MTDATA Modelling
(25%)
This coursework is based on the MTDATA software which is installed on 19 computers in the
Department of Materials Computer Room (S3.07). This software will be available until after the
coursework deadline. State clearly the thermodynamic database used for each answer.
Answer both of the following questions.
1. Aluminium alloys for aerospace applications
Background
Al-Cu-Mg and Al-Cu-Mg-Zn alloys are wrought aluminium alloys which can be used in aerospace
applications. If there is a need to fusion weld these alloys, then clearly the welding process will
involve melting of the alloys and therefore the temperature range over which they solidify, and any
possibly segregation as a result of the welding operation, will be important in determining the final
properties of the weld. It is possible in certain circumstances for them to form solidification cracks; the
factors which influence whether or not such cracks will form are:
? The absolute freezing range –alloys with a wide freezing range being more susceptible to
cracking
? The freezing range for dendrite cohesion, which is thought to occur at about 50% solid
? The volume fraction of low melting phases (since cracks might be healed if enough liquid remains
near the end of the solidification process to flow around the dendrites)
Questions
(Use the SGSOL database for these calculations).
(a) Explore the Al-rich corner of the Al-Cu-Mg ternary phase diagram.
(b) For an Al-4.5Cu-1.5Mg wt.% alloy, what differences would you expect to find in the alloy
microstructure as a result of rapid solidification compared to an alloy which was cooled incredibly
slowly?
(Hint: calculate both equilibrium (multiphase) and Scheil phase amounts as a function of
temperature)
(c) Explore the effect of different magnesium additions (0.5, 1.5, 2.5 and 3.5 wt.%) to an Al-4.5 wt.%
Cu base alloy under rapid cooling conditions. How does the Mg affect:
(i) the overall freezing range of the alloy
(ii) the freezing range between complete liquid and 50% solid
(iii) the temperature range over which the final liquid solidifies
(Hint: Use Scheil calculations to predict the amount of phase as a function of temperature in each
case)
Which Al-Cu-Mg alloy would you choose if you wanted to minimize the risk of solidification cracking?
(d) What differences do the addition of small amounts of Zn (up to 5 wt.%) make to these Al-Cu-Mg
alloys?
2.
The Design of Duplex Stainless Steels
Background
Stainless steels are based on additions of Cr and Ni to the iron-carbon system. Duplex stainless
steels are a particular type of stainless steels which, as their name implies, contain both the austenite
and ferrite phases and offer high resistance to general and stress corrosion cracking, good
weldability and high strength. Alloying elements are added such that there is a balance of
approximately 50% of each of the austenite and ferrite phases at the high temperature annealing (or
solution treatment) temperature, from which they are quenched to room temperature. The alloying
elements are also carefully controlled so as not to introduce intermetallic phases and nitrides into the
microstructure which may have deleterious effects. The carbon concentration in these steels is
normally kept below 0.03 wt.%.
Questions
(Use the MTAPPLIC database for part (a) and (b). For part (c) use the special database file named
duplex.mpi which can be downloaded from the LEARN server. To open the file in MTDATA Studio
or MTDATA for Windows use Open option in the File menu).
(a) The solution heat treatment is usually carried out between 1050 and 1200oC. Within this
temperature range, explore how important the chemical composition, and in particular the relative
amounts of Cr and Ni, is in determining the relative amounts of the austenite and ferrite phases.
(Hint: Consider a ternary phase diagram in the Fe, Cr, Ni system. Tie-lines between the austenite,
fcc, and ferrite, bcc, phases may be helpful.)
(b) After the solution heat treatment, duplex stainless steels are usually aged at lower temperatures.
It is possible that other phases will form during this ageing process. Demonstrate for what
compositions this may be the case when the ageing temperature is 500oC.
In practice, the sigma phase is very slow to precipitate and therefore may be neglected in your
calculations to a first approximation. How does this affect the choice of chemical composition of the
steel?
(Hint: Consider again the ternary diagram, and consider the list of allowed phases carefully.)
(c) There are a range of duplex stainless steels which are commercially available. Typical
compositions of two such steels are shown below, in weight %. The small addition of carbon (<0.03 wt.%) can be neglected for these calculations. How would you expect the heat treatments applied to differ for the two steels? Steel Cr Ni Mo N Mn Fe 2205 22.0 5.5 3.0 0.17 2.0 Bal 2207 25.0 7.0 4.0 0.28 1.2 Bal Bibliography “Practical Applications of Thermodynamics”: John Gisby, Hugh Davies, Alan Dinsdale (NPL Materials Centre, National Physical Laboratory) and Fred Hayes (Consultant to NPL) For Aluminium Alloys (2): JD Webster and P Prangnell, Manchester Materials Science Centre. For Stainless Steels (3): FH Hayes, A Watson, CALPHAD and Alloy Thermodynamics, Ed. PA Turchi, A Gonis, RD Shull, TMS, 2002 and FH Hayes, MG Hetherington, RD Longbottom; Materials Science and Technology, 1990, 6, 263-272. PLACE THIS ORDER OR A SIMILAR ORDER WITH US TODAY AND GET AN AMAZING DISCOUNT ?? find the cost of your paper Is this question part of your assignment? Place order Posted on May 13, 2016Author TutorCategories Question, Questions