In a new study, material scientists from Duke University and UC San Diego have found a new category of carbides, expected to be one of the hardest substances with high melting points that exist in nature.
The scientists developed the innovative material using inexpensive metals which may find potential application in various industries ranging from hardware and machinery to aerospace.
When carbide – comprising of carbon and one other element – combines with metal such as tungsten or titanium, it forms an exceptionally hard material which is difficult to melt. It makes carbide suitable for use in parts of space vehicle or coating the surface of sharp tools.
Different forms of carbides containing three or more elements are in existence but not commonly found in industrial applications or outside laboratories, due to challenges in determining the combinations that form a stable structure.
The research team, however, has revealed the discovery of new class of carbides that combines carbon with five distinctive metals at once. Findings of the study have been outlined in the journal Nature Communications. Instead of orderly atomic structure, the new materials achieve stability from disordered mixture of their atom, which were computationally predicted to exist by the Duke University scientists and synthesized at UC San Diego.
Stefano Curtarolo, professor of material science said that the new materials are made of relatively cheap material mixtures and not only have very high melting points but are also lighter in weight and harder than existing carbides. These five-metal carbides take the concept of basic molecular structures to the next level; without relying on bonds and crystalline structure for their stability, the new class of carbides solely depends on the disorder, the researchers reported.
However, it is difficult to predict the ideal combination of elements that will stand firm. Attempts to create new material is time-consuming as well as expensive and it costs even higher to compute the interaction of atoms through first principle stimulations. Moreover, five slots of metallic elements to choose from a total of 91 become even more horrifying.
First author Pranab Sarker said that it is necessary to conduct a spectral analysis based on entropy to determine which combination will mix well. As entropy consumes a lot of time and needs to calculate by building an atom-by-atom model, we tried something different, he added.
The researchers narrowed down the ingredients to 8 metallic elements which can create carbides with increased hardness and melting temperatures. Then, they measured the amount of energy needed by the new class of carbide to create a huge set of random configurations.
Spreading the results apart suggested that the combination is likely to favor just one configuration and fall apart, while if many combinations are brought together, the material can form many varying structure all at once, providing the disorder needed for a stable structure.
The team tested its theory in an attempt to create nine of the compounds, by joining the elements in each recipe in a finely powdered form, exploiting them to high temperature of about 4000 degrees Fahrenheit and transmitting direct current of 2000 Amps through them.
It was difficult to process these materials as they behave differently from any other material or conventional carbides, co-author Tyler Harrington said. The team selected three recipes that the system indicated to form a stable material, two of least probability, and four random recipes that scored in between. As predicted, three most likely candidates succeeded while the two least likely failed. Additionally, three out of four with intermediate scores formed stable structures.
According to the researchers, all the new carbides are likely to have potential industrial attributes, but they found an improbable combination called (MoNbTaVWC5) made out of molybdenum, niobium, tantalum, vanadium and tungsten. Though it is difficult to determine the exact properties of this combination as it hasn’t been fully tested, the researchers said that it won’t be surprising if it turns out to be the hardest material with the highest melting point.