Ray745 said:
What you said intruiged me because of the titanium midpipes that some people are developing now. I just googled around a little and it seems Titanium has a much higher melting point than most other metals, pure titanium has a mp of about 1670 degrees celcius, while Inconel has a mp of about 1370 celcius. Titanium also has lower thermal expansion coefficient than inconel. Is there something else about titanium that makes it unsuitable for turbine applications? I'm assuming there must something or I would figure many more turbines would use the material, being half the density of inconel.
I dont remember where exactly I got that information but looking back I believe it was from a Burns Stainless catalog I was sent a while back comparing the different metals and their usefullness in different applicaitons. I cant find the table on the website but here in my catalog I will write out for you the differences in the alloys they use for their tubing. For the most part I think the reason titanium is not used is because of its higher Coefficent of Thermal Conductivity. But here are the numbers so you have something to compare, I will compare 4 significant metals and the properties in a number in the following order. Aluminum 6061-T6, then 321 Stainless Annealed (Steel Alloy), Titanium CP-2 Grade 2 ASTM B338, and finally Inconel 625.
Tensile Strength in lb/in^2 @ 70 degrees F: 45000, 90000, 50000, 140000
Yield Strength in lb/in^2 @ 70 degrees F: 40000, 35000, 40000, 77000
Elongation: 12%, 55%, 20%, 47%
Density in lb/in^3: .098, .290, .163, .305
Modulus of Elasticity x10^6 lb/in^2: 10, 28, 15, 30
Coefficent of Thermal Expansion in/in-Fx10^-6(@70 degrees F): 13.1, 9.6, 4.8, 5.5
Coefficent of Thermal Conductivity BTU/ft-hr-F(@70 degrees F): 96.50, 9.30, 12.00, 5.65
I think the last one here is the significant number. I believe this meaning titanium will not get rid of the heat quick enough in an enclosed engine bay to be an efficent header or turbine wheel.
Hope this helps,