Electron microscopy
 
Cooling Rate to Make Metallic Glasses from Melts
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It has been accepted that any material can vitrify if cooled from the molten state to the glass transition temperature, Tg, at a cooling rate fast enough to prevent crystallization. The slowest a material can be cooled down to Tg without crystallization, the better the glass forming ability (GFA) is.

However, in practice, it is very challenging to make metallic glasses from melts as this process requires very high cooling rates (e.g. 105-106 K/s) and such a high cooling rate still results in a crystal percentage more than 0.1% in many cases. In general, only a material with a maximum allowed fraction of crystals, Xc, between 0.1% and 0.0001%, is conventionally classified as a glass. [1]

Figure 3070 shows the critical cooling rate (Rc) and critical casting thickness (dc) for formation of various metallic glass alloys from melts as a function of reduced glass transition temperature (Trg). In general, as the reduced glass transition temperature increases, the required cooling rate for glass formation decreases, and thus it is possible to form thicker glasses at slower cooling rates.

Critical cooling rate and critical casting thickness for formation of various metallic glass alloys from melts as a function of reduced glass transition temperature
1: Ni
2:Fe89B11
3:Fe83B17
4:Fe41.5Ni41.5B17
5:Fe79Si10B11
6:Au55Pb22.5Sn22.5
7:Pt60Ni15P25
8:Mg65Cu25Y10
9:Zr65Cu17.5Ni10Al7.5
10:Zr52.5Ti5Cu17.9Ni14.6Al10
11:Ce68Al10Cu20Nb2
12:Ni62.4Nb37.6
13:Te
14:Fe91B9
15:Au77.8Ge13.8Si8.4
16:Co75Si15B10
17:Fe80P13C7
18:Pd82Si18
19:Pd77.5Cu6Si16.5
20:Zr57Nb5Cu15.4Ni12.6Al10
21:Au49Ag5.5Pd2.3Cu26.9Si16.3
22:Pt57.5Cu14.7Ni5.3P22.5
23:Pd40Ni40P20
24:Pd40Cu30Ni10P20
25:Ni75Si8B17
26:Ti34Zr11Cu47Ni8
27:Zr41.2Ti13.6Cu12.5Ni10Be22.5
28: La55Al25Ni10Cu10
29: Fe40Ni40P14B6
30:La55Al25Ni20
31:Zr60Al20Ni20
32: Ge2Sb2Te5

Figure 3070. Critical cooling rate and critical casting thickness for formation of various metallic glass alloys from melts as a function of reduced glass transition temperature.

Note that only some techniques can be used to achieve the cooling rates which produce glass alloys as listed on page3041.

 

 

 

 

[1] Nascimento MLF, Souza LA, Ferreira EB, Zanotto ED. Journal of Non-Crystalline Solids 2005;351:3296.

 

 

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