Talk:Amorphous metal

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Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 17:14, 17 January 2022 (UTC)

Wiki Education Foundation-supported course assignment

This article was the subject of a Wiki Education Foundation-supported course assignment, between 1 April 2019 and 7 June 2019. Further details are available on the course page. Student editor(s): DavidThi1.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 14:05, 16 January 2022 (UTC)

Proposed changes to this article one section at a time

I'm proposing the following as the opening paragraph.

An amorphous metal (also known metallic glass or glassy metal) is a solid metallic material, usually an alloy, with a disordered atomic-scale structure. Most metals are crystalline in their solid state, which means they have a highly ordered arrangement of atoms. Amorphous metals have a disordered arrangement of atoms similar to liquids and glasses. The most common method for producing amorphous metals is to cool a molten metal alloy before the atoms have time to crystallize. The precise cooling rate necessary to quench a molten alloy as a metallic glass depends on the alloy composition, with eutectics having a lower critical cooling rate than pure metals, but the critical cooling rates are still often on the order of 100,000 to 10 million degrees per second. One method for achieving this cooling rate and producing an amorphous metal is to sputter the molten alloy onto a spinning metal disk (melt spinning). Other than extremely rapid cooling, methods such as physical vapor deposition, solid-state reaction, ion irradiation, and mechanical alloying have also been shown to produce amorphous alloys.

Compared to crystalline alloys, amorphous alloys are stronger, lighter, have better corrosion resistance, and are some of the best soft magnetic materials commercially available. Commercial production of amorphous alloys is largely for applications which require soft magnetic materials, like power transformers, anti-theft tags, and sensors. Amorphous metals have lower electrical conductivity than crystalline metals because the disordered structure reduces the electron mean free path, but this is a benefit for soft magnetic materials because a lower conductivity decreases eddy current losses in the MHz region. Although stronger and lighter than crystalline metals, it's difficult to make big pieces of amorphous metal because, when casting the piece, the center cools more slowly than the edges, producing a piece that might be amorphous on the outside but crystalline in the center. For this reason, pieces of amorphous metal are usually thinner than 1 mm. However, more recently a number of titanium-based alloys, developed in studies originally carried out at Caltech, were discovered with critical cooling rates low enough to allow formation of amorphous atomic structures in thick layers (over 1 millimeter); these are known as bulk metallic glasses (BMG).

Here are a few reasons why this should be changed:

1) The first section as it is now suggests that amorphous alloys are as conductive as crystalline metals, which is not true. They are more conductive than insulators but why are we comparing them to insulators? They are less conductive than crystalline metals because the mean free path is shorter because the atomic structure is disordered. The 3rd citation explains this.

2) The organization seems to be a mess. the first paragraph discusses what they are and how to make them, but then the second paragraph starts to talk about applications but misses entirely the biggest application, which is soft magnetic materials. In particular, high efficiency power transformers and anti-shoplifting tags. If an application is going to be mentioned is should be those. I combined and expanded on what was there before so that the first paragraph is about making these materials and the 2nd paragraph is about applications.

The youtube video is a good explanation of how these materials are formed, there should most definitely be a link to TTT diagrams somewhere in this article, if not a brief mention of them in the introduction. — Preceding unsigned comment added by Khagedor (talk • contribs) 01:57, 24 July 2014 (UTC)

References

WELL! I PROPOSE you write this for the layman. A person say who was looking at a Soviet watch on eBay and wondered what the heckarooney "metallic mineral glass" is. My eyes glazed over trying to read this and I am not unintelligent. I was wondering why they call it "glass" but chrome and stainless steal are not "metallic mineral glass". One thing I did get is that you can't really see through it. The idea I could see through metal (which doesn't sound possible) as the term suggests prompted me to look it up. --2600:6C65:747F:CD3F:D581:2D09:7FC6:A786 (talk) 13:09, 1 March 2020 (UTC)

Anything can be a glass if it's cooled correctly. When people think of glass, they are usually thinking of silicate glass, which is what windows and bottles are made of. But, scientifically speaking, anything that is non-crystalline is a glass. The only real requirement is that the material is cooled quickly enough that it can't crystallize before it turns solid. Even water can become a glass if cooled correctly. Most plastics are glasses, even the ones that aren't see through. Obsidian is an example of a natural glass made of rock, which of course is totally opaque. So is the porcelain that your toilet is made of.

