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This Ceramic Engineering and Science Proceedings (CESP) issue consists of 23 papers that were submitted and approved from select symposia held during the
41st International Conference on Advanced Ceramics and Composites (ICACC), held January 22–27, 2017 in Daytona Beach, Florida. ICACC is the most promi- nent international meeting in the area of advanced structural, functional, and nanoscopic ceramics, composites, and other emerging ceramic materials and technologies. This prestigious conference has been organized by the Engineering Ceramics Division (ECD) of The American Ceramic Society (ACerS) since 1977.
The 41st ICACC hosted more than 1,000 attendees from 41 countries that gave over 850 presentations. The topics ranged from ceramic nanomaterials to struc- tural reliability of ceramic components, which demonstrated the linkage between materials science developments at the atomic level and macro level structural ap- plications. Papers addressed material, model, and component development and investigated the interrelations between the processing, properties, and microstruc- ture of ceramic materials.
The 2017 conference was organized into the following 15 symposia and 3 Fo- cused Sessions and two Special Sessions:
| Symposium 1 | Mechanical Behavior and Performance of Ceramics and Composites |
| Symposium 2 | Advanced Ceramic Coatings for Structural, Environmental, and Functional Applications |
| Symposium 3 | 14th International Symposium on Solid Oxide Fuel Cells (SOFC): Materials, Science, and Technology |
| Symposium 4 | Armor Ceramics: Challenges and New Developments |
| Symposium 5 | Next Generation Bioceramics and Biocomposites |
| Symposium 6 | Advanced Materials and Technologies for Direct Thermal Energy Conversion and Rechargeable Energy Storage |
| Symposium 7 | 11th International Symposium on Functional Nanosmaterials and Thin Films for Sustainable Energy Harvesting, Environmental and Health Applications |
| Symposium 8 | 11th International Symposium on Advanced Processing & Manufacturing Technologies for Structural & Multifunctional Materials and Systems |
| Symposium 9 | Porous Ceramics: Novel Developments and Applications |
| Symposium 10 | Virtual Materials (Computational) Design and Ceramic Genome |
| Symposium 11 | Advanced Materials and Innovative Processing ideas for the Production Root Technology |
| Symposium 12 | Materials for Extreme Environments: Ultrahigh Temperature Ceramics (UHTCs) and Nano-laminated Ternary Carbides and Nitrides (MAX Phases) |
| Symposium 13 | Advanced Materials for Sustainable Nuclear Fission and Fusion Energy |
| Symposium 14 | Crystalline Materials for Electrical, Optical and Medical Applications |
| Symposium 15 | Additive Manufacturing and 3D Printing Technologies |
| Focused Session 1 | Geopolymers, Chemically Bonded Ceramics, Eco-friendly and Sustainable Materials |
| Focused Session 2 | Advanced Ceramic Materials and Processing for Photonics and Energy |
| Focused Session 3 Special Symposium Special Symposium | Carbon Nanostructures and 2D Materials and Composites 3rd Pacific Rim Engineering Ceramics Summit 6th Global Young Investigators Forum (GYIF) |
The proceedings papers from this meeting are published in the below two is- sues of the 2017 Ceramic Engineering and Science Proceedings (CESP):
The organization of the Daytona Beach meeting and the publication of these proceedings were possible thanks to the professional staff of ACerS and the tire- less dedication of many ECD members. We would especially like to express our sincere thanks to the symposia organizers, session chairs, presenters and confer-ence attendees, for their efforts and enthusiastic participation in the vibrant and cutting-edge conference.
ACerS and the ECD invite you to attend the 42nd International Conference on Advanced Ceramics and Composites (http://www.ceramics.org/icacc2018) Janu- ary 21-26, 2018 in Daytona Beach, Florida.
To purchase additional CESP issues as well as other ceramic publications, vis- it the ACerS-Wiley Publications home page at www.wiley.com/go/ceramics.
SUROJIT GUPTA, University of North Dakota, USA
JINGYANG WANG, Institute of Metal Research, Chinese Academy of Sciences, China
Volume Editors
August 2017 ICACC
Lifen Deng, Roger Nilen and Serdar Ozbayraktar
Global innovation centreElement Six Ltd., Harwell, Oxfordshire, UK
ABSTRACT
Polycrystalline diamond (PCD) compacts used on oil and gas drilling bits were sintered under high-pressure and high-temperature (HPHT) conditions. In this study, the microstructure of polycrystalline diamond composite portion of the compacts is analysed by using scanning electron microscopy (SEM) and image analysis methods. In addition, laboratory rock cutting tests were conducted as a direct measure of abrasion resistance of PDCs produced using different types of diamond powder. Microstructure and abrasion resistance relationships with the grain size, the nitrogen content and the surface quality of diamond grits are discussed. It is found that the PCDs’ abrasion resistance generally decreases with the increasing mean diamond grain size of a sintered PDC. Although the diamond grits with lower nitrogen levels show a higher compression fracture strength, it is not necessarily beneficial for the abrasion resistance of PCDs. It was observed that Type C diamond grits with a rougher surface tends to lead an increasing abrasion resistance of PCD in laboratory rock cutting tests.
