 10-4 10-6 Nabarro creep ≈ 1.0 ၆ SS Dislocation creep mechanism Dislocation glide climb, climb controlled Dislocation glide climb, glide controlled Dissolution of dislocation loops Dislocation climb without glide Dislocation climb by pipe diffusion ADGb b k T d Gw~160 GPa TABLE 17.6 Creep Equation Exponents and Diffusion Paths for Various Creep Mechanisms Creep mechanism Р p Diffusion path Diffusional creep mechanisms Vacancy flow through grains Vacancy flow along grain boundaries Interface reaction control Grain boundary sliding mechanisms Sliding with liquid Sliding without liquid (diffusion control) 0 0 0 0 0 2 3 1 3 2-3 n 4-5 3 4 3 5 р 1 1 2 1 n Lattice Lattice Lattice Lattice Dislocation core Lattice Grain boundary Lattice/grain boundary Liquid Lattice/grain boundary
Transcribed Image Text:13.13 Tungsten is being used at half its melting point (Tm 3,400 °C) and a stress level of 160 MPa. An engineer suggests increasing the grain size by a factor of 4 as an effective means of reducing the creep rate. (a) Do you agree with the engineer? Why? What if the stress level were equal to 1.6 MPa? (b) What is the predicted increase in length of the specimen after 10,000 hours if the initial length is 10 cm? (Hint: Use a Weertman--Ashby map.) 1) Where in the book/slides is this covered? = page # or slide session/number 2) What equations and concepts apply here? Normalized tensile stress, o/G 10-² 10-4 10-6 10-8 0 Tungsten d = 10um, p = 4x 1010/cm² Theoretical strength Dislocation glide Coble creep 0.2 10-10 0.4 Dislocation creep /s 10-6 0.6 0.8 Homologous temperature, T/TM 10-2 10-4 10-6 Nabarro creep ≈ 1.0 ၆ SS Dislocation creep mechanism Dislocation glide climb, climb controlled Dislocation glide climb, glide controlled Dissolution of dislocation loops Dislocation climb without glide Dislocation climb by pipe diffusion ADGb b k T d Gw~160 GPa TABLE 17.6 Creep Equation Exponents and Diffusion Paths for Various Creep Mechanisms Creep mechanism Р p Diffusion path Diffusional creep mechanisms Vacancy flow through grains Vacancy flow along grain boundaries Interface reaction control Grain boundary sliding mechanisms Sliding with liquid Sliding without liquid (diffusion control) 0 0 0 0 0 2 3 1 3 2-3 n 4-5 3 4 3 5 р 1 1 2 1 n Lattice Lattice Lattice Lattice Dislocation core Lattice Grain boundary Lattice/grain boundary Liquid Lattice/grain boundary
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