Now some materials will form a glass much easier than others. Honey is good example, which can become a glass if cooled over a period of months. Nearly all glues and adhesives are glass formers that are simply not cold enough to solidify. But metals must be cooled very, very fast to keep them from crystallizing. However, there are other ways to make metallic glass, such as electroplating, wet deposition of silver, or vacuum deposition. The most common example of a metallic glass is the coating on a mirror, which has better reflectivity than crystalline metals because there are no grain boundaries. Another example is the chrome plating on automobile parts. I hope that helps. Zaereth (talk) 19:43, 1 March 2020 (UTC)

Reheating

The article asserts that upon reheating amorphous metals start to flow. I believe that this is slightly misleading, it is a well known phenomenon that heating amorphous metals will cause them to recrystallise, at least in part, and take on the more stable form, i.e. a crystal. Where did the concept of reheating the glass to make it flow come from? 129.78.64.106 01:42, 12 October 2006 (UTC)

Well, upon heating above a temperature Tx, amorphous metal recrystalize, but there is a temperature "window" below Tx that metalic glass can flow. This window is Tg < T <Tx, where Tg is the glass transition temperature.

This effect is well known, See: "Effect of die-casting parameters on the production of high quality bulk metallic glass samples" By Laws, Gun & Ferry. 129.78.208.4 04:41, 14 March 2007 (UTC)

Indeed, keeping a glass between Tg and Tx allows forming with low stress (low force) due to low viscosity of the formed material. This process is similar to superplastic forming, although superplastic forming refers to crystalline materials. What's behind the argument betw. 129.78.64.106 and 129.78.208.4, is the fact that Tg and Tx are obtained from the continuous heating experiment, and their values depend on the heating rate. If the heating rate is lowered, Tg and Tx go down. On the other hand, the hot forming is usu. carried out in the isothermal mode (heating rate close to zero), so the values of Tg and Tx are just approximates. In the isothermal case, time is relevant, and the longer a glass is kept at elevated temperature, the more likely is crystallisation. Therefore, one has to remember that forming the metallic glass between Tg and Tx can not last too long (say, a few minutes), otherwise the glass (or - actually - supercooled liquid) will crystallise. JPFen (talk) 17:04, 6 November 2009 (UTC)

How easy an amorphous metal crystallizes depends a lot on the composition. A few are so stable that they can be heated above the glass temperature without fast crystallization. Other alloys crystallize before they become really soft.Ulrich67 (talk) 19:52, 26 May 2022 (UTC)

Very true. I learned a lot about metallic glass from mirror manufacture, because mirror coatings are amorphous, whether applied by vacuum deposition, wet deposition, electroplating, or fire gilding. Turns out, if the coating is too pure the metal can crystallize even when below the glass transition. In vacuum deposition, for example, some of the gas atoms become trapped in the amorphous network, which act like throwing a monkey wrench into the works to help prevent recrystallization. This actually increases reflectivity in the visual and NIR range, but for FIR mirrors a much higher vacuum can produce almost pure coatings which help enhance reflectivity but is not affected by recrystallization at that wavelength, due to the wavelength being larger than the crystals. Zaereth (talk) 20:16, 26 May 2022 (UTC)

titanium glass

http://www.sciencedaily.com/releases/2008/12/081219172129.htm --24.96.180.121 (talk) 00:46, 28 December 2008 (UTC)

Contradiction?

The introduction to the article states: "metals produced by these techniques are, strictly speaking, not glasses. However, materials scientists commonly consider amorphous alloys to be a single class of materials, regardless of how they are prepared."

