u/Heavy_Nose_2923

Hi everyone, i continued my "hard bronze" project, my goal being, as a bladesmith, to make knives from something i can cast myself, forge and heat treat. Yes a bronze will never remotely reach the wear/hardness properties of even a cheap carbon steel, but keep in mind that's mostly a project i do for fun, and i want a mediocre but golden-looking knife. (and of course corrosion resistance isn't that important to me).

After having problems due to very stable dendrites from high cobalt additions to my previous prototypes, i tried adjusting the composition to inhibit the formation of those dendrites, however after a while i just realized that lowering the cobalt content was probably the best solution. (i wanted to add cobalt in the first place to improve wear resistance, following a US patent from 1958. Here i added a ratio of 0.09 cobalt per aluminium %).

My current alloy has the following composition : CuAl11Ni6.5Fe6Co1Mn1.5

Picture 1 and 2 :

Those are the alloy after forging and air cooling. The grains seem to be in a coarse pearlitic structure and are surrounded by a corrosion prone phase that etched black. The high nickel content should prevent the formation of gamma2, and most importantly, this alloy can be worked cold by a decent amount without cracking (around 30% reduction), compared to basically nothing on high aluminium bronzes that have a gamma2 phase present at room temp.

Could it be that the dark phase is retained beta ? Apparently cobalt is a beta-phase stabilizer. I wouldn't expect this grain boundary phase to be something brittle because of the reasonably high ductility.

Picture 3 and 4 :

Same alloy after a 30 min soak at 900°C, so a bit below the kappa phase dissolution temperature according to this paper : https://www.researchgate.net/publication/281644067_INFLUENCE_OF_HEAT_TREATMENT_ON_THE_MICROSTRUCTURE_AND_MECHANICAL_PROPERTIES_OF_ALUMINIUM_BRONZE

So it pushes the beta phase transformation but keeps some grain stability. The sample was then water quenched. The structure appears quite even and homogenous, the white dots could be some kind of impurity (my polishing was rough on that one). There are a few darker spots here and there, but it looks martenitic overall. After snapping the sample, the grain appeared quite fine, but not silky smooth. An eutectoid steel like 1075 at 800°C would have this kind of grain size.

The ductility after quench is low but it's not completely brittle yet. So for a knife blade you can actually straighten it. The hardness barely increases however, wich can be expected following this paper : https://www.researchgate.net/publication/402701878_The_effect_of_heat_treatment_on_the_structure_and_hardness_of_CuAl10Ni5Fe4_nickel_aluminium_bronze

After 30min at 450°C, the hardness increased by a LOT and the ductility/toughness was gone.

This paper : https://www.tandfonline.com/doi/abs/10.1179/030716980803286423 shows that cobalt additions slows down the decomposition of the martensite, so i can expect a higher hardness after tempering/aging.

Indeed, i compared the hardness trough a scratch test (high-tech, i know) on a sample of commercially-bought and similarly heat treated C63000 sample. My prototype alloy scratched it rather easily.

However the second study i linked reported a max hardness of around 580 HV after a short aging time ?? I've never heared of this kind of hardness on a bronze (CuBe2 doesn't even go this high), and i never could replicate it with my factory made C63000 alloy. Could this be an error ? Have you heared of ultra high hardness bronzes of this kind? I guess we can also expect them to perform as well a a piece of glass.

The last photo is my crude arc furnace that i use for making samples and upgrading the composition after a quick polish and low-quality microscope examination. Yes it's low tech (carbon crucible, carbon electrodes, ceramic insulation, charcoal dust to reduce oxygen exposure). No i don't have access to higher tech equipment to make/test my sample, so i can't know the exact hardness for exemple, i'll see if a friend has a HRC tester.

I guess a normalizing at high temp (950°C), and air cooling/quenching before the hardening heat treatment could reditribute a bit better the kappa precipitates and lead to a finer grain ?

Once again this is more of a fun side project so don't take it too seriously. I'm curious to know if you got suggestions !

Have a nice day y'all !

UPDATE : This post has been re-edited with reworked pictures to give scale and other infos. Sorry for the inconvenience

Hi everyone, this might be a long post so i apologize in advance.

