Superalloys like Alloy X-750 are usually used for critical parts inside jet engines where the extremes of stress, temperature and corrosiveness would disintegrate most materials. X-750 was chosen for the milestone in human aviation where it was necessary to put the superalloy on the entire OUTSIDE of the aircraft.

Ask yourself this: “What could possibly be a better choice for my middleweight endcap than the same superalloy used for the exterior of NASA's X-15A-2 experimental aircraft?”

Next time your flights of writing fancy soar to altitudes of 354,200 feet above the Earth and speeds of 4534mph (mach 6.7, still the record) you will experience the pure bliss of not having your pen burst into flames as air friction heating nudges your writing implement toward temperatures of 1400°F.

Alloy X-750 is 73% Nickel, 15.5% Chromium, 1% Niobium, 2.5% Titanium, .7% Aluminum and 7% Iron. The metallurgy of nickel based superalloys is facinating. The object of the game is not to make the strongest material possible–at least not in normal conditions. No, the idea is to make the strongest material IN HELL–
the hell inside rocket and jet engines, turbochargers, heat treating furnaces, chemical and pharmacutical manufacturing plants, power stations and an endless list of less glamourous locations. Chances are good that you'll find Nickel any place you wouldn't want to stick your finger.

For all their amazing properties, Nickel and its alloys are the Rodney Dangerfields of metal–they get no respect. The name Nickel has become forever attached to a nearly worthless coin (especially unfair because nickel coinage is typically 70% Copper). Let's make a stab at changing that with some facts:

• We begin with the toaster; a modern icon of faithful and reliable service. A simple product that does one job and usually does it well–no instruction manual required. You can thank Nickel for making this wonderful appliance possible. Inside every toaster are wires that get red-hot without burning, corroding or otherwise falling apart; morning after morning, year after year. It's more than a little likely that these wires are made of Nichrome–a family of Nickel-Chromium alloys with typical formulations of 35 to 79% Nickel, 16 to 30% Chromium and 1 to 2% Silicon.

• Have you ever melted a glass bottle in a campfire? You tuck the bottle deep into a bed of coals and the next day are rewarded with a slumped bottle-like piece of art. Glass softens at about 1300°F so the fire was about that hot, deep in the coals. This is the temperature up to which X-750 was made to be useful and it's the temperature to which parts of the outside of the X-15 aircraft were routinely exposed–that's SO OUT THERE. Here's a flying, piloted, aircraft made to endure temperatures equivalent to packing it in brightly glowing, red-hot coals–for a little while anyway (very little inside the aircraft could withstand these temperatures, pilot included).

• Jet turbine blades are poster children for Nickel superalloys. They're big, they spin at tens of thousands of revolutions per minute directly in the exhaust jet, their coated surfaces coming into contact with 3000°F gasses and they're responsible for generating unbelievable amounts of power. The world would be a much different place without alloys like X-750, Astroloy, Inconel 718, MP-35N, Hastelloy X, Pyromet CTX-1, Rene 41, Udimet 710 and Nimonic 75 to name just a very few.

• The vast majority of nickel tonnage goes into stainless steels. Anywhere from 6 to 22% nickel content buys you higher strength, better corrosion resistence and greater formability. This last one, formability, is highly ironic (pun intended) since high Nickel alloys (like X-750) are notoriously hard to form (another little example of the little zigs in the zig-zag that is the world around us). Kitchenware is a familiar stainless product. Sometimes it's described as 18/8 or 20/10 stainless. That means it's 18% or 20% Chromium plus 8% or 10% Nickel.