Polycrystalline diamonds (PCDs) sintered by HPHT method have been widely used in oil and gas industry as the cutting element on the drilling bit since 1980’s and polycrystalline diamond compact drill bits have accounted for over 60% of drilled footage in 2004[1]. Due to the PCD's super abrasion resistance and reasonably good fracture toughness resistance compared to traditional cutting element materials such as tungsten carbide and hardened steel, PCD compacts have significantly increased the drilling footage and reduced the cost in oil and gas industry [2]. As conventional oil fields are becoming increasingly elusive and continuously reducing the drilling cost is always in demand, the drive for further enhanced abrasion resistance of PCD cutters but not sacrificing too much the fracture toughness is stronger than ever. In the present study, the relationship between the abrasion resistance of PCD cutters and the grain size was discussed. At the same time, 3 different types of Grade 30 (G30, the mean grain size = 30 ͮm) and Grade 22 (G22, the mean grain size = 22 ͮm) diamond grits were used to sinter PCD cutters. Type A diamond powders have a higher nitrogen content than Type B and Type C powders. The surface of Type C diamond grits are rougher than Type B. All PCD cutters were sintered under the same conditions. How the abrasion resistance of PCDs is affected by the nitrogen content and the surface quality of diamond grits was investigated.
The nitrogen content of diamond grits were measured by a LECO Nitrogen Analyzer. Each sample was measured 4 times and the average value calculated. In order to investigate the compaction response of diamond grits at high pressure, a cold compaction test was conducted on the three types of G22 and G30 diamond powders. The diamond powders were put into a metal cup and topped with a carbide substrate for the cold compaction at 7 GPa and 8 GPa at room temperature. The particle distribution of diamond grits were measured by Malvern Particle Master Analyzer before and after the cold compaction.
The PCD cutters were sintered under conditions of 1400 to 1600 °C and 5 to 8 GPa [3,4]. Figure 1 shows the schematic design of the pre-sintered unit and the microstructure of PCDs and the tungsten carbide after sintering. During the sintering of PCD, the cobalt in substrate becomes melted and infiltrated into the bed of diamond grits, assisting the sintering of diamonds.
Figure 1 The schematic picture showing the sintering of PCDs.
After sintering, all PCD cutters in the present study were processed to the same dimensions of Ø16mm × 12 mm. The abrasion resistance of PCD was measured through rock cutting tests conducted on vertical turret lathe. After the test, the wear scar were measured under an optical light microscopy. The larger the wear scar area of PDC, the lower the wear resistance. For each sample, 4 rock cutting tests were carried out on two locations of 2 PCD cutters, generateing a total 4 data points.
All PCDs were lapped and polished to 1ͮm before the microstructure observation under SEM. With the intention of quantify the microstructure of PCDs, 20 photos were taken on each sample and processed by the commercially available image analysis software package. The percentage of diamond area is one of the image analysis results of PCDs’ microstructure and used to present the sintering status of PCDs. Given the same powder feed, the higher the percentage of diamond area, the more PCD sintered.
A series of diamond powders with different average grain sizes were prepare and sintered into PCD cutters at 7 GPa. All PCDs were sintered under the same conditions. The SEM observations confirmed that the microstructures of all PCDs showed uniform diamond grain distribution and sintered well. Figure 2(a) and (b) show the microscopy photographs of PCDs with relatively fine and coarse grain sizes. The dark parts are diamond grains and the white dotted boundaries are cobalt binders. It is clearly observed that diamond grains are bonded to each other with some cobalt residual existing at the grain boundaries.
Figure 2 Microscopy photographs of PCDs with (a) fine and (b) coarse grain size. (Magnification: × 1000)
It is found that the wear scar area generally increases with the grain size of diamond grits although a linear relation is not strictly followed. In general, a negative correlation is observed between the abrasion resistance of PCDs and the grain size of diamond grits.
Figure 3 shows the average nitrogen contents of three different types of G30 and G22 measured using LECO Nitrogen Analyzer. It is shown that Type A diamond powders have a higher nitrogen content than Type B and Type C. For G30, the nitrogen level of Type B powders is slightly higher than Type C while for G22, the nitrogen content of Type B and Type C are nearly same.
Figure 3 The average nitrogen content of three types of G30 and G22 diamond grits.
Figure 4(a) and (b) show the SEM images of G30 diamond grits (Type A) before and after the compaction at 7 GPa. It is observed that the original, generally uniform coarse diamond grits were smashed into smaller grits with few relatively coarse ones. The original diamond powders have a relatively clear and smooth appearance while after compression, the smashed diamond grits showed sharp edges and rough surfaces. Obviously, the crushing occurred during the high pressure compaction helped the further dense of the diamond bed before the sintering with the infiltration of liquid cobalt. Figure 5(a) clearly displayed the particle distribution shifted after the compaction at 7 GPa.