A few days ago, i made a post about phases i didn't have the knowledge or equipment to identify (thank you to everyone who answered !). After more researches and reading tens of studies, i continued developping a new custom copper-aluminium-nickel-iron alloy, once again with some cobalt addition (because i like this metal and it often has weird effects on alloys). While some studies focused on the benefit from micro-alloying cobalt for grain refinement, or how larger amounts will reduce martensite decomposition during tempering, it seems few researchers have focused on the subject of cobalt in NAB bronzes.

First of all, my pictures are of mediocre quality because i am an amateur (tho i am a professional bladesmith specialized in damascus so i have a vaguely related knowledge on metal polishing and etching). I take the pictures by placing my phone in front of the microscope. It is a cheap Swift brand biology microscope and to light up the sample i hold a powerful flashlight next to the lens. I prepare my samples with hand sanding to around 2k grit using common SiC sandpaper. As someone suggested, i started using some car polish and it made the end result nicer, but i had so many samples to check that i was somewhat hasty and left some scratches. The etch is done with ferric chloride mixed with a dab of hydrochloric (i make copper and brass damascus blades and this kind of mix works well).

After bad results and multiple Salamander crucibles destroyed by aluminium borates (those crucibles contain borax it seems), i quit melting my alloys in a heat treating oven, and built myself a small arc furnace : a small graphite crucible encased in thick ceramic insulation fibre. I use two large carbon rods linked to my cheap welder and strike an arc. If you're wondering how hot such a crude setup can get, i did melt chromium once. I think the top temperature is about 2000°C. I use charcoal dust to both protect the crucible from oxygen and make it last longer, and to reduce oxygen exposure in the melt. With this new arc furnace, the mass loss from oxidation and slag formation is very small, so while oxygen and carbon contamination is possible, i've not observed problematic inclusions in my samples or suspicious brittleness during forging. I think carbon contamination is unlikely because the graphite is not eroded where the molten metal was, and when melting ferrous alloys, the graphite is eaten away and the alloys clearly contaminated. So i believe copper-based alloys won't eat up that much carbon (and if any gets in, i assume it will eat up the oxygen and bubble out, maybe). One added bonus from this kind of furnace is that i can exceed the melting point of all my elements, making sure the mix is homogenous (i stir with a carbon rod at the end of the melt), as i don't have access to master alloys and have to use the pure metals.

Let's now focus on what i made :

The new alloy prototype i tested was CuAl11Ni6.5Fe6Co3Mn2.5. My goal was to make a very hard bronze that can be forged hot, isn't too brittle cold, and can achieve extreme hardness with heat treating.

I don't have access to tools and don't know how to optimize the ratios in this alloy, so i just followed the infos i gathered trough my researches.

Here is my reasoning : 6.5% Nickel (according to isopleths) will stabilize the alpha phase enough to completely prevent gamma2 formation at room temperature despite the 11% aluminium. The iron has been increased to boost kappa precipitates, but kept below the nickel content to prevent large rosettes that seemed to make the alloy brittle both hot and cold in my previous prototypes (picture 5). The high cobalt and manganese can increase wear resistance according to a 50's patent, without specifying how, so i just said "let's try it and see".

The properties of this alloy are encouraging : it forges hot nicely, is still ductile at room temperature, and when broken after quench, the grain seems quite fine (and yes the alloy is brittle after quench, and possibly harder tho i don't have a rockwell tester).

The 2nd picture is the alloy after forging and air cooled. The 3rd picture is after a 900°C 30 min soak and water quench. Both pictures have a x100 magnification.

That's when i noticed something weird... There are large dendritic structures that did not dissolve during soaking and look very out of place in this homogenous (martensitic ?) background. You can see a close-up in the 4th picture, those dendrites contain smaller precipitates.

Despite weeks/months of study on various publicly available papers on NAB bronzes, i have never seen such shapes in the kappa precipitates. After this soak, i wouldn't expect it to be from the matrix, so i started making more samples with various compositions to try and isolate this exact phase.

