With January being our month to focus on emerging technologies, here are a few of them that affect us as metallurgists and heat treaters.
Improving Performance by Cryogenics
In thermal processing, our goal is to create a structure that results in the optimum properties for the material. Cryogenics is a thermal process that affects the material by reducing the number of point defects, thereby creating a more consistent crystal structure. It is believed that this structural modification results in improved heat dissipation in many metals and improved electrical conductivity in nonferrous materials. It may also improve the corrosion resistance of some materials.
The cryogenic process is able to accomplish this by bringing the temperature of a part down to -300°F over an eight-hour period. It is then held for 8-20 hours and brought back to room temperature slowly over a 15-hour period. Other properties found to be positively affected by the cryogenic process are abrasion resistance, fatigue life, surface finish, strength, toughness and dimensional stability.
Several studies show that, in some alloys, fine eta-carbides are apparently initiated during the slow cool-down and are precipitated during the ramp-up to room temperature. In addition to a martensitic transformation obtained by this thermal cycling, these carbides result in a marked improvement in abrasion resistance.
While it may be easier to understand why this process works for steels, it has also been found to improve the properties of various nonferrous materials, including some plastics. The concept of the creation of a more consistent crystal structure makes mechanical-strength improvements understandable in many materials. It is this same concept that increases the electrical conductivity of copper alloys used for electrical applications and improves the tonal qualities of musical instruments that use copper. This same crystal-structure improvement is also apparently responsible for the noted corrosion-resistance improvement of magnesium alloys, some of which are used in automotive castings.
Are you up to speed with nanotechnology? Nanotechnology, which is literally the understanding and control of materials on an atomic or molecular scale, has the potential for major improvements in a variety of applications.
Nanotechnology involves work with nanoparticles, which are about 100 nanometers in size. A nanoparticle is about one-thousandth of the width of a human hair – many are even smaller. The practical application of this technology is often called molecular manufacturing. Transitioning from laboratory-scale to full-scale production and manufacture is a challenge the industry faces.
A potential impact of nanotechnology on thermal processing involves the development of new materials. Property enhancements of nanometals include weldability, resistance to intergranular corrosion and cracking, high-temperature creep, greater strength, optimum hardness and improved wear resistance.
Material coatings seem to be the leading nanotechnology. Many of these nanocoatings are superhard with resistance to certain environments, such as water or hydrogen fuels. Another key development characteristic is a very low friction coefficient, which will result in energy savings as coated parts move more freely.
Hard chrome is a coating that has been used by industry for many years to provide a wear-resistant surface. Unfortunately, this coating technique is environmentally unfriendly and is being replaced by nickel-boride coatings, which have reduced mechanical properties and wear resistance due to a columnar grain structure. It was discovered that incorporating minute amounts of nanodiamond in the electroless deposition of the coatings decreases the columnar structure and grain size. This is the primary reason for the improved hardness, corrosion resistance and performance of the coating. Previously, the coatings were heat treated to attain the necessary hardness, but the nanodiamond additives result in the same hardness improvement without increasing the grain size.
Carbon nanotubes (CNT) are used in plastics and other materials to create composites with improved electrical, mechanical and thermal properties. Nanowires made from carbon nanotubes allow electrons to travel through them without resistance.
CNT have probably existed longer than we are aware, but the invention of the transmission electron microscope (TEM) allowed them to be seen for the first time. The initial buzz associated with CNT resulted after the 1991 discovery of multi-walled CNT in the insoluble material of arc-burned graphite rods.
This probably gave researchers the idea for how to make CNT using an arc process. Although there are a number of manufacturing methods, the two most common are arc discharge and chemical vapor deposition (CVD). These two methods operate at temperatures in excess of 1830°F (1000°C).
ORNL has found that laser ablation is one of the best ways to produce high-quality single-walled nanotubes. To keep costs in check, the ultimate goal would be to produce CNT at lower temperatures. Registered patents indicate these temperatures are as low as 660-750°F. In either case, metal catalysts are used to grow the CNT. The temperature stability of CNT is estimated to be higher than 5000°F in vacuum and nearly 1400°F in air.
