Fatigue Titanium Alloy 4

[Gillchevny]

Hi,
Would anyone be able to inform me where I can find fatigue characteristic info about Titanium 6% Aluminum 7% Niobium (alloy)? This is typically used in medical applications. In other words, i'd like to find out notch characteristics, endurance, surface def, etc specs. Thanks.

 

[kenvlach]

You can find limited data at the MatWeb.com site:

"TIMETAL® 367 (Ti-6Al-7Nb) Titanium Alloy

Features: TIMETAL 367 is a dedicated, medium strength, titanium alloy for surgical implants. The alloy was developed specifically for the manufacture of femoral component items for hip prostheses. Its metallurgy is closely analogous to that of TIMETAL 6-4 but biocompatibility is improved with the replacement of vanadium by niobium.

Typical heat treatment for this alloy: Anneal at 700°C for 1 hour, air cool.

Data provided by TIMET.

Physical Properties Metric English Comments
Density 4.52 g/cc 0.163 lb/in³ Typical

Mechanical Properties
Tensile Strength, Ult. Min 900 MPa Min 131000 psi
Tensile Strength, Yield Min 800 MPa Min 116000 psi
(0.2% Proof)
Stress Elongation at Break Min 10 % Min 10 %
Reduction of Area 35 % 35 %
Modulus of Elasticity 105 - 120 GPa 15200 - 17400 ksi
Typical Fatigue Strength 500 MPa 72500 psi
(rotating bend; limit at 10^7 cycles)

Thermal Properties
Beta Transus 1015 °C 1860 °F

*******************************************************
Another manufacturer is Allvac, An Allegheny Teledyne Company, whose alloy is
Allvac® 6-7 UNS R56700 Titanium Alloy

For more data on Ti-6Al-7Nb, contact either Timet

http://www.timet.com/367frame.html

or Allvacc

http://www.allvac.com/allvac/pages/Titanium/UNSR56700.htm

 

[TVP]

TIMET has some additional fatigue data on this alloy:

Rotating beam, fatigue strength at 10⁷ cycles:

highly polished, 620 MPa
shot blasted, R_a = 1 micron, 580 MPa
corundum blasted, R_a = 3 microns, 500 MPa
oxygen diffusion hardened (40 microns) + corundum blast = 360 MPa
ODH + highly polished = 340 MPa

Probably the best place to find additional information is from the comprehensive Titanium reference Materials Properties Handbook: Titanium Alloys. The reason I say probably is because I can't remember for sure if this alloy is covered. You can obtain this book directly from ASM using the following link:

http://www.asminternational.org/Tem...=Ecommerce/ProductDisplay.cfm&ProductID=11019

A good university engineering library should have this as well.

 

[Gillchevny]

Hi everyone.... What differences are there between the two medical implant titanium alloys Ti-6Al-7Nb and Ti-6Al-4V? I know in past, most used the latter, but I am aware of the former being used nowadays as well. In particular, is there any fatigue property differences between the two alloys?
I've found quite a bit of literature on the Ti-6Al-4V alloy, but cannot find much on the Ti-6Al-7Nb alloy besides the basic mech. props as provided earlier in this thread (and thanks to those who replied earlier!)

 

[boo1]

Ti-6Al-7Nb

367 is a dedicated, high-strength, titanium alloy with excellent biocompatibility for surgical implants.

Composition
Al 6.5-6.5%
Nb 6.5-7.5
Ta <0.50%
Fe <0.25%
N2 <0.05%
O2 <0.20%
C <0.08%
H2 <0.009%
Ti ~ Rem

Mechanical Data Typical
Tensile Strength MPa ksi) 1000 (145)
0.2% Proof StressMPa(ksi) 900 (130)
Elongation on 5D % 12
Reduction in Area % 35
Elastic Modulus GPa(Msi) 105 (15)

Ti-6Al-4V Grade 5

many aerospace engine and airframe components uses and also major non-aerospace applications in the marine, offshore and power generation industries in particular.

Composition

C <0.08%
Fe <0.25%
N2 <0.05%
O2 <0.2%
Al 5.5 - 6.76%
V 3.5 - 4.5%
H2(sheet) <0.015%
H2(bar) <0.0125%
H2(billet) <0.01%
Ti ~ Rem

Mechanical Data Minimal Typical
Tensile Strength MPa ksi) 897 (130) 1000 (145)
0.2% ProºF StressMPa(ksi) 828 (120) 910 (132)
Elongation Over 2 Inches % 10 18
Reduction in Area % 20
Elastic Modulus GPa(Msi) 114 (17)
Hardness RºCkwell C 36
Specified Bend Radius<0.070in x Thickness 4.5
Specified Bend Radius >0.070in x Thickness 5.0
Welded Bend Radius x Thickness 6
Charpy, V-Notch Impact J(ft lbf) 24 (18)

 

[TVP]

The two alloys are quite similar. Ti 6Al-7Nb was developed from Ti 6Al-4V. The Nb was used to replace V as the beta-stabilizer for improved biocompatibility. The microstructure will be very similar using the same heat treatment, therefore the fatigue properties will be very similar. One caveat is that Ti 6Al-4V is formed and heat treated using a wide variety of processes, whereas cast Ti 6Al-7Nb femoral components are typically given a singular annealing treatment-- 700 C for 1 hour followed by air cooling.

 

[Gillchevny]

Thanks everyone for the information. TVP... would you be able to provide a resource for the fatigue info you stated? (I believe what you stated ) It is just that I should use references in my report if I'm going to utilize Ti 6Al-4V data rather than Ti 6Al-7Nb (to show that it is justified). I have not found any fatigue info for Ti 6Al-7Nb, but a lot for Ti 6Al-4V. Thanks again.

 

[TVP]

You mean you can't just quote some quack from the internet?

In all seriousness, I recommend you do the following:

1. Read the data sheet from TIMET that Ken posted earlier. The information regarding alloying, heat treating, and fatigue data that I referenced can be found there. I will post the link again:

http://www.timet.com/367frame.html

2. Find a copy of Materials Properties Handbook: Titanium Alloys and see if Ti 367 is included.

3. Contact someone from Timet and/or Allvac. Timet will definitely be able to provide you with technical assistance regarding microstructure, fatigue, etc. I have received a lot of data from them in the form of technical papers and presentations with nothing more than an informal call to their technical center (Henderson, NV 702.566.4403).

And just as a clarification, I did not mean to include the word &quot;cast&quot; in my previous post. I was going in one direction and then changed the sentence, but forgot to delete &quot;cast&quot;. The heat treatment applies to this alloy regardless of product form.

 

[Metalguy]

Gillchevny,

There seems to be one very important (potentially) factor which is missing here-unless I missed it in the refs. Even tho Ti is very corrosion resistant, the fatigue properties may well be affected by the environment-in this case salty water or whatever is inside us besides blood. <g>

You need to search out fatigue data for this alloy that was performed in a simulated human body environment.

 

[Gillchevny]

Thanks Metalguy, your comment is noted... at present, I'm analysing the implant in an in vitro environment, but I'll be sure to find out whether the Ti alloy would act differently in vivo.