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Universitat Politecnica de Catalunya
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The major challenge in the field of cemented carbides and other hard materials is to obtain their... more The major challenge in the field of cemented carbides and other hard materials is to obtain their better combination of hardness, wear-resistance and fracture toughness. It is well known that the dependence of abrasion wear on fracture toughness for WC–Co cemented carbides is represented by a relatively narrow band and it is hardly possible to " break away " out from it by the use of conventional approaches based on varying the WC mean grain size and Co content. Also, it is well known that the wear-resistance of conventional cemented carbides depends mainly on their hardness. The major objective of this paper is to establish what will happen with the wear-resistance of hard materials as a result of their nanostructuring when the hardness is nearly the same as for conventional WC–Co cemented carbides. The results obtained provide clear evidence that, if one enters the region of nanostructured materials with the mean grain size of less than 10 nm, traditional wisdom indicating that the wear-resistance is directly related to the hardness appears not to be valid. In some cases of such nanostructured materials, it can be possible to achieve the dramatically improved wear-resistance compared to that of conventional WC–Co cemented carbides at nearly the same level of hardness and fracture toughness. The abovementioned is based on considering hard nanomaterials of the following four types: (1) WC–Co cemented carbides with nanograin reinforced binder, (2) near-nano WC–Co cemented carbides, (3) cemented carbides of the W–C–Cr–Si–Fe system for hard-facing having a nanostructured Fe-based binder, and (4) CVD hard materials consisting of nanostructured W 2 C grains embedded in a tungsten metal binder. It is well known that the abrasion wear-resistance of conventional WC–Co cemented carbides and other hard materials depends mainly on their hardness, and the dependence is represented by a relatively narrow band [1]. In turn, the dependence of hardness on fracture toughness for WC–Co materials having different combinations of WC mean grain size and Co content is represented by a relatively narrow hyper-bolic band [2]. It is hardly possible to " break away " out from the both bands by the use of conventional approaches based on varying the WC mean grain size and Co content. Therefore, the major challenge in the field of hard materials is to obtain their better combination of hardness, wear-resistance and fracture toughness; in other words, to " break away " out from the dependences relating the wear-resistance and hardness on the one hand, and the wear-resistance and fracture toughness on the other hand. There is a general trend in the modern carbide industry to produce WC–Co materials with WC mean grain size as small as possible with the target of achieving the range of nanomaterials. In recent time, there was a significant research effort with respect to the development of nanostructured cemented carbides with the WC mean grain size below 100 nm; numerous publications in this field are summarized in the review paper [3]. There are a great number of works in literature evaluating the possibility of fabricating nanostructured WC–Co materials from WC nanopowders (see e.g. [4–6]). However, these works did not result in obtaining fully dense cemented carbides with WC mean grain size significantly below 100 nm. All the attempts to obtain nanograined cemented carbides from WC nanopowders failed so far because of the very intensive growth of WC nanograins during sintering as a result of the high sintering activity of the nanostructured WC powders. The only industrial WC-based nanostructured materials having a full
The major challenge in the field of cemented carbides and other hard materials is to obtain their... more The major challenge in the field of cemented carbides and other hard materials is to obtain their better combination of hardness, wear-resistance and fracture toughness. It is well known that the dependence of abrasion wear on fracture toughness for WC–Co cemented carbides is represented by a relatively narrow band and it is hardly possible to " break away " out from it by the use of conventional approaches based on varying the WC mean grain size and Co content. Also, it is well known that the wear-resistance of conventional cemented carbides depends mainly on their hardness. The major objective of this paper is to establish what will happen with the wear-resistance of hard materials as a result of their nanostructuring when the hardness is nearly the same as for conventional WC–Co cemented carbides. The results obtained provide clear evidence that, if one enters the region of nanostructured materials with the mean grain size of less than 10 nm, traditional wisdom indicating that the wear-resistance is directly related to the hardness appears not to be valid. In some cases of such nanostructured materials, it can be possible to achieve the dramatically improved wear-resistance compared to that of conventional WC–Co cemented carbides at nearly the same level of hardness and fracture toughness. The abovementioned is based on considering hard nanomaterials of the following four types: (1) WC–Co cemented carbides with nanograin reinforced binder, (2) near-nano WC–Co cemented carbides, (3) cemented carbides of the W–C–Cr–Si–Fe system for hard-facing having a nanostructured Fe-based binder, and (4) CVD hard materials consisting of nanostructured W 2 C grains embedded in a tungsten metal binder. It is well known that the abrasion wear-resistance of conventional WC–Co cemented carbides and other hard materials depends mainly on their hardness, and the dependence is represented by a relatively narrow band [1]. In turn, the dependence of hardness on fracture toughness for WC–Co materials having different combinations of WC mean grain size and Co content is represented by a relatively narrow hyper-bolic band [2]. It is hardly possible to " break away " out from the both bands by the use of conventional approaches based on varying the WC mean grain size and Co content. Therefore, the major challenge in the field of hard materials is to obtain their better combination of hardness, wear-resistance and fracture toughness; in other words, to " break away " out from the dependences relating the wear-resistance and hardness on the one hand, and the wear-resistance and fracture toughness on the other hand. There is a general trend in the modern carbide industry to produce WC–Co materials with WC mean grain size as small as possible with the target of achieving the range of nanomaterials. In recent time, there was a significant research effort with respect to the development of nanostructured cemented carbides with the WC mean grain size below 100 nm; numerous publications in this field are summarized in the review paper [3]. There are a great number of works in literature evaluating the possibility of fabricating nanostructured WC–Co materials from WC nanopowders (see e.g. [4–6]). However, these works did not result in obtaining fully dense cemented carbides with WC mean grain size significantly below 100 nm. All the attempts to obtain nanograined cemented carbides from WC nanopowders failed so far because of the very intensive growth of WC nanograins during sintering as a result of the high sintering activity of the nanostructured WC powders. The only industrial WC-based nanostructured materials having a full