 Welcome. I'm very pleased to introduce Mr. Rich Barrett and the Fastener Design Course. Rich, as you may well know, is a NASA engineer. He has been an engineer for 40 years and with the Lewis Research Center for 34 of those 40 years. His advice in the materials of fasteners and materials is well sought by industry and by other government agencies besides NASA. His Fastener Design Manual has received widespread acclaim and distribution and it led to his earning of the Federal Laboratory Consortium Award for Technology Transfer. All the awards that Mr. Barrett has received are the NASA Exceptional Service Medal and the Elder Statement of Aviation Award. With not much more to say, here is Mr. Rich Barrett. Thank you very much. Thank you Mario for the nice introduction. We will be presenting in this course one of the, it will be the most extensive coverages of Fastener Design that I have done to date because it will be a, about 385 pages of presentation. So we will move into it and, as they say in the candy commercial, you're not going anywhere for a while so relax and we'll cover everything we can on fasteners. Thank you. So to start out with, I'd like to give you some acknowledgment here of the people that had a hand in this. Will Harkins and Mario Castro, Mario is my boss here at NASA Lewis. Will Harkins from NASA Headquarters sponsored this course, funded quite a bit of it. So this will be used by all of the different NASA centers. Harold Casper from Anilex Corporation, he wrote some of the sections and found some information for the others as well as editing the entire course. John Bickford who is the leading author actually in the Fastener field. He is the editor-in-chief of a book which I was contributing author for. We published the end of the year. I use a lot of John's stuff from his book on Fastener Design in this course. Bing Blendoff from Clemson University and he's actually chairman of the Bolting Technology Council, which is a council dedicated to furthering the knowledge on fastener design, has contributed some. And Betsy De La Cruz who did all of the typing, retyping, running, and so on to get this thing together and we just about ran out of time. But that's why we did not give it before and I say it's approximately a two-day course. Then Ray Holmick from ADF Corporation edited the entire course and had some very helpful comments. So with that in mind we'll proceed with the little introductory material. Now there's a statement everybody knows about bolts and nuts, but do they really know about bolts and nuts? Sometimes we oversimplify things because we think it causes something that a kid took off the wagon that it's simple for everybody. The Joseph Dudley who is a vice president of Automotive Marketing for Nyloch Fastener Corporation gave these to quote, 75% of the assembly labor cost of an automobile is spent on fasteners and 80 to 85% of all automobile recalls are fastener related. Now that gives you an idea about the importance of fasteners and putting things together. And of course some of you remember on the shuttle recently when they had to cancel a spacewalk because a couple screws came loose and fell out in the gears. They couldn't get the door open. So things do go wrong like that. Here is a summary of the causes for joint failures in NASA's Skylab program. Some of you say Ron Romanchuk will remember that. He was here that long back when that happened. And the thing that surprised me in this is the poor design improper assembly here. 24% poor design, 28% for improper assembly and yet only 10% for bad parts and the 24% for parts damaged and handling and the wrong preload 14%. Now we have been hearing in the news for the past several years about the counterfeit fasteners and all of that. And so it's gotten quite a bit of publicity and it should but it still boils down to the fact that the designer has more to do with it than the manufacturer of the fasteners. Now here is something from John Bickford's book on a bolded joint just a spring concept because actually you don't think of it this way but the joint material itself is a big heavy spring and you're compressing it with small springs which are fasteners and we even get into joint stiffness and stiffness ratios and so on. Now here's a summary of the different types of heads on fasteners just for your reference. And these, this is used some in the aerospace field although it's not that common but of course the flat, the socket head over here and the hex. All of these are very common. The carriage bolt of course that one is I guess dates back to building wagons when you drilled a hole and you pounded that one in and the square part under the head there locked it in place while you put the nut on. So let's see that's how you build wagons in case you ever go into it. Here's one on the internal drive systems and you can't read it too well on this one but over on the view graphs I think you can read them. And a lot of these are common only to the aerospace world like for instance something like this or something like the tri-wing type here. These are used only by certain manufacturers. The torques down here is very common in the automotive field. That one I thought that I'm always