Where as the Properties sections states "Amorphous metals, while technically glasses, are also much tougher and less brittle than oxide glasses and ceramics."

It seems to be unsure whether they are technically glasses or not. Although I may have missed something. Danno81 (talk) 10:10, 10 June 2009 (UTC)

Nope, no contradiction, it also says:

"Materials in which such a disordered structure is produced directly from the liquid state during cooling are called "glasses"

In other words, whether or not an amorphous metal is technically a "glass" depends not on its composition, but how it was formed. If it was cooled from the liquid state, it's a glass, but if it was produced by some other method, then it is not. The "other" methods listed in the article are physical vapor deposition, solid-state reaction, ion irradiation, melt spinning, and mechanical alloying. The sentence in the introduction that you cited above refers specifically to amorphous metals created using these other methods. Stonemason89 (talk) 15:22, 15 July 2009 (UTC)

Melt spinning is just one method for rapidly cooling a melt. So it should be removed from this list. --Ulrich67 (talk) 18:43, 8 August 2011 (UTC)

Very low induction of Metglass 2605 - should be over 1 tesla!

Surprisingly, the article provides the information: "Metglas-2605 is composed of 80% iron and 20% boron, has (...) a room temperature saturation magnetization of 125.7 milliteslas". This is 0.1257 tesla (T). Such a great content of iron and only 0.12 T? The successor of 2605, 2605SA1, has the saturation induction of 1.56 T, and the chemical composition of: iron 85-95%, boron 1–5%, silicon 5–10% (all in weight %). I guess the text should rather read "(...) a room temperature saturation magnetization of 1.257 teslas". I don't have the exact 2605 datasheet, so I don't feel like editing the article without quoting the source, but I'm sure B_s should be an order of magnitude larger. JPFen (talk) 17:29, 6 November 2009 (UTC)

Hi, thanks for bringing this up. Well, the magnetic properties is vastly dependant upon the alloy structure, not just composition (why is rust not mangetic?). Anyway, I dug up a reference to check this out:

• "Thermomagnetic and transport properties of metglas 2605 SC and 2605" Ratnamala Roya and A.K. Majumdara, Journal of Magnetism and Magnetic Materials

Volume 25, Issue 1, November 1981, Pages 83-89

They state for magnetic saturation that Fe₈₀B₂₀ is 1.56 T (table 2 -- comparison of transport properties for metglas2605SC and 2605). User A1 (talk) 00:28, 7 November 2009 (UTC)

Electrical Conductivity

The article needs to indicate how the electrical conductivity compares with crystalline metals. Most probably the lack of periodic wavefunctions will cause the resistivity to be higher, but by how much? —Preceding unsigned comment added by 193.188.46.249 (talk) 08:00, 18 March 2010 (UTC)

For the ferromagnetic alloys two manufacturers give values of about 1,2 -1,4 µOhm m. Refs: [1], [2]. This is about two times the resistivity of stainless steel. About the same ration should be valid for the thermal conductivity, as the Wiedemann-Franz law should be a reasonable approximation for the amorphous state as well. --Ulrich67 (talk) 20:26, 17 August 2011 (UTC)

Shouldn't we have a List of Amorphous Metals?

Shouldn't we have a list of amorphous metals as a new topic? The page describes about amorphous metals, but does not have a list of them. Valchemishnu 15:46, 17 June 2011 (UTC) — Preceding unsigned comment added by Valchemishnu (talk • contribs)

Amorphous Metals are a quite special topic, with not so much general interest. Except for specialists there is not much use of such a full list of alloys. One Problem with such lists is, that we may need a ref. for nearly every entry. Maybe if we limit the list to those alloys with real world applications it may be of some general interest.--Ulrich67 (talk) 19:39, 8 August 2011 (UTC)

Another way to make met-glass

The article has left out another perhaps interesting method for obtaining metals in an unusually glass-like form: electrodeposition. I know, because I've plated amorphous Nickel and verified its amorphous structure with x-ray diffraction as an undergrad physics project. I'd also like to point out, that I quite agree with an earlier post about the lack of information about the conductivity of metallic glasses. Whenever the properties of any metallic material is considered, conductivity is one of the first that comes to mind. Bu7fkl7 (talk) 04:25, 17 August 2011 (UTC)

