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Hardening (metallurgy)
About: Hardening (metallurgy) is a research topic. Over the lifetime, 25584 publications have been published within this topic receiving 376012 citations.
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TL;DR: It is shown that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall–Petch effect below a critical grain size or the twin thickness of ∼10–15 nm found in metals and alloys.
Abstract: The hardness, toughness and chemical stability of the well-known superhard material cubic boron nitride have been improved by using a synthesis technique based on specially prepared ‘onion-like’ precursor materials. Superhard polycrystalline cubic boron nitride, second only to diamond in hardness, is superior to diamond in terms of thermal and chemical stability and is used widely as an abrasive. The hardness of many materials can be improved by decreasing the grain size, and here Yongjun Tian and colleagues use this principle in a new synthesis technique — based on specially prepared 'onion-like' precursor materials — capable of increasing the hardness of cubic boron nitride. The structure of the resulting polycrystalline material is dominated by nanometre-scale twin domains, yielding a solid combining ultrahigh hardness (exceeding that of a synthetic diamond single crystal) with a high oxidization temperature and extreme fracture toughness. If nanotwins at similar scales can be reproduced in polycrystalline diamond, it may be possible to raise diamond itself to new levels of hardness and stability. Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall–Petch effect—the tendency for hardness to increase with decreasing grain size1,2. Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers3. Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as ∼14 nm (refs 1, 2, 4, 5). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness ∼3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (∼1,294 °C) and a large fracture toughness (>12 MPa m1/2, well beyond the toughness of commercial cemented tungsten carbide, ∼10 MPa m1/2). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall–Petch effect below a critical grain size or the twin thickness of ∼10–15 nm found in metals and alloys.
614 citations
TL;DR: In this paper, an experimental study has been performed on the cyclic deformation of copper single crystals at constant plastic resolved shear-strain amplitudes, over a range 1.55 × 10−5 < γpl < 2 × 10 −2.
612 citations
TL;DR: In this article, the influence of texture and grain size on work hardening behavior and dynamic recovery of magnesium alloys was studied, in addition to the direct effect of texture through the change in the orientation factor for basal and prismatic slip, effects were found on dynamic recovery and the appearance of stage II of workhardening.
598 citations
TL;DR: In this article, an atomic-scale simulation of the plastic behavior of nanocrystalline copper is presented, where the main deformation mode is sliding in the grain boundaries through a large number of uncorrelated events, where a few atoms (or tens of atoms) slide with respect to each other.
Abstract: Nanocrystalline metals, ie, metals in which the grain size is in the nanometer range, have a range of technologically interesting properties including increased hardness and yield strength We present atomic-scale simulations of the plastic behavior of nanocrystalline copper The simulations show that the main deformation mode is sliding in the grain boundaries through a large number of uncorrelated events, where a few atoms (or a few tens of atoms) slide with respect to each other Little dislocation activity is seen in the grain interiors The localization of the deformation to the grain boundaries leads to a hardening as the grain size is increased (reverse Hall-Petch effect), implying a maximum in hardness for a grain size above the ones studied here We investigate the effects of varying temperature, strain rate, and porosity, and discuss the relation to recent experiments At increasing temperatures the material becomes softer in both the plastic and elastic regime Porosity in the samples result in a softening of the material; this may be a significant effect in many experiments
592 citations
TL;DR: In this article, the cyclic elasto-plasticity of two types of steel sheets for press-forming (an aluminum-killed mild steel and a dual-phase high strength steel of 590 MPa ultimate tensile strength) under in-plane cyclic tension-compression at large strain (up to 25% strain for mild steel, and 13% for high-strength steel) was investigated.
582 citations