looking at conspiracy theories of designers and I thought the torques was developed by the automotive people just to make things more difficult on working on your car. But I found out that the reason they used it was that it centers better than the Philips which various types of Philips there and will not came out as much so therefore it will work better in automated assembly. Now getting into the agenda for this program. See we have a lot of stuff and each one of these is a section number in your handout. So we have a lot of stuff here to cover. I won't go over all of these but I'll point out that at the end we have do's and don'ts and frequently asked questions. Sections that will answer some of the various questions that I have been asked from time to time by people. So we'll move on into materials and this I feel is a very important section because you need to choose the right material to begin with for your dead in the water on a design. Now fasteners can be made for many materials but most of them that we're familiar with are made out of steel. The hardware store type that are made out of what's called low carbon steel then the alloy steel for the grades 5s and 8s that we use around here in the socket head cap screw. Titanium and aluminum bolts have limited usage in the aerospace industry but on the other hand aluminum and titanium are used a lot on the aircraft design. Particularly since you have aluminum skins on most airplanes and you want the rivets to be of the same material because of the differential temperature giving you problems on expansion and contraction. So now the alloy steel fasteners you can get them up to 300 KSI KSI being 1000 PSI so it's 300,000 PSI strength levels but I'll try to point out to you here that in most cases you really don't want to do that. Okay now carbon steels are not corrosion resistant so they usually have to have some kind of a coating to protect them from rusting. And the stainless steels you can get in all varieties of both heat treatable and non-heat treatable alloys with the tensile strength of 70 KSI to 260 to 70 being the ordinary 300 series stainless that we use here all the time. And the 260 you're talking work hardened Incanel 718 or 8286. And note that the 400 series materials contain only 12% chromium which will allow them to rust some so if you're building something that you want it to look pretty the 400 series stainless would not be advisable. And on some of these subsequent tables we will show various materials but just go on to the in order here on the selection of materials you should use common faster materials strength levels and coatings if you can. There is no sense in over killing on any design because it can it just costs you money and time usually. Weight savings versus cost must also be evaluated for flight articles and there you do spend a lot of money to save a little bit of weight. Galvanic and stress corrosion tolerance levels have to be established and checked out. And of course the operating temperatures has to have to be determined before the material is chosen both the high and the low to make sure that the materials are compatible in the entire range. And then the type of loading static or fatigue loading is also a factor in the material selection. Now as far as availability and materials the carbon steel faster materials of course everybody's familiar with the 10 10 10 20 that we use around here and that is just a iron with carbon in it a few impurities and it's up to 0.28 carbon. Now that's I'll explain this further in another chart but the carbon content is usually called out in points and it's actually hundreds of a percent. So this is 0.28 here it's hundreds of a percent of carbon and you need for heat treating unless you add something like boron to the material you need about 25 points of carbon. Really to get it to heat treat properly if you're going to heat treat a fastener. Now the grade 5's and grade 8's are in the 28 to 55 point carbon range so that they're heat treatable. And the 8's of course have other alloying elements in them in order that you can bring them up to the strength that you want. And 40 37 is one of the common materials for grade 8. Now here's something I just wanted to point out to you that Charlie Wilson from the Industrial Fasteners Institute has been trying to get this change for years but it's still in there in SAE J 429 spec which is for grade 8 fasteners. There's a footnote there that allows the manufacturer to furnish these in 1045 plain carbon steel if the buyer agrees to it. Well the only thing is if the buyer doesn't know he's agreeing to it he can get one that will not have very good impact resistance. And we had a problem that we were in on one time with the Army on some Abrams tanks that when they fired the cannon on them it broke the bolts on the turret because it remained out of 1045 steel. Okay moving on now the ASTM fasteners are used primarily in the construction industry. So since a lot of you are not familiar with them and I'm not that familiar with them either I put in some equivalency here like the A307 is a grade 1 in the SAE that we're familiar with and 449 354. And now the A193 there the B567 16s and also the B8 stainless