#brittleness

A New Superhard Material

Planting vacancies into the atomic lattice of a brittle material increases its toughness and hardness. [...] Superhard materials like diamond are useful for industrial cutting tools but are expensive, so researchers have been searching for alternatives. Unfortunately, hard materials are often brittle. Now Shanmin Wang of the Southern University of Science and Technology in China and his colleagues have created a superhard but nonbrittle material by adding vacancies to the atomic lattice [1]. Wang says that the technique could be applied to other materials. The mechanical properties of metals and alloys depend heavily on defects in their crystal lattices called dislocations. These are lines along which a plane of atoms comes to a sudden end. When a crystal is stressed, atomic bonds break and reform in a way that can cause a dislocation to move perpendicular to the planes. This ability for dislocations to “slide” allows metals to deform without breaking, but it also reduces a material’s rigidity and hardness. Treatments that prevent dislocation sliding can increase hardness but also brittleness.

Warm metalworking turns brittle semiconductors into flexible, high-performance electronic films

Inorganic semiconductors form the backbone of modern electronics due to their excellent physical properties, including high carrier mobility, thermal stability, and well-defined energy band structures, which enable precise control over electrical conductivity. Unfortunately, their intrinsic brittleness has traditionally required the use of costly, complex processing methods like deposition and sputtering—which apply inorganic materials to rigid substrates and limit their suitability for flexible or wearable electronics. Now, however, a recent breakthrough by researchers from the Shanghai Institute of Ceramics of the Chinese Academy of Sciences and Shanghai Jiao Tong University in the warm processing of traditionally brittle semiconductors offers tremendous potential to expand applications for inorganic semiconductors into these fields.

Liquid Metal Embrittlement

Ductile metals can turn brittle after contact with liquid metal and the presence of an applied stress (usually) in a phenomenon known as liquid metal embrittlement. (Also sometimes thought of as a collection of phenomena, based on the mechanisms involved.) Liquid metal embrittlement tends to occur with specific combinations of metals: zinc, mercury, and lithium are common liquid metals, with zinc able to embrittle some steels and aluminum alloys, mercury aluminum and copper alloys, and lithium some steels and copper alloys, for example. Mercury is the most common culprit of liquid metal embrittlement, which is one reason the metal is prohibited on commercial aircraft.

The last time you dropped a favorite mug or sat on your glasses, you may have been too preoccupied to take much notice of the intricate pattern of cracks that appeared in the broken object. But capturing the formation of such patterns is the specialty of John Kolinski and his team at the Laboratory of Engineering Mechanics of Soft Interfaces (EMSI) in EPFL's School of Engineering. They aim to understand how cracks propagate in brittle solids, which is essential for developing and testing safe and cost-effective composite materials for use in construction, sports, and aerospace engineering. But traditional mechanics approaches to analyzing crack formation assume that cracks are planar -- i.e., that they form on the two-dimensional surface of a material. In fact, simple planar cracks are just the tip of the iceberg: most cracks -- like those in everyday brittle solids like glass -- propagate into three-dimensional networks of ridges and other complex features.

A brittle interface with low modulus to improve the mechanical properties of multiphase ceramics

Barium strontium aluminum silicate (BaxSr1−xAl2Si2O8, BSAS) ceramics possess both phase stability and resistance to water vapor corrosion, making them ideal materials for radome technology and electronic packaging. To address the low tolerance of BSAS ceramics to damage and defects, the introduction of nano-reinforcements is an effective approach to enhance their strength and toughness. SiC nanowires (SiCnws) exhibit high strength and hardness inherited from SiC ceramics, along with the excellent toughness and elasticity characteristic of nanomaterials, making them ideal candidates for toughening BSAS ceramics. The reinforcing and toughening effects of nano-reinforcements are primarily related to their dispersion and interfacial bonding. Poor dispersion can result in the formation of closed pores during densification, while strong interfacial bonding can prevent effective crack deflection, thereby limiting the reinforcement and toughening effects of the nanomaterials.

Ductile to Brittle Transition Temperature

Of the two general types of fracture (ductile or brittle), not all materials fall neatly into one category or the other. Some materials experience what is known as the ductile to brittle transition temperature, or DBTT. Ferritic steels in particular, among other BCC metals, have two failure modes, switching from ductile failure at higher temperatures to brittle failure at lower ones. While the transition is perhaps more well known in metals, it can occur in other materials such as polymers and ceramics as well. Different forms of impact testing are used to determine the temperature.

Compared to metal and polymer-based materials, ceramics can better withstand high temperatures and corrosive environments, but their brittle nature often makes them susceptible to breakage. This behavior potentially causes problems for innovators trying to create lightweight porous versions of these materials, explaining why ceramic foams are not typically used as structural components.

Facing the challenging task of developing lightweight, high-strength ceramic materials, Mechanical Engineering Assistant Professor Ling Li has turned to an unexpected collaborator for design inspiration: the knobby sea star from the tropical Indo-Pacific. By investigating the complex and highly ordered mineralized skeletal system of this unusual marine species, Li and his research team discovered an unexpected combination of characteristics that may lead to developing an entirely new class of high-performance lightweight ceramic composites.  

Going light by going porous

Industries such as those in automobile and aerospace manufacturing have a strong interest in designing both strong and lightweight materials, combining the economy of better fuel efficiencies with strength. Industries find this balance difficult to strike, since stronger materials commonly possess high densities, and thus weigh more.

Nature, through millions of years of evolution, has come up with an ingenious way of solving this problem: using porous materials. The introduction of internal porosity potentially creates both extremely lightweight and mechanically efficient materials.