A section on the methods to produce amorphous metals would be a good idea. There are a view other methods: electroplating, ball-milling, heavy irradiation, inter-diffusion, Thin film deposition. — Preceding unsigned comment added by Ulrich67 (talk • contribs) 21:15, 16 September 2011 (UTC)

About grain boundaries

I disagree with the statement under Properties, "The absence of grain boundaries, the weak spots of crystalline materials..." Grain boundaries are a strengthening mechanism of pure metals, alloys and ceramics, not weak spots. Grain boundary strengthening works by being a barrier to dislocation motion, as quantified by the Hall-Petch equation. The exception to this rule is creep, where grain boundary sliding enables deformation under constant load above ~0.5 homologous temperature. Metal glasses, by virtue of not having a crystal lattice, cannot deform by dislocation movement.His Manliness (talk) 19:18, 30 November 2012 (UTC)

Grain boundaries usually increase the mechanical strength, but they are also placed where corrosion often starts. So the grain boundaries are the weak spots with respect to corrosion. --Ulrich67 (talk) 20:13, 30 November 2012 (UTC)

Actually grain boundaries are much weaker than the crystals themselves. This is why in heat treating efforts are used to keep the grains as small as possible, because the boundaries provide a place for a crack to form and a line for it to follow. In items that need exceptionally high tensile-strength and thermal resistance, the items may be cut from a single crystal, thereby removing all grain boundaries. A good example is the turbines of fighter jets. Zaereth (talk) 20:09, 16 February 2017 (UTC)

Here we go. As an example, bulk iron has a tensile strength of 180--250 MPa, yield strength of 14--103 MPa, and a Charpy v-notch of 200 joules. The individual crystals, on the other hand, have a tensile strength of 5000 and 13000 MPa (depending on crystal orientation) and a shear strength of 3500 and 8000 MPa. Zaereth (talk) 20:46, 16 February 2017 (UTC)

Other amorphous metals

I just read this article and found it to be very informative. I learned a lot, and thank those who put the time and effort into building it. My only observations are that it seems too focused on amorphous metals created by rapid cooling, and doesn't really mention non-mechanical properties like optical and electrical. Other methods for making amorphous metals exist, such as vacuum deposition, wet deposition, electroplating, or amalgam reduction. The reduction of amalgams is probably the oldest method, which has been used for mining precious metals for thousands of years. It was also applied to gilding and mirrors, because the reflectivity is much higher than crystalline metals. I don't know enough about the specifics to be any real help myself, but hopefully someone who does will read this and decide to help out. Zaereth (talk) 01:09, 16 February 2017 (UTC)

Electrical conductivity - high or low

Intro says "amorphous metals have good electrical conductivity" (no ref) but the only other mention of electical conductivity is of high resistivity. What can we say ? - Rod57 (talk) 12:41, 30 March 2020 (UTC)

From what I recall, metallic glasses have very good electrical-conductivity compared to insulators, but compared to crystalline metals of the same type the electrical resistivity is typically 3 to 6 times higher for metallic glasses. This is generally attributed to electron scattering due to the disordered atomic structure. A side effect is that this decreases inductance, skin effect, and the accompanying eddy currents, making them highly suitable for things like transformer cores with lower losses than iron cores. Another difference is that the resistivity is extremely temperature-dependent for amorphous metals. At extreme colds the conductivity will reach a maximum (resistivity reaches a minimum), and as temperature is further decreased the conductivity will decrease, which is usually attributed to the Kondo effect. In contrast, thermal conductivity tends to be higher in amorphous metals, due to their tendency to generate more phonons than crystalline metals, which tend to dissipate quickly in a crystalline lattice. I hope that helps. Zaereth (talk) 17:40, 30 March 2020 (UTC)