steel those are used a lot for the pipe flanges that we design around here. So a lot of you are probably familiar with them. The 320 is an alloy steel for low temperatures and the 325 is a sort of equivalent to a grade 8 in strength and then the 490 is the highest strength of the construction type fasteners. Stainless steel which is a crass you'll see that designation for it corrosion resisting steel stainless steel is the same generic terminology and the super alloy materials. Now the 300 series that we're familiar with around here you get it up to about 80 KSI because it's not a heat treatable material so the only way that you can get the strength up on it is by work hardening it and informing it. That's about the strength that they get starting with annealed material. A286 we use all the time in the aerospace world up to 160 KSI it is a very common aerospace material and you can you can get it in metric by special order and A286. The 400 series is available in limited strengths up to 125 KSI and it's also available in metric which I will show you further on. Now the super alloys here these are the ones that you guys come around looking for when you want something for a particularly stringent environmental set of conditions like high temperature corrosion and so on. These are all stainless here and well titanium of course is very corrosion resistant also. The MP35 and MP159 are made by SPS they have the patent on the material and they are super corrosion resistant and high strength up to about 220 KSI. Incanal X750 is used for high temperature and the Haynes alloys and then the A286 above 160 KSI strength is a special because in order to get it above about 180 KSI you have to work harden it in addition to heat treating it. Now here's a table of faster materials I won't go through each one of these but one of the things I just wanted to point out to you and you'll have to go to this one over here on it is how to figure out what the designation is. Now the AISI and SAE usually the numbers are the same for the steel and in this case here we have the two is the class of materials from over here which is a nickel steel in this case. The three is the approximate percentage of the main alloying element which in this case is nickel and then the seventeen is the carbon content so this is a low carbon alloy steel 2317 that has no special significance other than the fact that it's used to just illustrate the system. Now for the nickel chromium steels and molybdenum steels and so on here are the ones that are used mostly for fasteners and alloy steels the 4000 series you have 4037 4140 4340 that type of thing that is that are used for the fastener steels. Now on chemical compositions I guess I better stay with this one over here for that also. Here you see here the ordinary hardware store varieties and you notice that all of these other elements are not listed. One of the things you can run into if you if you're having a real problem sometimes you can get some of these steels that have things in them that you don't want. A guy was pointing this out to me from Lincoln Electric that in welding they're running into that because a lot of steel is made out of scrap so the scrap has most anything yet so they're getting a lot of impurities that they don't want in it. And then then you get down here the standard alloys the stainless steels one of the ones that I wanted to call to your attention on that is the in the 300 series stainless steel down here. One of the ones that they left out here was the the L designations the low carbon because a lot of the times you want to minimize the amount of carbon in it. So you use a 304 L or 316 L or something like that and they did not put that one in that table so you might want to just flag it. All right moving on now to operating temperatures here. I have grouped this in categories and so the minus 65 and below that's your cryogenic temperatures now of course those of you who have been around long enough remember the Atlas and Centaur. And of course they're liquid hydrogen fueled so the temperatures are running on on that type of a vehicle or anywhere from about 300 to minus 423. So you cannot use carbon steels at those temperatures because they will crack like glass. Even some of the stainless steels won't go below about minus 150 aluminum is good down to those temperatures. Then you go to the minus 65 to 450 which is an ordinary range for most engineering designs. Carbon steels are OK and stainless steels are OK. But then you get into the business of needing corrosion protection for the carbon steel with the various types of plating like zinc or cadmium or phosphate or black oxide or whatever. And those will be covered of course later on in the plating and coating section. Now for the 450 and above believe it or not you can use unplated carbon steel up to about 700 degrees because the only thing you're looking at there is how much does the allowable drop on it for the temperature. So if you go in one of the books like Mill Handbook 5 you can find the temperature curves for carbon steels and you find you can use it. But you see the reason I'm saying unplated is that an awful lot of the platings for steels burn up before you get