Development of a Cr-Based Hard Composite Processed by Spark Plasma Sintering
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INTRODUCTION
HARD composites exhibit a microstructure comprising a metallic matrix (usually Fe, Co, or Ni alloys) and an adequate proportion of hard compounds, including carbides, borides, or silicides.[1] These materials are especially suitable for wear resistance applications, in which corrosion resistance is also needed, such as grinding balls and tools, spikes, plungers, and seal rings.[1] In the last decades, there has been a continuous improvement of compositions and manufacturing techniques leading to a better performance of hard composite materials in order to use them in new applications.[2] Apart from these technological improvements, there is a recent health demand in the field of hard composite materials concerning the partial or total replacement of the frequently used Co binder by other metallic alloys less toxic, more economic, and with lower cost fluctuation.[3] This new trend is due to the fact that the inhalation of Co particles can produce an interstitial lung disease[4] and both Co powder and Co hardmetal have been included as ‘‘reasonably anticipated to be human carcinogens’’ in the 14th report on carcinogens on November 2016.[5] Other transition metals, such as Fe and Ni, have been employed in a limited extent as alternative alloys to Co. Ni-based hard materials have been extensively studied considering their good corrosion resistance.[6] However, the formation of undesirable graphite during cooling is one of the main drawbacks in Ni-based systems.[2] In addition, Ni compounds and
A. GARCI´A-JUNCEDA and X.X. DENG are with the IMDEA Materials Institute, Calle Eric Kandel 2, 28906 Getafe, Madrid, Spain. Contact e-mail: [email protected] I. SA´EZ and J.M. TORRALBA are with the Universidad Carlos III Madrid, Av. Universidad 30, 28911 Legane´s, Madrid, Spain. Manuscript submitted April 10, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
metallic Ni have also been listed by the National Toxicology Program as ‘‘known to be human carcinogens’’ and ‘‘reasonably anticipated to be human carcinogens,’’ respectively.[5] On the other hand, Fe-based systems (FeNi, Fe/Ni/Co, FeMn, and FeCr) have been used in hard materials since the early 1920s due to their reduced price, good availability, and low toxicity.[7–10] However, some of these studies have mentioned the inconvenience of simultaneously obtaining good hardness and toughness values in Fe-based hard composites compared to those obtained in WC-Co systems.[7,8,10] The first Fe-W-C ternary phase diagram was obtained in 1936, and it demonstrated the difficulty of avoiding the high thermodynamically stable brittle M6C eta-phase during sintering, reducing the mechanical properties of these hard materials.[11–13] Another disadvantage of this system is the fact that Fe dissolves a much lower quantity of WC than Co, at their respective eutectic temperatures.[2] On the other hand, it is not possible to find studies in the literature (to the knowledge of the present authors) assessing the possibility of using a sintered Cr-based alloy combined with a
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