Materials Monday: Titan of all Metal

In our recent blog article, Materials Monday: The Allure of Aluminum, we discussed the wonderful, profoundly useful metal, aluminum. With a few exceptions, each of its many alloys is strong, lightweight, corrosion-resistant, and easily machined, formed, or stamped, and when anodized or powder-coated, aluminum is also quite aesthetic. While aluminum has long been a favorite of manufacturers and product designers, here we look at titanium, a strong contender for manufacturing projects that demand a high-performance material.

Although considered a lightweight material, it’s approximately two-thirds heavier by volume than aluminum. If this were a boxing match and you placed aluminum in the featherweight category, titanium would box alongside Rocky Balboa and Mr. T (although nowhere close to Ivan Drago). That said, titanium is roughly half the weight of steel but just as strong, and twice as strong as aluminum but only 60 percent heavier. The takeaway? Compared to other metals, product designers can use less titanium than either of the alternatives to get the job done.

Even superheroes have weaknesses

It’s also darned corrosion-resistant, heat-resistant, and just plain tough—if there’s an evil environmental or structural force to be reckoned with, think of titanium as a metallic superhero. Its only Achilles’ heel (or kryptonite, since we’re talking superheroes) is its wear and abrasion resistance. Place titanium in contact with other metals or other titanium surfaces under even light loading and it tends to gall. Despite this unwillingness to play well with others, however, anodizing or the application of solid lubricants puts this concern to rest.

Titanium’s other weakness, if you can call it that, is its relatively high cost. Although increased use throughout a range of industries has made titanium’s price tag more palatable, it still ranks among the most expensive of all “everyday” metals. Adding insult to injury, titanium is quite difficult to process and hard on the tooling used to machine and fabricate it, further driving up manufacturing costs. Despite this, titanium’s many attributes—when required—more than outweigh any price considerations.

Quick history lesson

The name titanium comes from Martin Klaproth, the German scientist who in 1795 identified an unknown metal within the mineral known as red schorl. He called it titanium after the Titans in Greek mythology, due to its natural strength. Unfortunately for Klaproth, Reverend William Gregor beat him to the punch.

An English clergyman and amateur geologist, Gregor had discovered the same metal four years earlier, albeit from a different ore. While splashing around in a stream near the village Manaccan in Cornwall, he came across some black, metallic sand, which he took back to his laboratory for chemical analysis. Gregor soon realized that he’d found a new metal, which he promptly named “menaccanite” after the nearby village. Long story short, Gregor’s name remains in the history books as the discoverer of titanium, but it was Klaproth’s name that stuck.

It’s not surprising that two people discovered titanium within a few years of one another. After all, it is the 4th most abundant engineering-grade metal on earth and ranks 9th among all the elements in the earth’s crust. The only reason titanium is not used more often and remains expensive is that it’s difficult to extract. It wasn’t until 1910 that the first chemically pure titanium was produced, when General Electric metallurgist Matthew Hunter heated titanium chloride (TiCl4) with sodium in a pressurized vessel. Another 22 years would pass until Wilhelm Kroll (another German scientist) would make large-scale production possible. Titanium had hit the big time.

A multitasking marvel

There’s lots more to titanium, with mysterious terms like “sponge” and the “iodide process,” never mind the fact that titanium is considered the most biocompatible of all metals and readily bonds with human bone, a feat known as osseointegration. For obvious reasons, this makes titanium the first in line for parts like orthopedic implants and dental screws. Molten titanium is also quite friendly to other metals. Metallurgists like to blend it with iron, aluminum, molybdenum, and other elements, boldly taking this metal multitasker to places it could not have gone before.

Because of this affinity to its metal brethren, numerous titanium alloys exist. ASTM International provides dozens of titanium specifications, including B265, the Standard Specification for Titanium and Titanium Alloy Strip, Sheet, and Plate, which describes 41 distinct grades of strip, sheet, and plate, many alloyed with exotic minerals like palladium, cobalt, niobium, and vanadium, to name a few. Feel free to pick up a copy of B265 for a small fee, or just pick up the phone and call us here at Prismier to discuss your needs.

Manufacturing with titanium can be a bit tricky. We can tell you that welding must be performed in an inert atmosphere. Forming and bending can be troublesome as well due to titanium’s tendency to spring back under pressure. And as noted earlier, titanium is a real bear to cut, as any machinist or diemaker will attest. Still, these and other titanium manufacturing challenges are quite manageable given the right tooling and knowledgeable people.

Grading the titans

Given that there are literally dozens of commercially available titanium alloys to choose from, you might be wondering which one’s best for your project. No worries. The reality is that most of these are specialty alloys. Unless you’re building nuclear reactors or sending spacecraft to Mars (and maybe even then), the more common grades of titanium will work for most applications. For example, we might recommend one of the following:

• Grade 2 is the most widely used of the four “commercially pure” titaniums. It’s slightly stronger than Grade 1, though less so than Grade 4. It’s more manufacturing-friendly, though as we know, they all have challenges. It offers good formability and weldability, and like its pure cousins, provides exceptional corrosion resistance (but then again, so do most titanium grades).
• Ti-6Al-4V is more properly called Grade 5 titanium, although most in the industry refer to it by the longer name. Go figure. Whatever you call it, Ti-6Al-4V is the most common of all titanium alloys and includes 6% aluminum and 4% vanadium. It can be heat-treated to increase its already admirable strength, is weldable, and is found in everything from aircraft turbines to sports equipment.
• Grade 23 is the ELI (extra low interstitials) version of Ti-6Al-4V, a fancy way of saying it’s purer. Because of this, ELI is the metal of choice for the medical implants mentioned before, but especially for screws, pins, cables, and staples.
• Ti-5553 is a metastable β-titanium. Aerospace engineers lovingly refer to it as “triple nickel” titanium. It’s crazy tough. The machined components responsible for keeping the engines firmly attached to the wings of an Airbus A380? They’re made of Ti-5Al-5V-5Mo-3Cr (Ti-5553). As with Ti-6Al-4V, all the stuff after the “Ti-” stands for the alloying elements, which in this case means 5% each of aluminum, vanadium, and molybdenum, with 3% chromium thrown in for good measure.

As stated previously, there are plenty of other grades of titanium and plenty more to discuss. For one thing, there’s that whole alpha and beta phase thing we skimmed over just now, as well as the concept of H grades and similar minutiae, much of which is only of interest to material engineers and metallurgists. While we’re not going to do it here, you can reach out to us if you want to find out how titanium could solve your gnarly design problem.