That's how i got the first picture : a x100 and x500 magnification on an alloy of copper, 10% Al and 6% Co. After methodically eliminating all the other elements one by one, the last alloy that still showed these structures was the one that contained cobalt (in large amount to make the potential precipitates huge). So i conclude that these snowflake-shaped dendrites are a distinct phase from the common kappa phases observed in these bronzes, and they are mainly cobalt and aluminium based. An interesting detail is that these large dendrites appear homogenous and do not contain smaller "dots" or large visible phases, unlike in the iron/nickel containing prototype alloy.

I tried testing for the properties of this new phase. First of all, a 900°C soak will barely erode it (a bit but not much), therefore i can conclude that :

1. they are very stable
2. they are primary aluminides formed during solidification of the ingot. A very fast cooling in the melt seemed to reduce the size of these dendrites in an other sample.

CoAl intermetallics melt at 1600°C so we can expect such particles to be quite stable. The solubility of cobalt in copper is higher than that of iron, but still rather low.

This cobalt/aluminium/copper alloy was VERY malleable and ductile compared to NAB bronzes. It forged beautifully hot, could take a lot of strain cold without cracking. Compared to an other messed up attempt with too much iron (last picture with the ugly grain, cracks and rosettes), where the alloy became brittle hot and cold, the cobalt one was much softer and ductile.

I therefore assume that CoAl dendrites in my prototype alloy are not very brittle intermetallics or allow the matrix to flow around them during deformation.

It seems unlikely that the grains in the alloy can grow beyond those large particles and therefore will stabilize the structure even at very high heat. I could try pushing the soak to 1000°C for 1hr and quench, and see how much these intermetallics eroded.

According to Cu/Al/Ni/Fe isopleths, kappa phases in 11% aluminium NAB alloys will completely dissolve at around 920°C. The alloy then transitions to pure beta. If the large dendrites remain even at 1000°C, this means that cobalt makes NAB alloys basically immune to grain growth up until melting, wich can possibly be very useful (at the cost of not being able to dissolve or refine cobalt precipitates).

I believe this is why micro-alloying cobalt in NAB bronzes will refine the grain : at low concentrations we can expect very small precipitates of this kind, and pin grains efficiently.

To conclude, i must say i've never seen this shape of precipitate in NAB bronzes, and no mention of them, even in papers studying cobalt effects in CuAl bronzes.

Maybe my crude setup added impurities or changed the way the intermetallics form, therefore this dendritic phase is some kind of anomaly (but because the subject is scarcely researched, it could also be a "new" phase in such alloys).

Perhaps some of you already know about this kind of dendrites and how they appear in NAB bronzes ? If you can give me any feedback and info, i will greatly appreciate it, and i will keep having fun making samples and refining my alloy little by little.

Have a great day y'all !

Hi everyone, this might be a long post so i apologize in advance.

A few days ago, i made a post about phases i didn't have the knowledge or equipment to identify (thank you to everyone who answered !). After more researches and reading tens of studies, i continued developping a new custom copper-aluminium-nickel-iron alloy, once again with some cobalt addition (because i like this metal and it often has weird effects on alloys). While some studies focused on the benefit from micro-alloying cobalt for grain refinement, or how larger amounts will reduce martensite decomposition during tempering, it seems few researchers have focused on the subject of cobalt in NAB bronzes.

First of all, my pictures are of mediocre quality because i am an amateur (tho i am a professional bladesmith specialized in damascus so i have a vaguely related knowledge on metal polishing and etching). I take the pictures by placing my phone in front of the microscope. It is a cheap Swift brand biology microscope and to light up the sample i hold a powerful flashlight next to the lens. I prepare my samples with hand sanding to around 2k grit using common SiC sandpaper. As someone suggested, i started using some car polish and it made the end result nicer, but i had so many samples to check that i was somewhat hasty and left some scratches. The etch is done with ferric chloride mixed with a dab of hydrochloric (i make copper and brass damascus blades and this kind of mix works well).

