Electronics / Mechanics
Creating the Future Using Materials Science - Realizing Strong, Lightweight Materials
Seiji Miura , Professor
Faculty of Engineering, Graduate School of Engineering (Materials Science and Engineering, Department of Applied Science and Engineering, School of Engineering)
High school : Asamizodai High School (Kanagawa)
Academic background : Graduate School of Interdisciplinary Science and Engineering, Tokyo Institute of Technology
- Research areas
- Metallic Materials Science
- Research keywords
- Physical Metallurgy, Strength, Alloy Design, Lightweight Material, Super-Heat Resistant Material, Energy Science
What is the Goal of Your Research?
Recently, it has been very important to reduce energy consumption. What is energy consumption? In today’s society, transportation as well as electric power generation uses fossil energy, such as oil and natural gas, and this process generates a huge amount of CO2. We are working on two tasks: weight saving for reducing energy required for transportation, and creating materials that can withstand a high temperature so that a larger amount of electric power can be generated from less fossil consumption.
Material Research 1 - Unknown Features of Lightweight Material
An ordinary vehicle runs on fuel, and a plug-in hybrid vehicle runs on electricity generated in a power plant. One of effective methods for reducing consumption of the fuel or electricity and improving mileage is weight saving in the vehicle. Today, the mileage of some vehicles on the market is as high as 35 km/l. How is such high mileage achieved? It is said that weight saving by one gram leads to mileage improvement of several millimeters per litter for a certain type of vehicle(1). Replacement of various metallic parts including the body with ones made of lighter metallic material, having a strength equal to the original, can have a great impact.
Magnesium is one of the materials that is considered the lightest, practical metal today. And, its potential has not been realized to its fullest. The following diagram schematically shows the eformation behavior of a magnesium alloy obtained from our research. This diagram is similar to that of shape-memory alloys and super elastic alloys found in glassframes which can recover their shape even when being bent significantly(2). This was the world’s first case where the diagram of a magnesium alloy shows such behavior. This clearly shows that magnesium still has many unrealized features.
Figure 1 Stress-strain curve of magnesium ally (a) and super elastic titanium alloy (b). Note that it returns from the highest point to the point close to the origin.
While conducting research, we asked for help and input from various researchers. For example, with the help of Dr. Mikito Ueda, who is introduced in this volume, high-quality and high-purity single crystal magnesium was obtained by melting and solidifying it in salt. What was the state of the magnesium melted in salt? Why was the purity increased? Questions still remain.
Material Research 2 – Striving for Material that Can be Used at High Temperature
A simple way to generate a larger amount of electric power from less fossil fuel is to burn the fuel at a high temperature. However, what is a "high temperature?" Of course, when anything is burned, the temperature rises. However, the burning temperature becomes lower or higher depending on the burning method. A metallic material used for power generation becomes soft and weak when the temperature rises very high, and therefore it cannot withstand the high temperature when fuel is burned perfectly. The dream of material developers is to raise the upper limit of the application temperature of the material as close to the perfect burning temperature of fossil fuel as possible.
The perfect burning temperature of fossil fuel is as high as 2,000°C or higher. This is more than 500°C higher than the melting point of iron, and more than 1,300°C higher than the melting point of aluminum. Then, why don’t we create a new super heat resistant material from a substance having a higher melting point? Our research starts with this simple idea.
Known metallic materials having a melting point higher than 2,000°C include niobium, molybdenum, tantalum, tungsten, etc. However, all of them have a tendency to react with oxygen to form so-called rust. Among them, we selected niobium, which has a lower melting point than others (2,469°C, still much higher than 2,000oC!) but is relatively light weight, as an appropriate material. This is because the material will be used as a part that rotates at a high temperature and is subjected to centrifugal force. The lighter the part is, the smaller the generated centrifugal force becomes. The goal of this second research project is to produce a material that is stronger and more durable at a high temperature by adding various elements.
What Kind of Devices do You Use in Your Experiment?
By observing the yielding behavior at a high temperature, we discovered what was wrong. We used a piezo driver, a high temperature furnace and a laser microscope that can conduct an observation even under conditions where the temperature exceeds 1,000°C with a radiant light that is too bright to see. We combined them to create a new system that can bend and compress a test piece while observing its surface at a high temperature range. Also, using this system at room temperature helps shed light on the deformation of magnesium.
What Will be Your Next Goal?
I think the possibilities of a material are endless. Even only in terms of selection and amount of additional elements, many combinations have not yet been tested. I hope to uncover the principles and design the strength and distorting behavior, and then pursue what deviates from there.
(1) Nikkei electric edition, Apr. 14, 2014, Suzuki attained 35 km/l with desperation (suzuki, shinimonoguruide jitsugenshita rittaa 35 kiro).
(2) Nishi et al., Development of orthodontic appliances made of nickel free titanium alloy (Ni furii Ti goukinsei shiretsukyouseikiguno kaihatsu), Materia Japan, Vol. 49 (2010), 119-121.