MSE 513 Homework #1 Due Jan. 21, 2013

Transcription

1 Reading: My class notes, pgs Introduction to Phase diagrams, particularly: o Common terms o Binary diagrams o Features of phase diagrams o Problems in published phase diagrams Ragone chapter 9, particularly , 9.8, 9.9. Do not worry about the discussion of activities, enthalpies, solutions, etc. This will come later. Key concepts / phrases / terminology: Lever rule Composition Phase fraction Solubility limit Solidus Liquidus Solvus Eutectic Eutectoid Peritectic Miscibility / immiscibility Congruent melting Eutectic microstructure Eutectoid microstructure Warm up problems: Ragone 9.1(a,c), 9.6, 9.8(a,b), 9.9, 9.12 (a,b), 9.13

2 At right is the Pb-Sn phase diagram. Refer to this for the problems below. (Problems adapted from Callister, ch. 9.) (warm-up, not graded) Cite the phases that are present and the phase compositions for the following alloys: a. 15 wt-% Sn at 100 C b kg Sn and 14 kg Pb at 200 C. (warm-up, not graded) A lead-tin alloy of composition 30 wt-% Sn is slowly heated from a temperature of 150 C. a. At what temperature does the first liquid phase form? b. What is the composition of this liquid phase? c. At what temperature does complete melting of the alloy occur? d. What is the composition of the last solid remaining prior to complete melting? 1. A 2.0 kg specimen of an 85 wt-% Pb-15 wt-% Sn alloy is heated to 200 C. At this temperature it is entirely an α phase solid solution. The alloy is to be melted to the extent that 50% of the specimen is liquid, the remainder being the α phase. This may be accomplished by heating the alloy or changing its composition while holding the temperature constant. a. To what temperature must the specimen be heated? At this temperature, what is the composition of the liquid and solid phases? b. How much tin must be added to the 2.0 kg specimen to achieve this state? At this temperature, what is the composition of the liquid and solid phases? 2. For a lead-tin alloy of composition 30 wt-% Sn at 180 C, do the following, assuming the system has been formed by a slow cool from the melt: Determine the mass fractions of α and β phases. Determine the mass fractions of primary and eutectic microconstituents. Determine the mass fraction of eutectic β. Sketch the microstructure. 3. For 2.8 kg of a lead-tin alloy, is it possible to have the masses of primary β and total β of 2.21 kg and 2.53 kg, respectively, at 180 C? Why or why not?

3 4. At right is the Bi-Pb phase diagram. A. Label the unlabeled regions by the two phases that are present. B. Identify a peritectic reaction, including the phases involved, the temperatures at which they occur, and the composition ranges over which they occur. C. Give the temperature, reaction and composition range for the eutectic reaction. D. For a 60 wt% Pb alloy (as shown by the dotted line) describe the sequence of phases formed as the system is cooled from 300 C.

4 5. This is the Cu-Pb phase diagram. Note the critical point & phase separation that occurs near 1000 C, 70 wt-%. The vertical lines indicated by (Cu) and (Pb) indicate the nearly pure Cu and nearly pure Pb solid phases. For a 70 wt-% Pb system initially at 1200 C, describe what phases and phase transitions occur as the system is cooled. Be as specific as possible! Suppose you are given a piece of material that has 20 wt-% Pb in it, and you want to get most of the Pb out. How could you do this? 6. Below is the Al-Zn phase diagram. Label all of the unlabeled phase fields with the phases present. Identify (by temperature, pressure, and transformation on cooling) one eutectic transition, one critical point where phase separation occurs, and one monotectoid. For a 60 at-% (or mol-%) Zn system at 650 K, what phase or phases are present? What types of phases (solid solutions, liquid solution, ordered compound, line compound ) are each?

5 7. Consider the Fe-Fe 3 C phase diagram shown. For each range of compositions below, sketch the microstructure assuming slow cooling from the melt. Indicate the phases and microconstituents present. a wt-% < C 0 < 4.3 wt-% ( cast iron ) b wt-% < C 0 < 2.14 wt-% ( high carbon steel ) c wt-% < C 0 < 0.76 wt-% ( low carbon steel )