to that temperature. So these are some of the ones that don't hurt you at least. And I'm just giving these because of their temperature range rather than the fact that you normally would not silver plate a carbon steel but you do silver plate stainless steel. But silver nickel chromium plating and chromium plating is used on some high strength fasteners for aircraft landing gear that type of thing. The black oxide coating that you're all familiar with from your hardware store bolts looks good and all that but it burns off. Then you have diffused nickel chromium which is a special one that will be covered later. And then of course you can use the stainless steels and super alloys without anything. Now although we have a corrosion section I elected to put the, sorry about that, here's the table of summary of fastener materials. And you can't read this one so I'll go over to this one. One of the things that I wanted to point out to you here is that if you look at the useful design temperature on these you find that A286 is one of the best, minus 423 to 1200. But you get down through all of these and you find that this Haynes 230 at the bottom is the only one that will carry you up to 1800 degrees. Now the significance of this is that we've gone through on the NASP program, the National Aerospace Plane, developing all of these super duper materials to build airplanes out of. But we never did anything on developing fasteners to put them together because the regular metal fasteners are the only thing they have to put them together. Okay moving along now into the galvanic corrosion and stress corrosion area. Galvanic corrosion is something that we're all familiar with although we may not use that title for it. If you get a scratch on the chromium plating on your car it will rust faster than it would if it didn't have any plating on it because you have a very small anode and a large cathode being the rest of the surface. So the anode is deposited on the cathode which means that it rusts away. So rusting is a galvanic corrosion and later on we have a table on the galvanic series that will give you the location in the table of these. In the farther apart they are in the table the bigger galvanic corrosion cell you develop between the two of them. And of course cadmium and zinc are adjacent to aluminum in that table which makes them compatible as coatings for steel fasteners used in aluminum. And to further protect mating surfaces from galvanic corrosion particularly where you're putting in rivets and you drill, you pilot drill one piece and then drill it through you have raw surfaces that are not plated with anything. So you either use a zinc chromate paste or there's a mil 8802 sealer that will deter galvanic corrosion. Now here is the table of the galvanic series and this is something you can find I think Mark's handbook and various places have it. And one of the things that I wanted to point out in this is that if you look at cadmium over here see it is right in the aluminum also zinc is there. So if you use a cadmium plated faster in aluminum you will get less galvanic corrosion than you would say if you used a one of these down here like a brass or copper incanel or something like that. Now notice that there are two different designations for the stainless steel they have active and passive. Normally stainless steels are passivated which they're treated with an acid dip to remove any kind of scale they had on them from processing and to form a protective oxide on the surface. The passivation of steel corresponds to anodizing of aluminum so that's why they have it shown differently here passive and active because the passive is much less corrosion or much more corrosion resistant. Okay now going to stress corrosion that is something that we're all familiar with in a sense but there's not much available in textbooks on it because the study of it is a fairly recent thing. Now stress corrosion of course occurs when a sensitive material is loaded in tension in a corrosion environment. That sounds pretty easy and what happens is the surface develops pits or cracks from exposure and this of course gives you stress risers which will cause the component to fail as little as 20% of its calculated load capacity. Now the thing about it one of the reasons why I don't propose using the super high strength alloy steel fasteners if you can avoid it is the higher the strength the more sensitive it is to stress corrosion. So you try to steer clear of using super high strength fasteners in alloy steel for that reason. The stainless steels most of them are not stress corrosion susceptible other than the precipitation hardening 17.4 and 17.7. So you ought to look at that before you select the fasteners that you're going to use. Here's another one that you can run into although it's not that common as decarbonization. When you heat treat a carbon steel you can actually precipitate carbon out on the surface and I would compare this to like charred wood or something like that. You know charred wood is how it's very soft on the surface because this is essentially what you're getting. You're getting a heavy carbon coat in the outer surface and of course it's not as strong as the