After bad results and multiple Salamander crucibles destroyed by aluminium borates (those crucibles contain borax it seems), i quit melting my alloys in a heat treating oven, and built myself a small arc furnace : a small graphite crucible encased in thick ceramic insulation fibre. I use two large carbon rods linked to my cheap welder and strike an arc. If you're wondering how hot such a crude setup can get, i did melt chromium once. I think the top temperature is about 2000°C. I use charcoal dust to both protect the crucible from oxygen and make it last longer, and to reduce oxygen exposure in the melt. With this new arc furnace, the mass loss from oxidation and slag formation is very small, so while oxygen and carbon contamination is possible, i've not observed problematic inclusions in my samples or suspicious brittleness during forging. I think carbon contamination is unlikely because the graphite is not eroded where the molten metal was, and when melting ferrous alloys, the graphite is eaten away and the alloys clearly contaminated. So i believe copper-based alloys won't eat up that much carbon (and if any gets in, i assume it will eat up the oxygen and bubble out, maybe). One added bonus from this kind of furnace is that i can exceed the melting point of all my elements, making sure the mix is homogenous (i stir with a carbon rod at the end of the melt), as i don't have access to master alloys and have to use the pure metals.

Let's now focus on what i made :

The new alloy prototype i tested was CuAl11Ni6.5Fe6Co3Mn2.5. My goal was to make a very hard bronze that can be forged hot, isn't too brittle cold, and can achieve extreme hardness with heat treating.

I don't have access to tools and don't know how to optimize the ratios in this alloy, so i just followed the infos i gathered trough my researches.

Here is my reasoning : 6.5% Nickel (according to isopleths) will stabilize the alpha phase enough to completely prevent gamma2 formation at room temperature despite the 11% aluminium. The iron has been increased to boost kappa precipitates, but kept below the nickel content to prevent large rosettes that seemed to make the alloy brittle both hot and cold in my previous prototypes (picture 5). The high cobalt and manganese can increase wear resistance according to a 50's patent, without specifying how, so i just said "let's try it and see".

The properties of this alloy are encouraging : it forges hot nicely, is still ductile at room temperature, and when broken after quench, the grain seems quite fine (and yes the alloy is brittle after quench, and possibly harder tho i don't have a rockwell tester).

The 3rd picture is the alloy after forging and air cooled. The 4th picture is after a 900°C 30 min soak and water quench. Both pictures have a x100 magnification.

That's when i noticed something weird... There are large dendritic structures that did not dissolve during soaking and look very out of place in this homogenous (martensitic ?) background.

Despite weeks/months of study on various publicly available papers on NAB bronzes, i have never seen such shapes in the kappa precipitates. After this soak, i wouldn't expect it to be from the matrix, so i started making more samples with various compositions to try and isolate this exact phase.

That's how i got the first and second picture : a x100 and x500 magnification on an alloy of copper, 10% Al and 6% Co. After methodically eliminating all the other elements one by one, the last alloy that still showed these structures was the one that contained cobalt (in large amount to make the potential precipitates huge). So i conclude that these snowflake-shaped dendrites are a distinct phase from the common kappa phases observed in these bronzes, and they are mainly cobalt and aluminium based.

I tried testing for the properties of this new phase. First of all, a 900°C soak will barely erode it (a bit but not much), therefore i can conclude that :

1. they are very stable

2. they are primary aluminides formed during solidification of the ingot. A very fast cooling in the melt seemed to reduce the size of these dendrites in an other sample.

CoAl intermetallics melt at 1600°C so we can expect such particles to be quite stable. The solubility of cobalt in copper is higher than that of iron, but still rather low.

This cobalt/aluminium/copper alloy was VERY malleable and ductile compared to NAB bronzes. It forged beautifully hot, could take a lot of strain cold without cracking. Compared to an other messed up attempt with too much iron (last picture with the ugly grain, cracks and rosettes), where the alloy became brittle hot and cold, the cobalt one was much softer and ductile.

I therefore assume that CoAl dendrites in my prototype alloy are not very brittle intermetallics or allow the matrix to flow around them during deformation.

It seems unlikely that the grains in the alloy can grow beyond those large particles and therefore will stabilize the structure even at very high heat. I could try pushing the soak to 1000°C for 1hr and quench, and see how much these intermetallics eroded.

