Hypersonic Technology and MRF
MRF furnaces have been part of many R&D breakthroughs and discoveries over the years. Mass production of these new applications has helped us continue serving multiple markets even after the initial process has been defined or commercialized. One of these processes that have gained more interest within the public and private sectors of the markets in the last few years is the research of materials and elements required for hypersonic technology.
What is Hypersonic?
Hypersonic generally refers to speeds at Mach 5 or faster. Hypersonic is, obviously, supersonic on steroids. But while “supersonic” has the clear-cut definition of being faster than the speed of sound (Mach 1), hypersonic is a little fuzzier. Generally, Hypersonic speeds are the point at which the molecules of air that surround the aircraft start to change by breaking apart (dissociation) and/or picking up electrical charge (ionization). These things don’t happen at one particular speed, so the term “hypersonic” instead refers to the point at which they start to meaningfully affect the mechanics of flight—generally accepted to be Mach 5, or 3,836.35 mph in conditions of 20 degrees Celsius at sea level. 
However, speed is not the only goal of hypersonic research. It is also about the technology’s ability for accuracy, maneuverability, and the capability to avoid early detection that makes this technology so coveted. The example in Figures 1 and 2 depicts the differences in terrestrial-based radar detection timelines for ballistic missiles versus weapons delivered by hypersonic speed and how early detection is avoided.
Figure 1. CRS image based on an image in “Gliding missiles that fly
faster than Mach 5 are coming,” The Economist, April 6, 2019. 
Figure 2. 
Who Has Hypersonic Tech
In 2019, one of the two main US hypersonic prototypes was under development and meant to fly at speeds between Mach 15 and Mach 20, or more than 11,400 miles per hour.  However, China beat everyone to the punch and became the first country in that same year to publicly announce the deployment of hypersonic weapons when its DF-17 missile, in Figure 3, was featured in the National Day military parade on October 1, 2019.
Figure 3. The DF-17 is a 15 ton, 11 meter long missile capable of traveling at over 3,800 miles
per hour and can be fitted with conventional or thermonuclear warheads. 
A little over a year after China unveiled its DF-17 missile, Russia introduced their own hypersonic weapon into active service. Defense Minister Sergei Shoigu confirmed that the Avangard hypersonic glide vehicle, in Figure 4, was entered into their service “10:00 Moscow time on 27 December.” The most recent inductee into the circle of hypersonics is India. The successful test flight of their hypersonic missile technology demonstrator vehicle (HSTDV) on Sept 7, 2020, guaranteed them a spot among the elite league of hypersonic nations (US, China, and Russia).
Figure 4. 
Even though the idea of hypersonic technology is not a new concept, the US currently lags behind other global powers who have already put this technology into their services. This is largely due to the past technological hurdles such as the propulsion, control, and heat resistance that has caused the delay being experienced today in the hypersonic field. According to aerospace engineer Mark Lewis, “You see a flurry of activity, a lot of investment, and then we conclude it’s a bridge too far.” “The community was underfunded and largely forgotten for many years,” adds Daniel DeLaurentis, director of Purdue University’s Institute for Global Security and Defense Innovation. 
As other global powers are beginning to succeed in their own development of this technology, and partnerships and alliances emerge, predictions of a new arms race seem to have come true. India has partnered with Russia and Australia has partnered with the US with other countries making plans for their own hypersonic development/partnerships. The pressure is on for the United States to succeed in this international arms race for hypersonic speed. However, some experts are worried that this new technology could upset the existing norms of deterrence and renew Cold War-era tensions.  The US, Russia, and China are not the only major powers currently in this race. As mentioned earlier, India has also joined the elite 3 and now have their own development underway for this coveted technology. Countries around the world are scrambling to have their own plans for hypersonic weapons but are still years behind the current status quo.
Figure 5. CFD flow modeling around an HTV-2 configuration HGV.
(Qinglin et al, Chinese Journal of Aeronautics, April 2019). 
With extreme speed comes extreme heat. During a hypersonic flight, the air around its nose cone, wing leading edges, and air intakes can easily heat to temperatures hotter than the surface of the Sun (approximately 5,800 K or 10,000° F). The extreme heat causes the air molecules to dissociate and ionize making them chemically reactive to everything including the surface of the vehicle. 
The design of a hypersonic flight vehicle is characterized by stringent requirements of sharp leading edges that help maximize lift-to-drag ratios while still retaining the ability to withstand the extreme external gas temperatures that occur during flight. These 2 elements are essential for the survival of the airframe during its hypersonic flight and are also two of the major challenges that engineers are facing today in their development of this technology.
Figure 6. 
Figure 5 shows the details of CFD flow around HGVs while Figure 6 shows the airspeed of different engines in flight and what makes the hypersonic design so different and unique in comparison to conventional turbofan engines.
