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energy ball milled WC–Co powders and subsequent consolidat

作者:ihpa.net 发布时间:2017-10-13

Characterization of short-duration high-energy ball milled WC–Copowders and subsequent

consolidations

Rumman Md Raihanuzzaman a , Tae Sik Jeong b , Reza Ghomashchi a , Zonghan Xie a , Soon-Jik Hong b , ?

a b

School of Mechanical Engineering, The University of Adelaide, South Australia 5000, Australia

Division of Advanced Materials Engineering and Institute for Rare Metals, Kongju National University, Cheonan 330-717, South Korea

a r t i c l e i n f o a b s t r a c t

The aim of this study was to observe the effect of short-duration, high-energy ball milling on the mechan-ical properties of sintered WC–Co.Mixed powders of WC–7.5wt%nano Co were ball milled at three dif-ferent time using WC vial and balls, while other parameters were kept constant. The powders were then consolidated using spark plasma sintering. Density and hardness of the sintered samples were measured as a function of milling time, used to mix the powders prior to consolidation. It was found that both den-sity and hardness increased with milling time, with hardness reaching a maximum of 14.95GPa for the sample milled for 10min. Microstructures of the sintered samples suggested a slight decline in grain size and increase in Co distribution with increasing milling time. It was also evident that milling of WC–Copowders resulted in the sintered samples having overall irregular shaped grains.

Ó2013Elsevier B.V. All rights reserved.

Article history:

Available online 18December 2013Keywords:

Cemented carbides Powder morphology High-energy ball mill Sintering

Microstructure

1. Introduction

Cemented carbides have been termed as one of the hardest materials, and are suitable for a number of cutting and drilling applications [1–3]. Industrial interests have grown to attain high hardness, strength, corrosion and wear resistance, and chemical and thermal stability in such carbides at elevated temperature. Among all cemented carbides, Tungsten Carbide-Cobalt (WC–Co)is the most dominant in terms of industrial applications, and displays a unique combination of mechanical properties [4].

In order to ensure desired mechanical properties in sintered WC–Co,various processing techniques and tools have been applied and modi?ed,staring from synthesis to consolidation stage. While long duration mechanical alloying techniques have been mostly used in synthesizing hard materials, rapid MA techniques like ultrasonic ?eldor dielectric barrier discharge plasma (DBDP)as-sisted ball milling [5,6]have also been successfully employed. High-energy ball milling (HEBM)is also considered quite promi-nent and effective in controlling initial powder size through effec-tive re?nementof both WC and Co particles [7]. The idea is to mix and re?nepowders to comply with the required speci?cationsthrough a process that is both effective and inexpensive in nature. Such form of mechanical alloying has been widely used in mixing amorphous alloys, nitrides, nano-composites, etc. [7]. Most Corresponding author. Tel.:+82415219387; fax:+82415685776.

E-mail address:hongsj@kongju.ac.kr(S.-J.Hong).

0925-8388/$-see front matter Ó2013Elsevier B.V. All rights reserved.

reported studies that employed high energy ball milling on cemen-ted carbides have used 10–120h of long duration milling to either synthesize mixed WC–Copowders from elemental WC and Co, or to re?nemedium coarse and coarse carbides into nanocrystalline composites [8–10]. Co works as a metallic binder in the composi-tion, has a much lower melting point than WC, and helps the hard WC grains to join upon sintering, conventionally carried out at a temperature close to the melting point of the binder. Hence, a near homogeneous mix of Co and WC prior to consolidation is highly re-quired for ensuring good mechanical properties in the ?nalsin-tered product, which is why the use of high-energy ball milling has proven to be critical. Several parameters within HEBM can affect powder morphology; namely rotational speed, milling dura-tion, ball to powder ratio and so on [11]. Since cemented carbides are hard-to-consolidate materials, an effective change in parame-ters during high-energy ball milling can greatly impact the ?nalproperties of the sintered carbides. While the incorporation of con-ventional or nano Co as a binder increases the possibility of having reasonable fracture toughness and improved hardness, the use of HEBM introduces uneven breaking in powders, potentially leading to a change in mechanical properties upon consolidation [12,13]. The focus of the study was to observe the effect of short dura-tion milling on the mechanical properties of sintered WC–Co,and test them against conventional non-milled, sintered sample. In addition, microstructural behavior was analyzed to understand the role of milling in ensuring a proper distribution of WC and Co before and after sintering.

Silver powderBoron Nitride powderZinc Sulfide powderhafnium boride powderboron doped Silicon powder

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