Plastic is used in 3D FDM/FFF printing partly because it had a wide temperature range for its glass state - where it can be flowed with some force, but won't flow due only to gravity.
Most metals have a very narrow, or non-existant, glass state. They transition from solid to liquid with almost no flowable-but-not-liquid state.
Are there any metals or alloys that display a glass transition state?
A few things are required for effective extrusion-style 3d printing materials:
Liquid metals tend to have a conflict between "Staying where you put it" and "bonding with the previous layer." In order for deposited metal to fully bond, the interface material needs to reach the melting point so a true fusion weld occurs. And in order to supply enough heat to remelt the interface without an additional heat source like an arc, the deposited molten metal needs to be very hot. So it will tend to run while it cools. High density and high heat capacity makes it run fast and cool slowly.
Pretty much every DIY metal 3d print (such as made by wire-feed MIG welders) ends up looking something like this:
https://3dprint.com/29944/diy-metal-printing-garage/
In comparison, polymers have long molecular chains that allow them to "diffusion weld" and adhere WITHOUT fully remelting the interface. Molten liquid plastic will stick to solid plastic quite effectively. The interface only needs to get hot enough for appreciable diffusion to intertwine the molecular chains. This will occur between the glass point and melting point, without true fusion occurring. So you can print molten plastic at a temperature where it will stay in place long enough to harden, and still get good bonding.
Metals also tend to be very stiff, which encourages warping. It is difficult to build a heated environment of sufficient temperature to properly stress-relieve the thermal contraction stress as the print progresses, whereas with plastic a heated build plate and warm enclosure can permit warping stresses to start relaxing as the print progresses.
It is possible to "FDM-style" 3d print filament/wire made of metal alloys that have a wide range between solidus and liquidus. It has been done using solder and similar alloys. However, between the warping stresses, poor layer bonding from inadequate interface re-melting, and use of soft low-melting alloys, the resulting printed parts will usually end up being weaker than if they had simply been printed in a strong plastic. For example, PEEK is nearly as strong as aluminum, and carbon fiber or fiberglass composite plastics can exceed metals on various performance metrics. So what's the point of printing with weak, brittle metal alloys?
Over the years, lots of people have tried FDM-style metal printing, but no one has found it worthwhile to pursue in the long run. More typical DIY metal printing approaches like 3D MIG welding following by cleanup machining will produce better results.
I"m no expert on this, but the article at https://en.wikipedia.org/wiki/Amorphous_metal may be relevant for you.
There are some special alloys, such as gold/silicon and various titanium-based ones, that become "bulk metal glasses" if cooled extremely quickly (for example, by sputtering onto a spinning cold surface). The speed of cooling prevents crystal formation. Early BMGs were quite strong but brittle; improvements have reduced brittleness and required cooling speed.
I think the closest you're going to get is with a composite material. Over the last 2 years or so, there have been more and more composite filaments emerging on the market for consumer 3D printers. I good example of composite filaments can be seen on Proto-Pasta. Since the filament must mostly be comprised of the polymer "binder", the material will obviously not exhibit all the properties of both.
Without getting into too much Material Science, consider the composite of both ABS and Iron (or some other ferrous-based metal). You cannot expect to print a solid circuit out of the filament because the iron may not be represented throughout all directions of the filament, therefore resulting in resistance or flat out non-conductivity.
So, to answer your question: I'm not aware of a significantly larger glass state in a type of metal/alloy. Your best bet is a composite, but it depends on the requirements for your part if a composite will work. Then, you'll have another battle of finding the right type of composite and worst of all, a good supplier lol
I spent some time looking at making an FDM machine that would print bronze filament. An alloy commonly made into wire had a difference between the solidus and liquidus temperature of only 50 degrees C. I determined that one could make a conventional hot end, electrically heated, made of either molybdenum or tungsten.
I did not determine how the bronze would behave in the 50 degree solid-to-liquid zone. I was more concerned about the solubility of the nozzle material in copper, for which I could find very little published data.
From my experience welding, and from printing plastics with FDM, there could be a problem with layer adhesion. To really bond, the cooled material needs to be melted by the material being deposited in the next layer. This is complicated by the temperature of the cooled material, the thermal conductivity of the material, and the propensity of the material to form oxides. These could be mitigated by heating the object in an inert atmosphere.
So, to answer the question, I would suggest looking at bronze alloys because they melt at moderate temperatures, and are less prone to oxidation than aluminum alloys.
