u/Green-Respect-4244

Yesterday, I was trying to improve the visualization of the microstructure of my Cu-Mn-Sn alloy (Lupine Bronze) in the unetched condition using liver of sulfur.

Hi! I recently designed this alloy using the CALPHAD method, and I’m currently experimenting with its microstructure and properties. I’m planning to publish a paper about it, including properties such as hardness and fracture behavior, by the end of the year.

The nominal composition is:
Cu-15Zn-3.2Ni-1.2Mn-1Si-0.5Sn-0.1P (wt.%)

The idea was to develop a Cu-Zn matrix reinforced with G-phase (Ni₁₆Mn₆Si₇), a hard and relatively stable intermetallic compound.

According to my CALPHAD calculations, once the alloy is fully solid, it should consist mainly of an FCC Cu-rich phase and G-phase, with some phosphides also present. The FCC + G-phase mixture is predicted to remain stable down to room temperature.

The addition of Sn is also expected to improve the alloy’s corrosion resistance, particularly against dezincification and possibly intergranular corrosion. With only 15 wt.% Zn, I expect dezincification to be less of a concern than in conventional high-Zn brasses.

The as-cast microstructure shows very fine dendrites, which should make homogenization relatively fast. After homogenizing at 900 °C, the G-phase can be seen more clearly and appears to be fairly well distributed throughout the matrix.

The particle size concerns me a bit. The particles are relatively coarse, so I’m considering forging or otherwise mechanically deforming the alloy to break up the larger particles and improve their distribution.

I’m also having a hard time getting good metallographic images. So far, I’ve been sanding up to 2000 grit, followed by polishing with alumina, and then etching with ferric chloride + HCl.

From the metallographic images, the particles appear to be relatively homogeneously distributed rather than concentrated along the grain boundaries, which is encouraging.

The grain boundaries also appear lighter in some areas. I’m not sure whether this could be related to Sn segregation, since Sn can preferentially segregate to grain boundaries, or if it is simply an artifact of the polishing/etching process.

Image 1: As-cast structure
Images 2–4: Homogenized structure at 900 °C

I’d be interested to hear what you think about the microstructure, especially the particle size and the grain-boundary contrast. Any suggestions for improving the metallography would also be very welcome!

This is one of my favorite alloy systems.
It has been studied as a less toxic alternative to Cu-Be alloys.

I had previously tried making another blade from this alloy, but at the time I didn’t have the proper equipment for the required heat treatment.

With the right heat treatment, alloys in this system can achieve ultra-high strength. Unfortunately, I don’t have hardness measurements for this blade, but it is definitely harder than mild steel.

Alloy composition (wt.%): Cu-20Mn-20Ni-2Co-0.15Si, with a small residual amount of titanium for grain refinement.

A CALPHAD-based approach was used to determine the heat treatment temperatures. Unfortunately, I don’t have access to diffusion or precipitation simulation software, which would make the optimization process much easier.

This alloy is strengthened primarily by the precipitation of MnNi particles. In this composition, cobalt-rich precipitates and silicides are also present. If I make this alloy again, I would reduce the cobalt content because it stabilizes the FCC phase at high temperatures, delaying MnNi precipitation and requiring longer aging times.

The blade was produced by induction melting followed by sand casting. The processing route was:
Homogenization at 900 °C for 8 hours
Hot forging
Cold working
Annealing at 700 °C
Precipitation hardening (aging) at 350 °C for 12 hours (maximum hardness would likely require a considerably longer aging time)

The handle is made from resin with thermoelastic bronze details. The original idea was to improve vibration damping, although I doubt they make a noticeable difference.

The metallographic samples were etched using alcoholic ferric chloride and hydrochloric acid.
Image descriptions:
2nd image: As-cast microstructure.
3rd image: Homogenized microstructure.
4th image: Microstructure after forging, cold working, and annealing.
5th image: Microstructure after precipitation hardening.

That’s a Cu-Sn-Mn-Si-Ce alloy that shows good shape recovery.
It has a relatively simple composition in which Mn and Si help stabilize the beta phase in the Cu-Sn system, while Ce was added to help prevent the segregation of harmful intermetallic compounds, such as Cu4MnSn, at the grain boundaries.
I used a CALPHAD-based method to determine the composition and homogenized the alloy at 700 °C for about 4 hours.
Cu-Sn shape memory alloys are known to gradually lose their properties over time, so I plan to test it again in three months.
I don’t yet have precise measurements of the elastic modulus or hardness.