I have deposited pure Cr and W films by unbalanced magnetron sputtering method and then prepared films by doping them with Ag. The hardness and modulus of these coatings are lower than that of the pure films. What can be the main reason behind this ? Usually addition of another element increases hardness and modulus.I would really appreciate any research article or help from experts.
Thank you !!
Hello
The hardness and modulus increase in the case of W and Cr are expected since silver is softer than the initial pure metals (2.5 for Ag, 7.5 for W and 8.5 for Cr on Mohs hardness scale).
A modified film has intermediate properties between its initial pure elements not the summation of the properties.
Good luck
Regards
Loraine
Hi Mohammad,
Have a nice time !
Properties of metals are fundamentally determined by their electron behavior, which is largely reflected by the electron work function. There are many papers about this topic in the litterature. For example, I know that Dr. D. Y. Li has performed a thorough study upon this phenomenon. Please take a look to some papers in the following links :
1. http://onlinelibrary.wiley.com/doi/10.1002/pssb.201248051/full
2. Article Electron work function–a promising guiding parameter for mat...
3.http://211.81.50.59/education/qmcourse/8-Binding_Energy/ip_ea_en.pdf
If you need some help about electron work function measurements for metals, binary alloys of silver and silver-based pseudoalloys , please let me know.
Good luck.
Thank you Lorraine Youssef and Prof. Akbi for your valuable insight.
Two points. First, While the modulus is a function of atomic properties such as electronic bonding, the hardness is a function of film properties such as thickness and grain structure, e.g., dislocation mobility. Secondly, when you report hardness and modulus values, be sure to quote the appropriate precision, based on the statistics of the measurement, and don’t just quote the output from the machine. Your table shows the values to one, two, three, and four significant figures. I doubt the precision is three significant figures, let alone four. Also, the accuracy of the values, which is another issue altogether, depends on the models used to compute hardness and modulus.
Mohammad,
Ag can in-fact harden a material, but only if the Ag precipitate is fine. The Ag-Cu alloys are an example where spinodal decomposition leads to hardening. Ag forms a miscibility gap with many elements including W and Cr. When the Ag phase coarsens the mechanical properties will degrade, which may be the case. How did you "dope" the Ag. Process is going to be key in getting the properties you desire.
Dear Luke Autry,
During magnetron sputtering the Ag target current was varied while the Cr/W target current remained constant.
Sincerely,
Kabir
Hello Mohammad,
I think you need to characterize the microstructure of the coatings, especially the grain size, to see if the addition of Ag influences how the film grows. As Irwin Singer pointed out above, the microstructure is strongly influencing the hardness. What is the thickness of the films?
What is puzzling me more than the hardness decrease, are the Young's modulus values for your W films. For pure W I expect a value in the range of 400 GPa which should not be influenced too much by deposition condition, film thickness or the addition of silver. Do you have an explanation for this?
Best regards
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