Search Results (4)

High-Pressure (HP) technology allows new possibilities of processing by Spark Plasma Synthesis (SPS). This process is mainly involved in the sintering process and for bonding, growing and reaction. High-Pressure tools combined with SPS is applied for processing polycrystalline diamond without binder (binderless PCD) in this current work. Our described innovative Ultra High Pressure Spark Plasma Sintering (UHP-SPS) equipment shows the combination of our high-pressure apparatus (Belt-type) with conventional pulse electric current generator (Fuji). Our UHP-SPS equipment allows the processing up to 6 GPa, higher pressure than HP-SPS equipment, based on a conventional SPS equipment in which a non-graphite mold (metals, ceramics, composite and hybrid) with better mechanical properties (capable of 1 GPa) than graphite. The equipment of UHP-SPS and HP-SPS elements (pistons + die) conductivity of the non-graphite mold define a Hot-Pressing process. This study presents the results showing the ability of sintering diamond powder without additives at 4–5 GPa and 1300–1400 °C for duration between 5 and 30 min. Our described UHP-SPS innovative cell design allows the consolidation of diamond particles validated by the formation of grain boundaries on two different grain size powders, i.e., 0.75–1.25 μm and 8–12 μm. The phenomena explanation is proposed by comparison with the High Pressure High Temperature (HP-HT) (Belt, toroidal-Bridgman, multi-anvils (cubic)) process conventionally used for processing binderless polycrystalline diamond (binderless PCD). It is shown that using UHP-SPS, binderless diamond can be sintered at very unexpected P-T conditions, typically ~10 GPa and 500–1000 °C lower in typical HP-HT setups. This makes UHP-SPS a promising tool for the sintering of other high-pressure materials at non-equilibrium conditions and a potential industrial transfer with low environmental fingerprints could be considered. Full article

Nowadays, synthetic diamonds are easy to fabricate industrially, and a wide range of methods were developed during the last century. Among them, the high-pressure–high-temperature (HP–HT) process is the most used to prepare diamond compacts for cutting or drilling applications. However, these diamond compacts contain binder, limiting their mechanical and optical properties and their substantial uses. Binderless diamond compacts were synthesized more recently, and important developments were made to optimize the P–T conditions of sintering. Resulting sintered compacts had mechanical and optical properties at least equivalent to that of natural single crystal and higher than that of binder-containing sintered compacts, offering a huge potential market. However, pressure–temperature (P–T) conditions to sinter such bodies remain too high for an industrial transfer, making this the next challenge to be accomplished. This review gives an overview of natural diamond formation and the main experimental techniques that are used to synthesize and/or sinter diamond powders and compact objects. The focus of this review is the HP–HT process, especially for the synthesis and sintering of binderless diamonds. P–T conditions of the formation and exceptional properties of such objects are discussed and compared with classic binder-diamonds objects and with natural single-crystal diamonds. Finally, the question of an industrial transfer is asked and outlooks related to this are proposed. Full article

Binderless tungsten carbide (WC) finds widespread applications in precision glass molding (PGM). Grinding and polishing are the main processes to realize optical surface finish on binderless WC mold inserts. The laser assisted turning (LAT) by in-process heating is an efficient method to enhance the machinability of hard and brittle materials. In this paper, laser heating temperature was pre-calculated by the finite element analysis, and was utilized to facilitate laser power selection. The effects of rake angle, depth of cut, feed rate, and laser power are studied experimentally using the Taguchi method. The variance, range, and signal-to-noise ratio analysis methods are employed to evaluate the effects of the factors on the surface roughness. Based on the self-developed LAT system, binderless WC mold inserts with mirror finished surfaces are machined using the optimal parameters. PGM experiments of molding glass lenses for practical application are conducted to verify the machined mold inserts quality. The experiment results indicate that both the mold inserts and molded lenses with the required quality are achieved. Full article

Owing to their high hardness, fracture toughness and oxidation resistance, tungsten carbide (WC) coatings are extensively deposited on parts that operate in demanding applications, necessitating wear, erosion, and corrosion resistance. The application of thick and hard WC coatings has an inevitable effect on the original dimensions of the parts, affecting the geometrical tolerances and surface roughness. The capability of achieving a sub-micron surface finish and adhere to tight geometrical tolerances accurately and repeatably is an important requirement, particularly with components that operate in high-precision sliding motion. Meeting such requirements through conventional surface finishing methods, however, can be challenging due to the superior mechanical and tribological properties of WC coatings. A brief review into the synthesis techniques of cemented and binderless WC coatings is presented together with a comprehensive review into the available techniques which are used to surface finish WC-based coatings with reference to their fundamental mechanisms and capabilities to process parts with intricate and internal features. The binderless WC/W coating considered in this work is deposited through chemical vapour deposition (CVD) and unlike traditional cemented carbide coatings, it has a homogenous coating structure. This distinctive characteristic has the potential of eliminating key issues commonly encountered with machining and finishing of WC-based coatings. Here, six contact and non-contact surface finishing techniques, include diamond turning, precision grinding, superfinishing, vibratory polishing, electrical discharge machining, and electropolishing are discussed along with their current use in industry and limitations. Key challenges in the field are highlighted and potential directions for future investigation, particularly on binderless WC coatings, are proposed herein. Full article