Nanotubes belong to the fullerene family with their sister, the buckyball. The name comes from their size because the diameter of a CNT is a few nanometers. They are about 50,000 times thinner than a human hair. CNT can be either single-walled nanotubes (SWNT) or multi-walled nanotubes (MWNT). SWNT are important because of their unique electric properties. Double-walled carbon nanotubes (DWNT) – a variant of the MWNT – are important because their morphology and properties are similar to SWNT, but their resistance to chemicals is significantly improved. MWNTs nested within one another slide and rotate almost without friction. This property has already been used to create the world’s smallest rotational motor.
Based on their tensile strength and elastic modulus, CNT are the strongest and stiffest materials yet discovered. This extraordinary strength along with their unique electrical properties and their efficiency in heat conduction have resulted in new applications. CNT have been used in a variety of applications, including structural – clothes, concrete, sports equipment, bridges, etc. Electromagnetic applications include chemical nanowires, magnets, solar cells and more. Other chemical and mechanical applications include nanotube membranes, water filters, infrared detectors and a slick waterproof surface – slicker than Teflon.
CNT applications go well beyond the more-conventional products. A number of innovative applications take advantage of the unique properties of this material. NASA researchers combined nanotubes with other materials into composites to be used for lightweight spacecraft construction. Medical researchers have utilized the tubular shape by attaching molecules that are attracted to cancer cells to nanotubes to deliver drugs directly to the diseased cells. CNT are also being used to assist in the healing process for broken bones.
Ion propulsion systems have been utilized on Earth-orbiting and interplanetary spacecraft. Using CNT in this application results in a 10% improvement in the amount of propellant available for the actual mission. The greatest benefit of the technology will be for low-power spacecraft and small satellites.
In another application, researchers created an antenna from CNT thread. The electrical properties of CNT are due to the “skin effect.” Electrons transfer well because they travel across the skin of the material instead of through a bulk mass, as in copper wire. CNT thread, a fraction of the weight of copper conductors, could significantly benefit aerospace activities because there are several hundred pounds of copper wiring on any aircraft.
Utilizing the electrical properties of CNT to reduce the weight of aerospace vehicles is one way this technology will help save energy. The production of stronger and lighter composites for many types of vehicles is another. Larger and lighter wind-turbine rotor blades, for energy-generation optimization, can also be made with CNT technology. Whether assisting the green movement or making life better for cancer sufferers, carbon nanotubes will positively impact our lives for years to come.
It is believed that glass was first discovered in ancient Egypt as a by-product of ceramic firing. According to experts, glass was first produced independently of ceramics around 1500 B.C. From then until the late 1820s, all glass was handmade. The first machine technologies were introduced beginning in 1827. Little more than a decade later, Pittsburgh was the pressed-glass capital of the world. By 1920, 80% of America’s glass was made in western Pennsylvania.
Although glass is literally a prehistoric material, it is used in very high-tech applications such as flat-panel displays and fiber optics. In the early 1970s, researchers at Corning produced an optical fiber with low enough attenuation to usher in optical-fiber telecommunication, which enabled the Internet. In 1981, General Electric produced fused-quartz ingots that can be drawn into fiber-optic strands 25 miles long.
Another impact that glass has had on our world is in the insulation market. It is estimated that fiberglass house insulation has conserved more than 25 quadrillion BTUs. Now that’s a lot of green.
These are just a few examples of materials engineering on the cutting edge of technology. Without new materials and associated technologies, developments such as electric and autonomous vehicles and renewable energy would be impossible. The next time you read about an innovative technology, consider how materials research and development made it happen.
For more information on metallurgy in everyday life, check out Reed Miller’s book in our online bookstore: https://www.industrialheating.com/products/category/2166-books/product/597-everyday-metallurgy.