#materials hardness

Scientists just found a way to 3D print one of the hardest metals on Earth

Tungsten carbide-cobalt (WC-Co) is widely valued for its extreme hardness, but that same strength also makes it very difficult to shape and manufacture. Current production methods consume large amounts of costly material while delivering relatively modest yields. As a result, researchers have been searching for a more efficient and economical way to produce these exceptionally tough materials. WC-Co cemented carbides are essential for applications that demand strong resistance to wear and high hardness, including cutting and construction tools. Traditionally, these materials are produced through powder metallurgy. In this process, powders of WC and Co are compressed under high pressure and heated in sintering machines to form solid cemented carbide. While this method produces very durable final products, it uses significant quantities of expensive raw materials and generates inefficient yields.

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.

Advanced tungsten-based ceramics achieve high hardness and ablation resistance

A research team successfully synthesized tungsten carbide (WC) and tungsten boride (WB2) ceramics with excellent mechanical properties and ablation resistance. These findings were published in the journal of Ceramics International and Journal of the European Ceramic Society. The team was led by Prof. Huang Zhulin at the Institute of Solid State Physics, the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, Ultrahigh temperature ceramics (UHTCs) are essential materials for thermal protection systems with high melting points and excellent stability. Tungsten-based UHTCs offer excellent resistance to heat and radiation. However, they have faced several challenges in practical applications, such as difficulty in achieving high density during processing, grain coarsening during sintering, and limited oxidation and ablation resistance.

Researchers propose new physical model for predicting hardness of materials

Skoltech researchers have presented a new simple physical model for predicting the hardness of materials based on information about the shear modulus and equations of the state of crystal structures. The model is useful for a wide range of practical applications—all parameters in it can be determined through basic calculations or measured experimentally. The results of the study are presented in the Physical Review Materials journal. Hardness is an important property of materials that determines their ability to resist deformations and other damage (dents, scratches) due to external forces. It is typically determined by pressing the indenter into the test sample, and the indenter must be made of a harder material, usually diamond. In this case, the hardness is determined based on the ratio between the maximum indentation force and the imprint that remains on the sample.

Johan August Brinell (10 October 1849 – 17 November 1925)

A Swedish metallurgical engineer, Johan August Brinell is most well known for the hardness testing method that bears his name. He first proposed the test in 1900 and it became the first standardized method for testing materials hardness. Brinell hardness testing uses a round ball with a set load to make indents, with hardness calculated based on the size of the indent made. Given that this method uses are larger ball than many hardness testing methods that follow, it is still used today for macro-scale hardness measurements and for measurements on rougher surfaces.

Newly created ultra-hard material rivals diamond

Scientists have solved a decades-long puzzle and unveiled a near unbreakable substance that could rival diamond as the hardest material on Earth. The research is published in the journal Advanced Materials. Researchers found that when carbon and nitrogen precursors were subjected to extreme heat and pressure, the resulting materials—known as carbon nitrides—were tougher than cubic boron nitride, the second hardest material after diamond. The breakthrough opens doors for multifunctional materials to be used for industrial purposes including protective coatings for cars and spaceships, high-endurance cutting tools, solar panels and photodetectors, experts say. Materials researchers have attempted to unlock the potential of carbon nitrides since the 1980s, when scientists first noticed their exceptional properties, including high resistance to heat.

Study reveals inconsistency in nanoindentation testing using different Berkovich indenters

Nanoindentation testing is a high-precision instrumented indentation test technique that has the advantages of non-destructive testing and simplicity. However, researchers found that when testing the same sample with different Berkovich indenters, inconsistency still arises even if the indenters are regularly calibrated. This inconsistency poses challenges in accurately testing material hardness and comparing data from different laboratories. In a study published in the Journal of Materials Research and Technology, researchers from the Materials Research Center of the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) reported that using different Berkovich indenters for nanoindentation testing, excluding fused silica, yields inconsistent results, and they analyzed the reasons behind this inconsistency. The researchers identified two main factors contributing to the inconsistent experimental results, i.e., defects in the indenter tip and the indentation size effect.

Solving the strength-toughness dilemma in superhard ceramics with a chemically tuned solid solution approach

Materials with superior mechanical strengths are crucial to many areas of modern industries and the scientific enterprise by providing cutting and drilling tools, structural components, protective coatings, and abrasives that find wide applications. Solid solution strengthening is a well-established method to enhance hardness of metals by introducing solute atoms to create local distortions in the crystal lattice, which impedes dislocation motion and plastic deformation, leading to increased strength but reduced ductility and toughness. In sharp contrast, superhard materials with Vickers hardness HV > 40 GPa exhibit high strength but low toughness via a distinct mechanism dictated by brittle bond deformation, showcasing another prominent scenario of classic strength-toughness tradeoff dilemma. Solving this less-explored and poorly understood problem presents a formidable challenge that requires a viable strategy of tuning main load-bearing bonds in these strong but brittle materials to achieve concurrent enhancement of the peak stress and related strain range.