DPPA FAQs

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DPPA_FAQs

DPPA_FAQs

Contents

1 How do I get started?

The installation of DPPA is relatively simple. The steps are:

  1. Unpack the zip file onto your computer
  2. Run 'BIGdippa'
  • Either by typing BIGdippa into command window (when in correct folder)
  • Open BIGdippa.m and press the run button

2 It isn’t working?

One common problem occurs when the Matlab current folder is not that of DPPA. This will lead to errors such as: >>Undefined function or variable 'BIGdippa'. This can be corrected by going to the folder of DPPA in the Matlab GUI:

The code may encounter unusual problems. The best way to solve any errors is to look at any errors in the Command window and click on the line that the error occured at, you can then put a breakpoint on this line to try to find out why the error occured.

Otherwise email: info@dmata.co.uk

3 Does it work with more than 2 phases?

No currently it only works for 2 phases. Since the code is open source it is possible to introduce a 3rd phase into the code. However, the best way to incorporate a 3rd phase is by adding the peak position of each peak of the phase manually using the ‘+’ button on the left-hand side of the ‘Settings Panel’ within phase 1 or 2.

4 Does it work with beta characteristic peak?

No currently it only works for the alpha-1 and alpha-2 components. Since the code is open source it is possible to introduce the beta component in the same way that alpha-1 and alpha-2 have; i.e. there will be a set d-spacing difference and a set intensity ratio between K-alpha and K-beta peaks that can be added to functions ‘pk_alpha’ and associated functions.

5 Do I need an instrumental sample?

To gain quantifiable information about the microstructure through the Warren-Averbach and Williamson-Hall methods an instrumental sample is required. This can be an instrumental sample such as a silicon standard, but a defect free sample with a large grain size of the same crystal structure/material can be better due to changes in broadening with angle/d-spacing. The fitting part (BIGdippa) does not require an instrumental sample. In many cases the changes in full-width, intensity, or intergranular strains between samples provide more information and are more important than information gained from WA/WH analysis.

6 What do I do when I don’t know the crystal structure of my material?

These can be searched for online.

7 What peak profile analysis procedure should I use?

There are numerous peak profile methods that can be used, more details of some of them are given in [1] T.H. Simm, P.J. Withers, J. Quinta da Fonseca, An evaluation of diffraction peak profile analysis (DPPA) methods to study plastically deformed metals, Mater. Des. 111 (2016) 331–343. doi:10.1016/j.matdes.2016.08.091.

Other software options are available: * CMWP http://metal.elte.hu/cmwp/ * Within Reitveld refinement programs such as TOPAS

The advantage of this one (DPPA) is that the code is open source and can be changed and modified. It is also possible to see how the techniques work rather than be a black box. The biggest disadvantage though is that it is requires the proprietary software MATLAB.

8 How do I get information about the peak fitting for different analysis?

If you want to use the fitted data for different analysis:

Then the fit data can be obtained from the saved fit data. The fit data is in the form of a struct named 'fita'. The fit parameters are contained within the field 'aa'and can be accessed as 'fita(n).aa'. From the variable 'aa' the columns are for different peaks and the rows are for (1) peak position, (2) peak intensity, (3) full-width, (4) pseudo-Voigt mixing parameter of the peak.