What Are the Differences Between Dispersoids and Intermetallics?

[darkelf]

Hey there,

Can anyone tell me the difference if any between dispersoids and intermetallics? Especially with terms like fragmented intermetallics and precipitated dispersiods?

Would truly appreciate it.

Thanks

 

[Astronuc]

I've seen the terms used somewhat interchangeably, but that may depend on the alloy systems.

Dispersoids - http://www.sintef.no/static/mt/norlight/ProjectPortfolio/HeatTreatmentFundamentals/dispersoids.htm

dispersoids, which pin the growing subgrains (recrystallisation nuclei), and consequently leads to an improved recrystallisation resistance. Examples of dispersoid forming elements [in Al (and maybe Mg?)] are manganese, zirconium, scandium and hafnium. These are studied both alone and in combination in order to find ”optimised” additions.

Precipitation kinetic of Al₃(Sc,Zr) dispersoids in aluminium
The non-isothermal formation of Sc- and Zr-containing dispersoids in Al–Zr–Sc ternary alloys has been investigated by atom probe tomography (APT). In the early stages of precipitation, a high number density of Sc-rich clusters form.

Mg₂Si Dispersoids


In Zircaloy (Zr-Sn-Fe-Cr-(Ni)-O) we refer to Zr(Fe,Cr)₂ (forms Laves phase) and Zr₂(Fe,Ni) (forms Zintl phase) second phase particles, which are intermetallic compounds, and which are dispersed within the Zr-Sn solid solution. Silicon is present at about 100 ppm where is forms Zr₃Si upon preciptiation from the melt, and this is where the second phase intermetallic particles precipitate.

So perhaps the distinction between intermetallic compounds and dispersoids is the fact that intermetallic compounds form from the alloying constituents in repsonse to the thermodynamics of the system, whereas dispersoids are strictly added to form dispersed precipitates. But I'm not quite sure since I've seen examples where the terms 'intermetallic compound' and 'dispersoid' seem to be used (or referenced) interchangably.

I also think of dispersoids as metallic oxides, e.g., rare Earth oxides or heavy metal oxides, e.g., oxides (and carbides) of Ta, Hf and Th in metals like tungsten or certain nickel superalloys. In these cases the oxides have melting temperature well beyond that of the alloy.


Journal of Alloys and Compounds is a really good reference for this topic.