Figure 4 (a) The photoof original G30diamondgrits(Type A) beforethepress. (b) The photoof the samediamondgrits after compactionat 7 GPa. (Magnification: × 500)
Figure 5 Particle size distribution plots of G30 (a) before and after compaction, (b) after compaction at 7 GPa, (c) after compaction at 8 GPa. (d) Particle size distribution plots of G22 after compaction at 7 GPa.
Figure 5(b) and (c) are the particle distribution plots of G30 diamond grits after the compaction at 7 GPa and 8 GPa, respectively. Figure 5(b) clearly disclosed that the crushing rate of Type A diamond grits is higher than Type B and C. It does indicate that the diamond grits (Type B and C) with lower nitrogen contents exhibited a high compression fracture strength than Type A ones, which is agree with the literature [5]. Brookes and Daniel reported that [5] at room temperature, a reduction in the concentration of single substitutional diamond increases the indentation hardness of the diamond. Figure 5(c) showed that the particle distribution plots of G30 Type A and Type B are nearly same after the compaction at 8 GPa. Type C ones share the same particle distribution as Type A and Type B as well. Just for a clear appearance of the plots, the data of Type C is not included in Figure 5(c). It means that the advantage of higher compression fracture strength of Type B and C diamond powders due to the lower nitrogen content disappeared when the pressure increased from 7 GPa to 8 GPa. Figure 5(d) showed the particle distribution plots of G22 diamond grits after compaction at 7 GPa. The 3 different types of diamond grits shared a very similar particle distribution except Type C showed a marginally lower crushing rate than the other two types. It means that for G22 diamond, type B and C loose the advantage of higher compression fracture strength at lower pressures (say 4-5 GPa but no data available) and hence exhibit a similar grain size distribution at 7 GPa for all three types. Type C powders appeared to have a rougher surface s associated with reduced stress concentration sharp edges after an etching heat treatment, which might explain the slightly lower crushing rate if Fig. 5(d) is accurate. However, how the Type C powders’ surface quality affect the cold compaction, hot compaction and following diamond sintering is not clear yet. Because all three types of G22 diamonds already crushed similarly at 7 GPa, it is reasonable to believe that they would crush similarly at 8 GPa. Therefore no cold compaction test is carried out at 8 GPa.
Figure 6(a) (b) and (c) showed the microstructures of PCDs sintered from the three different types of G30 diamond grits. All PCD microstructures are uniform and look very similar. Figure 6(d) is the percentages of diamond areas extracted from the image analysis. Generally speaking, the three types of PCDs showed a similar diamond area percentage except that Type C one had a slightly lower diamond area.
Figure 6 (a) (b) and (c) Microscopy photographs of PCDs individually sintered from G30 Type A, B and C diamond grits with the magnification of × 1000. (d) The percentages of diamond area in the microstructure of PCDs sintered from G30 diamond grits.
Figure 7(a) (b) and (c) are the microstructure of PCDs sintered from the three different types of G22 diamond grits. They are uniform and look very similar as well. Figure 7(d) showed that the percentages of diamond area of PCDs from Type A and Type B are very similar, both lower than that from Type C.
Figure 7 (a) (b) and (c) Microscopy photographs of PCDs individually sintered from G22 Type A, B and C diamond grits with the magnification of × 1000. (d) The percentages of diamond area in the microstructure of PCDs sintered from G22 diamond grits.
Figure 8 (a) and (b) showed the wear scar areas of PCDs sintered from G30 and G22 at 8 GPa, respectively, after the vertical turret test. It turns out that although Type B diamond grits have higher compression fracture strength than Type A due to the lower nitrogen content, the abrasion resistance of PCDs is not necessarily improved. Actually, the abrasion resistance tested in this study decreased for both G22 and G30 as the diamond grits changed from Type A to Type B. The reason is unclear yet. It may rely on the vertical turret test which might be more sensitive to the grain boundary rather than the diamond grit itself. Or it may because less plastic deformation occurred at high temperature in diamond grits with lower nitrogen content, therefore the sintering process is affected accordingly. According to [5], when the temperature is high enough (1400C), an increase in nitrogen content is reflected in a decrease in the volume of plastic deformation associated with impressions. On the other hand, bearing in mind that after HPHT sintering, the total nitrogen level in PCDs changed. At HPHT conditions, nitrogen atoms become mobile in diamond lattice, therefore the original internal nitrogen interstitial can diffuse outside and the external nitrogen could enter diamond as well. However, it seems to suggest that Type C powders might be beneficial for the improvement of abrasion resistance of PCDs whatever the percentage of diamond area is higher or lower. The reason might be related to the increased surface area due to the enhanced roughness of diamond grit and also to the potential more active surface on the diamond grits after the etching process. The further study is needed for the surface quality of diamond grits and how they affect the bonding between diamond to diamond during sintering.
Figure 8 Plots of wear scar areas of PCDs sintered from 3 different types of G30 and G22 diamond grits at 8 GPa.
Considering the limited data and the complication of PCD cutters’ abrasion performance, it is too early to draw some solid conclusion. However, the main findings from the present study can be summarised as below.