parent material. And on machine parts they sometimes just machine that off and go ahead and they can use the part but of course on a fastener you can't do that. So you have to be careful about decarbonization and once again it's on the strength above 180 KSI. Now temper brittleness is another thing you can run into on the high strength fasteners. After you have quenched them then you need to go back and temper them which means holding them at a fairly low temperature to get the strength that you need. This also causes the material to be brittle. So carbon steel fasteners above 190 KSI are a real risk as far as having brittle failure. Now you can use some of the super alloys strength higher than that but not the ordinary carbon steel. Now going to carbide precipitation. This is something that gets people in trouble a lot where they don't want a stainless steel to rust. And believe it or not this is fairly recent at least recent for me maybe for you guys it's ancient. But we ran into this on the Atlas and Centaur programs in which we had joints rusting down at the Cape with this thing sitting on the pad. And this is stainless steel it's not supposed to rust. But what they had on that some of the sections were put together by fusion welding. And of course the only way that you can prevent it from rusting on the 300 these were 301 is to solution treat it after welding which means you take it up to about 1800 degrees or something like that and get the chromium back in solution. Because what happens the carbon will combine with the chromium to form chromium carbide in the weld joint and of course that pulls the chromium out so if you had your regular 301 is an 1818 chromium 8 nickel. So you pull the chromium out if it falls below about 12% the steel rust. So this is why that normally if you're going to have welded joints you try to use a 300 series with the L designation which is low carbon and even use a low carbon weld rod. Or better yet and this is what we did at Martin Marriott on the Titan you use 321 stainless because it has titanium in it or you can use 347 which has columbium and the titanium and columbium will combine with the carbon before the chromium weld so that will leave the chromium in solution so that you still have the corrosion resistance. So keep that in mind when selecting fasteners for anything above about 800 degrees in the stainless steel to use 321 or 347. Now on material strengths after the temperature and corrosion requirements have been determined then you've got to look at the material strength and once again keep in mind the higher the strength of the material the more stringent the manufacturing and quality requirements become because it's more sensitive to imperfections. If weight is not critical it's better to use a lot of fasteners of lower strengths than to use a few high strength fasteners. Use those old grade eights if you can use them and you don't have to worry about weight. Now here's metric fasteners and that is one of the least understood I think between most design engineers and I'll have to admit it's confusing to me although my buddy Bing Glendorf who came from Sweden says that metric is the way of the world. He thinks it's great but I still have trouble with it. So go through some of the peculiarities of metric fasteners. On the property classes is the way that they specify the strength and which is a tensile element and then yield as a percent of the element in megapascals. And somewhere here a megapascal is a hundred and forty five point oh four PSI for any of those who want need to convert. Now the material is not specified in the call out so you have to specify the material yourself or otherwise you don't know what you're getting. So if you have like a property class six point eight it's a carbon steel of some kind with an ultimate strength of six hundred megapascals and a yield of eight tenths times that because that's where the point eight comes from. Now for some stainless steels they don't use those rules and so I have a table further down the line here that shows the peculiar type stainless steels the way they're called out metric system. Now here's something I had a little trouble with getting people to understand around here because when we had a government decree to go to. The metric fasteners for the CM one project or for all new projects the metric aerospace fasteners are not available in the European market. They use American inch pound fasteners on their airplanes and I toured the Hux rivet plant in Tucson a couple of years ago and the chief engineer told me at the time that the A three hundred people were their biggest customer at that time on fasteners because there aren't any airspace fasteners available in the European market. So you can get them in this country on special order and due to the fact that the property class is not enough to define the fasteners. The NAS committee and our agency faster committee came up with doing it this way you put out these AIA it's actually NAS specifications that are for metric fasteners only and this is a very similar to the MS or NAS sheets that you see all the time for the inch stuff that you actually cover everything on there. The heat treat the material