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here is a quote from https://www.highpowermedia.com/blog/3342/piston-pins-material-choices
"Steel is not the only choice for piston pins though; a number of companies offer titanium pins. Titanium has a much lower density than that of steel, although its elastic modulus (a measure of stiffness) is also low compared with steel. Titanium Ti-6Al-4V is often used, although pins made from Ti-17 (Ti-5Al-2Sn-4Mo-2Zr-4Cr) are also commercially available.
We should not, however, expect to replace an optimised steel piston pin with one of the same dimensions made from titanium, and expect to find success. Titanium has particularly poor wear behaviour in sliding contacts, so titanium pins would need to be coated to achieve an acceptable level of durability. Again DLC is often used here, but pins are also marketed which have a titanium nitride coating."
from http://amt-advanced-materials-technology.com/app/download/.../Ti-Auto2.pdf
"Connecting rods require strength, fatigue performance, stiffness (particularly the big end)
and wear resistance. The strength and fatigue performance of titanium are more than
sufficient for this component, however stiffness and wear resistance need enhancement
via reinforcement particles and coating. Novel concepts such as bimetallic steel
(lower part of the big end) – titanium components allow a shifting of the connecting rod’s
center of gravity towards the crankshaft, giving a positive effect on piston guidance.
Reduced weight connecting rods, in combination with lighter weight pistons and
wrist pins lead to significantly reduced NVH (noise, vibration and harshness) and
improved engine performance including fuel economy.
Piston assemblies (piston, piston pin and the connecting rods discussed above) account
for a large amount of the friction losses in an engine over the full speed range.
Reduced mass here leads to improved fuel economy and reduced emissions. Titanium
use in these components could increase as the operating temperatures in the engine
exceeds the capabilities of aluminum alloys. For piston pins where strength, wear
resistance, high stiffness and high temperature capabilities are required the titanium
aluminides appear to be a good choice. "
"Steel is not the only choice for piston pins though; a number of companies offer titanium pins. Titanium has a much lower density than that of steel, although its elastic modulus (a measure of stiffness) is also low compared with steel. Titanium Ti-6Al-4V is often used, although pins made from Ti-17 (Ti-5Al-2Sn-4Mo-2Zr-4Cr) are also commercially available.
We should not, however, expect to replace an optimised steel piston pin with one of the same dimensions made from titanium, and expect to find success. Titanium has particularly poor wear behaviour in sliding contacts, so titanium pins would need to be coated to achieve an acceptable level of durability. Again DLC is often used here, but pins are also marketed which have a titanium nitride coating."
from http://amt-advanced-materials-technology.com/app/download/.../Ti-Auto2.pdf
"Connecting rods require strength, fatigue performance, stiffness (particularly the big end)
and wear resistance. The strength and fatigue performance of titanium are more than
sufficient for this component, however stiffness and wear resistance need enhancement
via reinforcement particles and coating. Novel concepts such as bimetallic steel
(lower part of the big end) – titanium components allow a shifting of the connecting rod’s
center of gravity towards the crankshaft, giving a positive effect on piston guidance.
Reduced weight connecting rods, in combination with lighter weight pistons and
wrist pins lead to significantly reduced NVH (noise, vibration and harshness) and
improved engine performance including fuel economy.
Piston assemblies (piston, piston pin and the connecting rods discussed above) account
for a large amount of the friction losses in an engine over the full speed range.
Reduced mass here leads to improved fuel economy and reduced emissions. Titanium
use in these components could increase as the operating temperatures in the engine
exceeds the capabilities of aluminum alloys. For piston pins where strength, wear
resistance, high stiffness and high temperature capabilities are required the titanium
aluminides appear to be a good choice. "
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