I was under the assumption that you shouldn’t put a titanium axle in a titanium yoyo, otherwise there’s a higher chance for the axle to gall and fuse with the yoyo.
It seems like every single mono steel design ships with just a completely normal steel axle though. None of them are using the coated black axles, but just completely standard, raw looking steel axles. Why is this fine?
Is the “never use a ti axle on a ti yoyo” claim bogus? Or is something about steel different. Or is this an oversight from the designers of steel yoyos, since steel is such a relatively unexplored matieral.
I’m not a materials science person, so I’d love some input.
As from my understanding from quick research is that:
Titanium is quite a magical material that can totally heal by itself and it is composed of only itself which is Ti in periodic table, even with manufacturing one it is still contain of more than 70% of Ti, which this still keep its characteristics of Titanium
For Stainless Steel it is compose of Iron as base and many other component like Chromium in order to make it rustless. This is when Chromium interact with Oxygen and create a Chromium (III) Oxide and this is treated as a protective coating and the melting and boiling point of Cr2O3 is way higher comparing to Titanium.
Please let me know if I got anything wrong here. Would love to learn some more in the field of material science as well.
If I’m understanding what you’re saying correctly:
A normal ti alloy used in yoyos is Ti-6Al-4V - Wikipedia. And while it contains other elements within the alloy, the base is itself (ti). Because none of the other elements in it are forming a “protective coating”, this is what leads to a ti axle having a very high likelihood of galling with the yoyo.
With steel alloys however, with the base of steel being iron, and the composition including chromium (which ti doesn’t contain (at least the ti alloys used in yoyos)), that chromium forms a protective layer that prevents the iron in the axle from fusing with the iron of the yoyo?
This makes logical sense to me. But like I said before, I’m very ignorant when it comes to information like this, so my understanding could still be wrong.
So I guess to piggy-back off this thread with a second question:
If the steel alloys used in yoyos are rated as being both harder and stronger than the titanium alloy used in ti axles, would using a ti axle in a steel yoyo mean that the threading on the titanium axle itself would be damaged before the steel threading on the yoyo body? Would it theoretically prolong the life of the yoyo to use ti axles within steel yoyos for this reason?
For the answer:
First one, yes since Chromium is unlikely to merge and the layer of Chromium Oxide seems to be unlikely to merge in normal condition since the layer make the material less likely to have corrosion
For ti axle in SS yoyo, I will have to based on this article, it states that it can be done however the merging can only be done in some kind of high temp and high pressure environment to make it work.
The “Merging” that is referenced in this thread is known as “Galvanic Corrosion”.
“Galvanic corrosion, also known as bimetallic corrosion, is an electrochemical process whereby one metal corrodes in preference to another metal that it is in contact with through an electrolyte .”
Basically when two dissimilar metals are in contact, one metal will rob the other at the atomic/melecular level.
One of the ways we deal with this is using a lube or thread sealant to place a barrier between the dissimilar metals.
Not every thread sealent is the same. For example if you use a Copper based sealent with Stainless steel, it will cause gauling. Nickle based on the other hand works really well.
The issue with threading Titanium to Titanium (the issue of gauling) is that the material itself is not self Lubricating. In this case you need a Lube to prevent the friction that causes gauling.
For the most part, Aluminum and steel have a low Galvanic Corrosion rate, however it still can and does occur between these metals.
Useless Knowledge for the win!
To expand on the intitial question; Similar metals will not “Fuse” together as they share the same melecular balance.
It would take a Catalyst to cause corosion in the threads. This “Can” be Oxygen causing Oxidation. Think surface rust on raw steel. Again easy to avoid with a little “Lube”. Like the lube we use on our bearing
Steel is a highly explored material and there are hundreds to thousands of “Recipes” each one having its strengths and weaknesses. Choosing the right “Recipe” can be very difficult depending on the use of that material. It is a balancing act; As you increase one atribute, another declines.
This is absolutely not useless info. Thank you for the detailed write up!
I’m still curious though about which material would be the better choice for the axle in a steel yoyo, if you have any knowledge surrounding that. Would the extra strength/hardness of steel mean that a titanium axle would be damaged before the threading on the steel yoyo body itself.
I’m thinking about very long term 5A drops on a steel yoyo design, and what the most durable setup would be.
Titanium has one of the highest strength to weight ratios of metals.
Strength to weight ratio;
Both axles the same size - “Strength” will be about the same. The key with Titanium is that it weighs about 45% less than steel.
My personal opinion on the matter; If strength is similar, and the weight difference of the axel is negligible, I would save the money and stick with steel.
If you are a High Speed, Low Drag best of everything type, go with Titanium.
I dont think you would be able to notice the difference between the two in play.
My question isn’t really from a play perspective. From a purely play perspective a magnesium axle would immediately be a better choice, especially since steel designs already struggle so much with minimizing center weight.
My question stems from how heavily 3A’d/5A’d ti yoyos will start exhibiting some serious vibe, despite not having any serious visible damage on the exterior, other than surface scratches. My suspicion is that it’s coming from damage to the threading in the yoyo.
So I’m curious if using a ti axle in a steel design would lead to the axle being damaged before the threading of the yoyo. Axles are cheap and easy to replace, 200+ dollar yoyos aren’t.
Ti and it’s alloys have a face centered cubic (fcc) crystal lattice. Two fcc materials in mechanical contact are more prone to cold welding than materials with a body centered cubic (bcc) structure like Fe and it’s alloys.
That’s why Fe-threadings with Fe-axles is not a problem, but Ti-threadings with Ti-axles can be.
This holds also true to other metals.
I hope this helps a little bit.
(Materials engineer here.)
As addition: when talking Yo-Yo materials most people just always say Ti Yoyos. But when you search for the properties of titanium you will find that they are very different from the actual used Ti-Alloys.(Same for al throws)
Pure metals are almost always considerable softer than its alloys
The best steel monos are using an 8mm axle and are needing to cut into the bearing/response groove area in a way that no other material needs to. Side effects are turning the 8mm axle into a 16mm axle while also adding in the extra material the SE uses itself. This is all just in addition though to the real issue, the amount of extra steel required just to form the SE hub. And it’s putting that material in basically the worst possible spot on the yoyo in regard to just performance.
Steel monos are very difficult to design as full sized yoyos while staying under 70g. This is why most of the steel designs on the market are so small. I think it just shows that steel is an incredibly unexplored material for yoyo designs, they don’t need to be undersized, designers just aren’t really trying to take full advantage of the material, and they’re being pigeonholed by consumer preference that “anything over 70g is too heavy.”
If we got over that hump of them needing to be under 70g then SE could reasonably be added because a lot more material could be added to the rims to compensate for it. As is, even with the intricately designed hubs to maximize centerweight reduction, full sized steel monos are already struggling hard to be as rimweighted as they should be for better performance.
TL;DR steel heavy, creating a full sized steel mono while staying under 70g and not having a mostly even weight distro is already a huge challenge
Thanks for the detailed respose! That makes sense. I don’t have any SS throws to look at. I was just thinking that replacing the steel bearing seat with Al SEs would be lighter, but didn’t take in consideration the amount of material needed to support the SE.
Sounds like you and Patrick Dressel should do a collab design for 3A players. I’ve never been able to figure out how to get one, but Hydrangea put out a few full size steel yoyos this year. I love the few steel throws I have, but most 1A players that have tried them have said they’re too heavy (talking about the Yoyobarista Geishas which on my scale are upper mid 60s iirc).
The SEs currently available may not fit the bill. However, it seems like something purpose built could resolve a lot of issues.
If the base material of the yoyo is steel, using AL or Ti (or Delrin?) for the SE could save weight. The larger bore in the yoyo itself would mean that much more steel potentially replaced by a lighter material. (The interface between the yoyo and tapers may limit the savings.)
A specialized SE assembly could be optimized for weight reduction, especially if lower durability is an acceptable tradeoff.
Obviously, there is a lot of speculation here. But the concept of an entirely replaceable threaded interface seems like a good fit.