everything and all the dimensions coatings and so on so that you're completely covered and you can also order metric fasteners from antsy specifications. Now here's here's that kind of a queer duct type table here for the stainless steel metric fasteners and these different classes here the A one A two A four and so on and then the 50 70 80 45 60 50 70 80 and so on. For some reason or other you need to add a zero to those in order to get the actual strength of the material. They made them a class like that with that so so in other words the 50 here is a 500 megapascal ultimate strength. And so so the only way to identify them is to put them in a table like that where you can refer back to them. Now the next table covers the different classes and the type of alloys that are normally used for them. The SE here is S and SE is S is for sulfur that's in SE is for selenium that's normally added to the 300 series to make it more machinable. So presumably on this one if you wanted to make your own and you wanted to cut them out of stainless steel then you could use those materials. Here you have the 304L and the 321 and 347 which are the titanium columbium stabilized. And then here the 400 series which are only 20 12% chromium and there's another table further over here that will show some of that. Now going to the figure two I will not go through all of this stuff but this is from the metals handbook. It just gives you a good overall view of the 300 series and the things that you do to it to tailor it to your needs. In fact you probably can't read that even here at all so it is in your handout so you can go through it and you can refer back to it at least when you're picking a material. The figure three shows the tailoring of the martensitic 400 series. And for those of you who always wonder what your scout knife is made out of it's 440C which is down there in the corner some place. And that's the one that has the highest in the upper right hand corner there has the highest carbon and a lot of chromium. So that it will give you a high strength you can go up to about a Rockwell 55 with its C55. But it will nickel up more readily it's not as ductile as carbon steel. Figure four is once again this is the standard ferritic stainless steel so the 430 series and the different ways of tailoring them so I won't go through that. Then we go into a glossary of terms for materials and once again there's more here than I will cover in this presentation. But some of the things I wanted to call to your attention here about the alloy steels that normally we use the 4000 series. Then on aluminum which I cover here if you want more information on those you can go to the aluminum handbook which is put out by the aluminum association. And we'll give you more information there. If you look under aluminum alloy is the 2024 2000 series is heat treatable the 3000 series isn't. The 5000 series is not heat treatable but some of them are corrosion stress corrosion sensitive. And of course the 6000 and 7000 we use all the time they are heat treatable. The down there the leaded steels they are used sometimes I guess for making one of a kind type screws the lead once again is added to steel to make it easier to machine. Okay going over to the next one there the stainless steels once again there's also a 200 series stainless steel it's very similar to the 300. And the other thing we had a problem down at the Cape one time that they couldn't determine whether they had used 300 or 400 series fasteners. So the way you check is with a magnet 400 series is magnetic 300 series is not. Okay moving on to the mechanical definitions part you get into cold working. Plain carbon steels will cold work can you read that one over there or not. The plain carbon steels you can you can cold work them during deformation in fact one of the reasons that they start out with the so called wire. If you will not wire it somehow three quarter inch wire doesn't strike me as being wire but that's what they call it in the faster plants they run it through. And they before they run it through they run it through an annealing furnace to get it as soft as possible before they start. And so the fasteners are actually formed out of this annealed wire and they are cold worked during the forming. In fact we had I was involved in a quick case on a product liability thing that the nut was actually harder than the bolt in this case. Because the nut had been cold worked more than the bolt and it stripped the threads off the bolt and caused a chair to fail and a guy got hurt. So just wanted to point those out to you. Now going on over to this next glossary of terms on the process definitions on one of the things I wanted to point out there killed steel is something that is defined here which normally you don't find and that is important because it makes the steel chemically stable so that you won't get into troubles on it. And I always point out defects that have happened along the line. And one of the things you remember the cars I believe was the Ford's and Lincoln's that had the bumper beam that disintegrated on them. That was because the steel was not killed properly as I understand it. And so you can get disastrous effects from