Aluminum is more expensive but it is better because it weighs less whereas steel is heavey but CHEAP
With regards to the orginial question. NS apparently has 400 aluminum hoppers. Go to the coal section:
I wonder if someone plans to make a railcar out of titanium.
No particular advantage in making railcars of titanium. Don’t have to run at hypersonic speeds, like Boeing’s 2707, don’t have to evade MADs like an Akula, DO have to be repairable with cheap materials by people without skill welding pyrophoric material…
Last I looked, there wasn’t that much of a good scrap market (outside Vladivostok) and the cost of producing titanium metal (and, more important, procuring formed section and sheet) was still… ah, rather high. I’d expect to see titanium automobiles first… and I’m not exactly holding my breath.