Nitrided case hardness profile 5

[eagertknow]

I want to get a quatitative measurement of hardness in the total case of a Nitrided specimen so that I can draw a profile and compare specimens on the basis of their hardness profile resulting from different Nitriding potentials and Furnace temperatures. Can anybody guide me?

 

[NickE]

Yes, Section mount and polish, etch. I'm not sure how deep your case is but you may be able to use Vickers/Knoop micro hardness to study the hardness profile. You also might be able to use some other charecterization method, like XRD or some sort of SEM technique to view the profile fo nitrogen diffusion.

Also possible is the creation of deiffusion profiles by the fundamental thermodynamics of the system.


Nick
I love materials science!

 

[metengr]

Your best bet is to either send nitrided specimens (if they can be easily handled) or coupons representative of the sample material you are using to a reputable metallurgical laboratory. Each specimen or coupon should be labeled for identification by the lab representing the specific nitriding heat treatment. The specimens or coupons will be destroyed because they will need to be sectioned at the lab to obtain microhardness data starting from the nitrided surface and traversing beyond the nitrided layer into the unaffected parent material.

The reason for my suggesting going to a competent metallurgical lab is that they have the equipment and expertise to obtain this data for you. The cost should not be that expensive to obtain only the microhardness traverses, you could review the results yourself and plot them on a graph, in lieu of having a professional engineer at the lab do this.

 

[swall]

First of all, you need to have a sufficently deep nitride case, I'd say at least .010" in order to get enough data points to get a meaningful graph. This means gas nitriding or ion (plasma) nitriding. Second, the microhardness test will need to use a low load in order to make the indentations small enough to fit 5-10 readings within the case. Unfortunately, the low loads (i.e. 100g or less) can introduce error and will also give higher apparent hardness values.So, you should run multiple samples from each process. If you get a hardness traverse that seems spurious, you will be able to re-run it.

 

[saxonsvn]

you want to compare the results to get the difference between serveral nitriding potential. I think you should analyse the compoud layer too. For that you can use Glow Discharge Optical Spectroscopy (GDOS), very fast and quite eccurate to get the N-, C- Profile in the Compound layer, or metallography (Light Microscopy, SEM) after etching with different etching agents (HNO3, Oberhoffer, Sodium Pikrat etc.)
Of course, you have to measure the hardness with Vicker (for normal layer thickness up to big thickness, indentation load 100 - 500 g, dependent on hardness value) or Knoop hardness for thin layer. You can better use Electron- Microprobe-Analyse (EMP)to get the N-distribution across your nitrided case, but it's expensive.
Good luck

 

[metman]

You will want to have the coupons sectioned at an angle so that the case depth is magnified. This allows for greater accuracy when plotting your results. Use trigonometry to calculate the actual depth with respect to the measured depth. With this technique you might get away with limithing case depth to .005" or less since a .010" depth will take a long furnace cycle.