it. The pickling is also a removal of oxide scale by dipping the steel in a bath. And these are important to have to prevent corrosion on the material during the manufacturing process whether it be fasteners or general hardware. Now the carburizing I covered so we'll not go nitriding and case hardening actually in cases like that it's where you have a material that you want it to remain ductile because it's some sort of an impact type thing. And so you case hard in the surface of it by putting enough carbon on it that you can harden the surface just to get it slightly hard. Okay. Now moving to platings and coatings. Nearly all commercial fasteners are made of since they're made of plain carbon or alloy carbon steel you need some sort of a protection on them from resting. So you can go from putting good old 10 W 30 oil on them down all the way to gold plating. Now gold plating is not used on fasteners usually but other than pins on tubes or something like that in the electrical field, electrical contacts and so on. But if something is small enough gold plating does not become that expensive to coat it. But usually we go with something that is less expensive. So but what you're looking for is a coating that will give you the protection at the lowest cost. So the other thing is with fasteners you've got to have a thin coating because the fastener threads have to be within tolerance after the coating which is important. Now I know that if you get nails or something like that Ron Romanchuk drives nails all the time have been galvanized and that's a dipping process but it's not used normally on threaded fasteners. Now on temperature limitations the coating is more likely to set the temperature limit than the fastener material itself. And some coatings can be a disaster when they decompose like cadmium you get hydrogen embrittlement from the decomposition of cadmium. And others like the good old familiar black oxide bake off without doing any harm. Now cadmium plating is although people say that it is going away because of environmental problems that's really not true. In fact when I talked to a guy at Boeing about their development of replacements for cadmium he said as far as we're concerned there is no replacement for cadmium we're going to go ahead using it. So it's just the idea that you have to control the process in order to keep EPA off your back. But it can be used for electro depositing alloy steel up to 190 KSI. If you get above 190 KSI then you can't prevent hydrogen embrittlement and you have to go to a vacuum deposit which runs the cost way up. Now here's something that is overlooked a lot and causes lots of problems. When parts are cadmium plated they have to be baked within 2 hours after plating. And the reason I said 8 to 23 hours it depends on who's baking them or if any baking is done. Because I have heard of cases in which no baking at all was done to bake the hydrogen out. Whenever you do an electro plating process it's done in some sort of an aqueous environment. So as you know from charging your battery you get free hydrogen whenever you put electrodes in water. So you have free hydrogen ions and of course hydrogen can go where anything else can't go. So you get hydrogen given off during the process so unless you bake the material right after it you're in trouble. Now cadmium melts at 610 degrees so its service temperature is limited to 450. Now the advantages of cadmium is good salt spray resistance so it's very good in marine environment for airplanes where they're exposed to salt all the time in the wintertime. It's consistent on the torque friction properties. It has a good calvanic corrosion location and it doesn't decrease the base material fatigue strength. But the disadvantages it generates cyanide during the plating process which is nasty stuff that the EPA watches very closely. And of course I mentioned the plating and baking has to be closely controlled in void hydrogen embrittlement. And it causes embrittlement of titanium. It's very expensive and it has to be vacuum deposited on high strength parts to avoid hydrogen embrittlement. So but one of the other advantages of it that I didn't list there it does not support fungus growth whereas a lot of platings will. Since cadmium is kind of a toxic type thing your moles and stuff like that in a marine environment can't grow on it. Now zinc plating zinc is very common most of the fasteners that you buy that are plated are probably zinc plated. And of course hot dip zinc plating is called galvanizing you get ripping nails that type of thing are galvanized. The corrugated roof and so on is galvanized. Now the zinc plating doesn't generate toxic byproducts that cadmium generates and it's a lot cheaper than cadmium. But it will heal itself over by migrating over scratched areas if you scratch an area in fact down at the Cape. They did a study on how far zinc would migrate and it would go over a scratch about an eighth of an inch wide. And go back and heal it will kind of heal itself to a certain extent. And it has a good galvanic location but it's not as good as cadmium for corrosion resistance and the torque tension friction characteristics. In other words when you're torquing up a