MSE307 Engineering Alloys
In third year, I teach 1/3 of a course on alloys. This is quite different to my other courses in that it is all about the skill of synthesis; taking all of the ideas and concepts and phenomena encountered so far in the degree and applying them to understand the domain of alloys. That is; how alloys are designed, how they are manufactured, and how they are used, and how all of these inter-relate.
It could be a course of unrelated facts! But the 1st and 2nd year material actually gives you a framework to put them together into a whole – to turn the trees into a forest, the threads into a tapestry – which is that skill of synthesis.
My intent is to add videos here and then to discuss in the class sessions for lectures 2-8 using learning catalytics, but the first lecture will be by classical exposition, at least for 2015. I will add the notes and videos to this page as I make them.
And so in the first lecture I first introduce the course, then we discuss materials selection, then jet engines to get into an application context, then lifing to think about the topic of failure. Notes for lecture 1. Video 1.1. Video 1.2.
The second session is about the melting and forging or speciality aerospace alloys (mostly Ni, Ti, Zr and some steels). Lecture 2 Notes. Video 2.
The third session is about the Sioux City air accident, examining the fault sequence, the causes of the failure and the underlying metallurgy. Lecture 3 Notes. Video 3. The air accident report is here.
In the fourth lecture we discuss some theoretical concepts in alloying. Lecture 4 notes. Video 4. A good paper on Blackman diagrams is here.
In the fifth lecture we turn to titanium alloys. The first lecture of the set of four is on the phase metallurgy. Video 5. Lecture 5 Notes.
The sixth lecture is about the formation of microstructure in titanium alloys. Video 6. Lecture 6 Notes.
Then, in lecture 7 we discuss mechanical properties, and begin a discussion on fatigue behaviour. Video 7. Lecture 7 Notes.
And finally in lecture 8 we wrap up the discussion of fatigue by discussing dwell fatigue, after which we review the non-mainstream Ti alloys. Video 8. Lecture 8 Notes.
Other links
Rolls-Royce – jet engine fly-through, assembly etc are here.
Animation from ORNL of Ti processing from Kroll to cold rolled sheet: here.
David Dye, Imperial College 
Looking forward to second video.
Great lecture, thank you for sharing!
Looking forward to seeing this course. Thank you for the huge effort you put into your courses!
I love you David Dye!
I still love you David!
My love for you is undying Dave!
I think it might be time for us to take this to the next step Davy!
My infatuation with you grows deeper with every passing day Davo!
Hello prof Dye,
I’d like to ask a question. For the lecture 5, in the phase diagram of Al Ti, if Al is less than 6 wt% and we cool down Ti to room temperature, how can we form a+b phase field which is desirable for forging? Thanks
Forging is, by definition, a hot deformation process. So by adding (any element) to pure X in a binary phase diagram, you create a two phase region (Gibbs phase rule, ref MSE104 and MSE204). So, in a Ti-Al alloy, there will necessarily be a 2-phase region to forge in. This is widely used for alloys with an allotropic transformation – the same is true for dual phase rolling in steels, for example.
Dear prof Dye,
I don’t understand the link between b stabilizer which can reduce the solvus temperature at above 600 C and the stabilisation of b phase at room temperature. Why b stabiliser which reduces the solvus temperature at high temperature can help to form b phase at room temperature? Many thanks.
A beta stabiliser is defined as an element that reduces the beta-> alpha+beta transformation (solvus) temperature. If you add enough beta stabiliser, then assuming that there are no eutectoids, it must be possible to stabilise beta all the way to room temperature – and in most Ti binaries, at least optically, this is so for quenching – although the beta might be metastable.
Thank you for your reply. But among the 4 phase diagrams showed in lecture 5, there is not one who has the beta-> alpha+beta transformation solvus line down to the room temperature. So only by quenching, it is possible to obtain beta, otherwise if we cool down slowly we can only obtain alpha. Is that right? Many thanks.
Below about 500C, we don’t know what happens to the true equilibrium phase diagram for most of these systems – because diffusion is too slow to reach equilibrium. So we are necessarily in a metastable state if we cool a beta alloy from, say, 700 or 800C. What happens then we find out by experimentation. Often if we take a heavily beta stabilised alloy and cool from a forging temperature, we form omega on low temperature (300C) ageing, which we may then be able to use to nucleate alpha at 400C. This is an active area of research.
Hello Prof. Dye,
The link to the paper on Blackman diagrams is broken. Could you find another paper to reference? Would be greatly appreciated!
Thanks!
How annoying, New US administration, I suppose. I will hunt down…
Link now updated using doi. Now it only works if you have a local subscription to the journal, sadly – the NIST mirror seems to have gone.
Dear Prof. Dye, In your lecture 6, you didnt discussed about the formation of martensite in Ti-6Al-4V system. Many papers report formation of martensite phase upon cooling at high cooling rate from beeta phase. In Figure 5 you have showed how the morphology changes from coarse lamellar to Widmanstatten in the transformed beeta. Is the Widmanstatten structure that you discussed same as the martensite phase? Can you please clarify on these terminologies. Thanks
hcp alpha prime martensite in Ti is the same phase alpha Ti, but with a distinct morphology that forms at high cooling rates. Typically it is recognised by the laths being at 90degrees to each other rather than 120 degrees. In Ti-64 it only really forms at high cooling rates, as you say, typically by water quenching thin sheet or bar <12mm in diameter, or in powder bed additive manufacturing. In industrial processing of forgings, it is quite an obscure phenomenon, because we tend to try and avoid forming it, so I don't discuss it in this lecture series *at all*.
Widmanstatten alpha is nearly the same idea as colony alpha. Both are regular alpha formed out of the beta that grows from the grain boundaries. The distinction between the two terms isn't all that precise in the literature. The term Widmanstatten appeals to the phenomenon of Widmanstatten ferrite in steels.
Dear Dr. Dye, Thanks for the prompt response and for putting the ambiguities to rest once and for all. I believe that Ti Alloys is relatively newer field (in comparison to Steels), there are still confusions related to the terminologies various people use. As to “Widmanstatten structure”, I observed that people tend to use it interchangeably with the term “basket-weave” structure. I believe, since at high cooling rate the alpha plates tend to be finer and finer, making its criss-cross structure more akin to a basket-weave structure, the terminology of “Widmanstatten” is often frequently used for high-cooling rate transformed beeta. Would you agree? (Or, is it something I over-deduced 🙂 ?)
No, these two terms aren’t interchangable. Basketweave is a microstructure where the plates are at 60/120degrees to eachother, colonies/lamellar/Widmanstatten are aligned together. The terminology isn’t confused on this point – if you read Lutjering and Williams it is crystal clear. Of course, there are many people publishing in this field (like many others) who don’t have the first clue what they are doing, but that’s true in every field.
Hello Dave,
I just started my PhD on Ti64, your lectures are of a great help for me in terms of understanding Ti metallurgy. I would like to ask you one question, namely do you think growing beta grains of the range of couple of centimeters is ever possible with any technique? If so, how would you do it?
Thank you in advance for your reply.
Bernadeta
Long term (days, months) vacuum heat treatments above the beta transus can be used to grow grains that are cm in size – I have just such a piece of material in my office.
Dear David,
Thank you for such a prompt reply, I find this advice very helpful. As an alternative, I am wondering If growing such a big grains is possible by AGG in Ti64…
Probably. Try looking for Vivian Tong’s PhD thesis on Zirconium in the IC Spiral repository, and associated publications. She did a PhD on this.