Question

Question 4 (25 marks) (a) Consider the hypothetical eutectic phase diagram for metal for lead-tin system. Assume that (1) A and B phase cutectic phase diagram for metals A and B, which is similar to that 1. Assume that (1) a and B phases exist at the A and B extremities of the phase diagram, respectively; (2) the eutectic composi m, respectively; (2) the eutectic composition is 36 wt% A-64 wt% B; and (3) the composition of the a phase at the eutectic temperatur merature is 88 wt% A - 12 wt% B. If the alloy contains primary B and total ß mass fractions of 0.367 tions of 0.367 and 0.768, respectively, just below the eutectic temperature, determine the composition of th perature, determine the composition of the B phase at the eutectic temperature (7 marks) (b) Which of a brass and a+B' brass is more difficult to cold work? Use mechanism involved during cold work plastic deformation to explain your answer. (4 marks) (c) Cite a difference and a similarity between solid-solution phase and intermetallic phase (4 marks) (d) Is graphite an isotropic or anisotropic material and why (3 marks) (e) A single crystal copper bar was subjected to 100 MPa tensile stress. Do you expect the critical resolved shear stress along [110] to be same or different from the critical resolved shear stress along [011] and why? (3 marks) (1) Give a similarity and a difference between peritectic and eutectoid reactions ? (4 marks) Sn) Composition at 60 100 327°C 600 300 Liquid 500 232°C ) + 2 400 183°C 97.8 Temperature (°C) Temperature 61.9 18.3 200 100 Composition ( %5ml

Answer 1

Cu = 88 wt% 6A + 12 wt% B; Cp = • Not given Ce = 36 wt% A + 64 wt%B: Wfpp = 0.367 : Wfp = 0.768 WfB = Ce-cd Cp-ca 0.768 = 36-88 B-88 0.768 Cp -88 (0.768) = 36-88 > Op = 2:291) (p = 20:291 . composition of ß phase at eutectic compose bon is Top = 20.29 wt% A +79.70 wt%B1 Co Lt ß Brass is more diffecult ton work. Because it brass' has identical atoms and arranged mostly in regular alloys, so the layer of atoms can slede over each other easily But in case of 'htß brass' atomic layers mostly are in Irregular arrangement due to which they cannot slede easily and deslocation moremen- hinder once ses large that as why in this case at is more difficult to cold work.

(c) demi harity in solid dution and intemetalic is that both formed with two or more different elements Main defferences are: olid solutions have the dute atoms and and matrix atoms distributed randomily, the lattice type is that of the matrix element. In case of Intermetallics they have ordered arrangements of the different atom types. The lattice type b different from that of the matrix materias. Also in soled solutions alloys atomic bond is mostly metallic only but an case of Intermetallics atom bond is metallic-covalent. d) • Guaphite 98 ar anisotropfc material. An & anisotropic material is a material that has lefferent pacoperties (Chemical physical or both) depending on the arystallographic direction in which the property is observed. The anisotropic behanour of graphite Ps kunstrated in its abilery to act as a solid folum lubal cant . The anisotropic behavior of graphine PQ exemplified in viatually au 9t physical and chemical properties. For example, thermal and Electrical Conductify.

(f perltectic and Eutectoid Reactions : pelkesbic reaction a bus, AM Eutectors Reaction = [5, +353 Souds/ towy Solid, Solid + solid? Neatis. Solid 2+ sididz. Differences blw peritechto and Eutectoid Reactions ? * pere tecto Reaction: The peritecto reaction also involves three solid In equalebium, the transition is from a solid + liquid phax to a different soled phase when coding The inverse reaction occurs when heaks. * Eutectoid kranspormation - Eutecold reaction of an e sothermal reversible reaction in which a solid phase to converted into two or more intimately mixed solids on cooling, the No of soleds formed being the same as the number of component. In the system.