According to Cu/Al/Ni/Fe isopleths, kappa phases in 11% aluminium NAB alloys will completely dissolve at around 920°C. The alloy then transitions to pure beta. If the large dendrites remain even at 1000°C, this means that cobalt makes NAB alloys basically immune to grain growth up until melting, wich can possibly be very useful (at the cost of not being able to dissolve or refine cobalt precipitates).

I believe this is why micro-alloying cobalt in NAB bronzes will refine the grain : at low concentrations we can expect very small precipitates of this kind, and pin grains efficiently.

To conclude, i must say i've never seen this shape of precipitate in NAB bronzes, and no mention of them, even in papers studying cobalt effects in CuAl bronzes.

Maybe my crude setup added impurities or changed the way the intermetallics form, therefore this dendritic phase is some kind of anomaly (but because the subject is scarcely researched, it could also be a "new" phase in such alloys).

Perhaps some of you already know about this kind of dendrites and how they appear in NAB bronzes ? If you can give me any feedback and info, i will greatly appreciate it, and i will keep having fun making samples and refining my alloy little by little.

Have a great day y'all !

Hello everyone,

i'm currently designing my own bronze alloy as an amateur. It's based on usual NAB alloys, aka Copper/aluminium/nickel/iron bronzes, wich can be water quenched and hardened. I've been studying research papers and documentation about those bronzes for weeks and checking samples of C63000 / CuAl10Ni5Fe4 alloy under the microscope (among other variants).

A patent from the 50's talks about how large additions of cobalt and manganese to Copper/aluminium/iron alloys will double its wear resistance (tho it wasn't studied with nickel containing alloys).

I'm currently designing an alloy for making knives (not good compared to steel, but still a fun project, my current bronze prototypes will scratch non-hardened tool steel), therefore i want to increase hardness but keep a little bit of toughness, with overall improved wear resistance.

Here's what i came up with : 72% Cu, 12% Al, 5.5% Ni, 5% Fe, 3% Co, 2.5% Mn

My reasoning is that the 12% aluminium places this alloy in the alpha+gamma2+kappa phase region at room temperature, but barely because of the other elements, wich eat up the excess aluminium to form kappa particles and reduce the effective aluminium content. I added slightly more nickel than iron to reduce large rosette iron aluminides and give finer kappa 3/4 aluminides. High cobalt additions with manganese should, according to the old patent, also form its own phases (Usually CoAl intermetallics), and help form the other kappa phases along with the manganese. Cobalt also reduces grain size, prolly from CoAl particles.

Once quenched, its martensite should be stabilized by the cobalt, give higher hardness after the temper, and help overall hardness.

Now, thats the theory, however when i checked it under the microscope, it did NOT look like anything i've seen yet. No flat plates of nickel kappa3 phases, no rosettes from iron (at least not big ones), and a LOT of bright white phase, with some grey phase.

The first picture is taken at x100 after slow cooling from 900°C. From other samples it seems the slower the cooling, the more grey phase expands and bright phase diminishes.

Second picture is water quenching from 900°C. All white (expected, should be martensite and kappa particles) It still has a few grey spots tho, either alpha (the alloy has barely enough aluminium to enter gamma2 pearlite when cold) or retained austenite.

Third and fourth pictures are x500 of previous samples.

I'm kinda confused at what those phases look like and i don't know what's happening in the slow cooled sample, because if the grey part is alpha (somehow, despite aluminium content) and the white phase is aluminides, then those aluminides should be brittle. But in an other sample a fast-ish air cool lead to the same structure, except the grey phase was barely present and the rest was that white phase (so it should be nearly all intermetallics, therefore brittle)... Except it deformed under the hammer just fine and could be cold worked a bit, whereas the martensite sample shattered like glass.

cobalt additions to NAB aluminium bronzes is scarcely researched it seems, and my new prototype alloy is probably very new and hasn't been researched by science yet (as far as i'm aware).

So, if among you some people know a lot about aluminium bronzes, their phases, interactions between iron/nickel/cobalt content and aluminium, i'd greatly appreciate some insights and feedback.

May the metallurgy be with y'all !

(If needed i got tens of photos of various samples to bring more context).