Hierarchical lightweight composite materials for structural applications
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Machining technologies and materials Materials for machining technologies encompass the broad class of tools used for cutting, drilling, grinding, and other methods for processing materials. The classes of materials used for machining technologies include tool steels, cemented carbides, ceramics, and composites based on superhard materials (SHMs). The main requirements for machining materials include high hardness, strength, fracture and wear resistance, thermal stability, manufacturability, and efficient performance. The use of multilevel hierarchical structures is a promising way to improve performance characteristics of machining materials. New materials with unique characteristics can be produced by forming hierarchical structures in individual components, reinforcing these components, and adding and distributing nano-dispersed components in specific ways.1–3 This article is dedicated to an overview of hierarchically structured tool steels, cemented carbides, ceramics and superhard material tools for the machining industry.
Tool steels with hierarchical structure High-alloy tool steels are among the most common and best studied cutting/drilling tool materials with a hierarchical structure. They usually contain combinations of alloying elements, including chromium (basic alloying component, up to 20 wt%),
vanadium, tungsten, molybdenum, cobalt, and other elements.4,5 This class of steels was developed specifically for high-speed cutting, with significant heating of the work surface of a tool (550–650°C) due to friction. These steels, typically characterized by high hardness, strength, and thermal stability, can be produced by special alloying and thermal treatment. The structure of high-alloy quenched steels is a good illustration of a hierarchical structure, with four hierarchical levels characterized by constituents with different chemical composition, crystallographic structure, and dimensions, including austenite, complex martensite phases, and carbide or intermetallic phases.6 Martensite, the key structural component of tool steels that ensures high hardness, plastic, and wear resistance, is formed at the quenching stage of the steelmaking process, representing the first hierarchical level. Martensite grains form the next (second) hierarchical level in the structure of tool steels, while a mixture of austenite and martensite mixture forms the highest structural level. Martensite has a complex structure and is formed (in descending size order) as packets, blocks, sub-blocks, and single-crystal laths at sites occupied by austenite grains prior to quenching (Figure 1).3 Several packets consisting of parallel blocks are formed in every austenite grain during quenching.
Daria Sidorenko, National University of Science and Technology, Moscow Institute of Steel and Alloys, Russian Federation; [email protected] Pavel Loginov, National University of Science and Technology, Moscow Institute of Steel and Alloys, Russian Federation; [email protected] Evgeny Levashov, Department of Powder Metallurgy and Functio
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