Hacker News new | ask | show | jobs
by durkie 4716 days ago
I did my master's thesis on aluminum/carbon fiber composites and typically they mean infiltrating liquid aluminum through weaves of carbon fiber.

But these materials are hard as hell to make. Carbon and aluminum do not get along for a variety of reasons, and aluminum/carbon composites remain a pie-in-the-sky concept. One of the ways they make Al/C composites now is through a process called squeeze casting, whereby they just force molten aluminum (>660C) to infiltrate a fiber preform at super high pressures. And even then IIRC their properties usually fall well short of theoretical. These are not things nature wants us to put together (at least not yet).
2 comments
derefr 4716 days ago
How much additional effort is that on top of the current process of making gorilla glass, though? I believe it already requires some mighty temperatures+pressures.
link
durkie 4716 days ago
High temperatures are true of glass work in general. I'm not 100% about the gorilla glass process, but I did not think it high pressure one.

And high pressure is not a deal breaker -- it's just the best way to make some things right now. But even after you've forced carbon and aluminum together, you have a variety of other issues then to deal with: large potential for galvanic corrosion and huge difference in coefficient of thermal expansion are two of the primary ones. The fact that they have horrible wetting behavior is another one, and is the reason they have to do squeeze casting in the first place, but likely also negatively affects the quality of the interface formed between the carbon and the aluminum (thus leading to poor properties even after you've spent all the effort of making it)

link
vl 4716 days ago
Well, then in this iPhone they should use carbon fiber titanium instead!
link
durkie 4716 days ago
they would likely run in to similar problems. metal matrix composites in general are hard to make and underperform. i just know the most about al/c composites.

also, aluminum and titanium are already really strong and light. the author wanted to include carbon fiber because "it's perfectly rigid and doesn't bend" and that "scratches are a thing of the past". i appreciate that he wants a bit of far-out flourish for his new design, but both of those statements are way off the mark technically, and would be poor and wrong reasons to pursue difficult to make metal-matrix composites.

and let's not even get started on the graphene...

link