fastener you can get such a variation in the coefficient of friction that you can get in real trouble on knowing what load you're putting on it. And but it can and here's one of the other bad things about it. It has a useful temperature limit of only about 250 degrees so you can't use it at all for your have elevated temperatures. And it can cause hydrogen embrittlement although it's not a serious a problem as it is with the cadmium. Now the phosphate coatings this is used a lot in the automotive business because it's cheap. You throw a cup of phosphate in a barrel and put a bunch of fasteners in and shake them a few times and you have phosphate coated fasteners more or less. And so the mildly protective layer of phosphate is formed on the surface and there's three different ones. There's zinc iron and manganese and the ones usually used for fasteners is the zinc or manganese. Now the advantages of phosphate coatings they're cheap. You can coat them with oil or wax to increase the corrosion resistance. And phosphate is a good primer for painting so if you're going to paint something after you've phosphate coated that's great. And you don't get hydrogen embrittlement from it. But disadvantage is not very good in corrosion. You get inconsistent torque tension friction properties which means if you are supposed to torque a head bolt to exactly 2,000 pounds tensile load you don't know what torque it will take to do it if you have different fasteners that were in a different location in the barrel. And they have a limited temperature of 225 to 400 degrees. Now nickel plating. Nickel with or without a copper strike is one of the oldest methods of preventing corrosion and improving the appearance of steel and brass. And it will tarnish unless it's chromium plated. But it has a fairly high allowable temperature and good corrosion resistance. The disadvantage it's more expensive than cadmium or zinc. It requires baking after plating to prevent hydrogen embrittlement and it doesn't look too good when it starts tarnishing. Now moving on to chromium plating. Chromium plating of course as you all know is used for automotive and appliance decoration in very thin coats. But it can be used for fasteners as I mentioned earlier. It's used for coating fasteners for landing gear. This type of thing where you require the super high strength fasteners or components. And so you can't use something else that would be like in a stainless steel. So you go to the very high strength carbon steel alloy steel and then you chrome plate it. But to get a good chrome plate you've got to put a copper strike on first and then a nickel over that and then the chromium goes over the two of them. Otherwise the chromium is porous to a certain extent. So unless you have something under it to help it it doesn't work out too well or you have to go with a fairly thick coat. So and it can be used up to about 1200 degrees and of course it looks good. But the thing you run into it's as expensive as stainless steel so you only use it for the special cases. And it requires very stringent quality control because you know what a disaster it would be if you get a hole through it and the salt gets in it. Then you have something rusting very fast. And of course you have to do the baking to prevent hydrogen embrittlement with it. Same as you do with the cadmium plating. Now here's the ion vapor deposited aluminum plating. This is a special one that was developed I believe by McDonald Douglas for coding of aircraft parts. And it was going to be used as an alternate to cadmium plating. Well it doesn't give you hydrogen embrittlement and it insulates to deter the galvanic corrosion and can be used up to 925 degrees. And it doesn't give off any toxic byproducts but it's expensive and has to be done in a vacuum. So you can send it out to Joe Dokes plating outfit to get it done. And it's not as good as cadmium in a salt spray test so it has not had that wide a usage that I know of. Diffuse nickel cadmium is another one that was developed by the aerospace industry as a high temperature cadmium plating. And you put a nickel coating on first and then put cadmium over it and bake it for one hour at 645 degrees. Now the advantage you get up to about 1000 degrees exposure temperature which is good versus 450 for plain cadmium plating. But once again it's expensive. You have to have extremely close process controls. And the nickel plate has to cover the fastener at all times to avoid cadmium damage to the fastener material. So and it's not recommended for parts above 200 KSI strength. OK silver plating. Silver plating is used to prevent corrosion and as a solid lubricant for fasteners. For instance it's customary to silver plate a stainless steel nut for a stainless steel bolt in order to prevent galling and service a lubricant. Now silver plating can be used up to about 1600 degrees. And it's disadvantages though it's expensive. It tarnishes and it shouldn't be used in direct contact with titanium. So it's primary use in the aerospace field is just to coat stainless steel parts on stainless steel to prevent the thing from galling. OK we will take a break now and resume with passivation and oxidation on the next session.