Hard Materials

Abstract

The article contains sections titled: 1. Introduction 1.1. Hardness Measurement (Overview) 1.2. Classification of Hard Materials 1.2.1. Occurrence 1.2.2. Appearance 1.2.3. Electrical Conductivity 1.2.4. Composition and Thermal Stability in Air 2. Nonmetallic Hard Materials 2.1. Diamond 2.2. Cubic Boron Nitride (c‐BN) 2.3. Silicon Nitrides 2.4. Transition Metal Nitrides M x N x +1 2.5. Silicon Carbide 2.6. Alumina 2.7. Cermets 3. Metallic Hard Materials (Cemented Carbides) 3.1. Production 3.1.1. Raw Materials 3.1.2. Powder Batch Manufacturing 3.1.3. Pressing and Forming 3.1.4. Sintering 3.1.5. Machining 3.1.6. Coating 3.1.7. Testing and Quality Control 3.2. Commercial Grades 3.3. Properties 3.4. Uses 3.5. Economic Aspects 3.6. Toxicology Hard materials are solid substances exhibiting a high resistance towards plastic (irreversible) deformation or damage of their surface by scratching (Mohs or Martens scale), grinding (Rosiwal method) or indentation (Brinell, Rockwell, Shore, Vickers, or Knoop testing). Some of them occur in nature but the majority is synthetic. They are also classified according to their appearance, electric conductivity, and chemical composition which defines their thermal stability in air. This article gives an overview of the synthesis routes, properties, and fields of application of the most important nonmetallic and metallic hard materials. A few recently discovered hard compounds are briefly introduced. Finally, the family of cemented carbides is discussed in more detail, which is broadly used today for cutting of ferrous alloys, in forming equipment, mining industry, and wear resistant components.

Synthesis of cubic zirconium(IV) nitride, c-Zr3N4, in the 6–8 GPa pressure region

“…Our XRD patterns did not permit to examine this possibility in more detail due to a small amount of the by-product and, accordingly, low intensities of the related diffraction peaks. If it indeed contained nitrogen then it would closely resemble the cubic solid solution of tungsten carbide in cobalt β-Co(WC) serving as the binder in cemented carbides of tungsten [9]: Independent of the structure and composition, such Pt-Zr or Pt-Zr-N alloy could play the same role by cementing of polycrystalline c-Zr 3 N 4 bodies. According to our Rietveld refinement, the alloy made ~0.5% of the whole sample weight (Table 1).…”

“…Similarly to the well known method of cementing of tungsten carbide by cobalt e.g. [9], this alloy could serve as a binder by fabrication of dense polycrystalline c-Zr 3 N 4 bodies. Finally, we maybe have succeeded to quench c-ZrO 2 to ambient conditions.…”

“…In addition, examination of the recovered products led us to a method potentially suitable for cementing of polycrystalline c-Zr 3 N 4 using a metallic binder, similar to the well-known industrial approach developed for the cemented tungsten carbide e.g. [9].…”

Elastic moduli and refractive index of γ-Ge 3 N 4

“…The higher density and cation coordination number resulted in advanced mechanical properties of γ-Ge 3 N 4 : its Vickers hardness, H V , measured to be between 23 and 33 GPa [6] is comparable with that of the well-known ceramics α- or β-Si 3 N 4 (31 and 20 GPa, respectively) or β-SiC (23 GPa) e.g. [18]. Empirical and theoretical works predicted, however, significantly lower H V between 18 and 24 GPa [13,19,20].…”