If in the Thermo-Calc analysis of a system of elements in ABCDE quinary alloy we have FCC
_A1 and FCC_L12 which one is better mechanical properties?
https://books.google.com/books?id=3h1KDwAAQBAJ&lpg=RA1-PA133&ots=L-59-aagPI&dq=FCC%20_A1%20and%20FCC_L12%20which%20one%20is%20better%20mechanical%20properties%3F&pg=PP1#v=onepage&q=FCC%20_A1%20and%20FCC_L12%20which%20one%20is%20better%20mechanical%20properties?&f=false
Dear Majid,
Please go through the physical metallurgy book. It’s easy to understand the difference. This is a order-disorder effects. Phase from the L12 to the D019 phase, as proved by the neutron diffraction and f.c.c.- derivative (A1 or L12) phases obtained by different heat treatment
The Face-Centered Cubic (A1) Lattice
In FCC (A1)
A1
=
½ a Y + ½ a Z
A2
=
½ a X + ½ a Z
A3
=
½ a X + ½ a Y
It can be understand by the Bragg –Williams phase diagram between the temperature and composition could be drawn ( I do not draw). Note that the two phase region ( A1 + L12) between the ordered L12 phase and disordered FCC phase. One is ordered and other is disordered phase, since the transition is first order.
The ordered L12 phase generally appears as dispersed precipitates in FCC multi-principal element alloys (MPEAs). A single L12 ordered intermetallic can be obtained in the annealed equimolar FeCoNiV alloy or in AlNi3 (metals and ceramics)[ they are superior to classic creep-resisting Ni-based superalloys].
Since, L12 ordered generally intermetallic, even is dispersed precipitates, but single L12 is ordered phase, so mechanical property will be higher in the L12 phase. (you must understand it is intermetallic). two-phase A1 +L12 microstructure, an exceptionally high yield strength can be observed. A1 phase has high entry suggested to be the result of the inability to accommodate shape change, leading to interphase cracking that results in brittle fracture.
Hope it is helpful for you.
Ashish
Hi Majid,
The typical microstructure of a superalloy is similar to a composite material with two phases, gamma (FCC_A1) and gamma prime (FCC_L12). So in order to understand the mechanical properties of a superalloy, it is important to study how the gamma and gamma prime phases interact with each other. The gamma phase is a supersaturated solid solution (FCC_A1), meanwhile the gamma prime (L12) is an intermetallic phase that precipitates inside the gamma matrix. The gamma prime (L12) phase is an intermetallic compound and provides strength to the super alloy. Superalloys containing the L12 ordered precipitates surrounded by a gamma matrix show better mechanical properties than either of the FCC_A1 and FCC_L12) phases by themselves. The volume fraction of gamma prime varies among different alloys, but most commonly, the volume fraction is in the rage of 60-70% to improve creep resistance.
Regards,
Gilberto
https://books.google.com/books?id=3h1KDwAAQBAJ&lpg=RA1-PA133&ots=L-59-aagPI&dq=FCC%20_A1%20and%20FCC_L12%20which%20one%20is%20better%20mechanical%20properties%3F&pg=PP1#v=onepage&q=FCC%20_A1%20and%20FCC_L12%20which%20one%20is%20better%20mechanical%20properties?&f=false
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys