Jaeger-LeCoultre

ThomasM
[PuristS]
14331

• Show profile
• Show other posts

a few quick thoughts...

Hi, Respo,

Your question touches on a very sophisticated and complex field, to be sure. Too often, discussions on this subject use terms that are not well defined by the parties engaged in the discussion, so the conclusions can be fraught with out of context misunderstandings.

Most basically, you need to distinguished between surface hardness and macro material hardness.

Coatings like PVD, CVD, DLC, and ADLC can improve surface hardness, and thus resistence to scratches (abrasion resistence), but does nothing for macro material hardness, which usually shows in dings, dents, deformations.

Ceramic has both micro hardness and macro material hardness, to the point of being brittle. That is, it will chip or crack before it will ding or dent or scratch or otherwise deform.

These qualities can be good or bad, depending on the application.

For example, in the world of wristwatches, do you tend to drop your watches, or bang them against granite countertops, or scratch them against rough surfaces like exposed brick? 

Aesthetically, I have not so far warmed to ceramic because it tends to be, with the typical formulations used in high watchmaking, shiney and reflective when. This can be attenuated with the composition, though, most commonly through the amount of yttrium used.

There are matte finishes as well, but it is still very very rare to find a case that can combine in the same case matte and polished finish in ceramic, as can with metal cases.

The haptics are different too.

Not sure if this is helpful, but I wrote the following for some background leading up to the introduction of the AP Grand Prix. The comments on the materials are obviously transferable to other brands...

Apologies in advance; I wrote it in a hurry and haven't had time to go back and clean it up.

The Royal Oak has frequently been referred to, endearingly or not, as a "scratch magnet." Since the Offshore has all those qualities and more, on a larger scale, it can fairly be called "the bigger scratch magnet."

Why has the Royal Oak and the Royal Oak Offshore earned these terms of endearment?

In fact, they are scratch magnets for the very reasons they are also nonpareil when it comes to exhibiting the high watchmakers' casemaking art - lots of surfaces with eyecatchingly beautiful angles and geometries, with an abundance of varied finishes that no one had tried before on one single watch case. Brushed; matte; high polish all stunningly presented on the different surfaces of one watch. And in a way that was harmonious, integrated, sublimely organic, all tied together by tight, fine linear transitions.

But with all the flat surfaces with such fine finishing, any scratch or surface imperfection "shows" much more clearly than if the surfaces were all matte, for example, or on a rounded, or radiused, surface.

The sobriquet is NOT a result of using inferior steel and other materials; AP, like most of the high end watch industry, uses 316L, an austenitic low carbon stainless steel which is also highly hypoallergenic. It also has the very important technical quality of being non-magnetic.

Most consumers of high end watches have been asking about the "hardness" of their watch cases for centuries, and it is commonly known that stainless steel (inox, from the French term "inoxydable" or non-oxidating) is "harder" than gold and platinum (though gold can be work hardened to be much "harder" than most people think)

The discussion often gets off-track, though, when technical terms and concepts are used loosely in "common usage" leading to confusing, and often misleading, conclusions. Afterall, the typical consumer cares about "how easily their watches scratch" and not necessarily what its surface Mohs, Vickers, Rockwell, or Brinell hardness rating is.

Throw into this chaos some new materials never before seen or used in watchmaking, some of which look or sound confusingly similar - carbon fiber and carbon forgé; ceramic: you mean that stuff you made in arts and crafts that you fired in a low temperature kiln and used to serve peanuts? - and all of a sudden you have all the ingredients for fan boy wars and "my watch is better than your watch because it doesn't scratch as easily. nyah nyah di nyah nyah"

Before we start to address the superiority of ceramics as a watch case material (some have already loudly proclaimed that ceramic is THE GREATEST SOLUTION TO WATCH CASE MATERIALS IN THE HISTORY OF THE UNIVERSE.) and its possible downsides, or whether or not carbon forgé is the greatest thing since sliced bread or just animal droppings being marketed as more precious than gold, let's try to define some basic materials science terminology and concepts.

Hardness: contrary to popular over-simplification, "hardness" is not the be-all and end-all in the discussion about case material superiority. Besides, there is surface hardness, and there is macro materials hardness...

Surface hardness can be addressed by coatings such as PVD, DLC/ADLC (a form of PVD), CVD, etc; macro-materials hardness cannot, and in fact, it is the disparity between coated surface hardness and the softer substrate macro-materials hardness that causes so many failures of coatings, at one time thought to be a panacea for scratch and wear resistence.

Whoa, wait a minute, "wear resistence?" Is that the same thing as scratching?

Before leaving the subject of coatings for the time being, I want to throw a concept out there - "buckling." As in, the substrate (the material UNDER the coating) buckling because of hardness differential from the surface coating, which results from an impact that would deform the substrate but not the coating. And Voila! buckling and separation, leading to flaking or other undesired phenomena.

Also, as one final aside, coatings were often created not only to increase surface hardness and / or wear resistence, but also for tribological qualities (basically, the reduction of friction between two contact surfaces, static or moving) which for the most part are irrelevant to watch cases. But it may explain some of the seemingly hard to understand trade offs of various coatings. (wait a minute: irrelevant to watch cases? Don't watch cases have fitted parts? screw down crowns, screwed backs, press-fit parts? Does friction, galling, cold welding apply in these cases?)

So, besides hardness, other important qualities of a material's fitness for use include

- Abrasion resistence (a quality often related to, but distinct from, hardness) - this is the quality that most discussions are centered around, as it directly relates to resistence to scratching (which, actually, can have different meanings to a materials scientist and the layman...tooling marks can be considered scratches by industry people, but not usually by the consumer, at least not in the "hey, I scratched my watch!" sense.)

- Strength;

- Toughness;

- Resistence to staining;

- Resistence to oxidation (related but a distinct sub-set of staining, a generic term for chemical reactivity. Patination is also a related term, but as often as not a positive term)

The last two can also be lumped together under "chemical inertness."

And in the world of watches,

being hypo-allergenic (does not cause allergenic reactions);
the ability to take and maintain various and high quality "finishes";
and of course, the ability to "look pretty" or "cool."

Part 2b: Hardness vs strength vs toughness: If this were a WWF Smackdown, who would win?

Before continuing on to practical implications of various materials qualities, and how they manifest in the world of watch cases, as well as how the various materials now being used in watch cases perform in these various qualities in real world usage, some final basic definitions are in order:

Hardness: simply, hardness is defined by the ASM Metals Handbook as the quality of a metal to resist plastic (ie, permanent) deformation, either by indentation or scratching, which can then lead up to fracture/cracking and catastrophic failure, the results that define the strength of a material.

There is micro or surface hardness, which is most directly related to scratching;

and there is macro hardness, which is most directly related to fundamental deformation of shape - think a squished, deformed and flattened corner where it used to be a sharp point, or an ovoid where there was once a sphere.

In fact, definitionally, hardness is actually a component quality of strength, the ability "to carry a load" which means not only resisting scratching and deformation (both plastic, or permanent, and elastic, or temporary) but also the limits at which the material will suffer fractures and cracking, and ultimately, catastrophic failure.

Toughness is the ability to absorb a force applied, and still maintain its fundamental defining characteristics, sometimes commonly described as the ability to "withstand abuse."

Can a material be strong but not tough? Tough but not strong?

Yes.

Glass is strong, but not tough.

Industrial ceramics (often a compound primarily made up of zirconium oxide and yttrium) is strong, very, very hard, but not tough.

Most forms of industrial rubber is very tough, but not strong, unable to resist abrasion or deformation.

In the world of steel and especially in the world of bladecraft, examples of the tradeoff between strength and toughness abound, resulting in the neverending pursuit of alchemy in trying various alloys and forging techniques, finished with heat and work hardening, to achieve "the best steel for all applications." Alas, so far, "the best" has proven an elusive beast, and very contextual - best for what?

The near exotic CPM-S60V/440V, S90V/420V, and even the truly rare and exotic S110V and S125V American steels, and their Japanese counterparts ZPD-189, and blue "super steel" are extremely hard (and can be hardened even more) and strong, but when they meet their limits, they chip, and later, break. But within their limits, they maintain their edge and resist abrasion like "super metals." "Lesser" more common steels might not hold their edge "as long" but they might also "roll" their edges before they chip; they might bend before they break.

Application is also important, of course - what is useful and important for a knife edge and cutting applications might not be for a drill bit, the receiver or slide of a pistol or the barrel to shoot a Nitro high pressure load, or a car frame, or an airplane space frame, or a bicycle.

What would that mean in the world of watch cases, which are not (usually) subjected to constant and heavy loads or abrasive surfaces in the course of performing their raison d'etre, sitting there and looking pretty on your wrist, and only occasionally having to stand up to the occasional mean, exposed brick wall or hooligan stray luggage cart?

Interesting question. As the British would say, horses for courses.

For those with metal working or bladecraft experience, even leaving aside the issue of allergenic reactions for the moment, can you imagine trying to form, let along high polish, satinate, and matte, a Royal Oak case made out of hardened ZPD-189 or S110V? Sure, it would resist scratching. But would scratch resistence be a reasonable goal by trading off the risk of shattering the case when dropping it on a hard granite floor from wrist height?

So here, workability is one crucial element; the other is the CALCULATED tradeoff between strength and toughness.

And this is before we even start considering consumer considerations like "coolness factor" (carbon fiber, carbon forgé) or wearing comfort and preferences (lightness like carbon fiber and other high strength to weight ratio composites, vs traditional "precious materials" like gold and platinum?)

Ceramics? Until the Survivor and now the Grand Prix, I HATED ceramics (even when used on the RBII - yes, I passed on my chance to get the RBII. Why? ) because it was impossible to "finish" and it was SHINEY. Yes, shiney. Only two finishes were possible during the time of the RBII (and before that, the Rados, and the IWC fliegers and the Panerai 232 and...) - shiney, and shiney-er.



And because it chipped and cracked and fractured and shattered much more easily than steel or Ti, or carbon forgé... Ceramic was hard, and ceramic was strong (to a point, and depending on the formulation, and depending on the process) but it was not tough.



Part 3: Brave New World

Site Info.