• Oceanside air is surprisingly corrosive. The combination of air, water, salt and cyclic drying and wetting really does a number on things. No stainless steel does a very good job of coping with it for long periods of time. A trip to any saltwater marina will quickly verify this. Iron stains flow from all older stainless steel parts. What's needed for really good salt air corrosion resistance is a Nickel-Chromium-Molybdenum alloy like:
  Alloy 825: 38-46%Ni, 19-24%Cr, 2-3%Mo, 22+%Fe, .6-1.2%Ti, .2%Al,1%Mn
  Alloy 625: 58+%Ni, 20-23%Cr, 8-10%Mo, 5%Fe, 1%Co, 3-4%Cb, .5% Ti,Al,Mn & Si
  C-22: Ni+ 20-23%Cr, 12.5-14.5%Mo, 2-6%Fe, 2.5%Co, 2.5-3.5%W, .5%Mn
  C-276: Ni+ 14.5-16.5%Cr, 15-17%Mo, 4-7%Fe, 2.5%Co, 3-4.5%W, 1% Mn
  Alloy G: Ni+ 21-24%Cr, 5-8%Mo, 18-21%Fe, 2.5%Co, 1.7-2.5Cb, 1W, 1-2%Mn, 1%Si
  But if you have to ask how much they cost...

• Like Platinum and Tungsten, early metal workers thought Nickel was a curse, an unwelcome impurity. They wanted copper. (Platinum was considered to be a pernicious inpurity in Inca silver. Tungsten was the scourge of tin smelting.)

• Most materials expand when they get warmer. Invar and Super Invar are Iron-Nickel alloys that are almost unaffected by changes in temperature (within the range from 0°C to 38°C). These alloys have become extremely important for holding optical components in laboratories as well as inside many commercially available lasers. You can bet dollars to doughnuts that the US laser fusion project uses literally tons of the stuff.
  The effects of thermal expansion over large temperature ranges can be non-intuitively large. For instance, the exterior tiles on the Space Shuttle have gaps about a millimeter wide between them at room temperature. They don't tighten up until re-entry heating expands them. The X-15 has been remarked to be a leaky, almost sloppy structure until it got hot. More recently, at least one technical journal fingers thermal expansion leading to buckling as the mechanism of failure of the World Trade Center towers. (No, heat didn't just soften everything to mush.)
  Invar is Iron plus 36% Nickel. Super Invar is Iron + 32% Nickel + 5% Cobalt.

• Shape memory alloys of Nickel and Titanium are quite strange: below a critical temperature they are soft and easy to form into most any tangle you might want to put them in. Above the critical temperature they spring back to whatever shape has been previously heat-set into them, resulting in a property called super-elasticity. Super-elasticity, like it sounds, is an unearthly springiness but to really appreciate it's weirdness you have to flex a piece with your hands. What happens when you flex it is that you quickly reach a point where the material bends and bends with very little extra force required. This is due to the microstructure forming layers of crystal twins as a response to stress–a real-world property so bizarre and unlikely that it shames the most creative works of science fiction writers. Called Nitinol, these alloys are typically 55% Nickel and 45% Titanium and are commonly found on expensive eyeglass frames and in flexible cell phone antennas. The eyeglass salespeople always "forget" to mention the Nickel.

• Alnico magnets are some of the most important and heavily used magnets in the world. They are heavily spiked Iron alloys with additions of 6-12% Aluminum, 14-27% Nickel, 5-35% Cobalt and 3-4% Copper. It's name is the first two letters of the main alloying elements: ALuminum, NIckel, CObalt.

• The material used for BOMApen endcaps is fully pedigreed military and aerospace material. Each batch comes with mill test certification of alloy content and strength. The current batch of endcaps comes from Allvac lot #08395, Mr. Ingot #3 and lists the following content percentages:
  Nickel: 71.80%
  Chromium: 15.48%
  Iron: 8.09%
  Titanium: 2.62%
  Niobium: 1.02%
  Aluminum: .80%
  Carbon: .058%
  Molybdenum: .07%
  Manganese: .05%
  Silicon: .04%
  Cobalt: .03%
  Copper: .03%
  Vanadium: .03%
  Zirconium: .03%
  Tantalum: .02%
  Tungsten: .01%
  Boron: .007%
  Phosphorus: .004%
  Sulfur: .0006%
  Strength data: Yield strength: 129,300psi; Ultimate tensile strength: 182,200psi; Elongation: 24.0%; Reduction of area: 46.8% (These last two values say just how ductile the X-750 was. They indicate that the alloy failed very gracefully–stretching and deforming rather than just busting with no warning. This is what engineers mean by a tough material.) Hardness was 39 on the Rockwell C scale. This batch of endcap material also meets the AMS 5667 standard.

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