Common engineering materials such as aluminum or titanium, cannot contend with the extreme environment created in a hypersonic flight and often will warp, melt or even vaporize. The thermal protection that is currently being used to combat the issues of extreme heat during a hypersonic flight is primarily built out of nickel-based alloys and/or ceramic composites. Research has begun on a new class of materials known as Ultra-High Temperature Ceramics (UHTC) made to exhibit a unique combination of refractory and oxidation-resistant properties.
Hypersonic Materials Research
Research into UHTC for hypersonic use has been widespread both in the private and public sectors of the market. The investigation below is done by the Nonequilibrium Gas & Plasma Dynamics Laboratory at the University of Colorado Boulder College of Engineering and Applied Science by Dr. Samuel Y. Chen & Dr. Nicholas S. Campbell.
Building on the latest theories and modeling techniques available in the NGPDL, new material-environment interaction models are being explored which will aid the hypersonic vehicle designer and improve understanding of high-temperature material capabilities. Of particular interest are various carbides, such as silicon-carbide (SiC) and di-borides, such as zirconium-diboride (ZrB2). A number of UHTC candidate materials are shown in Figure 1 below, plotting each in terms of their melting point and the melting point of their corresponding oxidation states. 
There are two parts to modeling material-environment interactions – the material model itself, and the Computational Fluid Dynamics (CFD) or material response framework. Material models describe the surface chemistry, morphology of the microstructure, change of phases, and any in-depth chemical processes that ultimately affect the surface chemistry, such as in Figure 2 below. Parameters such as the oxidation rate and composition of the oxidation products are important for predicting the resulting surface heating. 
The underlying material-environment interaction is treated as a coupled process, involving both the material itself, and the hypersonic flowfield environment, typically modeled using high-fidelity CFD techniques. Detailed gas-surface and gas-phase chemistry are modeled in the shock layer, including any thermal and chemical nonequilibrium between the chemically reacting surface and the hypersonic environment. Figure 3 below illustrates the predicted flowfield adjacent to the reacting surface of a SiC-coated leading edge in a hypersonic environment, showing the density of SiO, which is an oxidation product. 
Further Studies on UHTC
Researchers at the Purdue College of Engineering believe that ceramics is the solution. Using a rare-earth material called Samarium Oxide, alloyed with ceramic-based materials, the labs at Purdue hope to create a coating that will have the ability to emit, or throw off, thermal energy. The basic idea is to absorb and redirect the heat from the hypersonic flight back into the environment before it is absorbed into the leading-edge material.
Ping Xiao, a professor of materials science at the University of Manchester also looks towards ceramics as a solution to the issue of extreme heat that plagues hypersonic technology. Xiao believes that using an ultra-high temperature ceramic, or a UHTC, mated with a carbon-carbon composite will produce a coating that has the potential to survive the extreme conditions of hypersonic flight.
Xiao also explains that carbon-carbon composites have high melting points but cannot survive the oxidization at such speeds while UHTCs are incredibly hard but also incredibly brittle. But by combining the two elements together the weakness in each material no longer poses as an issue and has a strong possibility of surviving the extreme conditions in a hypersonic flight.
Figure 7. 
There is still much research needed in the hypersonic field and as other countries begin their own advancements into this field, we are destined to see a huge boom. Figure 7 shows the estimated increase for Hypersonic spending in 2021. The “hypersonic boom” is predicted to continue, with some believing that it will catalyze significant technological advancements in the aerospace industry. This is the perfect time for companies to position themselves within the market with not only novel and differentiated technology offerings, but also a strategy and operating model that supports the speed and scale that the market requires. 
ULTRA HIGH TEMPERATURE FURNACES
For ultra-high temperature requirements, MRF has several furnaces capable of continuous operating at 3000°C (5430°F). Not many materials can handle these extreme temperatures, hot zones are available in Graphite or Tungsten. MRF furnaces are designed for excellent uniformity, longevity, and ease of maintenance. We offer numerous sizes, designs, and supply spare graphite and metallic parts for all our hot zones.
Who We Are…
MRF is a global leader in precision thermal systems essential for the research, development, and production of advanced materials. These advanced materials include ceramic matrix composites (CMCs), advanced ceramics, and SiC crystals. For decades, we have pioneered some of the world’s most innovative, customized furnace systems, with a focus on enabling the processing of materials at high temperatures in controlled atmospheres or vacuum. For additional information about MRF’s capabilities, please visit our products page by clicking on this link: mrf-furnaces.com.
- Poerschke, D. L., Novak, M. D., Abdul-Jabbar, N., Kramer, S., and Levi, C. G., Selective active oxidation in hafnium boride-silicon carbide composites above 2000C, Journal of the European Ceramic Society, Vol. 36, No. 15, 2016, pp. 3697-3707.