This section deals with various aspects of the databases. In particular you will learn more about what happens when you type def sy 'Fe,Cr,Ni' sou plus ! and how to work differently (creating and using mpi files).

• If your system has a large number of elements (say 7 or more), you will find that MTDATA identifies a very large number of phases when you define the system. For example:

  MULTIPHASE OPTION ? def sy 'Fe,Cr,Ni,Si,Mn,Nb,Ti,C,N' sou plus sub_sgte !

  gives you no less than 153 phases ! If you work with such a system, and say want to include 10-15 phases in your calculations, a convenient method consists in saving the subset of the databases you are actually working with (as the def.mpi file above).
  Here is an example of how to do this:

  WHICH MODULE ? access
  ACCESS OPTION ? def sy 'Fe,Cr,Ni,Si,Mn,Nb,Ti,C,N' sou plus sub_sgte !
  ACCESS OPTION ? class ab p(*) no p(FCC_A1,BCC_A2,M23C6,LAVES,SIGMA,CNb,CTi,NNb,NTi,LIQUID) !
  ACCESS OPTION ? def out 'nf709' !
  ACCESS OPTION ? save
  ACCESS OPTION ? ret

• We now use the file we just created:

  WHICH MODULE ? mu
  MULTIPHASE OPTION ? def data 'nf709' !
  MULTIPHASE OPTION ? cl no p(*) !

  which should be easier than re-defining the system each time and looking for the right phases. You will also need to be able to create your mpi files if you want to program with MTDATA.

• To know a bit more about what is in the mpi files, follow this example:

  WHICH MODULE ? mu
  MULTIPHASE OPTION ? def sy 'Fe,Cr,Ni' sou plus !

  So far we have not said much about what happens when you define the system (the significance of the error messages is here). When you enter the above command, MTDATA searches in the indicated databases for all the phases that contain the given elements. It then saves all the information into a file called, unless you have specified otherwise, def.mpi.

  You can think of this file as a subset of the databases containing the informations for your system only. Let's have a look at it:

  MULTIPHASE OPTION ? $more def.mpi [Ret]
  

  Note the $ which means we are using a system command from MTDATA (in this case more which displays text in the console). The following is an example of entry in this file:

   'plus           ' = SOURCE OF UNARY DATA
    3 T RANGES FOR  Fe:Cr:Fe<SIGMA:8:4:18>                  
     298.150
     6
    1.02041240000E+05  3.82770000000E+03 -7.28203800000E+02 -1.01638120000E-01 -7.44094200000E-06  2.56833400000E+06
    1811.000
     7
   -5.91811386000E+05  8.32360638000E+03 -1.30363200000E+03  7.57740000000E-03 -5.90884000000E-06  5.57000000000E+05
      -9.000   6.363686000E+32
    2180.000
     7
   -6.95861002000E+05  9.07040638000E+03 -1.39600000000E+03  0.00000000000E+00  0.00000000000E+00  0.00000000000E+00
      -9.000  -5.177354000E+32
    6000.000
  

  And its meaning

   'database where this parameter comes from'
   number of temperature ranges for this parameter
   lower limit for first range
   number of parameters
   coefficients for 1, T, TlnT, T2,T3,1/T
   next power of T, coefficient (if more than 6 parameters)
   upper limit for this range (and lower for the following)
   
   similar for the next range
   upper limit for last temperature range