1. Indicate whether each of the following statements are TRUE or FALSE a. After
ID: 2086882 • Letter: 1
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1. Indicate whether each of the following statements are TRUE or FALSE a. After an edge dislocation has passed through some region of a crystal, the atomic arrangement of that region is disordered b. c. Reducing the grain size of a metal improves its toughness d. Most metals strain harden at high temperature e. Grain growth must always be preceded by recovery and recrystallization Dislocations move with the same degree of ease on all crystallographic planes of atoms and in all crystallographic directions? f. The atoms surrounding a screw dislocation experience shear strain. g. During the recovery of a cold-worked material, Grains with high strains are replaced with new, unstrained grains h. The process by which plastic deformation is produced by dislocation motion is i. j. called slip For a particular crystal structure, the slip direction is that direction in the slip plane having the lowest liner density As the impurity concentration (in solid solution) of a metal is increased, the tensile and yield strengths decreases k. Increased hindering of dislocation motion makes a metallic material softer I. On the average, dislocation-dislocation strain interactions are attractive m. During the recovery of a cold-worked material, there is a reduction in the number of dislocations A smaller impurity atom, when located near a dislocation, will nullify some of the compressive strains the dislocation introduces in the crystal lattice n. o. Strengthfine-grained-Strengthcoarse-grained in a polycrystalline material p. To prevent creep, just increase the number of grains/in2 q. In fracture failure, the failed pieces have the cup-and-cone specimen matching pair The origin of fracture failure is normally characterized by the chevron markings Cracks having shaper tips will propagate with some difficulty compare to cracks with blunt tips Materials can fail in fatigue even if the maximum stress level is below the yield stress of the material r. s. t. u. To avoid and minimized fatigue failure optimizing the geometry of our design to avoid sharp internal corners is one technique Creep does not occur in materials where T>0.4Tm In creep failure, time to rupture decreases as ? or T increases v. w. Solubility Limit is define as a maximum concentration for which only a single phase solution exists Phase can be define as a regions of material where physical and chemical state are distinct. Phase diagrams are useful tools to determine the number and types of phases present in a material x. y. z.Explanation / Answer
a. False ( Because Before and after an edge dislocation has passed through some region of a crystal, the atomic arrangement is ordered and perfect. It is only during the passage of the extra half-plane that there is disorder.)
b. False ( Dislocations do not move with the same degree of ease on all crystallographic planes of atoms and in all crystallographic directions)
c. True (Decreasing grain size has an advantage of both increasing the strength and improving the Impacttoughness.)
d. True
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